Function relay_fixed

crates/openshell-supervisor-network/src/l7/rest.rs:1735–1764

Relay exactly `len` bytes from reader to writer.

(
    reader: &mut R,
    writer: &mut W,
    len: u64,
    generation_guard: Option<&PolicyGenerationGuard>,
)

/// Relay exactly `len` bytes from reader to writer.
async fn relay_fixed<R, W>(
    reader: &mut R,
    writer: &mut W,
    len: u64,
    generation_guard: Option<&PolicyGenerationGuard>,
) -> Result<()>
where
    R: AsyncRead + Unpin,
    W: AsyncWrite + Unpin,
{
    let mut remaining = len;
    let mut buf = [0u8; RELAY_BUF_SIZE];
    while remaining > 0 {
        let to_read = usize::try_from(remaining)
            .unwrap_or(buf.len())
            .min(buf.len());
        let n = reader.read(&mut buf[..to_read]).await.into_diagnostic()?;
        if n == 0 {
            return Err(miette!(
                "Connection closed with {remaining} bytes remaining"
            ));
        }
        if let Some(guard) = generation_guard {
            guard.ensure_current()?;
        }
        writer.write_all(&buf[..n]).await.into_diagnostic()?;
        remaining -= n as u64;
    }
    Ok(())
}

/// Relay chunked transfer encoding from reader to writer.
///