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//! OpenPGP packet serializer.
//!
//! There are two interfaces to serialize OpenPGP data.  Which one is
//! applicable depends on whether or not the packet structure is
//! already assembled in memory, with all information already in place
//! (e.g. because it was parsed).
//!
//! If it is, you can use the `Serialize` or `SerializeKey`.
//!
//! Otherwise, please use our streaming serialization interface.

use std::io::{self, Write};
use std::cmp;

use crate::autocrypt;
use super::*;

mod partial_body;
mod sexp;
mod tpk;
pub use self::tpk::TSK;
mod tpk_armored;
use self::partial_body::PartialBodyFilter;
pub mod writer;
pub mod stream;
#[cfg(feature = "compression-deflate")]
pub mod padding;
use crate::crypto::s2k::S2K;
use crate::packet::header::{
    BodyLength,
    CTB,
    ctb::CTBNew,
    ctb::CTBOld,
};
use crate::packet::signature::subpacket::{
    Subpacket, SubpacketValue, SubpacketLengthTrait,
};
use crate::conversions::{
    Time,
    Duration,
};
use crate::packet::prelude::*;

// Whether to trace the modules execution (on stderr).
const TRACE : bool = false;

/// Serializes OpenPGP data structures.
pub trait Serialize {
    /// Writes a serialized version of the object to `o`.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()>;

    /// Exports a serialized version of the object to `o`.
    ///
    /// This is similar to [`serialize(..)`], with these exceptions:
    ///
    ///   - It is an error to export a [`Signature`] if it is marked
    ///     as non-exportable.
    ///   - When exporting a [`TPK`], non-exportable signatures are
    ///     not exported, and any component bound merely by
    ///     non-exportable signatures is not exported.
    ///
    ///   [`serialize(..)`]: #tymethod.serialize
    ///   [`Signature`]: ../packet/enum.Signature.html
    ///   [`TPK`]: ../struct.TPK.html
    fn export(&self, o: &mut dyn std::io::Write) -> Result<()> {
        self.serialize(o)
    }
}

/// Serializes OpenPGP data structures into pre-allocated buffers.
pub trait SerializeInto {
    /// Computes the maximal length of the serialized representation.
    ///
    /// # Errors
    ///
    /// If serialization would fail, this function underestimates the
    /// length.
    fn serialized_len(&self) -> usize;

    /// Serializes into the given buffer.
    ///
    /// Returns the length of the serialized representation.
    ///
    /// # Errors
    ///
    /// If the length of the given slice is smaller than the maximal
    /// length computed by `serialized_len()`, this function returns
    /// `Error::InvalidArgument`.
    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize>;

    /// Serializes the packet to a vector.
    fn to_vec(&self) -> Result<Vec<u8>> {
        let mut o = vec![0; self.serialized_len()];
        let len = self.serialize_into(&mut o[..])?;
        o.truncate(len);
        o.shrink_to_fit();
        Ok(o)
    }

    /// Exports into the given buffer.
    ///
    /// This is similar to [`serialize_into(..)`], with these
    /// exceptions:
    ///
    ///   - It is an error to export a [`Signature`] if it is marked
    ///     as non-exportable.
    ///   - When exporting a [`TPK`], non-exportable signatures are
    ///     not exported, and any component bound merely by
    ///     non-exportable signatures is not exported.
    ///
    ///   [`serialize_into(..)`]: #tymethod.serialize_into
    ///   [`Signature`]: ../packet/enum.Signature.html
    ///   [`TPK`]: ../struct.TPK.html
    ///
    /// Returns the length of the serialized representation.
    ///
    /// # Errors
    ///
    /// If the length of the given slice is smaller than the maximal
    /// length computed by `serialized_len()`, this function returns
    /// `Error::InvalidArgument`.
    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        self.serialize_into(buf)
    }

    /// Exports to a vector.
    ///
    /// This is similar to [`to_vec()`], with these exceptions:
    ///
    ///   - It is an error to export a [`Signature`] if it is marked
    ///     as non-exportable.
    ///   - When exporting a [`TPK`], non-exportable signatures are
    ///     not exported, and any component bound merely by
    ///     non-exportable signatures is not exported.
    ///
    ///   [`to_vec()`]: #method.to_vec
    ///   [`Signature`]: ../packet/enum.Signature.html
    ///   [`TPK`]: ../struct.TPK.html
    fn export_to_vec(&self) -> Result<Vec<u8>> {
        let mut o = vec![0; self.serialized_len()];
        let len = self.export_into(&mut o[..])?;
        o.truncate(len);
        o.shrink_to_fit();
        Ok(o)
    }
}

trait NetLength {
    /// Computes the maximal length of the serialized representation
    /// without framing.
    ///
    /// # Errors
    ///
    /// If serialization would fail, this function underestimates the
    /// length.
    fn net_len(&self) -> usize;

    /// Computes the maximal length of the serialized representation
    /// with framing.
    ///
    /// # Errors
    ///
    /// If serialization would fail, this function underestimates the
    /// length.
    fn gross_len(&self) -> usize {
        let net = self.net_len();

        1 // CTB
            + BodyLength::Full(net as u32).serialized_len()
            + net
    }
}

/// Provides a generic implementation for SerializeInto::serialize_into.
///
/// For now, we express SerializeInto using Serialize.  In the future,
/// we may provide implementations not relying on Serialize for a
/// no_std configuration of this crate.
fn generic_serialize_into<T: Serialize + SerializeInto>(o: &T, buf: &mut [u8])
                                                        -> Result<usize> {
    let buf_len = buf.len();
    let mut cursor = ::std::io::Cursor::new(buf);
    match o.serialize(&mut cursor) {
        Ok(_) => (),
        Err(e) => {
            let short_write =
                if let Some(ioe) = e.downcast_ref::<io::Error>() {
                    ioe.kind() == io::ErrorKind::WriteZero
                } else {
                    false
                };
            return if short_write {
                Err(Error::InvalidArgument(
                    format!("Invalid buffer size, expected {}, got {}",
                            o.serialized_len(), buf_len)).into())
            } else {
                Err(e)
            }
        }
    };
    Ok(cursor.position() as usize)
}

/// Provides a generic implementation for SerializeInto::export_into.
///
/// For now, we express SerializeInto using Serialize.  In the future,
/// we may provide implementations not relying on Serialize for a
/// no_std configuration of this crate.
fn generic_export_into<T: Serialize + SerializeInto>(o: &T, buf: &mut [u8])
                                                        -> Result<usize> {
    let buf_len = buf.len();
    let mut cursor = ::std::io::Cursor::new(buf);
    match o.export(&mut cursor) {
        Ok(_) => (),
        Err(e) => {
            let short_write =
                if let Some(ioe) = e.downcast_ref::<io::Error>() {
                    ioe.kind() == io::ErrorKind::WriteZero
                } else {
                    false
                };
            return if short_write {
                Err(Error::InvalidArgument(
                    format!("Invalid buffer size, expected {}, got {}",
                            o.serialized_len(), buf_len)).into())
            } else {
                Err(e)
            }
        }
    };
    Ok(cursor.position() as usize)
}

#[test]
fn test_generic_serialize_into() {
    let u = UserID::from("Mr. Pink");
    let mut b = vec![0; u.serialized_len()];
    u.serialize_into(&mut b[..]).unwrap();

    // Short buffer.
    let mut b = vec![0; u.serialized_len() - 1];
    let e = u.serialize_into(&mut b[..]).unwrap_err();
    assert_match!(Some(Error::InvalidArgument(_)) = e.downcast_ref());
}

#[test]
fn test_generic_export_into() {
    let u = UserID::from("Mr. Pink");
    let mut b = vec![0; u.serialized_len()];
    u.export_into(&mut b[..]).unwrap();

    // Short buffer.
    let mut b = vec![0; u.serialized_len() - 1];
    let e = u.export_into(&mut b[..]).unwrap_err();
    assert_match!(Some(Error::InvalidArgument(_)) = e.downcast_ref());
}

fn write_byte(o: &mut dyn std::io::Write, b: u8) -> io::Result<()> {
    let b : [u8; 1] = [b; 1];
    o.write_all(&b[..])
}

fn write_be_u16(o: &mut dyn std::io::Write, n: u16) -> io::Result<()> {
    let b : [u8; 2] = [ ((n >> 8) & 0xFF) as u8, (n & 0xFF) as u8 ];
    o.write_all(&b[..])
}

fn write_be_u32(o: &mut dyn std::io::Write, n: u32) -> io::Result<()> {
    let b : [u8; 4] = [ (n >> 24) as u8, ((n >> 16) & 0xFF) as u8,
                         ((n >> 8) & 0xFF) as u8, (n & 0xFF) as u8 ];
    o.write_all(&b[..])
}

// Compute the log2 of an integer.  (This is simply the most
// significant bit.)  Note: log2(0) = -Inf, but this function returns
// log2(0) as 0 (which is the closest number that we can represent).
fn log2(x: u32) -> usize {
    if x == 0 {
        0
    } else {
        31 - x.leading_zeros() as usize
    }
}

#[test]
fn log2_test() {
    for i in 0..32 {
        // eprintln!("log2(1 << {} = {}) = {}", i, 1u32 << i, log2(1u32 << i));
        assert_eq!(log2(1u32 << i), i);
        if i > 0 {
            assert_eq!(log2((1u32 << i) - 1), i - 1);
            assert_eq!(log2((1u32 << i) + 1), i);
        }
    }
}

impl Serialize for BodyLength {
    /// Emits the length encoded for use with new-style CTBs.
    ///
    /// Note: the CTB itself is not emitted.
    ///
    /// # Errors
    ///
    /// Returns [`Error::InvalidArgument`] if invoked on
    /// [`BodyLength::Indeterminate`].  If you want to serialize an
    /// old-style length, use [`serialize_old(..)`].
    ///
    /// [`Error::InvalidArgument`]: ../enum.Error.html#variant.InvalidArgument
    /// [`BodyLength::Indeterminate`]: ../packet/enum.BodyLength.html#variant.Indeterminate
    /// [`serialize_old(..)`]: #method.serialize_old
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &BodyLength::Full(l) => {
                if l <= 191 {
                    write_byte(o, l as u8)?;
                } else if l <= 8383 {
                    let v = l - 192;
                    let v = v + (192 << 8);
                    write_be_u16(o, v as u16)?;
                } else {
                    write_byte(o, 0xff)?;
                    write_be_u32(o, l)?;
                }
            },
            &BodyLength::Partial(l) => {
                if l > 1 << 30 {
                    return Err(Error::InvalidArgument(
                        format!("Partial length too large: {}", l)).into());
                }

                let chunk_size_log2 = log2(l);
                let chunk_size = 1 << chunk_size_log2;

                if l != chunk_size {
                    return Err(Error::InvalidArgument(
                        format!("Not a power of two: {}", l)).into());
                }

                let size_byte = 224 + chunk_size_log2;
                assert!(size_byte < 255);
                write_byte(o, size_byte as u8)?;
            },
            &BodyLength::Indeterminate =>
                return Err(Error::InvalidArgument(
                    "Indeterminate lengths are not support for new format packets".
                        into()).into()),
        }

