api: support passing delta to /elections/id endpoint

api/api_types.go

@@ -272,7 +272,8 @@ type Validator struct {
 	Score            uint32         `json:"score"`
 }
 
-type NextElectionID struct {
+type BuildElectionID struct {
+	Delta          int32          `json:"delta"` // 0 means build next ElectionID
 	OrganizationID types.HexBytes `json:"organizationId"`
 	CensusOrigin   int32          `json:"censusOrigin"`
 	EnvelopeType   struct {

api/elections.go

@@ -116,7 +116,7 @@ func (a *API) enableElectionHandlers() error {
 		"/elections/id",
 		"POST",
 		apirest.MethodAccessTypePublic,
-		a.nextElectionIDHandler,
+		a.buildElectionIDHandler,
 	); err != nil {
 		return err
 	}
@@ -684,18 +684,18 @@ func (a *API) electionFilterPaginatedHandler(msg *apirest.APIdata, ctx *httprout
 	return ctx.Send(data, apirest.HTTPstatusOK)
 }
 
-// nextElectionIDHandler
+// buildElectionIDHandler
 //
-//	@Summary		Get next election ID
-//	@Description	nextElectionIDHandler
+//	@Summary		Build an election ID
+//	@Description	buildElectionIDHandler
 //	@Tags			Elections
 //	@Accept			json
 //	@Produce		json
-//	@Param			transaction	body		NextElectionID	true	"OrganizationID, CensusOrigin and EnvelopeType"
+//	@Param			transaction	body		BuildElectionID	true	"Delta, OrganizationID, CensusOrigin and EnvelopeType"
 //	@Success		200			{object}	object{electionID=string}
 //	@Router			/elections/id [post]
-func (a *API) nextElectionIDHandler(msg *apirest.APIdata, ctx *httprouter.HTTPContext) error {
-	body := &NextElectionID{}
+func (a *API) buildElectionIDHandler(msg *apirest.APIdata, ctx *httprouter.HTTPContext) error {
+	body := &BuildElectionID{}
 	if err := json.Unmarshal(msg.Data, body); err != nil {
 		return err
 	}
@@ -710,10 +710,7 @@ func (a *API) nextElectionIDHandler(msg *apirest.APIdata, ctx *httprouter.HTTPCo
 			CostFromWeight: body.EnvelopeType.CostFromWeight,
 		},
 	}
-	pid, err := processid.BuildProcessID(
-		process,
-		a.vocapp.State,
-	)
+	pid, err := processid.BuildProcessID(process, a.vocapp.State, body.Delta)
 	if err != nil {
 		return ErrCantParseElectionID.WithErr(err)
 	}

apiclient/election.go

@@ -12,6 +12,7 @@ import (
 	"go.vocdoni.io/dvote/httprouter/apirest"
 	"go.vocdoni.io/dvote/log"
 	"go.vocdoni.io/dvote/types"
+	"go.vocdoni.io/dvote/vochain/processid"
 	"go.vocdoni.io/dvote/vochain/state/electionprice"
 	"go.vocdoni.io/proto/build/go/models"
 	"google.golang.org/protobuf/proto"
@@ -454,7 +455,8 @@ func (c *HTTPclient) ElectionPrice(election *api.ElectionDescription) (uint64, e
 // NextElectionID gets the next election ID for an organization.
 // POST /elections/id
 func (c *HTTPclient) NextElectionID(organizationID types.HexBytes, censusOrigin int32, envelopeType *models.EnvelopeType) (string, error) {
-	body := &api.NextElectionID{
+	body := &api.BuildElectionID{
+		Delta:          processid.BuildNextProcessID,
 		OrganizationID: organizationID,
 		CensusOrigin:   censusOrigin,
 		EnvelopeType: struct {

test/api_test.go

@@ -22,6 +22,7 @@ import (
 	"go.vocdoni.io/dvote/util"
 	"go.vocdoni.io/dvote/vochain"
 	"go.vocdoni.io/dvote/vochain/indexer/indexertypes"
+	"go.vocdoni.io/dvote/vochain/processid"
 	"go.vocdoni.io/dvote/vochain/state"
 	"go.vocdoni.io/dvote/vochain/state/electionprice"
 	"go.vocdoni.io/proto/build/go/models"
@@ -659,7 +660,7 @@ func sendTokensTx(t testing.TB, c *testutil.TestHTTPclient,
 	qt.Assert(t, code, qt.Equals, 200, qt.Commentf("response: %s", resp))
 }
 
-func TestAPINextElectionID(t *testing.T) {
+func TestAPIBuildElectionID(t *testing.T) {
 	server := testcommon.APIserver{}
 	server.Start(t,
 		api.ChainHandler,
@@ -692,7 +693,8 @@ func TestAPINextElectionID(t *testing.T) {
 	waitUntilHeight(t, c, 3)
 
 	// create request for calling api elections/id
-	body := api.NextElectionID{
+	body := api.BuildElectionID{
+		Delta:          processid.BuildNextProcessID,
 		OrganizationID: signer.Address().Bytes(),
 		CensusOrigin:   int32(models.CensusOrigin_OFF_CHAIN_TREE_WEIGHTED.Number()),
 		EnvelopeType: struct {
@@ -718,6 +720,17 @@ func TestAPINextElectionID(t *testing.T) {
 	err := json.Unmarshal(resp, &nextElectionID)
 	qt.Assert(t, err, qt.IsNil)
 
