fix: 修复gzip中间件ERR_INCOMPLETE_CHUNKED_ENCODING

- 首次Write时删除Content-Length头（压缩后大小不同）
- 非压缩类型直接透传，不经过gzip writer
- 移除有问题的noopWriter方案

backend/cmd/main.go

@@ -4,7 +4,6 @@ import (
 	"compress/gzip"
 	"embed"
 	"fmt"
-	"io"
 	"io/fs"
 	"log"
 	"mime"
@@ -370,54 +369,50 @@ func gzipMiddleware() gin.HandlerFunc {
 
 		c.Header("Vary", "Accept-Encoding")
 
-		c.Writer = &gzipWriter{Writer: gzip.NewWriter(c.Writer), ResponseWriter: c.Writer}
-
+		gw := &gzipResponseWriter{ResponseWriter: c.Writer, writer: gzip.NewWriter(c.Writer)}
+		c.Writer = gw
 		c.Next()
 
-		if gw, ok := c.Writer.(*gzipWriter); ok {
-			contentType := c.Writer.Header().Get("Content-Type")
-			if !isCompressibleContentType(contentType) {
-				gw.ResponseWriter = &noopWriter{}
-				gw.Writer.Close()
-				c.Writer = gw.ResponseWriter
-				return
-			}
-			gw.Writer.Close()
+		if gw.compressed {
+			gw.writer.Close()
 		}
 	}
 }
 
-type gzipWriter struct {
+type gzipResponseWriter struct {
 	gin.ResponseWriter
-	Writer *gzip.Writer
+	writer     *gzip.Writer
+	compressed bool
 }
 
-func (w *gzipWriter) Write(data []byte) (int, error) {
-	contentType := w.Header().Get("Content-Type")
-	if !isCompressibleContentType(contentType) {
-		return w.ResponseWriter.Write(data)
+func (w *gzipResponseWriter) Write(data []byte) (int, error) {
+	if !w.compressed {
+		contentType := w.Header().Get("Content-Type")
+		if isCompressibleContentType(contentType) {
+			w.Header().Del("Content-Length")
+			w.Header().Set("Content-Encoding", "gzip")
+			w.compressed = true
+		}
 	}
-	if w.Header().Get("Content-Encoding") == "" {
-		w.Header().Set("Content-Encoding", "gzip")
+
+	if w.compressed {
+		return w.writer.Write(data)
 	}
-	return w.Writer.Write(data)
+	return w.ResponseWriter.Write(data)
 }
 
-func (w *gzipWriter) WriteString(s string) (int, error) {
-	contentType := w.Header().Get("Content-Type")
-	if !isCompressibleContentType(contentType) {
-		return w.ResponseWriter.WriteString(s)
+func (w *gzipResponseWriter) WriteString(s string) (int, error) {
+	if !w.compressed {
+		contentType := w.Header().Get("Content-Type")
+		if isCompressibleContentType(contentType) {
+			w.Header().Del("Content-Length")
+			w.Header().Set("Content-Encoding", "gzip")
+			w.compressed = true
+		}
 	}
-	if w.Header().Get("Content-Encoding") == "" {
-		w.Header().Set("Content-Encoding", "gzip")
+
+	if w.compressed {
+		return w.writer.Write([]byte(s))
 	}
-	return io.WriteString(w.Writer, s)
-}
-
-type noopWriter struct {
-	gin.ResponseWriter
-}
-
-func (w *noopWriter) Write(data []byte) (int, error) {
-	return len(data), nil
+	return w.ResponseWriter.WriteString(s)
 }