Refactor API handlers to streamline response handling

- Replaced channel-based handling in `SendMessage` flow with direct synchronous execution.
- Introduced `hasFirstResponse` flag to manage keep-alive signals in streaming handler.
- Simplified error handling and removed redundant code for enhanced readability and maintainability.

internal/api/handlers.go

@@ -244,43 +244,19 @@ func (h *APIHandlers) handleNonStreamingResponse(c *gin.Context, rawJson []byte)
 
 	log.Debugf("Request use account: %s, project id: %s", cliClient.GetEmail(), cliClient.GetProjectID())
 
-	respChan := make(chan []byte)
-	errChan := make(chan *client.ErrorMessage)
-	go func() {
 	resp, err := cliClient.SendMessage(cliCtx, rawJson, modelName, contents, tools)
 	if err != nil {
-			errChan <- err
+		c.Status(err.StatusCode)
-		} else {
+		_, _ = fmt.Fprint(c.Writer, err.Error.Error())
-			respChan <- resp
+		flusher.Flush()
-		}
-	}()
-
-	for {
-		select {
-		case <-c.Request.Context().Done():
-			if c.Request.Context().Err().Error() == "context canceled" {
-				log.Debugf("Client disconnected: %v", c.Request.Context().Err())
 		cliCancel()
-				return
+	} else {
-			}
+		openAIFormat := translator.ConvertCliToOpenAINonStream(resp)
-		case respBody := <-respChan:
-			openAIFormat := translator.ConvertCliToOpenAINonStream(respBody)
 		if openAIFormat != "" {
 			_, _ = fmt.Fprintf(c.Writer, "data: %s\n\n", openAIFormat)
 			flusher.Flush()
 		}
 		cliCancel()
-			return
-		case err := <-errChan:
-			c.Status(err.StatusCode)
-			_, _ = fmt.Fprint(c.Writer, err.Error.Error())
-			flusher.Flush()
-			cliCancel()
-			return
-		case <-time.After(500 * time.Millisecond):
-			_, _ = c.Writer.Write([]byte("\n"))
-			flusher.Flush()
-		}
 	}
 }
 
@@ -345,6 +321,7 @@ func (h *APIHandlers) handleStreamingResponse(c *gin.Context, rawJson []byte) {
 	log.Debugf("Request use account: %s, project id: %s", cliClient.GetEmail(), cliClient.GetProjectID())
 	// Send the message and receive response chunks and errors via channels.
 	respChan, errChan := cliClient.SendMessageStream(cliCtx, rawJson, modelName, contents, tools)
+	hasFirstResponse := false
 	for {
 		select {
 		// Handle client disconnection.
@@ -364,6 +341,7 @@ func (h *APIHandlers) handleStreamingResponse(c *gin.Context, rawJson []byte) {
 				return
 			} else {
 				// Convert the chunk to OpenAI format and send it to the client.
+				hasFirstResponse = true
 				openAIFormat := translator.ConvertCliToOpenAI(chunk)
 				if openAIFormat != "" {
 					_, _ = fmt.Fprintf(c.Writer, "data: %s\n\n", openAIFormat)
@@ -381,8 +359,10 @@ func (h *APIHandlers) handleStreamingResponse(c *gin.Context, rawJson []byte) {
 			}
 		// Send a keep-alive signal to the client.
 		case <-time.After(500 * time.Millisecond):
+			if hasFirstResponse {
 				_, _ = c.Writer.Write([]byte(": CLI-PROXY-API PROCESSING\n\n"))
 				flusher.Flush()
 			}
 		}
+	}
 }