feat(api): expose vote memo and allow setting it from the client

- api: add `memo` to the Vote response and populate it in GET /votes/{voteId}
  from the authoritative state (the memo is not indexed).
- apiclient: add Memo to VoteData and attach it to the VoteEnvelope before the
  tx is marshaled and signed, so it is covered by the vote signature.

Author: lucasmenendez

api/api_types.go

@@ -218,6 +218,8 @@ type Vote struct {
 	BlockHeight      uint32          `json:"blockHeight,omitempty" extensions:"x-omitempty"`
 	TransactionIndex *int32          `json:"transactionIndex,omitempty" extensions:"x-omitempty"`
 	OverwriteCount   *uint32         `json:"overwriteCount,omitempty" extensions:"x-omitempty"`
+	// Optional free-text note attached by the voter (max 256 bytes)
+	Memo string `json:"memo,omitempty" extensions:"x-omitempty"`
 	// Date when the vote was emitted
 	Date *time.Time `json:"date,omitempty" extensions:"x-omitempty"`
 }

api/vote.go

@@ -129,6 +129,11 @@ func (a *API) getVoteHandler(_ *apirest.APIdata, ctx *httprouter.HTTPContext) er
 		Date:                 &voteData.Date,
 	}
 
+	// The memo is not indexed; read it from the authoritative state if present.
+	if sdbVote, err := a.vocapp.State.Vote(voteData.Meta.ProcessId, voteData.Meta.Nullifier, true); err == nil {
+		vote.Memo = sdbVote.GetMemo()
+	}
+
 	// If VotePackage is valid JSON, it's not encrypted, so we can include it direcectly.
 	if json.Valid(voteData.VotePackage) {
 		vote.VotePackage = voteData.VotePackage

apiclient/vote.go

@@ -39,6 +39,11 @@ type VoteData struct {
 	Election   *api.Election
 	VoteWeight *big.Int
 
+	// Memo is an optional free-text note (max 256 bytes) attached to the vote,
+	// e.g. an open "Other" answer. Only honored by the chain once the memo
+	// soft-fork is active.
+	Memo string
+
 	ProofMkTree  *CensusProof
 	ProofSIKTree *CensusProof
 	ProofCSP     types.HexBytes
@@ -71,6 +76,9 @@ func (cl *HTTPclient) Vote(v *VoteData) (types.HexBytes, error) {
 	if err != nil {
 		return nil, err
 	}
+	// Attach the optional memo before the envelope is wrapped, marshaled and
+	// signed, so it is covered by the vote signature.
+	vote.Memo = v.Memo
 
 	log.Debugw("generating a new vote", "electionId", v.Election.ElectionID, "voter", c.account.AddressString())
 	voteAPI := &api.Vote{}