Merge pull request #27 from acd/pluggable-backoff

Pluggable backoff

Author: pin

README.md

@@ -45,7 +45,7 @@ func readHandler(filename string, rf io.ReaderFrom) error {
 }
 
 // writeHandler is called when client starts file upload to server
-func writeHanlder(filename string, wt io.WriterTo) error {
+func writeHandler(filename string, wt io.WriterTo) error {
 	file, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%v\n", err)
@@ -62,7 +62,7 @@ func writeHanlder(filename string, wt io.WriterTo) error {
 
 func main() {
 	// use nil in place of handler to disable read or write operations
-	s := tftp.NewServer(readHandler, writeHanlder)
+	s := tftp.NewServer(readHandler, writeHandler)
 	s.SetTimeout(5 * time.Second) // optional
 	err := s.ListenAndServe(":69") // blocks until s.Shutdown() is called
 	if err != nil {
@@ -149,4 +149,22 @@ func readHandler(filename string, rf io.ReaderFrom) error {
         ...
         // ReadFrom ...
 
+Backoff
+-------
+
+The default backoff before retransmitting an unacknowledged packet is a
+random duration between 0 and 1 second.  This behavior can be overridden
+in clients and servers by providing a custom backoff calculation function.
+
+```go
+	s := tftp.NewServer(readHandler, writeHandler)
+	s.SetBackoff(func (attempts int) time.Duration {
+		return time.Duration(attempts) * time.Second
+	})
+```
+
+or, for no backoff
+
+```go
+	s.SetBackoff(func (int) time.Duration { return 0 })
 ```

backoff.go

@@ -10,8 +10,11 @@ const (
 	defaultRetries = 5
 )
 
+type backoffFunc func(int) time.Duration
+
 type backoff struct {
 	attempt int
+	handler backoffFunc
 }
 
 func (b *backoff) reset() {
@@ -23,6 +26,10 @@ func (b *backoff) count() int {
 }
 
 func (b *backoff) backoff() {
-	time.Sleep(time.Duration(rand.Int63n(int64(time.Second))))
+	if b.handler == nil {
+		time.Sleep(time.Duration(rand.Int63n(int64(time.Second))))
+	} else {
+		time.Sleep(b.handler(b.attempt))
+	}
 	b.attempt++
 }

client.go

@@ -39,10 +39,17 @@ func (c *Client) SetRetries(count int) {
 	c.retries = count
 }
 
+// SetBackoff sets a user provided function that is called to provide a
+// backoff duration prior to retransmitting an unacknowledged packet.
+func (c *Client) SetBackoff(h backoffFunc) {
+	c.backoff = h
+}
+
 type Client struct {
 	addr    *net.UDPAddr
 	timeout time.Duration
 	retries int
+	backoff backoffFunc
 	blksize int
 	tsize   bool
 }
@@ -57,7 +64,7 @@ func (c Client) Send(filename string, mode string) (io.ReaderFrom, error) {
 		send:    make([]byte, datagramLength),
 		receive: make([]byte, datagramLength),
 		conn:    conn,
-		retry:   &backoff{},
+		retry:   &backoff{handler: c.backoff},
 		timeout: c.timeout,
 		retries: c.retries,
 		addr:    c.addr,
@@ -90,7 +97,7 @@ func (c Client) Receive(filename string, mode string) (io.WriterTo, error) {
 		send:     make([]byte, datagramLength),
 		receive:  make([]byte, datagramLength),
 		conn:     conn,
-		retry:    &backoff{},
+		retry:    &backoff{handler: c.backoff},
 		timeout:  c.timeout,
 		retries:  c.retries,
 		addr:     c.addr,

server.go

@@ -25,6 +25,7 @@ func NewServer(readHandler func(filename string, rf io.ReaderFrom) error,
 type Server struct {
 	readHandler  func(filename string, rf io.ReaderFrom) error
 	writeHandler func(filename string, wt io.WriterTo) error
+	backoff      backoffFunc
 	conn         *net.UDPConn
 	quit         chan chan struct{}
 	wg           sync.WaitGroup
@@ -54,6 +55,12 @@ func (s *Server) SetRetries(count int) {
 	}
 }
 
+// SetBackoff sets a user provided function that is called to provide a
+// backoff duration prior to retransmitting an unacknowledged packet.
+func (s *Server) SetBackoff(h backoffFunc) {
+	s.backoff = h
+}
+
 // ListenAndServe binds to address provided and start the server.
 // ListenAndServe returns when Shutdown is called.
 func (s *Server) ListenAndServe(addr string) error {
@@ -129,7 +136,7 @@ func (s *Server) processRequest(conn *net.UDPConn) error {
 			send:    make([]byte, datagramLength),
 			receive: make([]byte, datagramLength),
 			conn:    conn,
-			retry:   &backoff{},
+			retry:   &backoff{handler: s.backoff},
 			timeout: s.timeout,
 			retries: s.retries,
 			addr:    remoteAddr,
@@ -166,7 +173,7 @@ func (s *Server) processRequest(conn *net.UDPConn) error {
 			receive: make([]byte, datagramLength),
 			tid:     remoteAddr.Port,
 			conn:    conn,
-			retry:   &backoff{},
+			retry:   &backoff{handler: s.backoff},
 			timeout: s.timeout,
 			retries: s.retries,
 			addr:    remoteAddr,