eggress_protocol_http/forward/

server.rs

use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};

use crate::error::HttpError;
use eggress_core::{BoxStream, TargetAddr, TargetHost};

/// Limits for body copying.
pub struct BodyCopyLimits {
    pub max_chunk_size_line: usize,
    pub max_chunk_size: u64,
    pub max_decoded_body: u64,
    pub max_trailer_line: usize,
    pub max_trailer_bytes: usize,
}

impl Default for BodyCopyLimits {
    fn default() -> Self {
        Self {
            max_chunk_size_line: 1024,
            max_chunk_size: 64 * 1024 * 1024,
            max_decoded_body: 1024 * 1024 * 1024,
            max_trailer_line: 8192,
            max_trailer_bytes: 32 * 1024,
        }
    }
}

/// Report from body copying.
#[derive(Debug, Default)]
pub struct BodyCopyReport {
    pub wire_bytes: u64,
    pub decoded_bytes: u64,
}

/// Report from forwarding a response.
#[derive(Debug, Default)]
pub struct ForwardResponseReport {
    pub bytes_forwarded: u64,
}

/// Copy a request body from reader to writer.
///
/// For Content-Length bodies, copies exactly `len` bytes.
/// For chunked bodies, parses and forwards chunks with proper bounds.
/// Returns byte counts for accounting.
pub async fn copy_request_body<R, W>(
    reader: &mut R,
    writer: &mut W,
    kind: RequestBodyKind,
    limits: &BodyCopyLimits,
) -> Result<BodyCopyReport, HttpError>
where
    R: AsyncRead + Unpin,
    W: AsyncWrite + Unpin,
{
    match kind {
        RequestBodyKind::None => Ok(BodyCopyReport::default()),
        RequestBodyKind::ContentLength(len) => {
            if len > limits.max_decoded_body {
                return Err(HttpError::MalformedRequest("decoded body too large".into()));
            }
            copy_content_length_body(reader, writer, len).await
        }
        RequestBodyKind::Chunked => copy_chunked_body(reader, writer, limits).await,
    }
}

async fn copy_content_length_body<R, W>(
    reader: &mut R,
    writer: &mut W,
    len: u64,
) -> Result<BodyCopyReport, HttpError>
where
    R: AsyncRead + Unpin,
    W: AsyncWrite + Unpin,
{
    let mut remaining = len;
    let mut buf = [0u8; 8192];
    while remaining > 0 {
        let to_read = (remaining as usize).min(buf.len());
        let n = reader.read(&mut buf[..to_read]).await?;
        if n == 0 {
            return Err(HttpError::MalformedRequest("unexpected EOF in body".into()));
        }
        writer.write_all(&buf[..n]).await?;
        remaining -= n as u64;
    }
    Ok(BodyCopyReport {
        wire_bytes: len,
        decoded_bytes: len,
    })
}

async fn copy_chunked_body<R, W>(
    reader: &mut R,
    writer: &mut W,
    limits: &BodyCopyLimits,
) -> Result<BodyCopyReport, HttpError>
where
    R: AsyncRead + Unpin,
    W: AsyncWrite + Unpin,
{
    let mut wire_bytes: u64 = 0;
    let mut decoded_bytes: u64 = 0;

    loop {
        // Read chunk size line
        let size_line = read_bounded_line(reader, limits.max_chunk_size_line).await?;
        wire_bytes += size_line.len() as u64;

        // Parse chunk size (ignore extensions after ';')
        let chunk_size = parse_chunk_size(&size_line)?;

        // Forward the size line
        writer.write_all(&size_line).await?;

        if chunk_size == 0 {
            // Read and forward trailers
            let mut trailer_bytes: u64 = 0;
            loop {
                let trailer = read_bounded_line(reader, limits.max_trailer_line).await?;
                wire_bytes += trailer.len() as u64;
                trailer_bytes += trailer.len() as u64;

                if trailer_bytes > limits.max_trailer_bytes as u64 {
                    return Err(HttpError::MalformedRequest("trailers too large".into()));
                }

                writer.write_all(&trailer).await?;

                if trailer == b"\r\n" {
                    break;
                }
            }
            break;
        }

        // Validate chunk size against limit
        if chunk_size > limits.max_chunk_size {
            return Err(HttpError::MalformedRequest("chunk too large".into()));
        }

        // Validate decoded body limit
        decoded_bytes = decoded_bytes
            .checked_add(chunk_size)
            .ok_or_else(|| HttpError::MalformedRequest("decoded body too large".into()))?;
        if decoded_bytes > limits.max_decoded_body {
            return Err(HttpError::MalformedRequest("decoded body too large".into()));
        }

        // Read exactly chunk_size data bytes
        let mut remaining = chunk_size;
        let mut buf = [0u8; 8192];
        while remaining > 0 {
            let to_read = (remaining as usize).min(buf.len());
            let n = reader.read(&mut buf[..to_read]).await?;
            if n == 0 {
                return Err(HttpError::MalformedRequest(
                    "unexpected EOF in chunk data".into(),
                ));
            }
            writer.write_all(&buf[..n]).await?;
            remaining -= n as u64;
            wire_bytes += n as u64;
        }

        // Read and verify CRLF after chunk data
        let mut crlf = [0u8; 2];
        reader.read_exact(&mut crlf).await?;
        wire_bytes += 2;
        if crlf != *b"\r\n" {
            return Err(HttpError::MalformedRequest(
                "missing CRLF after chunk data".into(),
            ));
        }
        writer.write_all(&crlf).await?;
    }

    Ok(BodyCopyReport {
        wire_bytes,
        decoded_bytes,
    })
}

/// Read a bounded line terminated by \r\n.
async fn read_bounded_line<R: AsyncRead + Unpin>(
    reader: &mut R,
    max_len: usize,
) -> Result<Vec<u8>, HttpError> {
    let mut line = Vec::new();
    let mut temp = [0u8; 1];
    loop {
        if line.len() >= max_len {
            return Err(HttpError::MalformedRequest("line too long".into()));
        }
        let n = reader.read(&mut temp).await?;
        if n == 0 {
            if line.is_empty() {
                return Err(HttpError::MalformedRequest("unexpected EOF".into()));
            }
            return Err(HttpError::MalformedRequest("incomplete line".into()));
        }
        line.push(temp[0]);
        if line.len() >= 2 && &line[line.len() - 2..] == b"\r\n" {
            break;
        }
    }
    Ok(line)
}

async fn read_bounded_line_into<R: AsyncRead + Unpin>(
    reader: &mut R,
    line: &mut Vec<u8>,
    max_len: usize,
) -> Result<(), HttpError> {
    let mut temp = [0u8; 1];
    loop {
        if line.len() >= max_len {
            return Err(HttpError::MalformedResponse("line too long".into()));
        }
        let n = reader.read(&mut temp).await?;
        if n == 0 {
            if line.is_empty() {
                return Err(HttpError::MalformedResponse("unexpected EOF".into()));
            }
            return Err(HttpError::MalformedResponse("incomplete line".into()));
        }
        line.push(temp[0]);
        if line.len() >= 2 && &line[line.len() - 2..] == b"\r\n" {
            break;
        }
    }
    Ok(())
}

