product-os-proxy 0.0.19

Product OS : Proxy builds on the work of hudsucker, taking it to the next level with a man-in-the-middle proxy server that can tunnel traffic through a VPN utilising Product OS : VPN.
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//! HTTP content encoding/decoding support.
//!
//! This module provides functions for decoding compressed HTTP request and response
//! bodies. It supports the following encoding types:
//!
//! - **gzip** / **x-gzip** - GNU zip compression
//! - **deflate** - zlib compression
//! - **br** - Brotli compression
//! - **zstd** - Zstandard compression
//! - **identity** - No compression (pass-through)
//!
//! The decoder handles multiple `Content-Encoding` headers and nested encodings,
//! decoding them in the correct order (outermost encoding first).
//!
//! # Feature Flag
//!
//! This module is only available when the `decoder` feature is enabled.
//!
//! # Examples
//!
//! ```ignore
//! use product_os_proxy::mitm::{decode_request, decode_response};
//!
//! // Decode a gzip-compressed request
//! let decoded_req = decode_request(request)?;
//!
//! // Decode a compressed response
//! let decoded_res = decode_response(response)?;
//! ```

use async_compression::tokio::bufread::{BrotliDecoder, GzipDecoder, ZlibDecoder, ZstdDecoder};
use hyper::{
    body::{Body as HttpBody, Bytes},
    header::{HeaderMap, HeaderValue, CONTENT_ENCODING, CONTENT_LENGTH},
    Request, Response,
};
use product_os_http_body::{BodyBytes as Body, BodyBytes, BodyError as Error};
use std::{
    io,
    pin::Pin,
    task::{ready, Context, Poll},
};
use tokio::io::{AsyncBufRead, AsyncRead, BufReader};
use tokio_util::io::{ReaderStream, StreamReader};

/// Adapter that converts an HTTP body into a `Stream` of `io::Result<Bytes>`.
///
/// This is used internally to bridge between the HTTP body abstraction and
/// the tokio IO ecosystem needed for decompression.
struct IoStream<T>(T);

impl<T: HttpBody<Data = Bytes, Error = Error> + Unpin> futures_util::Stream for IoStream<T> {
    type Item = Result<Bytes, io::Error>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
        loop {
            return match ready!(Pin::new(&mut self.0).poll_frame(cx)) {
                Some(Ok(frame)) => match frame.into_data() {
                    Ok(buf) => Poll::Ready(Some(Ok(buf))),
                    Err(_) => continue,
                },
                Some(Err(Error::Io(err))) => Poll::Ready(Some(Err(err))),
                Some(Err(err)) => Poll::Ready(Some(Err(io::Error::other(err)))),
                None => Poll::Ready(None),
            };
        }
    }
}

/// Creates a decoder for the given encoding type.
///
/// # Arguments
///
/// * `encoding` - The encoding type as bytes (e.g., `b"gzip"`, `b"br"`)
/// * `reader` - The input reader to decode from
///
/// # Errors
///
/// Returns `Error::Decode` if the encoding type is not supported.
fn decode(
    encoding: &[u8],
    reader: impl AsyncBufRead + Send + Sync + Unpin + 'static,
) -> Result<Box<dyn AsyncRead + Send + Sync + Unpin>, Error> {
    Ok(match encoding {
        b"gzip" | b"x-gzip" => Box::new(GzipDecoder::new(reader)),
        b"deflate" => Box::new(ZlibDecoder::new(reader)),
        b"br" => Box::new(BrotliDecoder::new(reader)),
        b"zstd" => Box::new(ZstdDecoder::new(reader)),
        _ => Err(Error::Decode)?,
    })
}

/// Internal enum representing either a raw body or a decoder chain.
enum Decoder<T> {
    /// Raw HTTP body (no decoding applied yet)
    Body(T),
    /// Decoded stream with one or more decoders applied
    Decoder(Box<dyn AsyncRead + Send + Sync + Unpin>),
}

impl Decoder<Body> {
    /// Apply an encoding layer to this decoder.
    ///
    /// Identity encoding is treated as a no-op. For other encodings,
    /// the appropriate decompression decoder is applied.
    pub fn decode(self, encoding: &[u8]) -> Result<Self, Error> {
        if encoding == b"identity" {
            return Ok(self);
        }

        Ok(Self::Decoder(match self {
            Self::Body(body) => decode(encoding, StreamReader::new(IoStream(body))),
            Self::Decoder(decoder) => decode(encoding, BufReader::new(decoder)),
        }?))
    }
}

impl From<Decoder<Body>> for Body {
    fn from(decoder: Decoder<Body>) -> Body {
        match decoder {
            Decoder::Body(body) => body,
            Decoder::Decoder(decoder) => BodyBytes::from_stream(ReaderStream::new(decoder)),
        }
    }
}

