Add comments for protocol hash IDs and tags. (#2774)

Add comments for protocol hash IDs and tags

Author: tolikzinovyev

protocol/hash.go

@@ -20,7 +20,8 @@ package protocol
 // This ensures, for example, the hash of a transaction will never collide with the hash of a vote
 type HashID string
 
-// Hash IDs for specific object types, in lexicographic order to avoid dups.
+// Hash IDs for specific object types, in lexicographic order.
+// Hash IDs must be PREFIX-FREE (no hash ID is a prefix of another).
 const (
 	AuctionBid        HashID = "aB"
 	AuctionDeposit    HashID = "aD"

protocol/tags.go

@@ -23,6 +23,7 @@ type Tag string
 // Tags, in lexicographic sort order of tag values to avoid duplicates.
 // These tags must not contain a comma character because lists of tags
 // are encoded using a comma separator (see network/msgOfInterest.go).
+// The tags must be 2 bytes long.
 const (
 	UnknownMsgTag      Tag = "??"
 	AgreementVoteTag   Tag = "AV"