From 3d629c93c5185be2bf824d4a04746acf413900a1 Mon Sep 17 00:00:00 2001
From: Laura <laura@wiese2.org>
Date: Fri, 29 Aug 2025 19:26:55 +0200
Subject: [PATCH] harden response streaming

---
 chat.go   |  6 ++---
 stream.go | 72 ++++++++++++++++++++++++++++++++++++++-----------------
 2 files changed, 53 insertions(+), 25 deletions(-)

diff --git a/chat.go b/chat.go
index 601418d..6dca2f1 100644
--- a/chat.go
+++ b/chat.go
@@ -256,7 +256,9 @@ func HandleChat(w http.ResponseWriter, r *http.Request) {
 
 	debug("preparing stream")
 
-	response, err := NewStream(w)
+	ctx := r.Context()
+
+	response, err := NewStream(w, ctx)
 	if err != nil {
 		RespondJson(w, http.StatusBadRequest, map[string]any{
 			"error": err.Error(),
@@ -267,8 +269,6 @@ func HandleChat(w http.ResponseWriter, r *http.Request) {
 
 	debug("handling request")
 
-	ctx := r.Context()
-
 	for iteration := range raw.Iterations {
 		debug("iteration %d of %d", iteration+1, raw.Iterations)
 
diff --git a/stream.go b/stream.go
index a50181c..8338fc5 100644
--- a/stream.go
+++ b/stream.go
@@ -1,9 +1,12 @@
 package main
 
 import (
+	"bytes"
+	"context"
 	"encoding/json"
 	"errors"
 	"net/http"
+	"sync"
 
 	"github.com/revrost/go-openrouter"
 )
@@ -14,42 +17,31 @@ type Chunk struct {
 }
 
 type Stream struct {
-	wr http.ResponseWriter
-	fl http.Flusher
-	en *json.Encoder
+	wr  http.ResponseWriter
+	ctx context.Context
 }
 
-func NewStream(w http.ResponseWriter) (*Stream, error) {
-	flusher, ok := w.(http.Flusher)
-	if !ok {
-		return nil, errors.New("failed to create flusher")
-	}
+var pool = sync.Pool{
+	New: func() interface{} {
+		return &bytes.Buffer{}
+	},
+}
 
+func NewStream(w http.ResponseWriter, ctx context.Context) (*Stream, error) {
 	w.Header().Set("Content-Type", "text/event-stream")
 	w.Header().Set("Cache-Control", "no-cache")
 	w.Header().Set("Connection", "keep-alive")
 
 	return &Stream{
-		wr: w,
-		fl: flusher,
-		en: json.NewEncoder(w),
+		wr:  w,
+		ctx: ctx,
 	}, nil
 }
 
 func (s *Stream) Send(ch Chunk) error {
 	debugIf(ch.Type == "error", "error: %v", ch.Text)
 
-	if err := s.en.Encode(ch); err != nil {
-		return err
-	}
-
-	if _, err := s.wr.Write([]byte("\n\n")); err != nil {
-		return err
-	}
-
-	s.fl.Flush()
-
-	return nil
+	return WriteChunk(s.wr, s.ctx, ch)
 }
 
 func ReasoningChunk(text string) Chunk {
@@ -94,3 +86,39 @@ func GetErrorMessage(err error) string {
 
 	return err.Error()
 }
+
+func WriteChunk(w http.ResponseWriter, ctx context.Context, chunk any) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+
+	buf := pool.Get().(*bytes.Buffer)
+
+	buf.Reset()
+
+	defer pool.Put(buf)
+
+	if err := json.NewEncoder(buf).Encode(chunk); err != nil {
+		return err
+	}
+
+	buf.Write([]byte("\n\n"))
+
+	if _, err := w.Write(buf.Bytes()); err != nil {
+		return err
+	}
+
+	flusher, ok := w.(http.Flusher)
+	if !ok {
+		return errors.New("failed to create flusher")
+	}
+
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+		flusher.Flush()
+
+		return nil
+	}
+}