/// Extracts content encodings from headers in reverse order.
///
/// Multiple `Content-Encoding` headers and comma-separated values are supported.
/// The encodings are returned in reverse order because the outermost encoding
/// (listed last in the header) must be decoded first.
fn extract_encodings(headers: &HeaderMap<HeaderValue>) -> impl Iterator<Item = &[u8]> {
    headers
        .get_all(CONTENT_ENCODING)
        .iter()
        .rev()
        .flat_map(|val| {
            val.as_bytes().split(|&b| b == b',').rev().map(|v| {
                let start = v
                    .iter()
                    .position(|&b| b != b' ' && b != b'\t')
                    .unwrap_or(v.len());
                let end = v
                    .iter()
                    .rposition(|&b| b != b' ' && b != b'\t')
                    .map_or(start, |i| i + 1);
                &v[start..end]
            })
        })
}

/// Decodes a body using the specified encoding chain.
///
/// Each encoding in the iterator is applied as a decoding layer.
fn decode_body<'a>(
    encodings: impl IntoIterator<Item = &'a [u8]>,
    body: Body,
) -> Result<Body, Error> {
    let mut decoder = Decoder::Body(body);

    for encoding in encodings {
        decoder = decoder.decode(encoding)?;
    }

    Ok(decoder.into())
}

/// Decode the body of an HTTP request.
///
/// Removes the `Content-Encoding` and `Content-Length` headers and replaces the body
/// with the decoded content. If no `Content-Encoding` header is present, the request
/// is returned unchanged.
///
/// # Arguments
///
/// * `req` - The HTTP request to decode
///
/// # Returns
///
/// The request with decoded body, or the original request if no encoding was present.
///
/// # Errors
///
/// Returns an error if:
/// - The `Content-Encoding` header contains an unsupported encoding
/// - The decompression fails
///
/// # Examples
///
/// ```ignore
/// use product_os_proxy::mitm::decode_request;
///
/// let decoded = decode_request(compressed_request)?;
/// // Body is now decompressed, Content-Encoding header removed
/// ```
#[cfg_attr(docsrs, doc(cfg(feature = "decoder")))]
pub fn decode_request(mut req: Request<Body>) -> Result<Request<Body>, Error> {
    if !req.headers().contains_key(CONTENT_ENCODING) {
        return Ok(req);
    }

    if let Some(val) = req.headers_mut().remove(CONTENT_LENGTH) {
        if val == "0" {
            req.headers_mut().remove(CONTENT_ENCODING);
            return Ok(req);
        }
    }

    let (mut parts, body) = req.into_parts();

    let body = {
        let encodings = extract_encodings(&parts.headers);
        decode_body(encodings, body)?
    };

    parts.headers.remove(CONTENT_ENCODING);

    Ok(Request::from_parts(parts, body))
}

/// Decode the body of an HTTP response.
///
/// Removes the `Content-Encoding` and `Content-Length` headers and replaces the body
/// with the decoded content. If no `Content-Encoding` header is present, the response
/// is returned unchanged.
///
/// # Arguments
///
/// * `res` - The HTTP response to decode
///
/// # Returns
///
/// The response with decoded body, or the original response if no encoding was present.
///
/// # Errors
///
/// Returns an error if:
/// - The `Content-Encoding` header contains an unsupported encoding
/// - The decompression fails
///
/// # Examples
///
/// ```ignore
/// use product_os_proxy::mitm::decode_response;
///
/// let decoded = decode_response(compressed_response)?;
/// // Body is now decompressed, Content-Encoding header removed
/// ```
#[cfg_attr(docsrs, doc(cfg(feature = "decoder")))]
pub fn decode_response(mut res: Response<Body>) -> Result<Response<Body>, Error> {
    if !res.headers().contains_key(CONTENT_ENCODING) {
        return Ok(res);
    }

    if let Some(val) = res.headers_mut().remove(CONTENT_LENGTH) {
        if val == "0" {
            res.headers_mut().remove(CONTENT_ENCODING);
            return Ok(res);
        }
    }

    let (mut parts, body) = res.into_parts();

    let body = {
        let encodings = extract_encodings(&parts.headers);
        decode_body(encodings, body)?
    };

    parts.headers.remove(CONTENT_ENCODING);

    Ok(Response::from_parts(parts, body))
}

#[cfg(test)]
mod tests {
    use super::*;

    mod extract_encodings {
        use super::*;

        #[test]
        fn no_headers() {
            let headers = HeaderMap::new();

            assert_eq!(extract_encodings(&headers).count(), 0);
        }

        #[test]
        fn single_header_single_value() {
            let mut headers = HeaderMap::new();
            headers.append(CONTENT_ENCODING, HeaderValue::from_static("gzip"));

            assert_eq!(
                extract_encodings(&headers).collect::<Vec<_>>(),
                vec![b"gzip"]
            );
        }

