Implemented BIP 0014 format for user agent

the new function AddUserAgent adds the user agent to the stack
and formats it as per BIP 0014
e.g: "/btcwire:0.1.4/myclient:1.2.3(optional; comments)/"

the validation on UserAgent has been moved to a new function
validateUserAgent

README.md

@@ -105,7 +105,6 @@ from a remote peer is:
 
 ## TODO
 
-- Implement functions for [BIP 0014](https://en.bitcoin.it/wiki/BIP_0014)
 - Implement alert message decoding/encoding
 - Implement bloom filter messages (filterload, filteradd, filterclear,
   merkleblock) as defined in [BIP 0037](https://en.bitcoin.it/wiki/BIP_0037)

doc.go

@@ -150,6 +150,7 @@ Bitcoin Improvement Proposals
 
 This package includes spec changes outlined by the following BIPs:
 
+		BIP0014 (https://en.bitcoin.it/wiki/BIP_0014)
 		BIP0031 (https://en.bitcoin.it/wiki/BIP_0031)
 		BIP0035 (https://en.bitcoin.it/wiki/BIP_0035)
 

message_test.go

@@ -51,7 +51,7 @@ func TestMessage(t *testing.T) {
 		t.Errorf("NewNetAddress: %v", err)
 	}
 	me.Timestamp = time.Time{} // Version message has zero value timestamp.
-	msgVersion := btcwire.NewMsgVersion(me, you, 123123, "/test:0.0.1/", 0)
+	msgVersion := btcwire.NewMsgVersion(me, you, 123123, 0)
 
 	msgVerack := btcwire.NewMsgVerAck()
 	msgGetAddr := btcwire.NewMsgGetAddr()
@@ -76,7 +76,7 @@ func TestMessage(t *testing.T) {
 		btcnet btcwire.BitcoinNet // Network to use for wire encoding
 		bytes  int                // Expected num bytes read/written
 	}{
-		{msgVersion, msgVersion, pver, btcwire.MainNet, 122},
+		{msgVersion, msgVersion, pver, btcwire.MainNet, 125},
 		{msgVerack, msgVerack, pver, btcwire.MainNet, 24},
 		{msgGetAddr, msgGetAddr, pver, btcwire.MainNet, 24},
 		{msgAddr, msgAddr, pver, btcwire.MainNet, 25},

msgversion.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"strings"
 	"time"
 )
 
@@ -16,6 +17,9 @@ import (
 // version message (MsgVersion).
 const MaxUserAgentLen = 2000
 
+// DefaultUserAgent for btcwire in the stack
+const DefaultUserAgent = "/btcwire:0.1.4/"
+
 // MsgVersion implements the Message interface and represents a bitcoin version
 // message.  It is used for a peer to advertise itself as soon as an outbound
 // connection is made.  The remote peer then uses this information along with
@@ -115,10 +119,9 @@ func (msg *MsgVersion) BtcDecode(r io.Reader, pver uint32) error {
 		if err != nil {
 			return err
 		}
-		if len(userAgent) > MaxUserAgentLen {
-			str := fmt.Sprintf("user agent too long [len %v, max %v]",
-				len(userAgent), MaxUserAgentLen)
-			return messageError("MsgVersion.BtcDecode", str)
+		err = validateUserAgent(userAgent)
+		if err != nil {
+			return err
 		}
 		msg.UserAgent = userAgent
 	}
@@ -152,13 +155,12 @@ func (msg *MsgVersion) BtcDecode(r io.Reader, pver uint32) error {
 // BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
 // This is part of the Message interface implementation.
 func (msg *MsgVersion) BtcEncode(w io.Writer, pver uint32) error {
-	if len(msg.UserAgent) > MaxUserAgentLen {
-		str := fmt.Sprintf("user agent too long [len %v, max %v]",
-			len(msg.UserAgent), MaxUserAgentLen)
-		return messageError("MsgVersion.BtcEncode", str)
+	err := validateUserAgent(msg.UserAgent)
+	if err != nil {
+		return err
 	}
 
