(goctl)feature: supported sse generation (#5082)

Co-authored-by: Kevin Wan <wanjunfeng@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

tools/goctl/api/gogen/sse_handler.tpl

@@ -0,0 +1,63 @@
+package {{.PkgName}}
+
+import (
+    "encoding/json"
+    "fmt"
+	"net/http"
+
+    "github.com/zeromicro/go-zero/core/logc"
+    "github.com/zeromicro/go-zero/core/threading"
+	{{if .HasRequest}}"github.com/zeromicro/go-zero/rest/httpx"{{end}}
+	{{.ImportPackages}}
+)
+
+{{if .HasDoc}}{{.Doc}}{{end}}
+func {{.HandlerName}}(svcCtx *svc.ServiceContext) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		{{if .HasRequest}}var req types.{{.RequestType}}
+		if err := httpx.Parse(r, &req); err != nil {
+			httpx.ErrorCtx(r.Context(), w, err)
+			return
+		}
+
+		{{end}}// Buffer size of 16 is chosen as a reasonable default to balance throughput and memory usage.
+		// You can change this based on your application's needs.
+		// if your go-zero version less than 1.8.1, you need to add 3 lines below.
+        // w.Header().Set("Content-Type", "text/event-stream")
+        // w.Header().Set("Cache-Control", "no-cache")
+        // w.Header().Set("Connection", "keep-alive")
+		client := make(chan {{.ResponseType}}, 16)
+        defer func() {
+            close(client)
+        }()
+        l := {{.LogicName}}.New{{.LogicType}}(r.Context(), svcCtx)
+        threading.GoSafeCtx(r.Context(), func() {
+            err := l.{{.Call}}({{if .HasRequest}}&req, {{end}}client)
+            if err != nil {
+                logc.Errorw(r.Context(), "{{.HandlerName}}", logc.Field("error", err))
+                return
+            }
+        })
+
+        for {
+            select {
+            case data := <-client:
+                output, err := json.Marshal(data)
+                if err != nil {
+                    logc.Errorw(r.Context(), "{{.HandlerName}}", logc.Field("error", err))
+                    continue
+                }
+
+                if _, err := fmt.Fprintf(w, "data: %s\n\n", string(output)); err != nil {
+                    logc.Errorw(r.Context(), "{{.HandlerName}}", logc.Field("error", err))
+                    return
+                }
+               if flusher, ok := w.(http.Flusher); ok {
+                   flusher.Flush()
+               }
+            case <-r.Context().Done():
+                return
+            }
+        }
+	}
+}