rust-libp2p/protocols/secio/src/codec/decode.rs

// Copyright 2017 Parity Technologies (UK) Ltd.
//
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//! Individual messages decoding.

use bytes::BytesMut;
use codec::StreamCipher;
use error::SecioError;
use futures::sink::Sink;
use futures::stream::Stream;
use futures::Async;
use futures::Poll;
use futures::StartSend;
use ring::hmac;

/// Wraps around a `Stream<Item = BytesMut>`. The buffers produced by the underlying stream
/// are decoded using the cipher and hmac.
///
/// This struct implements `Stream`, whose stream item are frames of data without the length
/// prefix. The mechanism for removing the length prefix and splitting the incoming data into
/// frames isn't handled by this module.
///
/// Also implements `Sink` for convenience.
pub struct DecoderMiddleware<S> {
    cipher_state: StreamCipher,
    hmac_key: hmac::VerificationKey,
    // TODO: when a new version of ring is released, we can use `hmac_key.digest_algorithm().output_len` instead
    hmac_num_bytes: usize,
    raw_stream: S,
}

impl<S> DecoderMiddleware<S> {
    #[inline]
    pub fn new(
        raw_stream: S,
        cipher: StreamCipher,
        hmac_key: hmac::VerificationKey,
        hmac_num_bytes: usize, // TODO: remove this parameter
    ) -> DecoderMiddleware<S> {
        DecoderMiddleware {
            cipher_state: cipher,
            hmac_key,
            raw_stream,
            hmac_num_bytes,
        }
    }
}

impl<S> Stream for DecoderMiddleware<S>
where
    S: Stream<Item = BytesMut>,
    S::Error: Into<SecioError>,
{
    type Item = Vec<u8>;
    type Error = SecioError;

    #[inline]
    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
        let frame = match self.raw_stream.poll() {
            Ok(Async::Ready(Some(t))) => t,
            Ok(Async::Ready(None)) => return Ok(Async::Ready(None)),
            Ok(Async::NotReady) => return Ok(Async::NotReady),
            Err(err) => return Err(err.into()),
        };

        // TODO: when a new version of ring is released, we can use `hmac_key.digest_algorithm().output_len` instead
        let hmac_num_bytes = self.hmac_num_bytes;

        if frame.len() < hmac_num_bytes {
            debug!("frame too short when decoding secio frame");
            return Err(SecioError::FrameTooShort);
        }

        let (crypted_data, expected_hash) = frame.split_at(frame.len() - hmac_num_bytes);
        debug_assert_eq!(expected_hash.len(), hmac_num_bytes);

        if hmac::verify(&self.hmac_key, crypted_data, expected_hash).is_err() {
            debug!("hmac mismatch when decoding secio frame");
            return Err(SecioError::HmacNotMatching);
        }

        // Note that there is no way to decipher in place with rust-crypto right now.
        let mut decrypted_data = crypted_data.to_vec();
        self.cipher_state
            .process(&crypted_data, &mut decrypted_data);

        Ok(Async::Ready(Some(decrypted_data)))
    }
}

impl<S> Sink for DecoderMiddleware<S>
where
    S: Sink,
{
    type SinkItem = S::SinkItem;
    type SinkError = S::SinkError;

    #[inline]
    fn start_send(&mut self, item: Self::SinkItem) -> StartSend<Self::SinkItem, Self::SinkError> {
        self.raw_stream.start_send(item)
    }

    #[inline]
    fn poll_complete(&mut self) -> Poll<(), Self::SinkError> {
        self.raw_stream.poll_complete()
    }
}