feat: add Gin HTTP API with SSE streaming chat

internal/api/handler_chat.go

@@ -0,0 +1,93 @@
+package api
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/cloudwego/eino/adk"
+	"github.com/cloudwego/eino/schema"
+	"github.com/gin-gonic/gin"
+)
+
+type ChatHandler struct {
+	supervisor adk.Agent
+}
+
+func NewChatHandler(supervisor adk.Agent) *ChatHandler {
+	return &ChatHandler{supervisor: supervisor}
+}
+
+func (h *ChatHandler) Chat(c *gin.Context) {
+	var req ChatRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.Header("Content-Type", "text/event-stream")
+	c.Header("Cache-Control", "no-cache")
+	c.Header("Connection", "keep-alive")
+	c.Header("X-Accel-Buffering", "no")
+
+	iter := h.supervisor.Run(c.Request.Context(), &adk.AgentInput{
+		Messages: []adk.Message{
+			schema.UserMessage(req.Message),
+		},
+		EnableStreaming: true,
+	})
+
+	c.Stream(func(w io.Writer) bool {
+		event, ok := iter.Next()
+		if !ok {
+			return false
+		}
+
+		if event.Err != nil {
+			writeSSE(w, "error", map[string]string{"error": event.Err.Error()})
+			return false
+		}
+
+		if event.Output == nil || event.Output.MessageOutput == nil {
+			return true
+		}
+
+		mv := event.Output.MessageOutput
+
+		if mv.IsStreaming && mv.MessageStream != nil {
+			stream := mv.MessageStream
+			for {
+				msg, err := stream.Recv()
+				if err == io.EOF {
+					break
+				}
+				if err != nil {
+					break
+				}
+				if msg.Content != "" {
+					writeSSE(w, "message", map[string]string{
+						"agent":   event.AgentName,
+						"content": msg.Content,
+						"role":    string(mv.Role),
+					})
+				}
+			}
+		} else if mv.Message != nil {
+			if mv.Message.Content != "" {
+				writeSSE(w, "message", map[string]string{
+					"agent":   event.AgentName,
+					"content": mv.Message.Content,
+					"role":    string(mv.Role),
+				})
+			}
+		}
+
+		return true
+	})
+}
+
+func writeSSE(w io.Writer, event string, data any) {
+	b, _ := json.Marshal(data)
+	fmt.Fprintf(w, "event: %s\ndata: %s\n\n", event, string(b))
+}