flare.http.streaming_serialize

Renders a StreamingResponse[B: Body] to wire bytes per RFC 7230 §3 (status line + headers) + RFC 7230 §4.1 (chunked transfer-coding) when B.content_length() is unknown, or plain Content-Length framing when it's known.

The reactor's view-aware write loop (a focused follow-up) calls this serializer per writable edge to pull-and-write one chunk at a time. Callers that don't need the streaming benefit (every existing handler that returns a Response) keep the buffer-then-send path through the existing _serialize_response in flare/http/_server_reactor_impl.

Why a standalone serializer rather than a parallel reactor:

C3's experience showed that adding a parallel reactor entry parametric over a trait-method-with-origin is currently slow to specialise in Mojo. The streaming serializer here is a plain function — no parametric trait dispatch, no per-handler specialization explosion — so it compiles fast and is easy to test independently. The reactor adoption that calls this serializer is a small follow-up commit (~30 lines of glue) that the user can review separately once Mojo's specialization slowness is resolved or the team commits to the slower compile times.

Wire-framing semantics:

• body.content_length() returns Some(n):

  • Header line: Content-Length: n\r\n.
  • Body bytes: emit each chunk inline until next_chunk returns None. Total emitted bytes equal n by contract.

• body.content_length() returns None:

  • Header line: Transfer-Encoding: chunked\r\n.
  • Body bytes: per chunk, emit hex_length\r\n + chunk + \r\n. Final terminator: 0\r\n\r\n.

The serializer is cancel-aware: if cancel.cancelled() flips between chunks, the write loop emits the final chunked terminator and returns — the connection closes cleanly without breaking the framing contract. Callers that need to abort mid-chunk should close the underlying socket; the framing guarantee covers cooperative cancel only.

def serialize_streaming_response[B: Body](var resp: StreamingResponse[B], cancel: Cancel, keep_alive: Bool = True) -> List[UInt8]