Update code to use pault.ag/go/sniff package (#5038)

* Update code to use pault.ag/go/sniff package

* Update go dependencies

vendor/github.com/armon/go-proxyproto/protocol.go

@@ -49,6 +49,7 @@ type Listener struct {
 	Listener           net.Listener
 	ProxyHeaderTimeout time.Duration
 	SourceCheck        SourceChecker
+	UnknownOK          bool // allow PROXY UNKNOWN
 }
 
 // Conn is used to wrap and underlying connection which
@@ -62,6 +63,7 @@ type Conn struct {
 	useConnAddr        bool
 	once               sync.Once
 	proxyHeaderTimeout time.Duration
+	unknownOK          bool
 }
 
 // Accept waits for and returns the next connection to the listener.
@@ -83,6 +85,7 @@ func (p *Listener) Accept() (net.Conn, error) {
 	}
 	newConn := NewConn(conn, p.ProxyHeaderTimeout)
 	newConn.useConnAddr = useConnAddr
+	newConn.unknownOK = p.UnknownOK
 	return newConn, nil
 }
 
@@ -119,6 +122,22 @@ func (p *Conn) Read(b []byte) (int, error) {
 	return p.bufReader.Read(b)
 }
 
+func (p *Conn) ReadFrom(r io.Reader) (int64, error) {
+	if rf, ok := p.conn.(io.ReaderFrom); ok {
+		return rf.ReadFrom(r)
+	}
+	return io.Copy(p.conn, r)
+}
+
+func (p *Conn) WriteTo(w io.Writer) (int64, error) {
+	var err error
+	p.once.Do(func() { err = p.checkPrefix() })
+	if err != nil {
+		return 0, err
+	}
+	return p.bufReader.WriteTo(w)
+}
+
 func (p *Conn) Write(b []byte) (int, error) {
 	return p.conn.Write(b)
 }
@@ -209,13 +228,20 @@ func (p *Conn) checkPrefix() error {
 
 	// Split on spaces, should be (PROXY <type> <src addr> <dst addr> <src port> <dst port>)
 	parts := strings.Split(header, " ")
-	if len(parts) != 6 {
+	if len(parts) < 2 {
 		p.conn.Close()
 		return fmt.Errorf("Invalid header line: %s", header)
 	}
 
 	// Verify the type is known
 	switch parts[1] {
+	case "UNKNOWN":
+		if !p.unknownOK || len(parts) != 2 {
+			p.conn.Close()
+			return fmt.Errorf("Invalid UNKNOWN header line: %s", header)
+		}
+		p.useConnAddr = true
+		return nil
 	case "TCP4":
 	case "TCP6":
 	default:
@@ -223,6 +249,11 @@ func (p *Conn) checkPrefix() error {
 		return fmt.Errorf("Unhandled address type: %s", parts[1])
 	}
 
+	if len(parts) != 6 {
+		p.conn.Close()
+		return fmt.Errorf("Invalid header line: %s", header)
+	}
+
 	// Parse out the source address
 	ip := net.ParseIP(parts[2])
 	if ip == nil {