+	// test building n+1 election ID
+	body.Delta = processid.BuildNextProcessID + 1
+	resp, code = c.Request("POST", body, "elections", "id")
+	qt.Assert(t, code, qt.Equals, 200, qt.Commentf("response: %s", resp))
+
+	futureElectionID := struct {
+		ElectionID string `json:"electionID"`
+	}{}
+	err = json.Unmarshal(resp, &futureElectionID)
+	qt.Assert(t, err, qt.IsNil)
+
 	// create a new election
 	electionParams := electionprice.ElectionParameters{ElectionDuration: 100, MaxCensusSize: 100}
 	response := createElection(t, c, signer, electionParams, censusRoot, 0, server.VochainAPP.ChainID(), false)
@@ -728,6 +741,33 @@ func TestAPINextElectionID(t *testing.T) {
 
 	// check next election id is the same as the election id created
 	qt.Assert(t, nextElectionID.ElectionID, qt.Equals, response.ElectionID.String())
+
+	// now build last processID, after election was created.
+	body.Delta = processid.BuildLastProcessID
+	resp, code = c.Request("POST", body, "elections", "id")
+	qt.Assert(t, code, qt.Equals, 200, qt.Commentf("response: %s", resp))
+
+	lastElectionID := struct {
+		ElectionID string `json:"electionID"`
+	}{}
+	err = json.Unmarshal(resp, &lastElectionID)
+	qt.Assert(t, err, qt.IsNil)
+
+	qt.Assert(t, lastElectionID, qt.Equals, nextElectionID)
+
+	// and finally query again next processID, should match futureProcessID
+	body.Delta = processid.BuildNextProcessID
+	resp, code = c.Request("POST", body, "elections", "id")
+	qt.Assert(t, code, qt.Equals, 200, qt.Commentf("response: %s", resp))
+
+	newNextElectionID := struct {
+		ElectionID string `json:"electionID"`
+	}{}
+	err = json.Unmarshal(resp, &newNextElectionID)
+	qt.Assert(t, err, qt.IsNil)
+
+	qt.Assert(t, newNextElectionID, qt.Equals, futureElectionID)
+
 }
 
 func TestAPIEncryptedMetadata(t *testing.T) {

vochain/hysteresis_test.go

@@ -57,7 +57,7 @@ func TestHysteresis(t *testing.T) {
 		MaxCensusSize: 10,
 		CensusOrigin:  models.CensusOrigin_OFF_CHAIN_TREE_WEIGHTED,
 	}
-	procID, err := processid.BuildProcessID(process, app.State)
+	procID, err := processid.BuildProcessID(process, app.State, processid.BuildNextProcessID)
 	c.Assert(err, qt.IsNil)
 	pid := procID.Marshal()
 	process.ProcessId = pid

vochain/processid/process_id.go

@@ -13,6 +13,12 @@ import (
 	"go.vocdoni.io/proto/build/go/models"
 )
 
+// These consts are sugar for calling BuildProcessID
+const (
+	BuildNextProcessID = 0
+	BuildLastProcessID = -1
+)
+
 // ProcessID is a 32 bytes identifier that holds the following information about the voting process:
 //
 // - chainID: a 6 bytes trunked hash of the blockchain identifier
@@ -180,8 +186,11 @@ func (p *ProcessID) EnvelopeType() *models.EnvelopeType {
 	}
 }
 
-// BuildProcessID returns a ProcessID constructed in a deterministic way
-func BuildProcessID(proc *models.Process, state *state.State) (*ProcessID, error) {
+// BuildProcessID returns a ProcessID constructed in a deterministic way.
+//   - with delta == 0, it will return the next process id
+//   - with delta != 0, it will return the (next + delta) process id (past or future)
+//   - for example, with delta == -1 it will return the last process id
+func BuildProcessID(proc *models.Process, state *state.State, delta int32) (*ProcessID, error) {
 	pid := new(ProcessID)
 	pid.SetChainID(state.ChainID())
 	if err := pid.SetEnvelopeType(proc.EnvelopeType); err != nil {
@@ -199,6 +208,9 @@ func BuildProcessID(proc *models.Process, state *state.State) (*ProcessID, error
 		return nil, fmt.Errorf("account not found %s", addr.Hex())
 	}
 	pid.SetAddr(addr)
-	pid.SetNonce(acc.GetProcessIndex())
+	if int32(acc.GetProcessIndex())+delta < 0 {
+		return nil, fmt.Errorf("invalid delta")
+	}
+	pid.SetNonce(uint32(int32(acc.GetProcessIndex()) + delta))
 	return pid, nil
 }

vochain/transaction/election_tx.go

@@ -161,7 +161,7 @@ func (t *TransactionHandler) NewProcessTxCheck(vtx *vochaintx.Tx) (*models.Proce
 	}
 
 	// build the deterministic process ID
-	pid, err := processid.BuildProcessID(tx.Process, t.state)
+	pid, err := processid.BuildProcessID(tx.Process, t.state, processid.BuildNextProcessID)
 	if err != nil {
 		return nil, ethereum.Address{}, fmt.Errorf("cannot build processID: %w", err)
 	}