/// Parse a chunk size from a line (without trailing CRLF).
/// Supports hex with optional extensions (after ';').
fn parse_chunk_size(line_without_crlf: &[u8]) -> Result<u64, HttpError> {
    let size_field = line_without_crlf
        .split(|b| *b == b';')
        .next()
        .ok_or_else(|| HttpError::MalformedRequest("empty chunk size".into()))?;

    if size_field.is_empty() {
        return Err(HttpError::MalformedRequest("empty chunk size".into()));
    }

    let size_str = std::str::from_utf8(size_field)
        .map_err(|_| HttpError::MalformedRequest("invalid chunk size encoding".into()))?;
    let size_str = size_str.trim();

    u64::from_str_radix(size_str, 16)
        .map_err(|_| HttpError::MalformedRequest("invalid chunk size".into()))
}

/// Describes how the request body is framed.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RequestBodyKind {
    None,
    ContentLength(u64),
    Chunked,
}

/// Determine the request body framing from parsed headers.
///
/// Validates:
/// - Content-Length values (reject conflicting, accept equal duplicates)
/// - Transfer-Encoding (reject TE + CL, require chunked to be final)
/// - Only "chunked" transfer coding is supported in Phase 1
pub fn determine_request_body_kind(
    headers: &[(String, String)],
) -> Result<RequestBodyKind, HttpError> {
    let mut content_lengths: Vec<u64> = Vec::new();
    let mut transfer_encodings: Vec<String> = Vec::new();

    for (name, value) in headers {
        if name.eq_ignore_ascii_case("Content-Length") {
            // Parse each Content-Length value
            let len = value
                .trim()
                .parse::<u64>()
                .map_err(|_| HttpError::InvalidContentLength)?;
            content_lengths.push(len);
        } else if name.eq_ignore_ascii_case("Transfer-Encoding") {
            // Split comma-separated transfer codings
            for coding in value.split(',') {
                let coding = coding.trim().to_string();
                if !coding.is_empty() {
                    transfer_encodings.push(coding);
                }
            }
        }
    }

    // Validate Content-Length
    if !content_lengths.is_empty() {
        // All values must be identical
        let first = content_lengths[0];
        if content_lengths.iter().any(|&cl| cl != first) {
            return Err(HttpError::ConflictingContentLength);
        }
    }

    // Validate Transfer-Encoding
    if !transfer_encodings.is_empty() {
        // TE + CL is rejected in Phase 1
        if !content_lengths.is_empty() {
            return Err(HttpError::TransferEncodingWithContentLength);
        }

        // Check if chunked is present but not the final coding
        let has_chunked = transfer_encodings
            .iter()
            .any(|c| c.eq_ignore_ascii_case("chunked"));
        if has_chunked {
            let last = transfer_encodings.last().unwrap();
            if !last.eq_ignore_ascii_case("chunked") {
                return Err(HttpError::ChunkedNotFinal);
            }
        }

        // Only "chunked" is supported in Phase 1
        for coding in &transfer_encodings {
            if !coding.eq_ignore_ascii_case("chunked") {
                return Err(HttpError::UnsupportedTransferEncoding(coding.clone()));
            }
        }

        return Ok(RequestBodyKind::Chunked);
    }

    if let Some(len) = content_lengths.first() {
        Ok(RequestBodyKind::ContentLength(*len))
    } else {
        Ok(RequestBodyKind::None)
    }
}

/// Maximum size for the HTTP request head (request line + headers).
const MAX_HEAD_SIZE: usize = 32 * 1024;

/// Maximum size for the HTTP response head.
const MAX_RESPONSE_HEAD_SIZE: usize = 32 * 1024;

/// Bound informational responses so an upstream cannot keep the proxy in a
/// response-head loop indefinitely.
const MAX_INFORMATIONAL_RESPONSES: usize = 8;

/// Maximum number of header lines.
const MAX_HEADER_LINES: usize = 128;

/// Headers that must not be forwarded across a proxy (RFC 2616 §13.5.1).
///
/// `Transfer-Encoding: chunked` is preserved because the chunked body is
/// forwarded unchanged.
fn is_hop_by_hop_header(name: &str, value: &str) -> bool {
    let lower = name.to_ascii_lowercase();
    match lower.as_str() {
        "transfer-encoding" => !value.eq_ignore_ascii_case("chunked"),
        _ => matches!(
            lower.as_str(),
            "connection"
                | "keep-alive"
                | "proxy-authenticate"
                | "proxy-authorization"
                | "te"
                | "trailers"
                | "upgrade"
                | "proxy-connection"
        ),
    }
}

/// Extract tokens from the `Connection` header value.
///
/// Per RFC 7230 §6.1, each token names a header that must be removed before
/// forwarding.
fn connection_tokens(headers: &[(String, String)]) -> std::collections::HashSet<String> {
    headers
        .iter()
        .filter(|(name, _)| name.eq_ignore_ascii_case("connection"))
        .flat_map(|(_, value)| value.split(','))
        .map(|token| token.trim().to_ascii_lowercase())
        .filter(|token| !token.is_empty())
        .collect()
}

/// Filter hop-by-hop headers from a header list, returning only end-to-end headers.
///
/// Removes standard hop-by-hop headers plus any headers nominated by
/// `Connection` tokens.  Preserves `Transfer-Encoding: chunked`.
pub fn filter_hop_by_hop(headers: &[(String, String)]) -> Vec<(String, String)> {
    let nominated = connection_tokens(headers);
    headers
        .iter()
        .filter(|(name, value)| {
            let lower = name.to_ascii_lowercase();
            !is_hop_by_hop_header(&lower, value) && !nominated.contains(&lower)
        })
        .cloned()
        .collect()
}

/// Return whether the request contains an expectation this forwarder cannot
/// negotiate. Expectation values are collected case-insensitively and comma-
/// separated values are treated independently.
pub fn has_unsupported_expectation(headers: &[(String, String)]) -> bool {
    headers.iter().any(|(name, value)| {
        name.eq_ignore_ascii_case("Expect")
            && value
                .split(',')
                .any(|expectation| !expectation.trim().is_empty())
    })
}

/// Build an origin-form HTTP request to send to the upstream server.
///
/// Converts the parsed absolute-form request into origin-form by:
/// - Using only the path component as the request target
/// - Filtering out hop-by-hop headers
/// - Adding `Connection: close` to avoid keep-alive complications
pub fn build_origin_request(request: &ForwardRequest) -> String {
    let filtered = filter_hop_by_hop(&request.headers);

    let mut req = format!(
        "{} {} {}\r\n",
        request.method, request.path, request.version
    );

    for (name, value) in &filtered {
        req.push_str(&format!("{}: {}\r\n", name, value));
    }

    // Ensure Connection: close for Phase 1 (no persistent forwarding)
    if !filtered
        .iter()
        .any(|(n, _)| n.eq_ignore_ascii_case("Connection"))
    {
        req.push_str("Connection: close\r\n");
    }

    req.push_str("\r\n");
    req
}

/// Parsed HTTP response from an upstream server.
#[derive(Debug)]
pub struct ForwardResponse {
    pub version: String,
    pub status: u16,
    pub reason: String,
    pub headers: Vec<(String, String)>,
    pub content_length: Option<u64>,
    pub is_chunked: bool,
    /// True if the upstream sent `Connection: close`.
    pub connection_close: bool,
}