        Ok(())
    }
}

impl SerializeInto for BodyLength {
    fn serialized_len(&self) -> usize {
        match self {
            &BodyLength::Full(l) => {
                if l <= 191 {
                    1
                } else if l <= 8383 {
                    2
                } else {
                    5
                }
            },
            &BodyLength::Partial(_) => 1,
            &BodyLength::Indeterminate => 0,
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl BodyLength {
    /// Emits the length encoded for use with old-style CTBs.
    ///
    /// Note: the CTB itself is not emitted.
    ///
    /// # Errors
    ///
    /// Returns [`Error::InvalidArgument`] if invoked on
    /// [`BodyLength::Partial`].  If you want to serialize a
    /// new-style length, use [`serialize(..)`].
    ///
    /// [`Error::InvalidArgument`]: ../enum.Error.html#variant.InvalidArgument
    /// [`BodyLength::Partial`]: ../packet/enum.BodyLength.html#variant.Partial
    /// [`serialize(..)`]: #impl-Serialize
    pub fn serialize_old<W: io::Write>(&self, o: &mut W) -> Result<()> {
        // Assume an optimal encoding is desired.
        let mut buffer = Vec::with_capacity(4);
        match self {
            &BodyLength::Full(l) => {
                match l {
                    // One octet length.
                    // write_byte can't fail for a Vec.
                    0 ..= 0xFF =>
                        write_byte(&mut buffer, l as u8).unwrap(),
                    // Two octet length.
                    0x1_00 ..= 0xFF_FF =>
                        write_be_u16(&mut buffer, l as u16).unwrap(),
                    // Four octet length,
                    _ =>
                        write_be_u32(&mut buffer, l as u32).unwrap(),
                }
            },
            &BodyLength::Indeterminate => {},
            &BodyLength::Partial(_) =>
                return Err(Error::InvalidArgument(
                    "Partial body lengths are not support for old format packets".
                        into()).into()),
        }

        o.write_all(&buffer)?;
        Ok(())
    }
}

impl Serialize for CTBNew {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        let tag: u8 = self.tag().into();
        o.write_all(&[0b1100_0000u8 | tag])?;
        Ok(())
    }
}

impl SerializeInto for CTBNew {
    fn serialized_len(&self) -> usize { 1 }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for CTBOld {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        let tag: u8 = self.tag().into();
        let length_type: u8 = self.length_type.into();
        o.write_all(&[0b1000_0000u8 | (tag << 2) | length_type])?;
        Ok(())
    }
}

impl SerializeInto for CTBOld {
    fn serialized_len(&self) -> usize { 1 }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for CTB {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &CTB::New(ref c) => c.serialize(o),
            &CTB::Old(ref c) => c.serialize(o),
        }?;
        Ok(())
    }
}

impl SerializeInto for CTB {
    fn serialized_len(&self) -> usize { 1 }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Header {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        self.ctb().serialize(o)?;
        self.length().serialize(o)?;
        Ok(())
    }
}

impl Serialize for KeyID {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        let raw = match self {
            &KeyID::V4(ref fp) => &fp[..],
            &KeyID::Invalid(ref fp) => &fp[..],
        };
        o.write_all(raw)?;
        Ok(())
    }
}

impl SerializeInto for KeyID {
    fn serialized_len(&self) -> usize {
        match self {
            &KeyID::V4(_) => 8,
            &KeyID::Invalid(ref fp) => fp.len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Fingerprint {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(self.as_slice())?;
        Ok(())
    }
}

impl SerializeInto for Fingerprint {
    fn serialized_len(&self) -> usize {
        match self {
            Fingerprint::V4(_) => 20,
            Fingerprint::Invalid(ref fp) => fp.len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for crypto::mpis::MPI {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        write_be_u16(w, self.bits() as u16)?;
        w.write_all(self.value())?;
        Ok(())
    }
}

impl SerializeInto for crypto::mpis::MPI {
    fn serialized_len(&self) -> usize {
        2 + self.value().len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for crypto::mpis::ProtectedMPI {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        write_be_u16(w, self.bits() as u16)?;
        w.write_all(self.value())?;
        Ok(())
    }
}

impl SerializeInto for crypto::mpis::ProtectedMPI {
    fn serialized_len(&self) -> usize {
        2 + self.value().len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for crypto::mpis::PublicKey {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        use crate::crypto::mpis::PublicKey::*;

        match self {
            &RSA { ref e, ref n } => {
                n.serialize(w)?;
                e.serialize(w)?;
            }

            &DSA { ref p, ref q, ref g, ref y } => {
                p.serialize(w)?;
                q.serialize(w)?;
                g.serialize(w)?;
                y.serialize(w)?;
            }

            &Elgamal { ref p, ref g, ref y } => {
                p.serialize(w)?;
                g.serialize(w)?;
                y.serialize(w)?;
            }

            &EdDSA { ref curve, ref q } => {
                w.write_all(&[curve.oid().len() as u8])?;
                w.write_all(curve.oid())?;
                q.serialize(w)?;
            }

            &ECDSA { ref curve, ref q } => {
                w.write_all(&[curve.oid().len() as u8])?;
                w.write_all(curve.oid())?;
                q.serialize(w)?;
            }

            &ECDH { ref curve, ref q, hash, sym } => {
                w.write_all(&[curve.oid().len() as u8])?;
                w.write_all(curve.oid())?;
                q.serialize(w)?;
                w.write_all(&[3u8, 1u8, u8::from(hash), u8::from(sym)])?;
            }

            &Unknown { ref mpis, ref rest } => {
                for mpi in mpis.iter() {
                    mpi.serialize(w)?;
                }
                w.write_all(rest)?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for crypto::mpis::PublicKey {
    fn serialized_len(&self) -> usize {
        use crate::crypto::mpis::PublicKey::*;
        match self {
            &RSA { ref e, ref n } => {
                n.serialized_len() + e.serialized_len()
            }

            &DSA { ref p, ref q, ref g, ref y } => {
                p.serialized_len() + q.serialized_len() + g.serialized_len()
                    + y.serialized_len()
            }

            &Elgamal { ref p, ref g, ref y } => {
                p.serialized_len() + g.serialized_len() + y.serialized_len()
            }

            &EdDSA { ref curve, ref q } => {
                1 + curve.oid().len() + q.serialized_len()
            }

            &ECDSA { ref curve, ref q } => {
                1 + curve.oid().len() + q.serialized_len()
            }

            &ECDH { ref curve, ref q, hash: _, sym: _ } => {
                1 + curve.oid().len() + q.serialized_len() + 4
            }

            &Unknown { ref mpis, ref rest } => {
                mpis.iter().map(|mpi| mpi.serialized_len()).sum::<usize>()
                    + rest.len()
            }
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for crypto::mpis::SecretKeyMaterial {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        use crate::crypto::mpis::SecretKeyMaterial::*;

        match self {
            &RSA{ ref d, ref p, ref q, ref u } => {
                d.serialize(w)?;
                p.serialize(w)?;
                q.serialize(w)?;
                u.serialize(w)?;
            }

            &DSA{ ref x } => {
                x.serialize(w)?;
            }

            &Elgamal{ ref x } => {
                x.serialize(w)?;
            }

            &EdDSA{ ref scalar } => {
                scalar.serialize(w)?;
            }

            &ECDSA{ ref scalar } => {
                scalar.serialize(w)?;
            }

            &ECDH{ ref scalar } => {
                scalar.serialize(w)?;
            }

            &Unknown { ref mpis, ref rest } => {
                for mpi in mpis.iter() {
                    mpi.serialize(w)?;
                }
                w.write_all(rest)?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for crypto::mpis::SecretKeyMaterial {
    fn serialized_len(&self) -> usize {
        use crate::crypto::mpis::SecretKeyMaterial::*;
        match self {
            &RSA{ ref d, ref p, ref q, ref u } => {
                d.serialized_len() + p.serialized_len() + q.serialized_len()
                    + u.serialized_len()
            }

            &DSA{ ref x } => {
                x.serialized_len()
            }

            &Elgamal{ ref x } => {
                x.serialized_len()
            }

            &EdDSA{ ref scalar } => {
                scalar.serialized_len()
            }

            &ECDSA{ ref scalar } => {
                scalar.serialized_len()
            }

            &ECDH{ ref scalar } => {
                scalar.serialized_len()
            }

            &Unknown { ref mpis, ref rest } => {
                mpis.iter().map(|mpi| mpi.serialized_len()).sum::<usize>()
                    + rest.len()
            }
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl crypto::mpis::SecretKeyMaterial {
    /// Writes this secret key with a checksum to `w`.
    pub fn serialize_chksumd<W: io::Write>(&self, w: &mut W) -> Result<()> {
        // First, the MPIs.
        self.serialize(w)?;

        // The checksum is SHA1 over the serialized MPIs.
        let mut hash = HashAlgorithm::SHA1.context().unwrap();
        self.serialize(&mut hash)?;
        let mut digest = [0u8; 20];
        hash.digest(&mut digest);
        w.write_all(&digest)?;

        Ok(())
    }
}

impl Serialize for crypto::mpis::Ciphertext {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        use crate::crypto::mpis::Ciphertext::*;

        match self {
            &RSA{ ref c } => {
                c.serialize(w)?;
            }

            &Elgamal{ ref e, ref c } => {
                e.serialize(w)?;
                c.serialize(w)?;
            }

            &ECDH{ ref e, ref key } => {
                e.serialize(w)?;

                w.write_all(&[key.len() as u8])?;
                w.write_all(&key)?;
            }

            &Unknown { ref mpis, ref rest } => {
                for mpi in mpis.iter() {
                    mpi.serialize(w)?;
                }
                w.write_all(rest)?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for crypto::mpis::Ciphertext {
    fn serialized_len(&self) -> usize {
        use crate::crypto::mpis::Ciphertext::*;
        match self {
            &RSA{ ref c } => {
                c.serialized_len()
            }

            &Elgamal{ ref e, ref c } => {
                e.serialized_len() + c.serialized_len()
            }

            &ECDH{ ref e, ref key } => {
                e.serialized_len() + 1 + key.len()
            }

