Enforce max block payload size of 1MB.

This commit changes MsgBlock to enforce a 1MB max payload per the spec.
Previously it was only limited to the max overall message size.  While
here, also enforce max payloads per message type (instead of only the max
overall message payload) when writing messages.

fakemessage_test.go

@@ -15,6 +15,7 @@ type fakeMessage struct {
 	command        string
 	payload        []byte
 	forceEncodeErr bool
+	forceLenErr    bool
 }
 
 // BtcDecode doesn't do anything.  It just satisfies the btcwire.Message
@@ -45,8 +46,14 @@ func (msg *fakeMessage) Command() string {
 	return msg.command
 }
 
-// MaxPayloadLength simply returns 0.  It is only here to satisfy the
-// btcwire.Message interface.
+// MaxPayloadLength returns the length of the payload field of fake message
+// or a smaller value if the forceLenErr flag of the fake message is set.  It
+// satisfies the btcwire.Message interface.
 func (msg *fakeMessage) MaxPayloadLength(pver uint32) uint32 {
-	return 0
+	lenp := uint32(len(msg.payload))
+	if msg.forceLenErr {
+		return lenp - 1
+	}
+
+	return lenp
 }

message.go

@@ -15,7 +15,7 @@ import (
 // header.  Shorter commands must be zero padded.
 const commandSize = 12
 
-// maxMessagePayload is the maximum byes a message can be regardless of other
+// maxMessagePayload is the maximum bytes a message can be regardless of other
 // individual limits imposed by messages themselves.
 const maxMessagePayload = (1024 * 1024 * 32) // 32MB
 
@@ -158,6 +158,7 @@ func discardInput(r io.Reader, n uint32) {
 func WriteMessage(w io.Writer, msg Message, pver uint32, btcnet BitcoinNet) error {
 	var command [commandSize]byte
 
+	// Enforce max command size.
 	cmd := msg.Command()
 	if len(cmd) > commandSize {
 		str := fmt.Sprintf("command [%s] is too long [max %v]",
@@ -166,6 +167,7 @@ func WriteMessage(w io.Writer, msg Message, pver uint32, btcnet BitcoinNet) erro
 	}
 	copy(command[:], []byte(cmd))
 
+	// Encode the message payload.
 	var bw bytes.Buffer
 	err := msg.BtcEncode(&bw, pver)
 	if err != nil {
@@ -174,7 +176,7 @@ func WriteMessage(w io.Writer, msg Message, pver uint32, btcnet BitcoinNet) erro
 	payload := bw.Bytes()
 	lenp := len(payload)
 
-	// Enforce maximum message payload.
+	// Enforce maximum overall message payload.
 	if lenp > maxMessagePayload {
 		str := fmt.Sprintf("message payload is too large - encoded "+
 			"%d bytes, but maximum message payload is %d bytes",
@@ -182,6 +184,15 @@ func WriteMessage(w io.Writer, msg Message, pver uint32, btcnet BitcoinNet) erro
 		return messageError("WriteMessage", str)
 	}
 
+	// Enforce maximum message payload based on the message type.
+	mpl := msg.MaxPayloadLength(pver)
+	if uint32(lenp) > mpl {
+		str := fmt.Sprintf("message payload is too large - encoded "+
+			"%d bytes, but maximum message payload size for "+
+			"messages of type [%s] is %d.", lenp, cmd, mpl)
+		return messageError("WriteMessage", str)
+	}
+
 	// Create header for the message.
 	hdr := messageHeader{}
 	hdr.magic = btcnet

message_test.go

@@ -317,10 +317,16 @@ func TestWriteMessageWireErrors(t *testing.T) {
 	// Fake message with a problem during encoding
 	encodeErrMsg := &fakeMessage{forceEncodeErr: true}
 
-	// Fake message that has a payload which exceed max.
-	exceedPayload := make([]byte, btcwire.MaxMessagePayload+1)
-	exceedPayloadErrMsg := &fakeMessage{payload: exceedPayload}
+	// Fake message that has payload which exceeds max overall message size.
+	exceedOverallPayload := make([]byte, btcwire.MaxMessagePayload+1)
+	exceedOverallPayloadErrMsg := &fakeMessage{payload: exceedOverallPayload}
 