/// Read and parse an HTTP response head from the upstream.
async fn read_response_head(stream: &mut BoxStream) -> Result<ForwardResponse, HttpError> {
    let mut head_buf = Vec::with_capacity(1024);
    let mut temp = [0u8; 1];

    loop {
        if head_buf.len() >= MAX_RESPONSE_HEAD_SIZE {
            return Err(HttpError::HeaderTooLarge);
        }

        let n = stream.read(&mut temp).await?;
        if n == 0 {
            return Err(HttpError::MalformedResponse(
                "unexpected EOF reading response".into(),
            ));
        }

        head_buf.push(temp[0]);

        if head_buf.len() >= 4 {
            let len = head_buf.len();
            if &head_buf[len - 4..] == b"\r\n\r\n" {
                break;
            }
        }
    }

    let head_str = String::from_utf8_lossy(&head_buf);
    let mut lines = head_str.split("\r\n");

    // Parse status line
    let status_line = lines
        .next()
        .ok_or_else(|| HttpError::MalformedResponse("empty response".into()))?;

    let parts: Vec<&str> = status_line.split_whitespace().collect();
    if parts.len() < 2 {
        return Err(HttpError::MalformedResponse(format!(
            "invalid status line: {}",
            status_line
        )));
    }

    let version = parts[0].to_string();
    let status: u16 = parts[1]
        .parse()
        .map_err(|e| HttpError::MalformedResponse(format!("invalid status code: {}", e)))?;
    let reason = parts.get(2).unwrap_or(&"").to_string();

    // Parse response headers
    let mut headers = Vec::new();
    let mut content_length = None;
    let mut is_chunked = false;
    let mut connection_close = false;

    for line in lines {
        if line.is_empty() {
            break;
        }
        if let Some((name, value)) = parse_header_line(line) {
            if name.eq_ignore_ascii_case("Content-Length") {
                content_length = Some(
                    value
                        .parse::<u64>()
                        .map_err(|_| HttpError::InvalidContentLength)?,
                );
            } else if name.eq_ignore_ascii_case("Transfer-Encoding") {
                for coding in value.split(',') {
                    let coding_name = coding.trim().split(';').next().unwrap_or("").trim();
                    if coding_name.eq_ignore_ascii_case("chunked") {
                        is_chunked = true;
                    }
                }
            } else if name.eq_ignore_ascii_case("Connection") {
                // Check for "close" token (case-insensitive)
                connection_close = value
                    .split(',')
                    .any(|t| t.trim().eq_ignore_ascii_case("close"));
            }
            headers.push((name, value));
        }
    }

    // Per RFC 7230 §3.3.3, when both Content-Length and Transfer-Encoding
    // are present, Transfer-Encoding takes precedence. A proxy MUST ignore
    // Content-Length if Transfer-Encoding is present.
    if is_chunked {
        content_length = None;
    }

    Ok(ForwardResponse {
        version,
        status,
        reason,
        headers,
        content_length,
        is_chunked,
        connection_close,
    })
}

fn format_response_head(response: &ForwardResponse, force_close: bool) -> String {
    let filtered = filter_hop_by_hop(&response.headers);
    let mut head = format!("HTTP/1.1 {} {}\r\n", response.status, response.reason);

    for (name, value) in &filtered {
        head.push_str(&format!("{}: {}\r\n", name, value));
    }

    if force_close
        && !filtered
            .iter()
            .any(|(n, _)| n.eq_ignore_ascii_case("Connection"))
    {
        head.push_str("Connection: close\r\n");
    }

    head.push_str("\r\n");
    head
}

/// Result of forwarding a response, including upstream connection state.
pub struct ForwardResult {
    pub report: ForwardResponseReport,
    /// HTTP status code of the forwarded response.
    pub status: u16,
    /// True if the upstream connection is still usable (no `Connection: close`).
    pub upstream_alive: bool,
    /// True if the response status indicates the client should not retry.
    pub client_should_close: bool,
}

/// Forward the upstream response back to the client stream.
///
/// Writes the response status line and filtered headers to the client,
/// then relays the body (if any) using content-length or chunked framing.
pub async fn forward_response(
    upstream: &mut BoxStream,
    client: &mut BoxStream,
) -> Result<ForwardResult, HttpError> {
    let mut informational_responses = 0;
    let mut bytes_forwarded: u64 = 0;
    let response = loop {
        let response = read_response_head(upstream).await?;
        if response.status == 101 {
            return Err(HttpError::UpgradeUnsupported);
        }
        if (100..200).contains(&response.status) {
            informational_responses += 1;
            if informational_responses > MAX_INFORMATIONAL_RESPONSES {
                return Err(HttpError::TooManyInformationalResponses);
            }
            let head = format_response_head(&response, false);
            client.write_all(head.as_bytes()).await?;
            bytes_forwarded += head.len() as u64;
            continue;
        }
        break response;
    };
    let head = format_response_head(&response, true);
    client.write_all(head.as_bytes()).await?;
    bytes_forwarded += head.len() as u64;

    // Relay body based on framing
    match (response.content_length, response.is_chunked) {
        (Some(len), _) => {
            let mut remaining = len;
            let mut buf = [0u8; 8192];
            while remaining > 0 {
                let to_read = (remaining as usize).min(buf.len());
                let n = upstream.read(&mut buf[..to_read]).await?;
                if n == 0 {
                    return Err(HttpError::MalformedResponse(
                        "unexpected EOF in response body".into(),
                    ));
                }
                client.write_all(&buf[..n]).await?;
                bytes_forwarded += n as u64;
                remaining -= n as u64;
            }
        }
        (None, true) => {
            let mut size_line_buf = Vec::new();
            loop {
                size_line_buf.clear();
                read_bounded_line_into(upstream, &mut size_line_buf, 1024).await?;

                let size_str = String::from_utf8_lossy(&size_line_buf);
                let size_str = size_str.trim_end_matches("\r\n");
                let size_str = size_str.split(';').next().unwrap_or("").trim();
                let chunk_size = usize::from_str_radix(size_str, 16).map_err(|e| {
                    HttpError::MalformedResponse(format!("invalid chunk size: {}", e))
                })?;

                client.write_all(&size_line_buf).await?;
                bytes_forwarded += size_line_buf.len() as u64;

                if chunk_size == 0 {
                    loop {
                        let mut trailer = Vec::new();
                        read_bounded_line_into(upstream, &mut trailer, 8192).await?;
                        client.write_all(&trailer).await?;
                        bytes_forwarded += trailer.len() as u64;
                        if trailer.len() >= 2 && &trailer[trailer.len() - 2..] == b"\r\n" {
                            if &trailer[..2] == b"\r\n" {
                                break;
                            }
                        } else {
                            break;
                        }
                    }
                    break;
                }

                let mut remaining = chunk_size + 2;
                let mut buf = [0u8; 8192];
                while remaining > 0 {
                    let to_read = remaining.min(buf.len());
                    let n = upstream.read(&mut buf[..to_read]).await?;
                    if n == 0 {
                        return Ok(ForwardResult {
                            report: ForwardResponseReport { bytes_forwarded },
                            status: response.status,
                            upstream_alive: false,
                            client_should_close: true,
                        });
                    }
                    client.write_all(&buf[..n]).await?;
                    bytes_forwarded += n as u64;
                    remaining -= n;
                }
            }
        }
        (None, false) => {
            let mut buf = [0u8; 8192];
            loop {
                let n = upstream.read(&mut buf).await?;
                if n == 0 {
                    break;
                }
                client.write_all(&buf[..n]).await?;
                bytes_forwarded += n as u64;
            }
        }
    }