            &Unknown { ref mpis, ref rest } => {
                mpis.iter().map(|mpi| mpi.serialized_len()).sum::<usize>()
                    + rest.len()
            }
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for crypto::mpis::Signature {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        use crate::crypto::mpis::Signature::*;

        match self {
            &RSA { ref s } => {
                s.serialize(w)?;
            }
            &DSA { ref r, ref s } => {
                r.serialize(w)?;
                s.serialize(w)?;
            }
            &Elgamal { ref r, ref s } => {
                r.serialize(w)?;
                s.serialize(w)?;
            }
            &EdDSA { ref r, ref s } => {
                r.serialize(w)?;
                s.serialize(w)?;
            }
            &ECDSA { ref r, ref s } => {
                r.serialize(w)?;
                s.serialize(w)?;
            }

            &Unknown { ref mpis, ref rest } => {
                for mpi in mpis.iter() {
                    mpi.serialize(w)?;
                }
                w.write_all(rest)?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for crypto::mpis::Signature {
    fn serialized_len(&self) -> usize {
        use crate::crypto::mpis::Signature::*;
        match self {
            &RSA { ref s } => {
                s.serialized_len()
            }
            &DSA { ref r, ref s } => {
                r.serialized_len() + s.serialized_len()
            }
            &Elgamal { ref r, ref s } => {
                r.serialized_len() + s.serialized_len()
            }
            &EdDSA { ref r, ref s } => {
                r.serialized_len() + s.serialized_len()
            }
            &ECDSA { ref r, ref s } => {
                r.serialized_len() + s.serialized_len()
            }

            &Unknown { ref mpis, ref rest } => {
                mpis.iter().map(|mpi| mpi.serialized_len()).sum::<usize>()
                    + rest.len()
            }
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for S2K {
    fn serialize(&self, w: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &S2K::Simple{ hash } => {
                w.write_all(&[0, hash.into()])?;
            }
            &S2K::Salted{ hash, salt } => {
                w.write_all(&[1, hash.into()])?;
                w.write_all(&salt[..])?;
            }
            &S2K::Iterated{ hash, salt, hash_bytes } => {
                w.write_all(&[3, hash.into()])?;
                w.write_all(&salt[..])?;
                w.write_all(&[S2K::encode_count(hash_bytes)?])?;
            }
            &S2K::Private(s2k) | &S2K::Unknown(s2k) => {
                w.write_all(&[s2k])?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for S2K {
    fn serialized_len(&self) -> usize {
        match self {
            &S2K::Simple{ .. } => 2,
            &S2K::Salted{ .. } => 2 + 8,
            &S2K::Iterated{ .. } => 2 + 8 + 1,
            &S2K::Private(_) | &S2K::Unknown(_) => 1,
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Unknown {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        let body = if let Some(body) = self.body() {
            &body[..]
        } else {
            &b""[..]
        };

        o.write_all(&body[..])?;

        Ok(())
    }
}

impl NetLength for Unknown {
    fn net_len(&self) -> usize {
        self.body().unwrap_or(&b""[..]).len()
    }
}

impl SerializeInto for Unknown {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl<'a> Serialize for Subpacket<'a> {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        let tag = u8::from(self.tag)
            | if self.critical { 1 << 7 } else { 0 };
        let len = 1 + self.value.len();

        len.serialize(o)?;
        o.write_all(&[tag])?;
        self.value.serialize(o)
    }
}

impl<'a> SerializeInto for Subpacket<'a> {
    fn serialized_len(&self) -> usize {
        (1 + self.value.len()).len() + 1 + self.value.serialized_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl<'a> Serialize for SubpacketValue<'a> {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        use self::SubpacketValue::*;
        match self {
            SignatureCreationTime(t) =>
                write_be_u32(o, t.to_pgp()?)?,
            SignatureExpirationTime(t) =>
                write_be_u32(o, t.to_pgp()?)?,
            ExportableCertification(e) =>
                o.write_all(&[if *e { 1 } else { 0 }])?,
            TrustSignature { ref level, ref trust } =>
                o.write_all(&[*level, *trust])?,
            RegularExpression(ref re) => {
                o.write_all(re)?;
                o.write_all(&[0])?;
            },
            Revocable(r) =>
                o.write_all(&[if *r { 1 } else { 0 }])?,
            KeyExpirationTime(t) =>
                write_be_u32(o, t.to_pgp()?)?,
            PreferredSymmetricAlgorithms(ref p) =>
                for a in p {
                    o.write_all(&[(*a).into()])?;
                },
            RevocationKey { ref class, ref pk_algo, ref fp } => {
                o.write_all(&[*class, (*pk_algo).into()])?;
                o.write_all(fp.as_slice())?;
            },
            Issuer(ref id) =>
                o.write_all(id.as_slice())?,
            NotationData(nd) => {
                write_be_u32(o, nd.flags().raw())?;
                write_be_u16(o, nd.name().len() as u16)?;
                write_be_u16(o, nd.value().len() as u16)?;
                o.write_all(nd.name())?;
                o.write_all(nd.value())?;
            },
            PreferredHashAlgorithms(ref p) =>
                for a in p {
                    o.write_all(&[(*a).into()])?;
                },
            PreferredCompressionAlgorithms(ref p) =>
                for a in p {
                    o.write_all(&[(*a).into()])?;
                },
            KeyServerPreferences(ref p) =>
                o.write_all(&p.as_vec())?,
            PreferredKeyServer(ref p) =>
                o.write_all(p)?,
            PrimaryUserID(p) =>
                o.write_all(&[if *p { 1 } else { 0 }])?,
            PolicyURI(ref p) =>
                o.write_all(p)?,
            KeyFlags(ref f) =>
                o.write_all(&f.as_vec())?,
            SignersUserID(ref uid) =>
                o.write_all(uid)?,
            ReasonForRevocation { ref code, ref reason } => {
                o.write_all(&[(*code).into()])?;
                o.write_all(reason)?;
            },
            Features(ref f) =>
                o.write_all(&f.as_vec())?,
            SignatureTarget { pk_algo, hash_algo, ref digest } => {
                o.write_all(&[(*pk_algo).into(), (*hash_algo).into()])?;
                o.write_all(digest)?;
            },
            EmbeddedSignature(ref p) => match p {
                &Packet::Signature(ref sig) => sig.serialize(o)?,
                _ => return Err(Error::InvalidArgument(
                    format!("Not a signature: {:?}", p)).into()),
            },
            IssuerFingerprint(ref fp) => match fp {
                Fingerprint::V4(_) => {
                    o.write_all(&[4])?;
                    o.write_all(fp.as_slice())?;
                },
                _ => return Err(Error::InvalidArgument(
                    "Unknown kind of fingerprint".into()).into()),
            }
            PreferredAEADAlgorithms(ref p) =>
                for a in p {
                    o.write_all(&[(*a).into()])?;
                },
            IntendedRecipient(ref fp) => match fp {
                Fingerprint::V4(_) => {
                    o.write_all(&[4])?;
                    o.write_all(fp.as_slice())?;
                },
                _ => return Err(Error::InvalidArgument(
                    "Unknown kind of fingerprint".into()).into()),
            }
            Unknown(ref raw) =>
                o.write_all(raw)?,
            Invalid(ref raw) =>
                o.write_all(raw)?,
        }
        Ok(())
    }
}

impl<'a> SerializeInto for SubpacketValue<'a> {
    fn serialized_len(&self) -> usize {
        use self::SubpacketValue::*;
        match self {
            SignatureCreationTime(_) => 4,
            SignatureExpirationTime(_) => 4,
            ExportableCertification(_) => 1,
            TrustSignature { .. } => 2,
            RegularExpression(ref re) => re.len() + 1,
            Revocable(_) => 1,
            KeyExpirationTime(_) => 4,
            PreferredSymmetricAlgorithms(ref p) => p.len(),
            RevocationKey { ref fp, .. } => 2 + fp.serialized_len(),
            Issuer(ref id) => id.serialized_len(),
            NotationData(nd) => 4 + 2 + 2 + nd.name().len() + nd.value().len(),
            PreferredHashAlgorithms(ref p) => p.len(),
            PreferredCompressionAlgorithms(ref p) => p.len(),
            KeyServerPreferences(ref p) => p.as_vec().len(),
            PreferredKeyServer(ref p) => p.len(),
            PrimaryUserID(_) => 1,
            PolicyURI(ref p) => p.len(),
            KeyFlags(ref f) => f.as_vec().len(),
            SignersUserID(ref uid) => uid.len(),
            ReasonForRevocation { ref reason, .. } => 1 + reason.len(),
            Features(ref f) => f.as_vec().len(),
            SignatureTarget { ref digest, .. } => 2 + digest.len(),
            EmbeddedSignature(ref p) => match p {
                &Packet::Signature(ref sig) => sig.serialized_len(),
                _ => 0,
            },
            IssuerFingerprint(ref fp) => match fp {
                Fingerprint::V4(_) => 1 + fp.serialized_len(),
                _ => 0,
            },
            PreferredAEADAlgorithms(ref p) => p.len(),
            IntendedRecipient(ref fp) => match fp {
                Fingerprint::V4(_) => 1 + fp.serialized_len(),
                _ => 0,
            },
            Unknown(ref raw) => raw.len(),
            Invalid(ref raw) => raw.len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Signature {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &Signature::V4(ref s) => s.serialize(o),
        }
    }

    fn export(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &Signature::V4(ref s) => s.export(o),
        }
    }
}

impl SerializeInto for Signature {
    fn serialized_len(&self) -> usize {
        match self {
            &Signature::V4(ref s) => s.serialized_len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &Signature::V4(ref s) => s.serialize_into(buf),
        }
    }

    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &Signature::V4(ref s) => s.export_into(buf),
        }
    }

    fn export_to_vec(&self) -> Result<Vec<u8>> {
        match self {
            &Signature::V4(ref s) => s.export_to_vec(),
        }
    }
}

impl Serialize for Signature4 {
    /// Writes a serialized version of the specified `Signature`
    /// packet to `o`.
    ///
    /// # Errors
    ///
    /// Returns [`Error::InvalidArgument`] if either the hashed-area
    /// or the unhashed-area exceeds the size limit of 2^16.
    ///
    /// [`Error::InvalidArgument`]: ../../enum.Error.html#variant.InvalidArgument
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        assert_eq!(self.version(), 4);
        write_byte(o, self.version())?;
        write_byte(o, self.typ().into())?;
        write_byte(o, self.pk_algo().into())?;
        write_byte(o, self.hash_algo().into())?;

        if self.hashed_area().data.len() > std::u16::MAX as usize {
            return Err(Error::InvalidArgument(
                "Hashed area too large".into()).into());
        }
        write_be_u16(o, self.hashed_area().data.len() as u16)?;
        o.write_all(&self.hashed_area().data[..])?;

        if self.unhashed_area().data.len() > std::u16::MAX as usize {
            return Err(Error::InvalidArgument(
                "Unhashed area too large".into()).into());
        }
        write_be_u16(o, self.unhashed_area().data.len() as u16)?;
        o.write_all(&self.unhashed_area().data[..])?;

        write_byte(o, self.hash_prefix()[0])?;
        write_byte(o, self.hash_prefix()[1])?;

        self.mpis().serialize(o)?;