+	// Fake message that has payload which exceeds max allowed per message.
+	exceedPayload := make([]byte, 1)
+	exceedPayloadErrMsg := &fakeMessage{payload: exceedPayload, forceLenErr: true}
+
+	// Fake message that is used to force errors in the header and payload
+	// writes.
 	bogusPayload := []byte{0x01, 0x02, 0x03, 0x04}
 	bogusMsg := &fakeMessage{command: "bogus", payload: bogusPayload}
 
@@ -335,7 +341,9 @@ func TestWriteMessageWireErrors(t *testing.T) {
 		{badCommandMsg, pver, btcnet, 0, btcwireErr},
 		// Force error in payload encode.
 		{encodeErrMsg, pver, btcnet, 0, btcwireErr},
-		// Force error due to exceeding max payload size.
+		// Force error due to exceeding max overall message payload size.
+		{exceedOverallPayloadErrMsg, pver, btcnet, 0, btcwireErr},
+		// Force error due to exceeding max payload for message type.
 		{exceedPayloadErrMsg, pver, btcnet, 0, btcwireErr},
 		// Force error in header write.
 		{bogusMsg, pver, btcnet, 0, io.ErrShortWrite},

msgblock.go

@@ -12,6 +12,9 @@ import (
 // MaxBlocksPerMsg is the maximum number of blocks allowed per message.
 const MaxBlocksPerMsg = 500
 
+// maxBlockPayload is the maximum bytes a block message can be.
+const maxBlockPayload = (1024 * 1024) // 1MB
+
 // TxLoc holds locator data for the offset and length of where a transaction is
 // located within a MsgBlock data buffer.
 type TxLoc struct {
@@ -131,8 +134,8 @@ func (msg *MsgBlock) Command() string {
 // receiver.  This is part of the Message interface implementation.
 func (msg *MsgBlock) MaxPayloadLength(pver uint32) uint32 {
 	// Block header at 81 bytes + max transactions which can vary up to the
-	// max message payload.
-	return maxMessagePayload
+	// maxBlockPayload (including the block header).
+	return maxBlockPayload
 }
 
 // BlockSha computes the block identifier hash for this block.

msgblock_test.go

@@ -35,7 +35,7 @@ func TestBlock(t *testing.T) {
 
 	// Ensure max payload is expected value for latest protocol version.
 	// Num addresses (varInt) + max allowed addresses.
-	wantPayload := uint32(1024 * 1024 * 32)
+	wantPayload := uint32(1024 * 1024)
 	maxPayload := msg.MaxPayloadLength(pver)
 	if maxPayload != wantPayload {
 		t.Errorf("MaxPayloadLength: wrong max payload length for "+

test_coverage.txt

@@ -1,6 +1,6 @@
 
 github.com/conformal/btcwire/message.go		 ReadMessage				 100.00% (37/37)
-github.com/conformal/btcwire/message.go		 WriteMessage				 100.00% (27/27)
+github.com/conformal/btcwire/message.go		 WriteMessage				 100.00% (31/31)
 github.com/conformal/btcwire/msgtx.go		 MsgTx.BtcDecode			 100.00% (25/25)
 github.com/conformal/btcwire/msgversion.go	 MsgVersion.BtcDecode			 100.00% (25/25)
 github.com/conformal/btcwire/msgtx.go		 MsgTx.Copy				 100.00% (24/24)
@@ -149,5 +149,5 @@ github.com/conformal/btcwire/msgversion.go	 NewMsgVersion				 100.00% (1/1)
 github.com/conformal/btcwire/netaddress.go	 NetAddress.AddService			 100.00% (1/1)
 github.com/conformal/btcwire/shahash.go		 ShaHash.IsEqual			 100.00% (1/1)
 github.com/conformal/btcwire/invvect.go		 NewInvVect				 100.00% (1/1)
-github.com/conformal/btcwire			 ---------------------------------	 100.00% (923/923)
+github.com/conformal/btcwire			 ---------------------------------	 100.00% (927/927)