add example for serve file (#3193)

example/httpserver/serve_file/main.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gogf/gf/v2/frame/g"
+	"github.com/gogf/gf/v2/net/ghttp"
+)
+
+// pathMap is used for URL mapping
+var pathMap = map[string]string{
+	"/aaa/": "/tmp/",
+}
+
+// ServeFile serves the file to the response.
+func ServeFile(r *ghttp.Request) {
+	truePath := r.URL.Path
+	hasPrefix := false
+	// Replace the path prefix.
+	for k, v := range pathMap {
+		if strings.HasPrefix(truePath, k) {
+			truePath = strings.Replace(truePath, k, v, 1) // Replace only once.
+			hasPrefix = true
+			break
+		}
+	}
+
+	if !hasPrefix {
+		r.Response.WriteStatus(http.StatusForbidden)
+		return
+	}
+
+	r.Response.ServeFile(truePath)
+}
+
+func main() {
+	s := g.Server()
+	s.Use(ghttp.MiddlewareHandlerResponse)
+	s.BindHandler("/*", ServeFile)
+	s.SetPort(8080)
+	s.Run()
+}
+
+// http://127.0.0.1:8080/aaa/main.go