        Ok(())
    }

    fn export(&self, o: &mut dyn std::io::Write) -> Result<()> {
        if ! self.exportable_certification().unwrap_or(true) {
            return Err(Error::InvalidOperation(
                "Cannot export non-exportable certification".into()).into());
        }

        self.serialize(o)
    }
}

impl NetLength for Signature4 {
    fn net_len(&self) -> usize {
        1 // Version.
            + 1 // Signature type.
            + 1 // PK algorithm.
            + 1 // Hash algorithm.
            + 2 // Hashed area size.
            + self.hashed_area().data.len()
            + 2 // Unhashed area size.
            + self.unhashed_area().data.len()
            + 2 // Hash prefix.
            + self.mpis().serialized_len()
    }
}

impl SerializeInto for Signature4 {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }

    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        if ! self.exportable_certification().unwrap_or(true) {
            return Err(Error::InvalidOperation(
                "Cannot export non-exportable certification".into()).into());
        }

        self.serialize_into(buf)
    }

    fn export_to_vec(&self) -> Result<Vec<u8>> {
        if ! self.exportable_certification().unwrap_or(true) {
            return Err(Error::InvalidOperation(
                "Cannot export non-exportable certification".into()).into());
        }

        self.to_vec()
    }
}

impl Serialize for OnePassSig {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &OnePassSig::V3(ref s) => s.serialize(o),
        }
    }
}

impl SerializeInto for OnePassSig {
    fn serialized_len(&self) -> usize {
        match self {
            &OnePassSig::V3(ref s) => s.serialized_len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &OnePassSig::V3(ref s) => s.serialize_into(buf),
        }
    }
}

impl Serialize for OnePassSig3 {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        write_byte(o, 3)?; // Version.
        write_byte(o, self.typ().into())?;
        write_byte(o, self.hash_algo().into())?;
        write_byte(o, self.pk_algo().into())?;
        o.write_all(self.issuer().as_slice())?;
        write_byte(o, self.last_raw())?;

        Ok(())
    }
}

impl NetLength for OnePassSig3 {
    fn net_len(&self) -> usize {
        1 // Version.
            + 1 // Signature type.
            + 1 // Hash algorithm
            + 1 // PK algorithm.
            + 8 // Issuer.
            + 1 // Last.
    }
}

impl SerializeInto for OnePassSig3 {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl<P: key::KeyParts, R: key::KeyRole> Serialize for Key<P, R> {
    fn serialize(&self, o: &mut dyn io::Write) -> Result<()> {
        match self {
            &Key::V4(ref p) => p.serialize(o),
        }
    }
}

impl<P: key::KeyParts, R: key::KeyRole> Key<P, R> {
    fn net_len_key(&self, serialize_secrets: bool) -> usize {
        match self {
            &Key::V4(ref p) => p.net_len_key(serialize_secrets),
        }
    }
}

impl<P: key::KeyParts, R: key::KeyRole> SerializeInto for Key<P, R> {
    fn serialized_len(&self) -> usize {
        match self {
            &Key::V4(ref p) => p.serialized_len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &Key::V4(ref p) => p.serialize_into(buf),
        }
    }
}

impl<P, R> Serialize for Key4<P, R>
    where P: key::KeyParts,
          R: key::KeyRole,
{
    fn serialize(&self, o: &mut dyn io::Write) -> Result<()> {
        self.serialize_key(o, true)
    }
}

impl<P, R> Key4<P, R>
    where P: key::KeyParts,
          R: key::KeyRole,
{
    pub(crate) // For tests in key.
    fn serialize_key(&self, o: &mut dyn io::Write, serialize_secrets: bool)
                     -> Result<()> {
        let have_secret_key = self.secret().is_some() && serialize_secrets;

        write_byte(o, 4)?; // Version.
        write_be_u32(o, self.creation_time().to_pgp()?)?;
        write_byte(o, self.pk_algo().into())?;
        self.mpis().serialize(o)?;

        if have_secret_key {
            match self.secret().unwrap() {
                SecretKeyMaterial::Unencrypted(ref u) => u.map(|mpis| -> Result<()> {
                    // S2K usage.
                    write_byte(o, 0)?;

                    // To compute the checksum, serialize to a buffer first.
                    let mut buf = Vec::new(); // XXX: Protect this vec.
                    mpis.serialize(&mut buf)?;
                    let checksum: usize = buf.iter().map(|x| *x as usize)
                        .sum();

                    // Then, just write out the buffer.
                    o.write_all(&buf)?;
                    write_be_u16(o, checksum as u16)?;
                    Ok(())
                })?,
                SecretKeyMaterial::Encrypted(ref e) => {
                    // S2K usage.
                    write_byte(o, 254)?;
                    write_byte(o, e.algo().into())?;
                    e.s2k().serialize(o)?;
                    o.write_all(e.ciphertext())?;
                },
            }
        }

        Ok(())
    }

    fn net_len_key(&self, serialize_secrets: bool) -> usize {
        let have_secret_key = self.secret().is_some() && serialize_secrets;

        1 // Version.
            + 4 // Creation time.
            + 1 // PK algo.
            + self.mpis().serialized_len()
            + if have_secret_key {
                1 + match self.secret().as_ref().unwrap() {
                    SecretKeyMaterial::Unencrypted(ref u) =>
                        u.map(|mpis| mpis.serialized_len())
                        + 2, // Two octet checksum.
                    SecretKeyMaterial::Encrypted(ref e) =>
                        1 + e.s2k().serialized_len() + e.ciphertext().len(),
                }
            } else {
                0
            }
    }
}

impl<P, R> SerializeInto for Key4<P, R>
    where P: key::KeyParts,
          R: key::KeyRole,
{
    fn serialized_len(&self) -> usize {
        self.net_len_key(true)
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Marker {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(Marker::BODY)?;
        Ok(())
    }
}

impl NetLength for Marker {
    fn net_len(&self) -> usize {
        Marker::BODY.len()
    }
}

impl SerializeInto for Marker {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Trust {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(self.value())?;
        Ok(())
    }
}

impl NetLength for Trust {
    fn net_len(&self) -> usize {
        self.value().len()
    }
}

impl SerializeInto for Trust {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for UserID {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(self.value())?;
        Ok(())
    }
}

impl NetLength for UserID {
    fn net_len(&self) -> usize {
        self.value().len()
    }
}

impl SerializeInto for UserID {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for UserAttribute {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(self.value())?;
        Ok(())
    }
}

impl NetLength for UserAttribute {
    fn net_len(&self) -> usize {
        self.value().len()
    }
}

impl SerializeInto for UserAttribute {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for user_attribute::Subpacket {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            user_attribute::Subpacket::Image(image) =>
                image.serialize(o)?,
            user_attribute::Subpacket::Unknown(tag, data) => {
                BodyLength::Full(1 + data.len() as u32)
                    .serialize(o)?;
                write_byte(o, *tag)?;
                o.write_all(&data[..])?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for user_attribute::Subpacket {
    fn serialized_len(&self) -> usize {
        match self {
            user_attribute::Subpacket::Image(image) =>
                image.serialized_len(),
            user_attribute::Subpacket::Unknown(_tag, data) => {
                let header_len = BodyLength::Full(1 + data.len() as u32)
                    .serialized_len();
                header_len + 1 + data.len()
            }
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for user_attribute::Image {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            user_attribute::Image::JPEG(data) => {
                let header = BodyLength::Full(1 + data.len() as u32);
                header.serialize(o)?;
                write_byte(o, 0)?;
                o.write_all(&data[..])?;
            }
            user_attribute::Image::Unknown(tag, data)
            | user_attribute::Image::Private(tag, data) => {
                let header = BodyLength::Full(1 + data.len() as u32);
                header.serialize(o)?;
                write_byte(o, *tag)?;
                o.write_all(&data[..])?;
            }
        }

        Ok(())
    }
}

impl SerializeInto for user_attribute::Image {
    fn serialized_len(&self) -> usize {
        match self {
            user_attribute::Image::JPEG(data)
            | user_attribute::Image::Unknown(_, data)
            | user_attribute::Image::Private(_, data) =>
                1 + BodyLength::Full(1 + data.len() as u32).serialized_len()
                + data.len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Literal {
    /// Writes the headers of the `Literal` data packet to `o`.
    pub(crate) fn serialize_headers(&self, o: &mut dyn std::io::Write,
                                    write_tag: bool) -> Result<()>
    {
        let filename = if let Some(ref filename) = self.filename() {
            let len = cmp::min(filename.len(), 255) as u8;
            &filename[..len as usize]
        } else {
            &b""[..]
        };

        let date = if let Some(d) = self.date() {
            d.to_pgp()?
        } else {
            0
        };

        if write_tag {
            let len = 1 + (1 + filename.len()) + 4
                + self.body().as_ref().map(|b| b.len()).unwrap_or(0);
            CTB::new(Tag::Literal).serialize(o)?;
            BodyLength::Full(len as u32).serialize(o)?;
        }
        write_byte(o, self.format().into())?;
        write_byte(o, filename.len() as u8)?;
        o.write_all(filename)?;
        write_be_u32(o, date)?;
        Ok(())
    }
}

impl Serialize for Literal {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        let body = if let Some(body) = self.body() {
            &body[..]
        } else {
            &b""[..]
        };

        if TRACE {
            let prefix = &body[..cmp::min(body.len(), 20)];
            eprintln!("Literal::serialize({}{}, {} bytes)",
                      String::from_utf8_lossy(prefix),
                      if body.len() > 20 { "..." } else { "" },
                      body.len());
        }

        self.serialize_headers(o, false)?;
        o.write_all(body)?;

        Ok(())
    }
}

impl NetLength for Literal {
    fn net_len(&self) -> usize {
        1 + (1 + self.filename().map(|f| f.len()).unwrap_or(0)) + 4
            + self.body().as_ref().map(|b| b.len()).unwrap_or(0)
    }
}

impl SerializeInto for Literal {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for CompressedData {
    /// Writes a serialized version of the specified `CompressedData`
    /// packet to `o`.
    ///
    /// This function works recursively: if the `CompressedData` packet
    /// contains any packets, they are also serialized.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        if TRACE {
            eprintln!("CompressedData::serialize(\
                       algo: {}, {:?} children, {:?} bytes)",
                      self.algorithm(),
                      self.children().count(),
                      self.body().as_ref().map(|body| body.len()));
        }

        let o = stream::Message::new(o);
        let mut o = stream::Compressor::new_naked(
            o, self.algorithm(), Default::default(), 0)?;