    // Determine upstream alive: HTTP/1.1 default is keep-alive, HTTP/1.0 default is close
    let upstream_alive = if response.connection_close {
        false
    } else if response.version.contains("1.1") {
        true
    } else {
        // HTTP/1.0: alive only if explicitly requested via Keep-Alive
        response
            .headers
            .iter()
            .any(|(n, v)| n.eq_ignore_ascii_case("Keep-Alive") && !v.is_empty())
    };

    // Client should close if the upstream said close
    let client_should_close = response.connection_close;

    Ok(ForwardResult {
        report: ForwardResponseReport { bytes_forwarded },
        status: response.status,
        upstream_alive,
        client_should_close,
    })
}

/// A parsed HTTP request ready for forwarding.
#[derive(Debug, Clone)]
pub struct ForwardRequest {
    pub method: String,
    pub path: String,
    pub version: String,
    pub headers: Vec<(String, String)>,
    pub target: TargetAddr,
    pub has_body: bool,
    pub content_length: Option<u64>,
    pub is_chunked: bool,
    /// True if the client sent `Connection: close`.
    pub connection_close: bool,
}

impl ForwardRequest {
    /// Compute the request body kind from parsed fields.
    pub fn body_kind(&self) -> RequestBodyKind {
        if self.is_chunked {
            RequestBodyKind::Chunked
        } else if let Some(len) = self.content_length {
            RequestBodyKind::ContentLength(len)
        } else {
            RequestBodyKind::None
        }
    }
}

/// Forward an HTTP request from a client to the target server.
///
/// Parses the absolute-form request, converts to origin-form, forwards
/// the request, and returns the response.
///
/// # Arguments
/// * `stream` - The client stream
///
/// # Returns
/// The parsed forward request and the target address to connect to.
pub async fn forward_request(
    mut stream: BoxStream,
) -> Result<(ForwardRequest, BoxStream), HttpError> {
    let request = read_forward_request(&mut stream).await?;
    Ok((request, stream))
}

/// Read and parse an HTTP forward request from an existing stream.
///
/// Unlike [`forward_request`], this borrows the stream rather than
/// consuming it, enabling persistent-session loops.
pub async fn forward_request_stream(stream: &mut BoxStream) -> Result<ForwardRequest, HttpError> {
    read_forward_request(stream).await
}

/// Read and parse an HTTP forward request with absolute-form target.
async fn read_forward_request(stream: &mut BoxStream) -> Result<ForwardRequest, HttpError> {
    let mut head_buf = Vec::with_capacity(1024);
    let mut temp = [0u8; 1];
    let mut header_count = 0;

    loop {
        if head_buf.len() >= MAX_HEAD_SIZE {
            return Err(HttpError::HeaderTooLarge);
        }

        let n = stream.read(&mut temp).await?;
        if n == 0 {
            return Err(HttpError::MalformedRequest(
                "unexpected EOF reading request".into(),
            ));
        }

        head_buf.push(temp[0]);

        // Check for end of headers
        if head_buf.len() >= 4 {
            let len = head_buf.len();
            if &head_buf[len - 4..] == b"\r\n\r\n" {
                break;
            }
            if head_buf.len() >= 2 && &head_buf[len - 2..] == b"\r\n" {
                header_count += 1;
                if header_count > MAX_HEADER_LINES {
                    return Err(HttpError::TooManyHeaders);
                }
            }
        }
    }

    let head_str = String::from_utf8_lossy(&head_buf);
    let mut lines = head_str.split("\r\n");

    // Parse request line
    let request_line = lines
        .next()
        .ok_or_else(|| HttpError::MalformedRequest("empty request".into()))?;

    let parts: Vec<&str> = request_line.split_whitespace().collect();
    if parts.len() != 3 {
        return Err(HttpError::MalformedRequest(format!(
            "expected 3 parts in request line, got {}",
            parts.len()
        )));
    }

    let method = parts[0].to_string();
    let raw_target = parts[1].to_string();
    let version = parts[2].to_string();

    // Parse absolute-form target: http://host:port/path
    let (target, path) = parse_absolute_uri(&raw_target)?;

    // Parse headers
    let mut headers = Vec::new();

    for line in lines {
        if line.is_empty() {
            break;
        }
        if let Some((name, value)) = parse_header_line(line) {
            // Skip Proxy-Authorization header (don't forward it)
            if name.eq_ignore_ascii_case("Proxy-Authorization") {
                continue;
            }

            headers.push((name, value));
        }
    }

    // Determine body framing from headers
    let body_kind = determine_request_body_kind(&headers)?;
    let (has_body, content_length, is_chunked) = match body_kind {
        RequestBodyKind::None => (false, None, false),
        RequestBodyKind::ContentLength(len) => (len > 0, Some(len), false),
        RequestBodyKind::Chunked => (true, None, true),
    };

    // Determine Connection: close
    let connection_close = headers.iter().any(|(n, v)| {
        n.eq_ignore_ascii_case("Connection")
            && v.split(',').any(|t| t.trim().eq_ignore_ascii_case("close"))
    });

    Ok(ForwardRequest {
        method,
        path,
        version,
        headers,
        target,
        has_body,
        content_length,
        is_chunked,
        connection_close,
    })
}

/// Parse an absolute-form URI into target and path.
///
/// Supports: http://host:port/path, http://host/path
fn parse_absolute_uri(uri: &str) -> Result<(TargetAddr, String), HttpError> {
    // Remove scheme and determine default port
    let (rest, default_port) = if let Some(stripped) = uri.strip_prefix("http://") {
        (stripped, 80)
    } else if let Some(stripped) = uri.strip_prefix("https://") {
        // For HTTPS, we'd need TLS, but for now treat as HTTP
        (stripped, 443)
    } else {
        return Err(HttpError::MalformedRequest(format!(
            "absolute URI required, got: {}",
            uri
        )));
    };

    // Find path separator
    let path_start = rest.find('/').unwrap_or(rest.len());
    let authority = &rest[..path_start];
    let path = if path_start < rest.len() {
        &rest[path_start..]
    } else {
        "/"
    };

    // Parse authority with default port
    let target = parse_authority_with_default(authority, default_port)?;

