uacp: add support for read timeouts

This prevents io.ReadFull to hang.

config.go

@@ -81,7 +81,7 @@ func NewDialer(cfg *Config) *uacp.Dialer {
 // ApplyConfig applies the config options to the default configuration.
 // todo(fs): Can we find a better name?
 //
-// Note: Starting with v0.5 this function will will return an error.
+// Note: Starting with v0.5 this function will return an error.
 func ApplyConfig(opts ...Option) *Config {
 	cfg := &Config{
 		sechan:  DefaultClientConfig(),
@@ -501,6 +501,16 @@ func DialTimeout(d time.Duration) Option {
 	}
 }
 
+// ReadTimeout sets the timeout for every read operation.
+func ReadTimeout(d time.Duration) Option {
+	return func(cfg *Config) {
+		initDialer(cfg)
+		cfg.dialer.ReadTimeout = d
+	}
+}
+	}
+}
+
 // MaxMessageSize sets the maximum message size for the UACP handshake.
 func MaxMessageSize(n uint32) Option {
 	return func(cfg *Config) {

uacp/conn.go

@@ -64,6 +64,10 @@ type Dialer struct {
 	// ClientACK defines the connection parameters requested by the client.
 	// Defaults to DefaultClientACK.
 	ClientACK *Acknowledge
+
+	// ReadTimeout sets a read timeout for reading a full response from the
+	// underlying network connection. ReadTimeout is ignored if it is <= 0.
+	ReadTimeout time.Duration
 }
 
 func (d *Dialer) Dial(ctx context.Context, endpoint string) (*Conn, error) {
@@ -88,6 +92,7 @@ func (d *Dialer) Dial(ctx context.Context, endpoint string) (*Conn, error) {
 		c.Close()
 		return nil, err
 	}
+	conn.readTimeout = d.ReadTimeout
 
 	debug.Printf("uacp %d: start HEL/ACK handshake", conn.id)
 	if err := conn.Handshake(ctx, endpoint); err != nil {
@@ -174,7 +179,8 @@ type Conn struct {
 	id  uint32
 	ack *Acknowledge
 
-	closeOnce sync.Once
+	closeOnce   sync.Once
+	readTimeout  time.Duration
 }
 
 func NewConn(c *net.TCPConn, ack *Acknowledge) (*Conn, error) {
@@ -351,15 +357,25 @@ const hdrlen = 8
 // The size of b must be at least ReceiveBufSize. Otherwise,
 // the function returns an error.
 func (c *Conn) Receive() ([]byte, error) {
-	// TODO(kung-foo): allow user-specified buffer
-	// TODO(kung-foo): sync.Pool
+	// todo(kung-foo): allow user-specified buffer
+	// todo(kung-foo): sync.Pool
 	b := make([]byte, c.ack.ReceiveBufSize)
 
-	if _, err := io.ReadFull(c, b[:hdrlen]); err != nil {
+	if c.readTimeout > 0 {
+		if err := c.SetReadDeadline(time.Now().Add(c.readTimeout)); err != nil {
+			return nil, errors.Errorf("uacp: failed to set read timeout: %w", err)
+		}
+	}
+
+	n, err := c.Read(b[:hdrlen])
+	if err != nil {
 		// todo(fs): do not wrap this error since it hides io.EOF
 		// todo(fs): use golang.org/x/xerrors
 		return nil, err
 	}
+	if n != hdrlen {
+		return nil, errors.Errorf("uacp: short read on header. got %d bytes, want %d ", n, hdrlen)
+	}
 
 	var h Header
 	if _, err := h.Decode(b[:hdrlen]); err != nil {
@@ -370,18 +386,26 @@ func (c *Conn) Receive() ([]byte, error) {
 		return nil, errors.Errorf("uacp: message too large: %d > %d bytes", h.MessageSize, c.ack.ReceiveBufSize)
 	}
 
-	if _, err := io.ReadFull(c, b[hdrlen:h.MessageSize]); err != nil {
+	n, err = c.Read(b[hdrlen:h.MessageSize])
+	if err != nil {
 		// todo(fs): do not wrap this error since it hides io.EOF
 		// todo(fs): use golang.org/x/xerrors
 		return nil, err
 	}
 
+	// clear the deadline
+	c.SetReadDeadline(time.Time{})
+
+	if uint32(n) != h.MessageSize-hdrlen {
+		return nil, fmt.Errorf("uacp %d: short read on message. got %d bytes, want %d", c.id, n, h.MessageSize-hdrlen)
+	}
+
 	debug.Printf("uacp %d: recv %s%c with %d bytes", c.id, h.MessageType, h.ChunkType, h.MessageSize)
 
 	if h.MessageType == "ERR" {
 		errf := new(Error)
 		if _, err := errf.Decode(b[hdrlen:h.MessageSize]); err != nil {
-			return nil, errors.Errorf("uacp: failed to decode ERRF message: %s", err)
+			return nil, errors.Errorf("uacp: failed to decode ERRF message: %w", err)
 		}
 		return nil, errf
 	}