        // Serialize the packets.
        for p in self.children() {
            p.serialize(&mut o)?;
        }

        // Append the data.
        if let Some(data) = self.body() {
            o.write_all(data)?;
        }

        o.finalize()
    }
}

impl NetLength for CompressedData {
    fn net_len(&self) -> usize {
        let inner_length =
            self.children().map(|p| p.serialized_len()).sum::<usize>()
            + self.body().as_ref().map(|body| body.len()).unwrap_or(0);

        // Worst case, the data gets larger.  Account for that.
        let inner_length = inner_length + cmp::max(inner_length / 2, 128);

        1 // Algorithm.
            + inner_length // Compressed data.
    }
}

impl SerializeInto for CompressedData {
    /// Computes the maximal length of the serialized representation.
    ///
    /// The size of the serialized compressed data packet is tricky to
    /// predict.  First, it depends on the data being compressed.
    /// Second, we emit partial body encoded data.
    ///
    /// This function tries overestimates the length.  However, it may
    /// happen that `serialize_into()` fails.
    ///
    /// # Errors
    ///
    /// If serialization would fail, this function returns 0.
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for PKESK {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &PKESK::V3(ref p) => p.serialize(o),
        }
    }
}

impl SerializeInto for PKESK {
    fn serialized_len(&self) -> usize {
        match self {
            &PKESK::V3(ref p) => p.serialized_len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &PKESK::V3(ref p) => generic_serialize_into(p, buf),
        }
    }
}

impl Serialize for PKESK3 {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        write_byte(o, 3)?; // Version.
        self.recipient().serialize(o)?;
        write_byte(o, self.pk_algo().into())?;
        self.esk().serialize(o)?;

        Ok(())
    }
}

impl NetLength for PKESK3 {
    fn net_len(&self) -> usize {
        1 // Version.
            + 8 // Recipient's key id.
            + 1 // Algo.
            + self.esk().serialized_len()
    }
}

impl SerializeInto for PKESK3 {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for SKESK {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &SKESK::V4(ref s) => s.serialize(o),
            &SKESK::V5(ref s) => s.serialize(o),
        }
    }
}

impl NetLength for SKESK {
    fn net_len(&self) -> usize {
        match self {
            &SKESK::V4(ref s) => s.net_len(),
            &SKESK::V5(ref s) => s.net_len(),
        }
    }
}

impl SerializeInto for SKESK {
    fn serialized_len(&self) -> usize {
        match self {
            &SKESK::V4(ref s) => s.serialized_len(),
            &SKESK::V5(ref s) => s.serialized_len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &SKESK::V4(ref s) => generic_serialize_into(s, buf),
            &SKESK::V5(ref s) => generic_serialize_into(s, buf),
        }
    }
}

impl Serialize for SKESK4 {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        write_byte(o, 4)?; // Version.
        write_byte(o, self.symmetric_algo().into())?;
        self.s2k().serialize(o)?;
        if let Some(ref esk) = self.esk() {
            o.write_all(&esk[..])?;
        }

        Ok(())
    }
}

impl NetLength for SKESK4 {
    fn net_len(&self) -> usize {
        1 // Version.
            + 1 // Algo.
            + self.s2k().serialized_len()
            + self.esk().map(|esk| esk.len()).unwrap_or(0)
    }
}

impl SerializeInto for SKESK4 {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for SKESK5 {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        write_byte(o, 5)?; // Version.
        write_byte(o, self.symmetric_algo().into())?;
        write_byte(o, self.aead_algo().into())?;
        self.s2k().serialize(o)?;
        o.write_all(self.aead_iv())?;
        if let Some(ref esk) = self.esk() {
            o.write_all(&esk[..])?;
        }
        o.write_all(self.aead_digest())?;

        Ok(())
    }
}

impl NetLength for SKESK5 {
    fn net_len(&self) -> usize {
        1 // Version.
            + 1 // Cipher algo.
            + 1 // AEAD algo.
            + self.s2k().serialized_len()
            + self.aead_iv().len()
            + self.esk().map(|esk| esk.len()).unwrap_or(0)
            + self.aead_digest().len()
    }
}

impl SerializeInto for SKESK5 {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for SEIP {
    /// Writes a serialized version of the specified `SEIP`
    /// packet to `o`.
    ///
    /// # Errors
    ///
    /// Returns `Error::InvalidOperation` if this packet has children.
    /// To construct an encrypted message, use
    /// `serialize::stream::Encryptor`.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        if self.children().next().is_some() {
            return Err(Error::InvalidOperation(
                "Cannot encrypt, use serialize::stream::Encryptor".into())
                       .into());
        } else {
            o.write_all(&[self.version()])?;
            if let Some(body) = self.body() {
                o.write_all(&body[..])?;
            }
        }

        Ok(())
    }
}

impl NetLength for SEIP {
    fn net_len(&self) -> usize {
        1 // Version.
            + self.body().as_ref().map(|b| b.len()).unwrap_or(0)
    }
}

impl SerializeInto for SEIP {
    fn serialized_len(&self) -> usize {
        if self.children().next().is_some() {
            0 // XXX
        } else {
            self.gross_len()
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for MDC {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(self.hash())?;
        Ok(())
    }
}

impl NetLength for MDC {
    fn net_len(&self) -> usize {
        20
    }
}

impl SerializeInto for MDC {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for AED {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        match self {
            &AED::V1(ref p) => p.serialize(o),
        }
    }
}

impl SerializeInto for AED {
    fn serialized_len(&self) -> usize {
        match self {
            &AED::V1(ref p) => p.serialized_len(),
        }
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        match self {
            &AED::V1(ref p) => p.serialize_into(buf),
        }
    }
}

impl AED1 {
    /// Writes the headers of the `AED` data packet to `o`.
    fn serialize_headers(&self, o: &mut dyn std::io::Write) -> Result<()> {
        o.write_all(&[1, // Version.
                      self.symmetric_algo().into(),
                      self.aead().into(),
                      self.chunk_size().trailing_zeros() as u8 - 6])?;
        o.write_all(self.iv())?;
        Ok(())
    }
}

impl Serialize for AED1 {
    /// Writes a serialized version of the specified `AED`
    /// packet to `o`.
    ///
    /// # Errors
    ///
    /// Returns `Error::InvalidOperation` if this packet has children.
    /// To construct an encrypted message, use
    /// `serialize::stream::Encryptor`.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        if self.children().next().is_some() {
            return Err(Error::InvalidOperation(
                "Cannot encrypt, use serialize::stream::Encryptor".into())
                       .into());
        } else {
            self.serialize_headers(o)?;

            if let Some(body) = self.body() {
                o.write_all(&body[..])?;
            }
        }

        Ok(())
    }
}

impl NetLength for AED1 {
    fn net_len(&self) -> usize {
        if self.children().next().is_some() {
            0
        } else {
            4 // Headers.
                + self.iv().len()
                + self.body().as_ref().map(|b| b.len()).unwrap_or(0)
        }
    }
}

impl SerializeInto for AED1 {
    fn serialized_len(&self) -> usize {
        self.net_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }
}

impl Serialize for Packet {
    /// Writes a serialized version of the specified `Packet` to `o`.
    ///
    /// This function works recursively: if the packet contains any
    /// packets, they are also serialized.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        CTB::new(self.tag()).serialize(o)?;

        // Special-case the compressed data packet, because we need
        // the accurate length, and CompressedData::net_len()
        // overestimates the size.
        if let Packet::CompressedData(ref p) = self {
            let mut body = Vec::new();
            p.serialize(&mut body)?;
            BodyLength::Full(body.len() as u32).serialize(o)?;
            o.write_all(&body)?;
            return Ok(());
        }

        BodyLength::Full(self.net_len() as u32).serialize(o)?;
        match self {
            &Packet::Unknown(ref p) => p.serialize(o),
            &Packet::Signature(ref p) => p.serialize(o),
            &Packet::OnePassSig(ref p) => p.serialize(o),
            &Packet::PublicKey(ref p) => p.serialize_key(o, false),
            &Packet::PublicSubkey(ref p) => p.serialize_key(o, false),
            &Packet::SecretKey(ref p) => p.serialize_key(o, true),
            &Packet::SecretSubkey(ref p) => p.serialize_key(o, true),
            &Packet::Marker(ref p) => p.serialize(o),
            &Packet::Trust(ref p) => p.serialize(o),
            &Packet::UserID(ref p) => p.serialize(o),
            &Packet::UserAttribute(ref p) => p.serialize(o),
            &Packet::Literal(ref p) => p.serialize(o),
            &Packet::CompressedData(_) => unreachable!("handled above"),
            &Packet::PKESK(ref p) => p.serialize(o),
            &Packet::SKESK(ref p) => p.serialize(o),
            &Packet::SEIP(ref p) => p.serialize(o),
            &Packet::MDC(ref p) => p.serialize(o),
            &Packet::AED(ref p) => p.serialize(o),
        }
    }

    /// Exports a serialized version of the specified `Packet` to `o`.
    ///
    /// This function works recursively: if the packet contains any
    /// packets, they are also serialized.
    fn export(&self, o: &mut dyn std::io::Write) -> Result<()> {
        CTB::new(self.tag()).serialize(o)?;

        // Special-case the compressed data packet, because we need
        // the accurate length, and CompressedData::net_len()
        // overestimates the size.
        if let Packet::CompressedData(ref p) = self {
            let mut body = Vec::new();
            p.export(&mut body)?;
            BodyLength::Full(body.len() as u32).export(o)?;
            o.write_all(&body)?;
            return Ok(());
        }