    Ok((target, path.to_string()))
}

/// Parse an authority (host:port) into a TargetAddr with a default port.
fn parse_authority_with_default(
    authority: &str,
    default_port: u16,
) -> Result<TargetAddr, HttpError> {
    // Handle IPv6 bracketed addresses
    if authority.starts_with('[') {
        let bracket_end = authority.find(']').ok_or_else(|| {
            HttpError::TargetParseError("unclosed bracket in IPv6 address".into())
        })?;

        let ip_str = &authority[1..bracket_end];
        let ip: std::net::IpAddr = ip_str
            .parse()
            .map_err(|e| HttpError::TargetParseError(format!("invalid IPv6 address: {}", e)))?;

        // Check for port after bracket
        let port = if authority
            .as_bytes()
            .get(bracket_end + 1)
            .is_some_and(|&b| b == b':')
        {
            let port_str = authority.get(bracket_end + 2..).ok_or_else(|| {
                HttpError::TargetParseError("missing port after IPv6 address".into())
            })?;
            port_str
                .parse()
                .map_err(|e| HttpError::TargetParseError(format!("invalid port: {}", e)))?
        } else {
            default_port
        };

        return Ok(TargetAddr {
            host: TargetHost::Ip(ip),
            port,
        });
    }

    // Find the last ':' to split host and port
    let colon_pos = authority.rfind(':');

    let (host_str, port) = if let Some(colon_pos) = colon_pos {
        let host_str = &authority[..colon_pos];
        let port_str = &authority[colon_pos + 1..];
        let port: u16 = port_str
            .parse()
            .map_err(|e| HttpError::TargetParseError(format!("invalid port: {}", e)))?;
        (host_str, port)
    } else {
        (authority, default_port)
    };

    // Try to parse as IP first
    if let Ok(ip) = host_str.parse::<std::net::IpAddr>() {
        return Ok(TargetAddr {
            host: TargetHost::Ip(ip),
            port,
        });
    }

    // Otherwise treat as domain
    if host_str.is_empty() {
        return Err(HttpError::TargetParseError("empty host".into()));
    }

    Ok(TargetAddr {
        host: TargetHost::Domain(host_str.to_string()),
        port,
    })
}

/// Parse a header line into (name, value).
///
/// Rejects header names or values containing control characters (NUL, CR, LF)
/// per RFC 7230 §3.2.4.
fn parse_header_line(line: &str) -> Option<(String, String)> {
    let colon_pos = line.find(':')?;
    let name = line[..colon_pos].trim().to_string();
    let value = line[colon_pos + 1..].trim().to_string();

    if name.is_empty() {
        return None;
    }
    if name.bytes().any(|b| b == b'\0' || b == b'\r' || b == b'\n') {
        return None;
    }
    if value
        .bytes()
        .any(|b| b == b'\0' || b == b'\r' || b == b'\n')
    {
        return None;
    }

    Some((name, value))
}

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

    #[test]
    fn test_parse_absolute_uri() {
        let (target, path) = parse_absolute_uri("http://example.com:8080/path").unwrap();
        assert_eq!(
            target,
            TargetAddr {
                host: TargetHost::Domain("example.com".to_string()),
                port: 8080,
            }
        );
        assert_eq!(path, "/path");
    }

    #[test]
    fn test_parse_absolute_uri_no_path() {
        let (target, path) = parse_absolute_uri("http://example.com:80").unwrap();
        assert_eq!(
            target,
            TargetAddr {
                host: TargetHost::Domain("example.com".to_string()),
                port: 80,
            }
        );
        assert_eq!(path, "/");
    }

    #[test]
    fn test_parse_absolute_uri_ipv4() {
        let (target, path) = parse_absolute_uri("http://192.168.1.1:3000/api").unwrap();
        assert_eq!(
            target,
            TargetAddr {
                host: TargetHost::Ip("192.168.1.1".parse().unwrap()),
                port: 3000,
            }
        );
        assert_eq!(path, "/api");
    }

    #[test]
    fn test_parse_absolute_uri_no_scheme() {
        assert!(parse_absolute_uri("example.com/path").is_err());
    }

    #[test]
    fn test_parse_header_line() {
        let (name, value) = parse_header_line("Content-Type: text/html").unwrap();
        assert_eq!(name, "Content-Type");
        assert_eq!(value, "text/html");
    }

    #[test]
    fn test_parse_header_line_no_colon() {
        assert!(parse_header_line("NoColon").is_none());
    }

    #[test]
    fn test_filter_hop_by_hop_connection_nominated() {
        let headers = vec![
            ("Connection".into(), "X-Custom, Keep-Alive".into()),
            ("X-Custom".into(), "value".into()),
            ("Keep-Alive".into(), "timeout=5".into()),
            ("Content-Type".into(), "text/html".into()),
        ];
        let filtered = filter_hop_by_hop(&headers);
        // X-Custom and Keep-Alive should be removed (nominated by Connection),
        // plus connection itself is always removed.
        assert_eq!(filtered.len(), 1);
        assert_eq!(filtered[0].0, "Content-Type");
    }

    #[test]
    fn test_filter_hop_by_hop_preserves_transfer_encoding_chunked() {
        let headers = vec![
            ("Transfer-Encoding".into(), "chunked".into()),
            ("Content-Type".into(), "application/json".into()),
        ];
        let filtered = filter_hop_by_hop(&headers);
        assert_eq!(filtered.len(), 2);
        assert!(filtered.iter().any(|(n, _)| n == "Transfer-Encoding"));
    }

    #[test]
    fn test_filter_hop_by_hop_removes_transfer_encoding_non_chunked() {
        let headers = vec![
            ("Transfer-Encoding".into(), "gzip".into()),
            ("Content-Type".into(), "text/html".into()),
        ];
        let filtered = filter_hop_by_hop(&headers);
        assert_eq!(filtered.len(), 1);
        assert_eq!(filtered[0].0, "Content-Type");
    }

    #[test]
    fn test_filter_connection_tokens_empty() {
        let headers = vec![("Content-Type".into(), "text/html".into())];
        let tokens = connection_tokens(&headers);
        assert!(tokens.is_empty());
    }

    #[test]
    fn test_filter_connection_tokens_multiple() {
        let headers = vec![("Connection".into(), "close, Upgrade".into())];
        let tokens = connection_tokens(&headers);
        assert!(tokens.contains("close"));
        assert!(tokens.contains("upgrade"));
    }

    #[test]
    fn test_determine_body_none() {
        let headers = vec![("Host".into(), "example.com".into())];
        assert_eq!(
            determine_request_body_kind(&headers).unwrap(),
            RequestBodyKind::None
        );
    }

    #[test]
    fn test_determine_body_content_length() {
        let headers = vec![("Content-Length".into(), "42".into())];
        assert_eq!(
            determine_request_body_kind(&headers).unwrap(),
            RequestBodyKind::ContentLength(42)
        );
    }

    #[test]
    fn test_determine_body_duplicate_equal_cl() {
        let headers = vec![
            ("Content-Length".into(), "42".into()),
            ("Content-Length".into(), "42".into()),
        ];
        assert_eq!(
            determine_request_body_kind(&headers).unwrap(),
            RequestBodyKind::ContentLength(42)
        );
    }