-	err := writeElements(w, msg.ProtocolVersion, msg.Services,
+	err = writeElements(w, msg.ProtocolVersion, msg.Services,
 		msg.Timestamp.Unix())
 	if err != nil {
 		return err
@@ -224,7 +226,7 @@ func (msg *MsgVersion) MaxPayloadLength(pver uint32) uint32 {
 // Message interface using the passed parameters and defaults for the remaining
 // fields.
 func NewMsgVersion(me *NetAddress, you *NetAddress, nonce uint64,
-	userAgent string, lastBlock int32) *MsgVersion {
+	lastBlock int32) *MsgVersion {
 
 	// Limit the timestamp to one second precision since the protocol
 	// doesn't support better.
@@ -235,7 +237,7 @@ func NewMsgVersion(me *NetAddress, you *NetAddress, nonce uint64,
 		AddrYou:         *you,
 		AddrMe:          *me,
 		Nonce:           nonce,
-		UserAgent:       userAgent,
+		UserAgent:       DefaultUserAgent,
 		LastBlock:       lastBlock,
 		DisableRelayTx:  false,
 	}
@@ -244,7 +246,7 @@ func NewMsgVersion(me *NetAddress, you *NetAddress, nonce uint64,
 // NewMsgVersionFromConn is a convenience function that extracts the remote
 // and local address from conn and returns a new bitcoin version message that
 // conforms to the Message interface.  See NewMsgVersion.
-func NewMsgVersionFromConn(conn net.Conn, nonce uint64, userAgent string,
+func NewMsgVersionFromConn(conn net.Conn, nonce uint64,
 	lastBlock int32) (*MsgVersion, error) {
 
 	// Don't assume any services until we know otherwise.
@@ -259,5 +261,33 @@ func NewMsgVersionFromConn(conn net.Conn, nonce uint64, userAgent string,
 		return nil, err
 	}
 
-	return NewMsgVersion(lna, rna, nonce, userAgent, lastBlock), nil
+	return NewMsgVersion(lna, rna, nonce, lastBlock), nil
+}
+
+// validateUserAgent checks userAgent length against MaxUserAgentLen
+func validateUserAgent(userAgent string) error {
+	if len(userAgent) > MaxUserAgentLen {
+		str := fmt.Sprintf("user agent too long [len %v, max %v]",
+			len(userAgent), MaxUserAgentLen)
+		return messageError("MsgVersion", str)
+	}
+	return nil
+}
+
+// AddUserAgent adds a custom user agent
+func (msg *MsgVersion) AddUserAgent(name string, version string,
+	comments ...string) error {
+
+	newUserAgent := fmt.Sprintf("%s:%s", name, version)
+	if len(comments) != 0 {
+		newUserAgent = fmt.Sprintf("%s(%s)", newUserAgent,
+			strings.Join(comments, "; "))
+	}
+	newUserAgent = fmt.Sprintf("%s%s/", msg.UserAgent, newUserAgent)
+	err := validateUserAgent(newUserAgent)
+	if err != nil {
+		return err
+	}
+	msg.UserAgent = newUserAgent
+	return nil
 }

msgversion_test.go

@@ -21,7 +21,6 @@ func TestVersion(t *testing.T) {
 	pver := btcwire.ProtocolVersion
 
 	// Create version message data.
-	userAgent := "/btcdtest:0.0.1/"
 	lastBlock := int32(234234)
 	tcpAddrMe := &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 8333}
 	me, err := btcwire.NewNetAddress(tcpAddrMe, btcwire.SFNodeNetwork)
@@ -39,7 +38,7 @@ func TestVersion(t *testing.T) {
 	}
 