        BodyLength::Full(self.net_len() as u32).export(o)?;
        match self {
            &Packet::Unknown(ref p) => p.export(o),
            &Packet::Signature(ref p) => p.export(o),
            &Packet::OnePassSig(ref p) => p.export(o),
            &Packet::PublicKey(ref p) => p.serialize_key(o, false),
            &Packet::PublicSubkey(ref p) => p.serialize_key(o, false),
            &Packet::SecretKey(ref p) => p.serialize_key(o, true),
            &Packet::SecretSubkey(ref p) => p.serialize_key(o, true),
            &Packet::Marker(ref p) => p.export(o),
            &Packet::Trust(ref p) => p.export(o),
            &Packet::UserID(ref p) => p.export(o),
            &Packet::UserAttribute(ref p) => p.export(o),
            &Packet::Literal(ref p) => p.export(o),
            &Packet::CompressedData(_) => unreachable!("handled above"),
            &Packet::PKESK(ref p) => p.export(o),
            &Packet::SKESK(ref p) => p.export(o),
            &Packet::SEIP(ref p) => p.export(o),
            &Packet::MDC(ref p) => p.export(o),
            &Packet::AED(ref p) => p.export(o),
        }
    }
}

impl NetLength for Packet {
    fn net_len(&self) -> usize {
        match self {
            &Packet::Unknown(ref p) => p.net_len(),
            &Packet::Signature(ref p) => p.net_len(),
            &Packet::OnePassSig(ref p) => p.net_len(),
            &Packet::PublicKey(ref p) => p.net_len_key(false),
            &Packet::PublicSubkey(ref p) => p.net_len_key(false),
            &Packet::SecretKey(ref p) => p.net_len_key(true),
            &Packet::SecretSubkey(ref p) => p.net_len_key(true),
            &Packet::Marker(ref p) => p.net_len(),
            &Packet::Trust(ref p) => p.net_len(),
            &Packet::UserID(ref p) => p.net_len(),
            &Packet::UserAttribute(ref p) => p.net_len(),
            &Packet::Literal(ref p) => p.net_len(),
            &Packet::CompressedData(ref p) => p.net_len(),
            &Packet::PKESK(ref p) => p.net_len(),
            &Packet::SKESK(ref p) => p.net_len(),
            &Packet::SEIP(ref p) => p.net_len(),
            &Packet::MDC(ref p) => p.net_len(),
            &Packet::AED(ref p) => p.net_len(),
        }
    }
}

impl SerializeInto for Packet {
    fn serialized_len(&self) -> usize {
        (match self {
            &Packet::Unknown(ref p) => p.serialized_len(),
            &Packet::Signature(ref p) => p.serialized_len(),
            &Packet::OnePassSig(ref p) => p.serialized_len(),
            &Packet::PublicKey(ref p) => p.serialized_len(),
            &Packet::PublicSubkey(ref p) => p.serialized_len(),
            &Packet::SecretKey(ref p) => p.serialized_len(),
            &Packet::SecretSubkey(ref p) => p.serialized_len(),
            &Packet::Marker(ref p) => p.serialized_len(),
            &Packet::Trust(ref p) => p.serialized_len(),
            &Packet::UserID(ref p) => p.serialized_len(),
            &Packet::UserAttribute(ref p) => p.serialized_len(),
            &Packet::Literal(ref p) => p.serialized_len(),
            &Packet::CompressedData(ref p) => p.serialized_len(),
            &Packet::PKESK(ref p) => p.serialized_len(),
            &Packet::SKESK(ref p) => p.serialized_len(),
            &Packet::SEIP(ref p) => p.serialized_len(),
            &Packet::MDC(ref p) => p.serialized_len(),
            &Packet::AED(ref p) => p.serialized_len(),
        })
            + 1 // CTB.
            + BodyLength::Full(self.net_len() as u32).serialized_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }

    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_export_into(self, buf)
    }
}

/// References packet bodies.
///
/// Like [`openpgp::Packet`], but instead of owning the packet's bodies,
/// they are referenced.  `PacketRef` is only used to serialize packet
/// bodies (like [`packet::Signature`]) encapsulating them in OpenPGP
/// frames.
///
/// [`openpgp::Packet`]: ../enum.Packet.html
/// [`packet::Signature`]: ../packet/enum.Signature.html
pub enum PacketRef<'a> {
    /// Unknown packet.
    Unknown(&'a packet::Unknown),
    /// Signature packet.
    Signature(&'a packet::Signature),
    /// One pass signature packet.
    OnePassSig(&'a packet::OnePassSig),
    /// Public key packet.
    PublicKey(&'a packet::key::PublicKey),
    /// Public subkey packet.
    PublicSubkey(&'a packet::key::PublicSubkey),
    /// Public/Secret key pair.
    SecretKey(&'a packet::key::SecretKey),
    /// Public/Secret subkey pair.
    SecretSubkey(&'a packet::key::SecretSubkey),
    /// Marker packet.
    Marker(&'a packet::Marker),
    /// Trust packet.
    Trust(&'a packet::Trust),
    /// User ID packet.
    UserID(&'a packet::UserID),
    /// User attribute packet.
    UserAttribute(&'a packet::UserAttribute),
    /// Literal data packet.
    Literal(&'a packet::Literal),
    /// Compressed literal data packet.
    CompressedData(&'a packet::CompressedData),
    /// Public key encrypted data packet.
    PKESK(&'a packet::PKESK),
    /// Symmetric key encrypted data packet.
    SKESK(&'a packet::SKESK),
    /// Symmetric key encrypted, integrity protected data packet.
    SEIP(&'a packet::SEIP),
    /// Modification detection code packet.
    MDC(&'a packet::MDC),
    /// AEAD Encrypted Data Packet.
    AED(&'a packet::AED),
}

impl<'a> PacketRef<'a> {
    /// Returns the `PacketRef's` corresponding OpenPGP tag.
    ///
    /// Tags are explained in [Section 4.3 of RFC 4880].
    ///
    ///   [Section 4.3 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-4.3
    fn tag(&self) -> packet::Tag {
        match self {
            PacketRef::Unknown(ref packet) => packet.tag(),
            PacketRef::Signature(_) => Tag::Signature,
            PacketRef::OnePassSig(_) => Tag::OnePassSig,
            PacketRef::PublicKey(_) => Tag::PublicKey,
            PacketRef::PublicSubkey(_) => Tag::PublicSubkey,
            PacketRef::SecretKey(_) => Tag::SecretKey,
            PacketRef::SecretSubkey(_) => Tag::SecretSubkey,
            PacketRef::Marker(_) => Tag::Marker,
            PacketRef::Trust(_) => Tag::Trust,
            PacketRef::UserID(_) => Tag::UserID,
            PacketRef::UserAttribute(_) => Tag::UserAttribute,
            PacketRef::Literal(_) => Tag::Literal,
            PacketRef::CompressedData(_) => Tag::CompressedData,
            PacketRef::PKESK(_) => Tag::PKESK,
            PacketRef::SKESK(_) => Tag::SKESK,
            PacketRef::SEIP(_) => Tag::SEIP,
            PacketRef::MDC(_) => Tag::MDC,
            PacketRef::AED(_) => Tag::AED,
        }
    }
}

impl<'a> Serialize for PacketRef<'a> {
    /// Writes a serialized version of the specified `Packet` to `o`.
    ///
    /// This function works recursively: if the packet contains any
    /// packets, they are also serialized.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        CTB::new(self.tag()).serialize(o)?;

        // Special-case the compressed data packet, because we need
        // the accurate length, and CompressedData::net_len()
        // overestimates the size.
        if let PacketRef::CompressedData(ref p) = self {
            let mut body = Vec::new();
            p.serialize(&mut body)?;
            BodyLength::Full(body.len() as u32).serialize(o)?;
            o.write_all(&body)?;
            return Ok(());
        }

        BodyLength::Full(self.net_len() as u32).serialize(o)?;
        match self {
            PacketRef::Unknown(p) => p.serialize(o),
            PacketRef::Signature(p) => p.serialize(o),
            PacketRef::OnePassSig(p) => p.serialize(o),
            PacketRef::PublicKey(p) => p.serialize_key(o, false),
            PacketRef::PublicSubkey(p) => p.serialize_key(o, false),
            PacketRef::SecretKey(p) => p.serialize_key(o, true),
            PacketRef::SecretSubkey(p) => p.serialize_key(o, true),
            PacketRef::Marker(p) => p.serialize(o),
            PacketRef::Trust(p) => p.serialize(o),
            PacketRef::UserID(p) => p.serialize(o),
            PacketRef::UserAttribute(p) => p.serialize(o),
            PacketRef::Literal(p) => p.serialize(o),
            PacketRef::CompressedData(_) => unreachable!("handled above"),
            PacketRef::PKESK(p) => p.serialize(o),
            PacketRef::SKESK(p) => p.serialize(o),
            PacketRef::SEIP(p) => p.serialize(o),
            PacketRef::MDC(p) => p.serialize(o),
            PacketRef::AED(p) => p.serialize(o),
        }
    }

    /// Exports a serialized version of the specified `Packet` to `o`.
    ///
    /// This function works recursively: if the packet contains any
    /// packets, they are also serialized.
    fn export(&self, o: &mut dyn std::io::Write) -> Result<()> {
        CTB::new(self.tag()).serialize(o)?;

        // Special-case the compressed data packet, because we need
        // the accurate length, and CompressedData::net_len()
        // overestimates the size.
        if let PacketRef::CompressedData(ref p) = self {
            let mut body = Vec::new();
            p.export(&mut body)?;
            BodyLength::Full(body.len() as u32).export(o)?;
            o.write_all(&body)?;
            return Ok(());
        }

        BodyLength::Full(self.net_len() as u32).export(o)?;
        match self {
            PacketRef::Unknown(p) => p.export(o),
            PacketRef::Signature(p) => p.export(o),
            PacketRef::OnePassSig(p) => p.export(o),
            PacketRef::PublicKey(p) => p.serialize_key(o, false),
            PacketRef::PublicSubkey(p) => p.serialize_key(o, false),
            PacketRef::SecretKey(p) => p.serialize_key(o, true),
            PacketRef::SecretSubkey(p) => p.serialize_key(o, true),
            PacketRef::Marker(p) => p.export(o),
            PacketRef::Trust(p) => p.export(o),
            PacketRef::UserID(p) => p.export(o),
            PacketRef::UserAttribute(p) => p.export(o),
            PacketRef::Literal(p) => p.export(o),
            PacketRef::CompressedData(_) => unreachable!("handled above"),
            PacketRef::PKESK(p) => p.export(o),
            PacketRef::SKESK(p) => p.export(o),
            PacketRef::SEIP(p) => p.export(o),
            PacketRef::MDC(p) => p.export(o),
            PacketRef::AED(p) => p.export(o),
        }
    }
}

impl<'a> NetLength for PacketRef<'a> {
    fn net_len(&self) -> usize {
        match self {
            PacketRef::Unknown(p) => p.net_len(),
            PacketRef::Signature(p) => p.net_len(),
            PacketRef::OnePassSig(p) => p.net_len(),
            PacketRef::PublicKey(p) => p.net_len_key(false),
            PacketRef::PublicSubkey(p) => p.net_len_key(false),
            PacketRef::SecretKey(p) => p.net_len_key(true),
            PacketRef::SecretSubkey(p) => p.net_len_key(true),
            PacketRef::Marker(p) => p.net_len(),
            PacketRef::Trust(p) => p.net_len(),
            PacketRef::UserID(p) => p.net_len(),
            PacketRef::UserAttribute(p) => p.net_len(),
            PacketRef::Literal(p) => p.net_len(),
            PacketRef::CompressedData(p) => p.net_len(),
            PacketRef::PKESK(p) => p.net_len(),
            PacketRef::SKESK(p) => p.net_len(),
            PacketRef::SEIP(p) => p.net_len(),
            PacketRef::MDC(p) => p.net_len(),
            PacketRef::AED(p) => p.net_len(),
        }
    }
}

impl<'a> SerializeInto for PacketRef<'a> {
    fn serialized_len(&self) -> usize {
        (match self {
            PacketRef::Unknown(p) => p.serialized_len(),
            PacketRef::Signature(p) => p.serialized_len(),
            PacketRef::OnePassSig(p) => p.serialized_len(),
            PacketRef::PublicKey(p) => p.serialized_len(),
            PacketRef::PublicSubkey(p) => p.serialized_len(),
            PacketRef::SecretKey(p) => p.serialized_len(),
            PacketRef::SecretSubkey(p) => p.serialized_len(),
            PacketRef::Marker(p) => p.serialized_len(),
            PacketRef::Trust(p) => p.serialized_len(),
            PacketRef::UserID(p) => p.serialized_len(),
            PacketRef::UserAttribute(p) => p.serialized_len(),
            PacketRef::Literal(p) => p.serialized_len(),
            PacketRef::CompressedData(p) => p.serialized_len(),
            PacketRef::PKESK(p) => p.serialized_len(),
            PacketRef::SKESK(p) => p.serialized_len(),
            PacketRef::SEIP(p) => p.serialized_len(),
            PacketRef::MDC(p) => p.serialized_len(),
            PacketRef::AED(p) => p.serialized_len(),
        })
            + 1 // CTB.
            + BodyLength::Full(self.net_len() as u32).serialized_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }

    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_export_into(self, buf)
    }
}

impl Serialize for PacketPile {
    /// Writes a serialized version of the specified `PacketPile` to `o`.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        for p in self.children() {
            p.serialize(o)?;
        }

        Ok(())
    }

    /// Exports a serialized version of the specified `PacketPile` to `o`.
    fn export(&self, o: &mut dyn std::io::Write) -> Result<()> {
        for p in self.children() {
            dbg!(dbg!(p).export(o))?;
        }

        Ok(())
    }
}

impl SerializeInto for PacketPile {
    fn serialized_len(&self) -> usize {
        self.children().map(|p| p.serialized_len()).sum()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_serialize_into(self, buf)
    }

    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        generic_export_into(self, buf)
    }
}

impl Serialize for Message {
    /// Writes a serialized version of the specified `Message` to `o`.
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        use std::ops::Deref;
        self.deref().serialize(o)
    }
}

impl SerializeInto for Message {
    fn serialized_len(&self) -> usize {
        use std::ops::Deref;
        self.deref().serialized_len()
    }

    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
        use std::ops::Deref;
        self.deref().serialize_into(buf)
    }

    fn export_into(&self, buf: &mut [u8]) -> Result<usize> {
        use std::ops::Deref;
        self.deref().export_into(buf)
    }
}

impl Serialize for autocrypt::AutocryptHeader {
    fn serialize(&self, o: &mut dyn std::io::Write) -> Result<()> {
        if self.key.is_none() {
            return Err(Error::InvalidOperation("No key".into()).into());
        }

        for attr in self.attributes.iter() {
            write!(o, "{}={}; ", attr.key, attr.value)?;
        }

        let mut buf = Vec::new();
        self.key.as_ref().unwrap().serialize(&mut buf)?;
        write!(o, "keydata={} ", base64::encode(&buf))?;
        Ok(())
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::constants::CompressionAlgorithm;
    use crate::parse::to_unknown_packet;
    use crate::parse::PacketParserBuilder;
    use crate::parse::Parse;

    // A convenient function to dump binary data to stdout.
    fn binary_pp(data: &[u8]) -> String {
        let mut output = Vec::with_capacity(data.len() * 2 + 3 * data.len() / 4);

        for i in 0..data.len() {
            if i > 0 && i % (4 * 4 * 2) == 0 {
                output.push('\n' as u8);
            } else {
                if i > 0 && i % 2 == 0 {
                    output.push(' ' as u8);
                }
                if i > 0 && i % (4 * 2) == 0 {
                    output.push(' ' as u8);
                }
            }

            let top = data[i] >> 4;
            let bottom = data[i] & 0xFu8;

            if top < 10u8 {
                output.push('0' as u8 + top)
            } else {
                output.push('A' as u8 + (top - 10u8))
            }

            if bottom < 10u8 {
                output.push('0' as u8 + bottom)
            } else {
                output.push('A' as u8 + (bottom - 10u8))
            }
        }

        // We know the content is valid UTF-8.
        String::from_utf8(output).unwrap()
    }

    // Does a bit-wise comparison of two packets ignoring the CTB
    // format, the body length encoding, and whether partial body
    // length encoding was used.
    fn packets_bitwise_compare(filename: &str, packet: &Packet,
                               expected: &[u8], got: &[u8]) {
        let expected = to_unknown_packet(expected).unwrap();
        let got = to_unknown_packet(got).unwrap();

        let expected_body = if let Some(ref data) = expected.body() {
            &data[..]
        } else {
            &b""[..]
        };
        let got_body = if let Some(ref data) = got.body() {
            &data[..]
        } else {
            &b""[..]
        };

        let mut fail = false;
        if expected.tag() != got.tag() {
            eprintln!("Expected a {:?}, got a {:?}", expected.tag(), got.tag());
            fail = true;
        }
        if expected_body != got_body {
            eprintln!("Packet contents don't match (for {}):",
                      filename);
            eprintln!("Expected ({} bytes):\n{}",
                      expected_body.len(), binary_pp(&expected_body));
            eprintln!("Got ({} bytes):\n{}",
                      got_body.len(), binary_pp(&got_body));
            eprintln!("Packet: {:#?}", packet);
            fail = true;
        }
        if fail {
            panic!("Packets don't match (for {}).", filename);
        }
    }

    #[test]
    fn serialize_test_1() {
        // Given a packet in serialized form:
        //
        // - Parse and reserialize it;
        //
        // - Do a bitwise comparison (modulo the body length encoding)
        //   of the original and reserialized data.
        //
        // Note: This test only works on messages with a single packet.
        //
        // Note: This test does not work with non-deterministic
        // packets, like compressed data packets, since the serialized
        // forms may be different.

        let filenames = [
            "literal-mode-b.gpg",
            "literal-mode-t-partial-body.gpg",

            "sig.gpg",

            "public-key-bare.gpg",
            "public-subkey-bare.gpg",
            "userid-bare.gpg",

            "s2k/mode-0-password-1234.gpg",
            "s2k/mode-0-password-1234.gpg",
            "s2k/mode-1-password-123456-1.gpg",
            "s2k/mode-1-password-foobar-2.gpg",
            "s2k/mode-3-aes128-password-13-times-0123456789.gpg",
            "s2k/mode-3-aes192-password-123.gpg",
            "s2k/mode-3-encrypted-key-password-bgtyhn.gpg",
            "s2k/mode-3-password-9876-2.gpg",
            "s2k/mode-3-password-qwerty-1.gpg",
            "s2k/mode-3-twofish-password-13-times-0123456789.gpg",
        ];

        for filename in filenames.iter() {
            // 1. Read the message byte stream into a local buffer.
            let data = crate::tests::message(filename);

            // 2. Parse the message.
            let pile = PacketPile::from_bytes(&data[..]).unwrap();

            // The following test only works if the message has a
            // single top-level packet.
            assert_eq!(pile.children().len(), 1);

            // 3. Serialize the packet it into a local buffer.
            let p = pile.descendants().next().unwrap();
            let mut buffer = Vec::new();
            match p {
                Packet::Literal(_) | Packet::Signature(_)
                    | Packet::PublicKey(_) | Packet::PublicSubkey(_)
                    | Packet::UserID(_) | Packet::SKESK(_) => (),
                ref p => {
                    panic!("Didn't expect a {:?} packet.", p.tag());
                },
            }
            p.serialize(&mut buffer).unwrap();

            // 4. Modulo the body length encoding, check that the
            // reserialized content is identical to the original data.
            packets_bitwise_compare(filename, p, &data[..], &buffer[..]);
        }
    }

    #[test]
    fn serialize_test_1_unknown() {
        // This is an variant of serialize_test_1 that tests the
        // unknown packet serializer.
        let filenames = [
            "compressed-data-algo-1.gpg",
            "compressed-data-algo-2.gpg",
            "compressed-data-algo-3.gpg",
            "recursive-2.gpg",
            "recursive-3.gpg",
        ];

        for filename in filenames.iter() {
            // 1. Read the message byte stream into a local buffer.
            let data = crate::tests::message(filename);

            // 2. Parse the message.
            let u = Packet::Unknown(to_unknown_packet(&data[..]).unwrap());

            // 3. Serialize the packet it into a local buffer.
            let data2 = u.to_vec().unwrap();

            // 4. Modulo the body length encoding, check that the
            // reserialized content is identical to the original data.
            packets_bitwise_compare(filename, &u, &data[..], &data2[..]);
        }

    }

    #[cfg(feature = "compression-deflate")]
    #[test]
    fn serialize_test_2() {
        // Given a packet in serialized form:
        //
        // - Parse, reserialize, and reparse it;
        //
        // - Compare the messages.
        //
        // Note: This test only works on messages with a single packet
        // top-level packet.
        //
        // Note: serialize_test_1 is a better test, because it
        // compares the serialized data, but serialize_test_1 doesn't
        // work if the content is non-deterministic.
        let filenames = [
            "compressed-data-algo-1.gpg",
            "compressed-data-algo-2.gpg",
            "compressed-data-algo-3.gpg",
            "recursive-2.gpg",
            "recursive-3.gpg",
        ];

        for filename in filenames.iter() {
            eprintln!("{}...", filename);

            // 1. Read the message into a local buffer.
            let data = crate::tests::message(filename);

            // 2. Do a shallow parse of the messsage.  In other words,
            // never recurse so that the resulting message only
            // contains the top-level packets.  Any containers will
            // have their raw content stored in packet.content.
            let pile = PacketParserBuilder::from_bytes(&data[..]).unwrap()
                .max_recursion_depth(0)
                .buffer_unread_content()
                //.trace()
                .into_packet_pile().unwrap();

            // 3. Get the first packet.
            let po = pile.descendants().next();
            if let Some(&Packet::CompressedData(ref cd)) = po {
                // 4. Serialize the container.
                let buffer =
                    Packet::CompressedData(cd.clone()).to_vec().unwrap();

                // 5. Reparse it.
                let pile2 = PacketParserBuilder::from_bytes(&buffer[..]).unwrap()
                    .max_recursion_depth(0)
                    .buffer_unread_content()
                    //.trace()
                    .into_packet_pile().unwrap();