    #[test]
    fn test_determine_body_conflicting_cl() {
        let headers = vec![
            ("Content-Length".into(), "42".into()),
            ("Content-Length".into(), "100".into()),
        ];
        assert!(matches!(
            determine_request_body_kind(&headers),
            Err(HttpError::ConflictingContentLength)
        ));
    }

    #[test]
    fn test_determine_body_invalid_cl() {
        let headers = vec![("Content-Length".into(), "abc".into())];
        assert!(matches!(
            determine_request_body_kind(&headers),
            Err(HttpError::InvalidContentLength)
        ));
    }

    #[test]
    fn test_determine_body_chunked() {
        let headers = vec![("Transfer-Encoding".into(), "chunked".into())];
        assert_eq!(
            determine_request_body_kind(&headers).unwrap(),
            RequestBodyKind::Chunked
        );
    }

    #[test]
    fn test_determine_body_te_plus_cl() {
        let headers = vec![
            ("Transfer-Encoding".into(), "chunked".into()),
            ("Content-Length".into(), "42".into()),
        ];
        assert!(matches!(
            determine_request_body_kind(&headers),
            Err(HttpError::TransferEncodingWithContentLength)
        ));
    }

    #[test]
    fn test_determine_body_unsupported_te() {
        let headers = vec![("Transfer-Encoding".into(), "gzip".into())];
        assert!(matches!(
            determine_request_body_kind(&headers),
            Err(HttpError::UnsupportedTransferEncoding(_))
        ));
    }

    #[test]
    fn test_determine_body_chunked_not_final() {
        let headers = vec![("Transfer-Encoding".into(), "chunked, gzip".into())];
        assert!(matches!(
            determine_request_body_kind(&headers),
            Err(HttpError::ChunkedNotFinal)
        ));
    }

    #[test]
    fn test_determine_body_mixed_header_casing() {
        let headers = vec![
            ("content-length".into(), "42".into()),
            ("CONTENT-LENGTH".into(), "42".into()),
        ];
        assert_eq!(
            determine_request_body_kind(&headers).unwrap(),
            RequestBodyKind::ContentLength(42)
        );
    }

    // ===== Body copy tests =====

    #[tokio::test]
    async fn test_copy_chunked_body_simple() {
        let input = b"5\r\nhello\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits)
            .await
            .unwrap();
        assert_eq!(report.decoded_bytes, 5);
        assert_eq!(writer, input);
    }

    #[tokio::test]
    async fn test_copy_chunked_body_multiple_chunks() {
        let input = b"5\r\nhello\r\n6\r\n world\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits)
            .await
            .unwrap();
        assert_eq!(report.decoded_bytes, 11);
        assert_eq!(writer, input);
    }

    #[tokio::test]
    async fn test_copy_chunked_body_uppercase_hex() {
        let input = b"5\r\nhello\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits)
            .await
            .unwrap();
        assert_eq!(report.decoded_bytes, 5);
    }

    #[tokio::test]
    async fn test_copy_chunked_body_with_extension() {
        let input = b"5;ext=value\r\nhello\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits)
            .await
            .unwrap();
        assert_eq!(report.decoded_bytes, 5);
    }

    #[tokio::test]
    async fn test_copy_chunked_body_with_trailer() {
        let input = b"5\r\nhello\r\n0\r\nTrailer: value\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits)
            .await
            .unwrap();
        assert_eq!(report.decoded_bytes, 5);
    }

    #[tokio::test]
    async fn test_copy_chunked_body_malformed_hex() {
        let input = b"ZZ\r\nhello\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let result =
            copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_copy_chunked_body_empty_size() {
        let input = b"\r\nhello\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let result =
            copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_copy_chunked_body_missing_crlf() {
        let input = b"5\r\nhelloX\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let result =
            copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_copy_chunked_body_oversized_chunk() {
        let input = b"FFFFFFFFFFFFFFFF\r\nhello\r\n0\r\n\r\n";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits {
            max_chunk_size: 1024,
            ..Default::default()
        };

        let result =
            copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits).await;
        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_copy_content_length_body() {
        let input = b"hello world";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(
            &mut reader,
            &mut writer,
            RequestBodyKind::ContentLength(11),
            &limits,
        )
        .await
        .unwrap();
        assert_eq!(report.wire_bytes, 11);
        assert_eq!(report.decoded_bytes, 11);
        assert_eq!(writer, input);
    }

    #[tokio::test]
    async fn test_copy_none_body() {
        let mut reader = &b""[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(&mut reader, &mut writer, RequestBodyKind::None, &limits)
            .await
            .unwrap();
        assert_eq!(report.wire_bytes, 0);
        assert_eq!(report.decoded_bytes, 0);
    }

    #[tokio::test]
    async fn test_copy_content_length_body_premature_eof() {
        let input = b"hel"; // only 3 bytes but Content-Length says 11
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let result = copy_request_body(
            &mut reader,
            &mut writer,
            RequestBodyKind::ContentLength(11),
            &limits,
        )
        .await;
        assert!(result.is_err());
        let err = result.unwrap_err();
        let msg = format!("{}", err);
        assert!(
            msg.contains("unexpected EOF"),
            "error should mention EOF: {}",
            msg
        );
    }

    #[tokio::test]
    async fn test_copy_content_length_body_zero_length() {
        let input = b"";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let report = copy_request_body(
            &mut reader,
            &mut writer,
            RequestBodyKind::ContentLength(0),
            &limits,
        )
        .await
        .unwrap();
        assert_eq!(report.wire_bytes, 0);
        assert_eq!(report.decoded_bytes, 0);
    }

    #[tokio::test]
    async fn test_copy_chunked_body_decoded_limit_exceeded() {
        // A single valid chunk of 100 bytes but max_decoded_body is 10
        let chunk_data = "x".repeat(100);
        let input = format!("64\r\n{}\r\n0\r\n\r\n", chunk_data);
        let mut reader = input.as_bytes();
        let mut writer = Vec::new();
        let limits = BodyCopyLimits {
            max_decoded_body: 10,
            ..Default::default()
        };

        let result =
            copy_request_body(&mut reader, &mut writer, RequestBodyKind::Chunked, &limits).await;
        assert!(result.is_err());
        let msg = format!("{}", result.unwrap_err());
        assert!(
            msg.contains("decoded body too large"),
            "error should mention decoded body limit: {}",
            msg
        );
    }

    // ===== Phase 2: HTTP framing and connection-state invariants =====

    #[test]
    fn test_te_plus_cl_rejected_not_forwarded() {
        let headers = vec![
            ("Transfer-Encoding".into(), "chunked".into()),
            ("Content-Length".into(), "0".into()),
        ];
        let result = determine_request_body_kind(&headers);
        assert!(
            matches!(result, Err(HttpError::TransferEncodingWithContentLength)),
            "TE+CL must be rejected to prevent ambiguous framing: {:?}",
            result
        );
    }

    #[test]
    fn test_conflicting_cl_values_rejected() {
        let headers = vec![
            ("Content-Length".into(), "10".into()),
            ("Content-Length".into(), "20".into()),
        ];
        let result = determine_request_body_kind(&headers);
        assert!(
            matches!(result, Err(HttpError::ConflictingContentLength)),
            "conflicting CL values must be rejected: {:?}",
            result
        );
    }

