feat(server): Implements RunFd method (#1609)

gin.go

@@ -5,6 +5,7 @@
 package gin
 
 import (
+	"fmt"
 	"html/template"
 	"net"
 	"net/http"
@@ -321,6 +322,23 @@ func (engine *Engine) RunUnix(file string) (err error) {
 	return
 }
 
+// RunFd attaches the router to a http.Server and starts listening and serving HTTP requests
+// through the specified file descriptor.
+// Note: this method will block the calling goroutine indefinitely unless an error happens.
+func (engine *Engine) RunFd(fd int) (err error) {
+	debugPrint("Listening and serving HTTP on fd@%d", fd)
+	defer func() { debugPrintError(err) }()
+
+	f := os.NewFile(uintptr(fd), fmt.Sprintf("fd@%d", fd))
+	listener, err := net.FileListener(f)
+	if err != nil {
+		return
+	}
+	defer listener.Close()
+	err = http.Serve(listener, engine)
+	return
+}
+
 // ServeHTTP conforms to the http.Handler interface.
 func (engine *Engine) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	c := engine.pool.Get().(*Context)