Add GoSRT & improvements (repo-merge)

Commits (Ingo Oppermann):
- Add experimental SRT connection stats and logs
- Hide /config/reload endpoint in reade-only mode
- Add SRT server
- Create v16 in go.mod
- Fix data races, tests, lint, and update dependencies
- Add trailing slash for routed directories (datarhei/restreamer#340)
- Allow relative URLs in content in static routes

Co-Authored-By: Ingo Oppermann <57445+ioppermann@users.noreply.github.com>

vendor/github.com/datarhei/gosrt/server.go

@@ -0,0 +1,98 @@
+package srt
+
+import (
+	"errors"
+)
+
+// Server is a framework for a SRT server
+type Server struct {
+	// The address the SRT server should listen on, e.g. ":6001".
+	Addr string
+
+	// Config is the configuration for a SRT listener.
+	Config *Config
+
+	// HandleConnect will be called for each incoming connection. This
+	// allows you to implement your own interpretation of the streamid
+	// and authorization. If this is nil, all connections will be
+	// rejected.
+	HandleConnect AcceptFunc
+
+	// HandlePublish will be called for a publishing connection.
+	HandlePublish func(conn Conn)
+
+	// HandlePublish will be called for a subscribing connection.
+	HandleSubscribe func(conn Conn)
+
+	ln Listener
+}
+
+// ErrServerClosed is returned when the server is about to shutdown.
+var ErrServerClosed = errors.New("srt: server closed")
+
+// ListenAndServe starts the SRT server. It blocks until an error happens.
+// If the error is ErrServerClosed the server has shutdown normally.
+func (s *Server) ListenAndServe() error {
+	// Set some defaults if required.
+	if s.HandlePublish == nil {
+		s.HandlePublish = s.defaultHandler
+	}
+
+	if s.HandleSubscribe == nil {
+		s.HandleSubscribe = s.defaultHandler
+	}
+
+	if s.Config == nil {
+		config := DefaultConfig()
+		s.Config = &config
+	}
+
+	// Start listening for incoming connections.
+	ln, err := Listen("srt", s.Addr, *s.Config)
+	if err != nil {
+		return err
+	}
+
+	defer ln.Close()
+
+	s.ln = ln
+
+	for {
+		// Wait for connections.
+		conn, mode, err := ln.Accept(s.HandleConnect)
+		if err != nil {
+			if err == ErrListenerClosed {
+				return ErrServerClosed
+			}
+
+			return err
+		}
+
+		if conn == nil {
+			// rejected connection, ignore
+			continue
+		}
+
+		if mode == PUBLISH {
+			go s.HandlePublish(conn)
+		} else {
+			go s.HandleSubscribe(conn)
+		}
+	}
+}
+
+// Shutdown will shutdown the server. ListenAndServe will return a ErrServerClosed
+func (s *Server) Shutdown() {
+	if s.ln == nil {
+		return
+	}
+
+	// Close the listener
+	s.ln.Close()
+	s.ln = nil
+}
+
+func (s *Server) defaultHandler(conn Conn) {
+	// Close the incoming connection
+	conn.Close()
+}