        #[test]
        fn single_header_multiple_values() {
            let mut headers = HeaderMap::new();
            headers.append(CONTENT_ENCODING, HeaderValue::from_static("gzip, deflate"));

            assert_eq!(
                extract_encodings(&headers).collect::<Vec<_>>(),
                vec![&b"deflate"[..], &b"gzip"[..]]
            );
        }

        #[test]
        fn multiple_headers_single_value() {
            let mut headers = HeaderMap::new();
            headers.append(CONTENT_ENCODING, HeaderValue::from_static("gzip"));
            headers.append(CONTENT_ENCODING, HeaderValue::from_static("deflate"));

            assert_eq!(
                extract_encodings(&headers).collect::<Vec<_>>(),
                vec![&b"deflate"[..], &b"gzip"[..]]
            );
        }

        #[test]
        fn multiple_headers_multiple_values() {
            let mut headers = HeaderMap::new();
            headers.append(CONTENT_ENCODING, HeaderValue::from_static("gzip, deflate"));
            headers.append(CONTENT_ENCODING, HeaderValue::from_static("br, zstd"));

            assert_eq!(
                extract_encodings(&headers).collect::<Vec<_>>(),
                vec![&b"zstd"[..], &b"br"[..], &b"deflate"[..], &b"gzip"[..]]
            );
        }
    }

    async fn to_bytes<H: HttpBody>(body: H) -> Bytes
    where
        H::Error: std::fmt::Debug,
    {
        use http_body_util::BodyExt;
        body.collect().await.unwrap().to_bytes()
    }

    mod decode_body {
        use super::*;
        use async_compression::tokio::bufread::{BrotliEncoder, GzipEncoder};

        #[tokio::test]
        async fn no_encodings() {
            let content = "hello, world";
            let body = Body::from(content);

            assert_eq!(
                &to_bytes(decode_body(vec![], body).unwrap()).await[..],
                content.as_bytes()
            );
        }

        #[tokio::test]
        async fn identity_encoding() {
            let content = "hello, world";
            let body = Body::from(content);

            assert_eq!(
                &to_bytes(decode_body(vec![&b"identity"[..]], body).unwrap()).await[..],
                content.as_bytes()
            );
        }

        #[tokio::test]
        async fn single_encoding() {
            let content = b"hello, world";
            let encoder = GzipEncoder::new(&content[..]);
            let body = Body::from_stream(ReaderStream::new(encoder));

            assert_eq!(
                &to_bytes(decode_body(vec![&b"gzip"[..]], body).unwrap()).await[..],
                content
            );
        }

        #[tokio::test]
        async fn multiple_encodings() {
            let content = b"hello, world";
            let encoder = GzipEncoder::new(&content[..]);
            let encoder = BrotliEncoder::new(BufReader::new(encoder));
            let body = Body::from_stream(ReaderStream::new(encoder));

            assert_eq!(
                &to_bytes(decode_body(vec![&b"br"[..], &b"gzip"[..]], body).unwrap()).await[..],
                content
            );
        }

        #[test]
        fn invalid_encoding() {
            let body = Body::empty();

            assert!(decode_body(vec![&b"invalid"[..]], body).is_err());
        }
    }

    mod decode_request {
        use super::*;
        use async_compression::tokio::bufread::GzipEncoder;

        #[tokio::test]
        async fn decodes_request() {
            let content = b"hello, world";
            let encoder = GzipEncoder::new(&content[..]);
            let req = Request::builder()
                .header(CONTENT_LENGTH, 123)
                .header(CONTENT_ENCODING, "gzip")
                .body(Body::from_stream(ReaderStream::new(encoder)))
                .unwrap();

            let req = decode_request(req).unwrap();

            assert!(!req.headers().contains_key(CONTENT_LENGTH));
            assert!(!req.headers().contains_key(CONTENT_ENCODING));
            assert_eq!(&to_bytes(req.into_body()).await[..], content);
        }
    }

    mod decode_response {
        use super::*;
        use async_compression::tokio::bufread::GzipEncoder;

        #[tokio::test]
        async fn decodes_response() {
            let content = b"hello, world";
            let encoder = GzipEncoder::new(&content[..]);
            let res = Response::builder()
                .header(CONTENT_LENGTH, 123)
                .header(CONTENT_ENCODING, "gzip")
                .body(Body::from_stream(ReaderStream::new(encoder)))
                .unwrap();

            let res = decode_response(res).unwrap();

            assert!(!res.headers().contains_key(CONTENT_LENGTH));
            assert!(!res.headers().contains_key(CONTENT_ENCODING));
            assert_eq!(&to_bytes(res.into_body()).await[..], content);
        }
    }
}