    #[test]
    fn test_equal_duplicate_cl_deterministic() {
        let headers = vec![
            ("Content-Length".into(), "42".into()),
            ("Content-Length".into(), "42".into()),
        ];
        let kind = determine_request_body_kind(&headers).unwrap();
        assert_eq!(kind, RequestBodyKind::ContentLength(42));
    }

    #[test]
    fn test_connection_nominated_headers_removed() {
        let headers = vec![
            ("Connection".into(), "X-Foo, X-Bar".into()),
            ("X-Foo".into(), "a".into()),
            ("X-Bar".into(), "b".into()),
            ("Content-Type".into(), "text/html".into()),
        ];
        let filtered = filter_hop_by_hop(&headers);
        let names: Vec<_> = filtered.iter().map(|(n, _)| n.as_str()).collect();
        assert_eq!(names, vec!["Content-Type"]);
    }

    #[test]
    fn test_ipv6_literal_authority_roundtrip() {
        let (target, path) = parse_absolute_uri("http://[::1]:8080/api").unwrap();
        assert_eq!(
            target,
            TargetAddr {
                host: TargetHost::Ip("::1".parse().unwrap()),
                port: 8080,
            }
        );
        assert_eq!(path, "/api");
    }

    #[test]
    fn test_ipv6_literal_no_port() {
        let (target, _path) = parse_absolute_uri("http://[::1]/path").unwrap();
        assert_eq!(target.port, 80);
        assert_eq!(target.host, TargetHost::Ip("::1".parse().unwrap()));
    }

    #[test]
    fn test_chunked_not_final_rejected() {
        // When chunked is not the final coding and a non-chunked coding is present,
        // the unsupported encoding is rejected first (since only chunked is supported).
        let headers = vec![("Transfer-Encoding".into(), "gzip, chunked".into())];
        let result = determine_request_body_kind(&headers);
        assert!(
            matches!(
                result,
                Err(HttpError::UnsupportedTransferEncoding(_)) | Err(HttpError::ChunkedNotFinal)
            ),
            "chunked not final with unsupported coding must be rejected: {:?}",
            result
        );
    }

    #[test]
    fn test_unsupported_transfer_encoding_rejected() {
        let headers = vec![("Transfer-Encoding".into(), "deflate".into())];
        let result = determine_request_body_kind(&headers);
        assert!(
            matches!(result, Err(HttpError::UnsupportedTransferEncoding(_))),
            "unsupported TE must be rejected: {:?}",
            result
        );
    }

    #[tokio::test]
    async fn test_upstream_connection_close_detected() {
        let response = b"HTTP/1.1 200 OK\r\nContent-Length: 5\r\nConnection: close\r\n\r\nhello";
        // Upstream: server writes response into duplex, forward_response reads from the other end
        let (upstream_read, mut upstream_write) = tokio::io::duplex(4096);
        tokio::spawn(async move {
            upstream_write.write_all(response).await.unwrap();
            upstream_write.shutdown().await.ok();
        });
        // Client: forward_response writes to client_write, we read from client_read
        let (mut client_read, client_write) = tokio::io::duplex(4096);

        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);
        let result = forward_response(&mut upstream, &mut client).await;
        assert!(result.is_ok());
        let fwd = result.unwrap();
        assert!(
            !fwd.upstream_alive,
            "Connection: close should make upstream not alive"
        );
        assert!(
            fwd.client_should_close,
            "client should close when upstream says close"
        );
        // Verify the client received the forwarded response
        let mut buf = Vec::new();
        let _ = tokio::time::timeout(
            std::time::Duration::from_secs(1),
            client_read.read_to_end(&mut buf),
        )
        .await;
        let resp = String::from_utf8_lossy(&buf);
        assert!(
            resp.contains("200 OK"),
            "client should receive response: {resp}"
        );
        assert!(resp.contains("hello"), "client should receive body: {resp}");
    }

    #[tokio::test]
    async fn test_upstream_http11_keepalive_default() {
        let response = b"HTTP/1.1 200 OK\r\nContent-Length: 5\r\n\r\nhello";
        let (upstream_read, mut upstream_write) = tokio::io::duplex(4096);
        tokio::spawn(async move {
            upstream_write.write_all(response).await.unwrap();
            tokio::time::sleep(std::time::Duration::from_millis(200)).await;
        });
        let (mut client_read, client_write) = tokio::io::duplex(4096);

        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);
        let result = forward_response(&mut upstream, &mut client).await;
        assert!(result.is_ok());
        let fwd = result.unwrap();
        assert!(
            fwd.upstream_alive,
            "HTTP/1.1 without Connection: close should be alive"
        );
        assert!(!fwd.client_should_close);
        let mut buf = Vec::new();
        let _ = tokio::time::timeout(
            std::time::Duration::from_secs(1),
            client_read.read_to_end(&mut buf),
        )
        .await;
        let resp = String::from_utf8_lossy(&buf);
        assert!(
            resp.contains("200 OK"),
            "client should receive response: {resp}"
        );
    }

    #[test]
    fn test_filter_hop_by_hop_removes_upgrade() {
        let headers = vec![
            ("Upgrade".into(), "websocket".into()),
            ("Content-Type".into(), "text/html".into()),
        ];
        let filtered = filter_hop_by_hop(&headers);
        assert_eq!(filtered.len(), 1);
        assert_eq!(filtered[0].0, "Content-Type");
    }

    #[test]
    fn test_filter_hop_by_hop_removes_proxy_connection() {
        let headers = vec![
            ("Proxy-Connection".into(), "keep-alive".into()),
            ("Content-Type".into(), "text/html".into()),
        ];
        let filtered = filter_hop_by_hop(&headers);
        assert_eq!(filtered.len(), 1);
        assert_eq!(filtered[0].0, "Content-Type");
    }

    #[tokio::test]
    async fn test_request_body_kind_none_has_no_body() {
        let headers = vec![("Host".into(), "example.com".into())];
        let kind = determine_request_body_kind(&headers).unwrap();
        assert_eq!(kind, RequestBodyKind::None);
        assert!(!matches!(kind, RequestBodyKind::ContentLength(0)));
    }

    #[test]
    fn test_forward_request_body_kind_dispatches_correctly() {
        let req_none = ForwardRequest {
            method: "GET".into(),
            path: "/".into(),
            version: "HTTP/1.1".into(),
            headers: vec![],
            target: TargetAddr {
                host: TargetHost::Domain("example.com".into()),
                port: 80,
            },
            has_body: false,
            content_length: None,
            is_chunked: false,
            connection_close: false,
        };
        assert_eq!(req_none.body_kind(), RequestBodyKind::None);

        let req_cl = ForwardRequest {
            content_length: Some(100),
            has_body: true,
            ..req_none.clone()
        };
        assert_eq!(req_cl.body_kind(), RequestBodyKind::ContentLength(100));

        let req_chunked = ForwardRequest {
            is_chunked: true,
            has_body: true,
            ..req_none.clone()
        };
        assert_eq!(req_chunked.body_kind(), RequestBodyKind::Chunked);
    }

