Function parse_body_length

crates/openshell-supervisor-network/src/l7/rest.rs:1691–1732

Parse Content-Length or Transfer-Encoding from HTTP headers. Per RFC 7230 Section 3.3.3, rejects requests containing both `Content-Length` and `Transfer-Encoding` headers to prevent request smuggling via CL/TE ambiguity.

(headers: &str)

/// `Content-Length` and `Transfer-Encoding` headers to prevent request
/// smuggling via CL/TE ambiguity.
pub(crate) fn parse_body_length(headers: &str) -> Result<BodyLength> {
    let mut has_te_chunked = false;
    let mut cl_value: Option<u64> = None;

    for line in headers.lines().skip(1) {
        let lower = line.to_ascii_lowercase();
        if lower.starts_with("transfer-encoding:") {
            let val = lower.split_once(':').map_or("", |(_, v)| v.trim());
            if val.split(',').any(|enc| enc.trim() == "chunked") {
                has_te_chunked = true;
            }
        }
        if lower.starts_with("content-length:") {
            let val = lower.split_once(':').map_or("", |(_, v)| v.trim());
            let len: u64 = val
                .parse()
                .map_err(|_| miette!("Request contains invalid Content-Length value"))?;
            if let Some(prev) = cl_value
                && prev != len
            {
                return Err(miette!(
                    "Request contains multiple Content-Length headers with differing values ({prev} vs {len})"
                ));
            }
            cl_value = Some(len);
        }
    }

    if has_te_chunked && cl_value.is_some() {
        return Err(miette!(
            "Request contains both Transfer-Encoding and Content-Length headers"
        ));
    }

    if has_te_chunked {
        return Ok(BodyLength::Chunked);
    }
    if let Some(len) = cl_value {
        return Ok(BodyLength::ContentLength(len));
    }
    Ok(BodyLength::None)
}

/// Relay exactly `len` bytes from reader to writer.
async fn relay_fixed<R, W>(