                // 6. Make sure the original message matches the
                // serialized and reparsed message.
                if pile != pile2 {
                    eprintln!("Orig:");
                    let p = pile.children().next().unwrap();
                    eprintln!("{:?}", p);
                    let body = p.body().unwrap();
                    eprintln!("Body: {}", body.len());
                    eprintln!("{}", binary_pp(body));

                    eprintln!("Reparsed:");
                    let p = pile2.children().next().unwrap();
                    eprintln!("{:?}", p);
                    let body = p.body().unwrap();
                    eprintln!("Body: {}", body.len());
                    eprintln!("{}", binary_pp(body));

                    assert_eq!(pile, pile2);
                }
            } else {
                panic!("Expected a compressed data data packet.");
            }
        }
    }

    // Create some crazy nesting structures, serialize the messages,
    // reparse them, and make sure we get the same result.
    #[test]
    fn serialize_test_3() {
        use crate::constants::DataFormat::Text as T;

        // serialize_test_1 and serialize_test_2 parse a byte stream.
        // This tests creates the message, and then serializes and
        // reparses it.

        let mut messages = Vec::new();

        // 1: CompressedData(CompressedData { algo: 0 })
        //  1: Literal(Literal { body: "one (3 bytes)" })
        //  2: Literal(Literal { body: "two (3 bytes)" })
        // 2: Literal(Literal { body: "three (5 bytes)" })
        let mut one = Literal::new(T);
        one.set_body(b"one".to_vec());
        let mut two = Literal::new(T);
        two.set_body(b"two".to_vec());
        let mut three = Literal::new(T);
        three.set_body(b"three".to_vec());
        let mut four = Literal::new(T);
        four.set_body(b"four".to_vec());
        let mut five = Literal::new(T);
        five.set_body(b"five".to_vec());
        let mut six = Literal::new(T);
        six.set_body(b"six".to_vec());

        let mut top_level = Vec::new();
        top_level.push(
            CompressedData::new(CompressionAlgorithm::Uncompressed)
                .push(one.clone().into())
                .push(two.clone().into())
                .into());
        top_level.push(three.clone().into());
        messages.push(top_level);

        // 1: CompressedData(CompressedData { algo: 0 })
        //  1: CompressedData(CompressedData { algo: 0 })
        //   1: Literal(Literal { body: "one (3 bytes)" })
        //   2: Literal(Literal { body: "two (3 bytes)" })
        //  2: CompressedData(CompressedData { algo: 0 })
        //   1: Literal(Literal { body: "three (5 bytes)" })
        //   2: Literal(Literal { body: "four (4 bytes)" })
        let mut top_level = Vec::new();
        top_level.push(
            CompressedData::new(CompressionAlgorithm::Uncompressed)
                .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                      .push(one.clone().into())
                      .push(two.clone().into())
                      .into())
                .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                      .push(three.clone().into())
                      .push(four.clone().into())
                      .into())
                .into());
        messages.push(top_level);

        // 1: CompressedData(CompressedData { algo: 0 })
        //  1: CompressedData(CompressedData { algo: 0 })
        //   1: CompressedData(CompressedData { algo: 0 })
        //    1: CompressedData(CompressedData { algo: 0 })
        //     1: Literal(Literal { body: "one (3 bytes)" })
        //     2: Literal(Literal { body: "two (3 bytes)" })
        //  2: CompressedData(CompressedData { algo: 0 })
        //   1: CompressedData(CompressedData { algo: 0 })
        //    1: Literal(Literal { body: "three (5 bytes)" })
        //   2: Literal(Literal { body: "four (4 bytes)" })
        let mut top_level = Vec::new();
        top_level.push(
            CompressedData::new(CompressionAlgorithm::Uncompressed)
                .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                    .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                        .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                            .push(one.clone().into())
                            .push(two.clone().into())
                            .into())
                        .into())
                    .into())
                .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                    .push(CompressedData::new(CompressionAlgorithm::Uncompressed)
                        .push(three.clone().into())
                        .into())
                    .push(four.clone().into())
                    .into())
                .into());
        messages.push(top_level);

        // 1: CompressedData(CompressedData { algo: 0 })
        //  1: Literal(Literal { body: "one (3 bytes)" })
        //  2: Literal(Literal { body: "two (3 bytes)" })
        // 2: Literal(Literal { body: "three (5 bytes)" })
        // 3: Literal(Literal { body: "four (4 bytes)" })
        // 4: CompressedData(CompressedData { algo: 0 })
        //  1: Literal(Literal { body: "five (4 bytes)" })
        //  2: Literal(Literal { body: "six (3 bytes)" })
        let mut top_level = Vec::new();
        top_level.push(
            CompressedData::new(CompressionAlgorithm::Uncompressed)
                .push(one.clone().into())
                .push(two.clone().into())
                .into());
        top_level.push(
            three.clone().into());
        top_level.push(
            four.clone().into());
        top_level.push(
            CompressedData::new(CompressionAlgorithm::Uncompressed)
                .push(five.into())
                .push(six.into())
                .into());
        messages.push(top_level);

        // 1: UserID(UserID { value: "Foo" })
        let mut top_level = Vec::new();
        let uid = UserID::from("Foo");
        top_level.push(uid.into());
        messages.push(top_level);

        for m in messages.into_iter() {
            // 1. The message.
            let pile = PacketPile::from(m);

            pile.pretty_print();

            // 2. Serialize the message into a buffer.
            let mut buffer = Vec::new();
            pile.clone().serialize(&mut buffer).unwrap();

            // 3. Reparse it.
            let pile2 = PacketParserBuilder::from_bytes(&buffer[..]).unwrap()
                //.trace()
                .buffer_unread_content()
                .into_packet_pile().unwrap();

            // 4. Compare the messages.
            if pile != pile2 {
                eprintln!("ORIG...");
                pile.pretty_print();
                eprintln!("REPARSED...");
                pile2.pretty_print();
                panic!("Reparsed packet does not match original packet!");
            }
        }
    }

    #[test]
    fn body_length_edge_cases() {
        {
            let mut buf = vec![];
            BodyLength::Full(0).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\x00"[..]);
        }

        {
            let mut buf = vec![];
            BodyLength::Full(1).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\x01"[..]);
        }
        {
            let mut buf = vec![];
            BodyLength::Full(191).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\xbf"[..]);
        }
        {
            let mut buf = vec![];
            BodyLength::Full(192).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\xc0\x00"[..]);
        }
        {
            let mut buf = vec![];
            BodyLength::Full(193).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\xc0\x01"[..]);
        }
        {
            let mut buf = vec![];
            BodyLength::Full(8383).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\xdf\xff"[..]);
        }
        {
            let mut buf = vec![];
            BodyLength::Full(8384).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\xff\x00\x00\x20\xc0"[..]);
        }
        {
            let mut buf = vec![];
            BodyLength::Full(0xffffffff).serialize(&mut buf).unwrap();
            assert_eq!(&buf[..], &b"\xff\xff\xff\xff\xff"[..]);
        }
    }

    #[test]
    fn export_signature() {
        use crate::tpk::TPKBuilder;

        let (tpk, _) = TPKBuilder::new().generate().unwrap();
        let mut keypair = tpk.primary().clone().mark_parts_secret()
            .into_keypair().unwrap();
        let uid = UserID::from("foo");

        // Make a signature w/o an exportable certification subpacket.
        let sig = uid.bind(
            &mut keypair, &tpk,
            signature::Builder::new(SignatureType::GenericCertificate),
            None, None).unwrap();

        // The signature is exportable.  Try to export it in
        // various ways.
        sig.export(&mut Vec::new()).unwrap();
        sig.export_into(&mut vec![0; sig.serialized_len()]).unwrap();
        sig.export_to_vec().unwrap();
        PacketRef::Signature(&sig).export(&mut Vec::new()).unwrap();
        PacketRef::Signature(&sig).export_into(
            &mut vec![0; PacketRef::Signature(&sig).serialized_len()]).unwrap();
        PacketRef::Signature(&sig).export_to_vec().unwrap();
        let p = Packet::Signature(sig);
        p.export(&mut Vec::new()).unwrap();
        p.export_into(&mut vec![0; p.serialized_len()]).unwrap();
        p.export_to_vec().unwrap();
        let pp = PacketPile::from(vec![p]);
        pp.export(&mut Vec::new()).unwrap();
        pp.export_into(&mut vec![0; pp.serialized_len()]).unwrap();
        pp.export_to_vec().unwrap();

        // Make a signature that is explicitly marked as exportable.
        let sig = uid.bind(
            &mut keypair, &tpk,
            signature::Builder::new(SignatureType::GenericCertificate)
                .set_exportable_certification(true).unwrap(),
            None, None).unwrap();

        // The signature is exportable.  Try to export it in
        // various ways.
        sig.export(&mut Vec::new()).unwrap();
        sig.export_into(&mut vec![0; sig.serialized_len()]).unwrap();
        sig.export_to_vec().unwrap();
        PacketRef::Signature(&sig).export(&mut Vec::new()).unwrap();
        PacketRef::Signature(&sig).export_into(
            &mut vec![0; PacketRef::Signature(&sig).serialized_len()]).unwrap();
        PacketRef::Signature(&sig).export_to_vec().unwrap();
        let p = Packet::Signature(sig);
        p.export(&mut Vec::new()).unwrap();
        p.export_into(&mut vec![0; p.serialized_len()]).unwrap();
        p.export_to_vec().unwrap();
        let pp = PacketPile::from(vec![p]);
        pp.export(&mut Vec::new()).unwrap();
        pp.export_into(&mut vec![0; pp.serialized_len()]).unwrap();
        pp.export_to_vec().unwrap();

        // Make a non-exportable signature.
        let sig = uid.bind(
            &mut keypair, &tpk,
            signature::Builder::new(SignatureType::GenericCertificate)
                .set_exportable_certification(false).unwrap(),
            None, None).unwrap();

        // The signature is not exportable.  Try to export it in
        // various ways.
        sig.export(&mut Vec::new()).unwrap_err();
        sig.export_into(&mut vec![0; sig.serialized_len()]).unwrap_err();
        sig.export_to_vec().unwrap_err();
        PacketRef::Signature(&sig).export(&mut Vec::new()).unwrap_err();
        PacketRef::Signature(&sig).export_into(
            &mut vec![0; PacketRef::Signature(&sig).serialized_len()])
            .unwrap_err();
        PacketRef::Signature(&sig).export_to_vec().unwrap_err();
        let p = Packet::Signature(sig);
        p.export(&mut Vec::new()).unwrap_err();
        p.export_into(&mut vec![0; p.serialized_len()]).unwrap_err();
        p.export_to_vec().unwrap_err();
        let pp = PacketPile::from(vec![p]);
        pp.export(&mut Vec::new()).unwrap_err();
        pp.export_into(&mut vec![0; pp.serialized_len()]).unwrap_err();
        pp.export_to_vec().unwrap_err();
    }
}