fixup! multi: decode zero-length onion message payloads

Author: gijswijs

payload.go

@@ -44,6 +44,10 @@ type HopPayload struct {
 	// HMAC is an HMAC computed over the entire per-hop payload that also
 	// includes the higher-level (optional) associated data bytes.
 	HMAC [HMACSize]byte
+
+	// TLVPayloadGuaranteed is set to true if the payload is guaranteed to
+	// be a TLVPayload. E.g. in the case of an onion message.
+	TLVPayloadGuaranteed bool
 }
 
 // NewTLVHopPayload creates a new TLV encoded HopPayload. The payload will be
@@ -87,13 +91,8 @@ func (hp *HopPayload) Encode(w io.Writer) error {
 }
 
 // Decode unpacks an encoded HopPayload from the passed reader into the target
-// HopPayload. The isMessage boolean should be set to true if we're parsing a
-// payload that is known to be for an onion message.
-func (hp *HopPayload) Decode(r io.Reader, isMessage ...bool) error {
-	// To preserve backwards compatibility, we'll default to isMessage being
-	// false if it is not provided.
-	isMsg := len(isMessage) > 0 && isMessage[0]
-
+// HopPayload.
+func (hp *HopPayload) Decode(r io.Reader) error {
 	bufReader := bufio.NewReader(r)
 
 	// In order to properly parse the payload, we'll need to check the
@@ -104,12 +103,9 @@ func (hp *HopPayload) Decode(r io.Reader, isMessage ...bool) error {
 		return err
 	}
 
-	// Per BOLT 7, onion messages MUST use the TLV format.
-	if isMsg {
-		return decodeTLVHopPayload(hp, bufReader)
-	}
-
-	if isLegacyPayloadByte(peekByte[0]) {
+	// If the HopPayload is guaranteed to be a TLV payload, we can skip the
+	// check for the legacy payload byte.
+	if !hp.TLVPayloadGuaranteed && isLegacyPayloadByte(peekByte[0]) {
 		return decodeLegacyHopPayload(hp, bufReader)
 	}
 

sphinx.go

@@ -750,8 +750,8 @@ func unwrapPacket(onionPkt *OnionPacket, sharedSecret *Hash256,
 	// With the MAC checked, and the payload decrypted, we can now parse
 	// out the payload so we can derive the specified forwarding
 	// instructions.
-	var hopPayload HopPayload
-	err := hopPayload.Decode(bytes.NewReader(hopInfo), isOnionMessage)
+	hopPayload := HopPayload{TLVPayloadGuaranteed: isOnionMessage}
+	err := hopPayload.Decode(bytes.NewReader(hopInfo))
 	if err != nil {
 		return nil, nil, err
 	}