fix: always stream from upstream, accumulate for non-streaming clients

handler.go

@@ -103,12 +103,12 @@ func handleChatCompletions(w http.ResponseWriter, r *http.Request) {
 
 	// Convert to Anthropic format
 	anthropicReq := ConvertOpenAIRequest(&req)
+	anthropicReq.Stream = true // Always stream from upstream for reliability
 
-	// Check streaming
-	isStream := req.Stream != nil && *req.Stream
+	log.Printf("[debug] Sending to upstream %s, model=%s", config.UpstreamURL, req.Model)
 
-	// Proxy to upstream
-	resp, err := proxyToUpstream(anthropicReq, apiKey, sessionID, isStream)
+	// Proxy to upstream (always streaming)
+	resp, err := proxyToUpstream(anthropicReq, apiKey, sessionID, true)
 	if err != nil {
 		writeError(w, http.StatusBadGateway, fmt.Sprintf("Upstream request failed: %v", err), "upstream_error", "proxy_error")
 		return
@@ -117,20 +117,20 @@ func handleChatCompletions(w http.ResponseWriter, r *http.Request) {
 
 	if resp.StatusCode != http.StatusOK {
 		respBody, _ := io.ReadAll(resp.Body)
+		log.Printf("[debug] Upstream error status %d: %s", resp.StatusCode, string(respBody))
 		writeError(w, http.StatusBadGateway, fmt.Sprintf("Upstream returned error: %s", string(respBody)), "upstream_error", fmt.Sprintf("status_%d", resp.StatusCode))
 		return
 	}
 
+	isStream := req.Stream != nil && *req.Stream
+
 	if isStream {
-		// Handle streaming response
+		// Stream to client
 		w.Header().Set("content-type", "text/event-stream")
 		w.Header().Set("cache-control", "no-cache")
 		w.Header().Set("connection", "keep-alive")
 
-		// Convert SSE stream on the fly
-		reader := io.NopCloser(resp.Body)
-		scanner := bufio.NewScanner(reader)
-		// Use a larger buffer for potential large JSON lines
+		scanner := bufio.NewScanner(resp.Body)
 		buf := make([]byte, 0, 64*1024)
 		scanner.Buffer(buf, 1024*1024)
 
@@ -144,9 +144,7 @@ func handleChatCompletions(w http.ResponseWriter, r *http.Request) {
 			}
 			dataStr := strings.TrimPrefix(line, "data: ")
 			if dataStr == "[DONE]" {
-				fmt.Fprintf(w, "data: [DONE]\n\n")
-				w.(http.Flusher).Flush()
-				continue
+				break
 			}
 
 			var event struct {
@@ -156,7 +154,6 @@ func handleChatCompletions(w http.ResponseWriter, r *http.Request) {
 				continue
 			}
 
-			// Process event and write OpenAI SSE
 			openAIData := processAnthropicEvent(dataStr, chunkID, req.Model, created)
 			if openAIData != "" {
 				fmt.Fprintf(w, "data: %s\n\n", openAIData)
@@ -166,20 +163,89 @@ func handleChatCompletions(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintf(w, "data: [DONE]\n\n")
 		w.(http.Flusher).Flush()
 	} else {
-		// Non-streaming response
-		respBody, err := io.ReadAll(resp.Body)
-		if err != nil {
-			writeError(w, http.StatusBadGateway, "Failed to read upstream response", "upstream_error", "body_read_error")
-			return
+		// Non-streaming to client: accumulate upstream stream into a single response
+		scanner := bufio.NewScanner(resp.Body)
+		buf := make([]byte, 0, 64*1024)
+		scanner.Buffer(buf, 1024*1024)
+
+		var textContent string
+		var stopReason string
+		var usage AnthropicUsage
+		msgID := ""
+
+		for scanner.Scan() {
+			line := scanner.Text()
+			if !strings.HasPrefix(line, "data: ") {
+				continue
+			}
+			dataStr := strings.TrimPrefix(line, "data: ")
+			if dataStr == "[DONE]" {
+				break
 			}
 
-		var anthropicResp AnthropicResponse
-		if err := json.Unmarshal(respBody, &anthropicResp); err != nil {
-			writeError(w, http.StatusBadGateway, "Failed to parse upstream response", "upstream_error", "json_decode_error")
-			return
+			var event struct {
+				Type string `json:"type"`
+			}
+			if err := json.Unmarshal([]byte(dataStr), &event); err != nil {
+				continue
 			}
 
-		openAIResp := ConvertAnthropicResponse(&anthropicResp, req.Model)
+			switch event.Type {
+			case "message_start":
+				var msgStart struct {
+					Message struct {
+						Id    string         `json:"id"`
+						Usage AnthropicUsage `json:"usage"`
+					} `json:"message"`
+				}
+				if json.Unmarshal([]byte(dataStr), &msgStart) == nil {
+					msgID = msgStart.Message.Id
+					usage.InputTokens = msgStart.Message.Usage.InputTokens
+				}
+
+			case "content_block_delta":
+				var delta struct {
+					Delta struct {
+						Text string `json:"text,omitempty"`
+					} `json:"delta"`
+				}
+				if json.Unmarshal([]byte(dataStr), &delta) == nil {
+					textContent += delta.Delta.Text
+				}
+
+			case "message_delta":
+				var msgDelta struct {
+					Delta      struct{}               `json:"delta"`
+					Usage      *AnthropicUsage        `json:"usage,omitempty"`
+					StopReason string                 `json:"stop_reason,omitempty"`
+				}
+				if json.Unmarshal([]byte(dataStr), &msgDelta) == nil {
+					stopReason = msgDelta.StopReason
+					if msgDelta.Usage != nil {
+						usage.OutputTokens = msgDelta.Usage.OutputTokens
+					}
+				}
+			}
+		}
+
+		openAIResp := &ChatCompletionResponse{
+			ID:      msgID,
+			Object:  "chat.completion",
+			Created: time.Now().Unix(),
+			Model:   req.Model,
+			Choices: []Choice{
+				{
+					Index:        0,
+					Message:      Message{Role: "assistant", Content: textContent},
+					FinishReason: mapStopReason(stopReason),
+				},
+			},
+			Usage: Usage{
+				PromptTokens:     usage.InputTokens,
+				CompletionTokens: usage.OutputTokens,
+				TotalTokens:      usage.InputTokens + usage.OutputTokens,
+			},
+		}
 
 		w.Header().Set("content-type", "application/json")
 		json.NewEncoder(w).Encode(openAIResp)
@@ -195,12 +261,6 @@ func processAnthropicEvent(dataStr, chunkID, model string, created int64) string
 	}
 
 	switch event.Type {
-	case "message_start":
-		return ""
-
-	case "content_block_start":
-		return ""
-
 	case "content_block_delta":
 		var delta struct {
 			Index int `json:"index"`
@@ -301,7 +361,7 @@ func proxyToUpstream(req *AnthropicRequest, apiKey, sessionID string, stream boo
 		httpReq.Header.Set("anthropic-sse-beta", "output-2025-05-14")
 	}
 
-	ctx, cancel := context.WithTimeout(context.Background(), 120*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), 300*time.Second)
 	defer cancel()
 
 	httpReq = httpReq.WithContext(ctx)