    // ===== Phase 2 gap coverage: invariants 6–9 =====

    #[tokio::test]
    async fn test_copy_request_body_premature_eof() {
        let input = b"short";
        let mut reader = &input[..];
        let mut writer = Vec::new();
        let limits = BodyCopyLimits::default();

        let result = copy_request_body(
            &mut reader,
            &mut writer,
            RequestBodyKind::ContentLength(100),
            &limits,
        )
        .await;
        assert!(
            result.is_err(),
            "Content-Length body with premature EOF must fail"
        );
        let msg = format!("{}", result.unwrap_err());
        assert!(
            msg.contains("unexpected EOF"),
            "error should mention unexpected EOF: {msg}"
        );
    }

    #[tokio::test]
    async fn test_forward_request_stream_after_failure() {
        use tokio::io::AsyncWriteExt;

        let (client_read, mut client_write) = tokio::io::duplex(4096);
        let mut stream: BoxStream = Box::new(client_read);

        let bad_request = b"INVALID\r\n\r\n";
        client_write.write_all(bad_request).await.unwrap();

        let result = forward_request_stream(&mut stream).await;
        assert!(result.is_err(), "malformed request must fail");

        let good_request = b"GET http://example.com/ HTTP/1.1\r\nHost: example.com\r\n\r\n";
        client_write.write_all(good_request).await.unwrap();

        let result2 = forward_request_stream(&mut stream).await;
        assert!(
            result2.is_ok(),
            "valid request after failure must succeed: {:?}",
            result2.err()
        );
        let req = result2.unwrap();
        assert_eq!(req.method, "GET");
        assert_eq!(req.path, "/");
    }

    #[test]
    fn test_build_origin_request_strips_upgrade() {
        let req = ForwardRequest {
            method: "GET".into(),
            path: "/".into(),
            version: "HTTP/1.1".into(),
            headers: vec![
                ("Host".into(), "example.com".into()),
                ("Upgrade".into(), "websocket".into()),
                ("Connection".into(), "Upgrade".into()),
            ],
            target: TargetAddr {
                host: TargetHost::Domain("example.com".into()),
                port: 80,
            },
            has_body: false,
            content_length: None,
            is_chunked: false,
            connection_close: false,
        };
        let origin = build_origin_request(&req);
        assert!(
            !origin.to_lowercase().contains("upgrade"),
            "Upgrade header must be stripped from forwarded request: {origin}"
        );
        assert!(
            !origin.to_lowercase().contains("connection: upgrade"),
            "Connection: Upgrade must be stripped: {origin}"
        );
        assert!(
            origin.contains("Connection: close"),
            "proxy must add Connection: close: {origin}"
        );
    }

    #[test]
    fn test_expectation_detection_is_case_insensitive_and_comma_aware() {
        assert!(has_unsupported_expectation(&[(
            "eXpEcT".into(),
            "foo, 100-continue".into()
        ),]));
        assert!(!has_unsupported_expectation(&[(
            "Expect".into(),
            "  ,  ".into()
        )]));
    }

    #[tokio::test]
    async fn test_forward_response_forwards_informational_responses_before_final() {
        use tokio::io::{AsyncReadExt, AsyncWriteExt};

        let response = b"HTTP/1.1 103 Early Hints\r\nLink: </style.css>\r\n\r\nHTTP/1.1 100 Continue\r\n\r\nHTTP/1.1 200 OK\r\nContent-Length: 5\r\n\r\nhello";
        let (upstream_read, mut upstream_write) = tokio::io::duplex(4096);
        tokio::spawn(async move {
            upstream_write.write_all(response).await.unwrap();
        });
        let (mut client_read, client_write) = tokio::io::duplex(4096);

        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);

        let result = forward_response(&mut upstream, &mut client).await.unwrap();
        assert_eq!(result.status, 200);
        client.shutdown().await.unwrap();

        let mut buf = Vec::new();
        client_read.read_to_end(&mut buf).await.unwrap();
        let resp = String::from_utf8_lossy(&buf);
        assert!(
            resp.starts_with("HTTP/1.1 103 Early"),
            "unexpected forwarded response: {resp:?}"
        );
        assert!(resp.contains("HTTP/1.1 100 Continue"));
        assert!(resp.contains("HTTP/1.1 200 OK"));
        assert!(resp.ends_with("hello"));
        assert!(resp.find("103").unwrap() < resp.find("100").unwrap());
        assert!(resp.find("100").unwrap() < resp.find("200").unwrap());
    }

    #[tokio::test]
    async fn test_forward_response_rejects_switching_protocols() {
        use tokio::io::AsyncWriteExt;

        let (upstream_read, mut upstream_write) = tokio::io::duplex(1024);
        tokio::spawn(async move {
            upstream_write
                .write_all(b"HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\n\r\n")
                .await
                .unwrap();
        });
        let (_client_read, client_write) = tokio::io::duplex(1024);
        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);

        assert!(matches!(
            forward_response(&mut upstream, &mut client).await,
            Err(HttpError::UpgradeUnsupported)
        ));
    }

    #[tokio::test]
    async fn test_forward_response_rejects_invalid_content_length() {
        use tokio::io::AsyncWriteExt;

        let (upstream_read, mut upstream_write) = tokio::io::duplex(1024);
        tokio::spawn(async move {
            upstream_write
                .write_all(b"HTTP/1.1 200 OK\r\nContent-Length: invalid\r\n\r\n")
                .await
                .unwrap();
        });
        let (_client_read, client_write) = tokio::io::duplex(1024);
        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);

        assert!(matches!(
            forward_response(&mut upstream, &mut client).await,
            Err(HttpError::InvalidContentLength)
        ));
    }

    #[tokio::test]
    async fn test_forward_response_rejects_invalid_chunk_size() {
        use tokio::io::AsyncWriteExt;

        let (upstream_read, mut upstream_write) = tokio::io::duplex(1024);
        tokio::spawn(async move {
            upstream_write
                .write_all(b"HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\n\r\nnope\r\n")
                .await
                .unwrap();
        });
        let (_client_read, client_write) = tokio::io::duplex(1024);
        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);

        assert!(matches!(
            forward_response(&mut upstream, &mut client).await,
            Err(HttpError::MalformedResponse(message)) if message.contains("invalid chunk size")
        ));
    }

    #[tokio::test]
    async fn test_forward_response_bounds_informational_responses() {
        use tokio::io::AsyncWriteExt;

        let response = b"HTTP/1.1 103 Early Hints\r\n\r\n";
        let (upstream_read, mut upstream_write) = tokio::io::duplex(4096);
        tokio::spawn(async move {
            for _ in 0..=MAX_INFORMATIONAL_RESPONSES {
                upstream_write.write_all(response).await.unwrap();
            }
        });
        let (_client_read, client_write) = tokio::io::duplex(4096);
        let mut upstream: BoxStream = Box::new(upstream_read);
        let mut client: BoxStream = Box::new(client_write);

        assert!(matches!(
            forward_response(&mut upstream, &mut client).await,
            Err(HttpError::TooManyInformationalResponses)
        ));
    }
}