lnwire: document commitment+HTLC update msgs

This commit adds some cursory documentation along wit minor field
modifications to all messages which deal with adding HTLC’s, or
updating remote commitment transactions.

The messages for dual funding of channel is left purposefully
undocumented as all initial negotiations will be single funder by
default.

A revamp of the testing infrastructure of lnwire will be committed in
the near future.

lnwire/commit_revocation.go

@@ -5,17 +5,38 @@ import (
 	"io"
 )
 
-// Multiple Clearing Requests are possible by putting this inside an array of
-// clearing requests
+// CommitRevocation is sent by either side once a CommitSignature message has
+// been received, and validated. This message serves to revoke the prior
+// commitment transaction, which was the most up to date version until a
+// CommitSignature message referencing the specified ChannelID was received.
+// Additionally, this message also piggyback's the next revocation hash that
+// Alice should use when constructing the Bob's version of the next commitment
+// transaction (which would be done before sending a CommitSignature message).
+// This piggybacking allows Alice to send the next CommitSignature message
+// modifying Bob's commitment transaction without first asking for a revocation
+// hash initially.
 type CommitRevocation struct {
-	//Next revocation to use
+	// ChannelID uniquely identifies to which currently active channel this
+	// CommitRevocation applies to.
+	ChannelID uint64
+
+	// Revocation is the pre-image to the revocation hash of the now prior
+	// commitment transaction.
+	Revocation [20]byte
+
+	// NextRevocationHash is the next revocation hash to use to create the
+	// next commitment transaction which is to be created upon receipt of a
+	// CommitSignature message.
 	NextRevocationHash [20]byte
-	Revocation         [20]byte
 }
 
+// Decode deserializes a serialized CommitRevocation message stored in the
+// passed io.Reader observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
 func (c *CommitRevocation) Decode(r io.Reader, pver uint32) error {
-	// NextRevocationHash(20)
-	// Revocation(20)
+	// NextRevocationHash (20)
+	// Revocation (20)
 	err := readElements(r,
 		&c.NextRevocationHash,
 		&c.Revocation,
@@ -27,13 +48,19 @@ func (c *CommitRevocation) Decode(r io.Reader, pver uint32) error {
 	return nil
 }
 
-// Creates a new CommitRevocation
+// NewCommitRevocation creates a new CommitRevocation message.
 func NewCommitRevocation() *CommitRevocation {
 	return &CommitRevocation{}
 }
 
-// Serializes the item from the CommitRevocation struct
-// Writes the data to w
+// A compile time check to ensure CommitRevocation implements the lnwire.Message
+// interface.
+var _ Message = (*CommitRevocation)(nil)
+
+// Encode serializes the target CommitRevocation into the passed io.Writer
+// observing the protocol version specified.
+//
+// This is part of the lnwire.Message interface.
 func (c *CommitRevocation) Encode(w io.Writer, pver uint32) error {
 	err := writeElements(w,
 		c.NextRevocationHash,
@@ -46,22 +73,38 @@ func (c *CommitRevocation) Encode(w io.Writer, pver uint32) error {
 	return nil
 }
 
+// Command returns the integer uniquely identifying this message type on the
+// wire.
+//
+// This is part of the lnwire.Message interface.
 func (c *CommitRevocation) Command() uint32 {
 	return CmdCommitRevocation
 }
 
+// MaxPayloadLength returns the maximum allowed payload size for a
+// CommitRevocation complete message observing the specified protocol version.
+//
+// This is part of the lnwire.Message interface.
 func (c *CommitRevocation) MaxPayloadLength(uint32) uint32 {
+	// 8 + 20 + 20
 	return 48
 }
 
-// Makes sure the struct data is valid (e.g. no negatives or invalid pkscripts)
+// Validate performs any necessary sanity checks to ensure all fields present
+// on the CommitRevocation are valid.
+//
+// This is part of the lnwire.Message interface.
 func (c *CommitRevocation) Validate() error {
 	// We're good!
 	return nil
 }
 
+// String returns the string representation of the target CommitRevocation.
+//
+// This is part of the lnwire.Message interface.
 func (c *CommitRevocation) String() string {
 	return fmt.Sprintf("\n--- Begin CommitRevocation ---\n") +
+		fmt.Sprintf("ChannelID:\t%d\n", c.ChannelID) +
 		fmt.Sprintf("NextRevocationHash:\t%x\n", c.NextRevocationHash) +
 		fmt.Sprintf("Revocation:\t%x\n", c.Revocation) +
 		fmt.Sprintf("--- End CommitRevocation ---\n")