Added function for lazy message reading per #222

client.go

@@ -201,14 +201,16 @@ func (co *Conn) ReadMsg() (*Msg, error) {
 		}
 	}
 	n, err := co.Read(p)
-	if err != nil && n == 0 {
+	if err != nil {
 		return nil, err
+	} else if n < 12 {
+		return nil, ErrShortRead
 	}
+
 	p = p[:n]
 	if err := m.Unpack(p); err != nil {
 		return nil, err
 	}
-	co.rtt = time.Since(co.t)
 	if t := m.IsTsig(); t != nil {
 		if _, ok := co.TsigSecret[t.Hdr.Name]; !ok {
 			return m, ErrSecret
@@ -219,6 +221,40 @@ func (co *Conn) ReadMsg() (*Msg, error) {
 	return m, err
 }
 
+// ReadMsgBytes reads a message bytes from the connection. Parses and fills
+// dns message wire header (passing nil would skip header parsing) and
+// returns message bytes to process them later.
+//
+// Note that this function would not be able to report TSIG error or
+// check it got actual DNS payload.
+func (co *Conn) ReadMsgBytes(hdr *Header) ([]byte, error) {
+	var p []byte
+	if _, ok := co.Conn.(*net.TCPConn); ok {
+		p = make([]byte, MaxMsgSize)
+	} else {
+		if co.UDPSize > MinMsgSize {
+			p = make([]byte, co.UDPSize)
+		} else {
+			p = make([]byte, MinMsgSize)
+		}
+	}
+
+	n, err := co.Read(p)
+	if err != nil {
+		return nil, err
+	} else if n < 12 {
+		return nil, ErrShortRead
+	}
+
+	p = p[:n]
+	if hdr != nil {
+		if _, err = UnpackStruct(hdr, p, 0); err != nil {
+			return nil, err
+		}
+	}
+	return p, err
+}
+
 // Read implements the net.Conn read method.
 func (co *Conn) Read(p []byte) (n int, err error) {
 	if co.Conn == nil {
@@ -259,6 +295,8 @@ func (co *Conn) Read(p []byte) (n int, err error) {
 	if err != nil {
 		return n, err
 	}
+
+	co.rtt = time.Since(co.t)
 	return n, err
 }
 

client_test.go

@@ -32,7 +32,7 @@ func TestClientSync(t *testing.T) {
 	if err != nil {
 		t.Errorf("failed to exchange: %v", err)
 	}
-	if r != nil && r.Rcode != RcodeSuccess {
+	if r == nil || r.Rcode != RcodeSuccess {
 		t.Errorf("failed to get an valid answer\n%v", r)
 	}
 }
@@ -235,3 +235,52 @@ func ExampleUpdateLeaseTSIG(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+func TestClientConn(t *testing.T) {
+	HandleFunc("miek.nl.", HelloServer)
+	defer HandleRemove("miek.nl.")
+
+	// This uses TCP just to make it slightly different than TestClientSync
+	s, addrstr, err := RunLocalTCPServer("127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Unable to run test server: %v", err)
+	}
+	defer s.Shutdown()
+
+	m := new(Msg)
+	m.SetQuestion("miek.nl.", TypeSOA)
+
+	cn, err := Dial("tcp", addrstr)
+	if err != nil {
+		t.Errorf("failed to dial %s: %v", addrstr, err)
+	}
+
+	err = cn.WriteMsg(m)
+	if err != nil {
+		t.Errorf("failed to exchange: %v", err)
+	}
+	r, err := cn.ReadMsg()
+	if r == nil || r.Rcode != RcodeSuccess {
+		t.Errorf("failed to get an valid answer\n%v", r)
+	}
+
+	err = cn.WriteMsg(m)
+	if err != nil {
+		t.Errorf("failed to exchange: %v", err)
+	}
+	h := new(Header)
+	buf, err := cn.ReadMsgBytes(h)
+	if buf == nil {
+		t.Errorf("failed to get an valid answer\n%v", r)
+	}
+	if int(h.Bits&0xF) != RcodeSuccess {
+		t.Errorf("failed to get an valid answer in ReadMsgBytes\n%v", r)
+	}
+	if h.Ancount != 0 || h.Qdcount != 1 || h.Nscount != 0 || h.Arcount != 1 {
+		t.Errorf("expected to have question and additional in response; got something else: %+v", h)
+	}
+	if err = r.Unpack(buf); err != nil {
+		t.Errorf("unable to unpack message fully: %v", err)
+	}
+
+}