 	// Ensure we get the correct data back out.
-	msg := btcwire.NewMsgVersion(me, you, nonce, userAgent, lastBlock)
+	msg := btcwire.NewMsgVersion(me, you, nonce, lastBlock)
 	if msg.ProtocolVersion != int32(pver) {
 		t.Errorf("NewMsgVersion: wrong protocol version - got %v, want %v",
 			msg.ProtocolVersion, pver)
@@ -56,9 +55,9 @@ func TestVersion(t *testing.T) {
 		t.Errorf("NewMsgVersion: wrong nonce - got %v, want %v",
 			msg.Nonce, nonce)
 	}
-	if msg.UserAgent != userAgent {
+	if msg.UserAgent != btcwire.DefaultUserAgent {
 		t.Errorf("NewMsgVersion: wrong user agent - got %v, want %v",
-			msg.UserAgent, userAgent)
+			msg.UserAgent, btcwire.DefaultUserAgent)
 	}
 	if msg.LastBlock != lastBlock {
 		t.Errorf("NewMsgVersion: wrong last block - got %v, want %v",
@@ -69,6 +68,29 @@ func TestVersion(t *testing.T) {
 			"default - got %v, want %v", msg.DisableRelayTx, false)
 	}
 
+	msg.AddUserAgent("myclient", "1.2.3", "optional", "comments")
+	customUserAgent := btcwire.DefaultUserAgent + "myclient:1.2.3(optional; comments)/"
+	if msg.UserAgent != customUserAgent {
+		t.Errorf("AddUserAgent: wrong user agent - got %s, want %s",
+			msg.UserAgent, customUserAgent)
+	}
+
+	msg.AddUserAgent("mygui", "3.4.5")
+	customUserAgent += "mygui:3.4.5/"
+	if msg.UserAgent != customUserAgent {
+		t.Errorf("AddUserAgent: wrong user agent - got %s, want %s",
+			msg.UserAgent, customUserAgent)
+	}
+
+	// accounting for ":", "/"
+	err = msg.AddUserAgent(strings.Repeat("t",
+		btcwire.MaxUserAgentLen-len(customUserAgent)-2+1), "")
+	if _, ok := err.(*btcwire.MessageError); !ok {
+		t.Errorf("AddUserAgent: expected error not received "+
+			"- got %v, want %T", err, btcwire.MessageError{})
+
+	}
+
 	// Version message should not have any services set by default.
 	if msg.Services != 0 {
 		t.Errorf("NewMsgVersion: wrong default services - got %v, want %v",
@@ -111,7 +133,7 @@ func TestVersion(t *testing.T) {
 
 	// Use a fake connection.
 	conn := &fakeConn{localAddr: tcpAddrMe, remoteAddr: tcpAddrYou}
-	msg, err = btcwire.NewMsgVersionFromConn(conn, nonce, userAgent, lastBlock)
+	msg, err = btcwire.NewMsgVersionFromConn(conn, nonce, lastBlock)
 	if err != nil {
 		t.Errorf("NewMsgVersionFromConn: %v", err)
 	}
@@ -131,7 +153,7 @@ func TestVersion(t *testing.T) {
 		localAddr:  &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 8333},
 		remoteAddr: tcpAddrYou,
 	}
-	msg, err = btcwire.NewMsgVersionFromConn(conn, nonce, userAgent, lastBlock)
+	msg, err = btcwire.NewMsgVersionFromConn(conn, nonce, lastBlock)
 	if err != btcwire.ErrInvalidNetAddr {
 		t.Errorf("NewMsgVersionFromConn: expected error not received "+
 			"- got %v, want %v", err, btcwire.ErrInvalidNetAddr)
@@ -142,7 +164,7 @@ func TestVersion(t *testing.T) {
 		localAddr:  tcpAddrMe,
 		remoteAddr: &net.UDPAddr{IP: net.ParseIP("192.168.0.1"), Port: 8333},
 	}
-	msg, err = btcwire.NewMsgVersionFromConn(conn, nonce, userAgent, lastBlock)
+	msg, err = btcwire.NewMsgVersionFromConn(conn, nonce, lastBlock)
 	if err != btcwire.ErrInvalidNetAddr {
 		t.Errorf("NewMsgVersionFromConn: expected error not received "+
 			"- got %v, want %v", err, btcwire.ErrInvalidNetAddr)