feat(delivery): stream task updates with SSE

server/internal/handler/delivery.go

@@ -2,7 +2,9 @@ package handler
 
 import (
 	"crypto/subtle"
+	"encoding/json"
 	"errors"
+	"fmt"
 	"net/http"
 	"strconv"
 	"strings"
@@ -167,6 +169,55 @@ func (h *DeliveryHandler) Get(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"task": task, "events": events})
 }
 
+func (h *DeliveryHandler) Stream(c *gin.Context) {
+	claims, ok := CurrentClaims(c)
+	if !ok {
+		c.JSON(http.StatusUnauthorized, gin.H{"error": "missing current user"})
+		return
+	}
+	taskID := c.Param("id")
+	task, events, err := h.service.GetTask(c.Request.Context(), taskID, claims.UserID, claims.IsAdmin)
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		c.JSON(http.StatusNotFound, gin.H{"error": "task not found"})
+		return
+	}
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+	updates, cancel := h.service.SubscribeTask(taskID)
+	defer cancel()
+
+	c.Header("Content-Type", "text/event-stream")
+	c.Header("Cache-Control", "no-cache")
+	c.Header("Connection", "keep-alive")
+	c.Header("X-Accel-Buffering", "no")
+	c.Status(http.StatusOK)
+	writeSSE(c.Writer, "snapshot", service.DeliveryTaskSnapshot{Task: task, Events: events})
+	c.Writer.Flush()
+
+	for {
+		select {
+		case <-c.Request.Context().Done():
+			return
+		case snapshot, ok := <-updates:
+			if !ok {
+				return
+			}
+			writeSSE(c.Writer, "snapshot", snapshot)
+			c.Writer.Flush()
+		}
+	}
+}
+
+func writeSSE(w http.ResponseWriter, event string, payload any) {
+	raw, err := json.Marshal(payload)
+	if err != nil {
+		return
+	}
+	_, _ = fmt.Fprintf(w, "event: %s\ndata: %s\n\n", event, raw)
+}
+
 // Cancel 取消交付任务
 // @Summary      取消交付任务
 // @Description  取消一个正在执行或等待中的交付任务