mixpool: Remove Receive expectedMessages argument

The number of expected messages can be determined by the capacity of the
intended message type's slice.

mixing/mixclient/blame.go

@@ -80,8 +80,8 @@ func (c *Client) blame(ctx context.Context, sesRun *sessionRun) (err error) {
 	// Receive currently-revealed secrets
 	rcv := new(mixpool.Received)
 	rcv.Sid = sesRun.sid
-	rcv.RSs = make([]*wire.MsgMixSecrets, 0, len(sesRun.prs))
-	_ = mp.Receive(ctx, 0, rcv)
+	rcv.RSs = make([]*wire.MsgMixSecrets, 0, 1)
+	_ = mp.Receive(ctx, rcv)
 	rsHashes := make([]chainhash.Hash, len(rcv.RSs))
 	for _, rs := range rcv.RSs {
 		rsHashes = append(rsHashes, rs.Hash())
@@ -101,8 +101,8 @@ func (c *Client) blame(ctx context.Context, sesRun *sessionRun) (err error) {
 	}
 
 	// Wait for all secrets, or timeout.
-	rcv.RSs = rcv.RSs[:0]
-	_ = mp.Receive(ctx, len(sesRun.prs), rcv)
+	rcv.RSs = make([]*wire.MsgMixSecrets, 0, len(sesRun.prs))
+	_ = mp.Receive(ctx, rcv)
 	rss := rcv.RSs
 	for _, rs := range rcv.RSs {
 		if idx, ok := identityIndices[rs.Identity]; ok {

mixing/mixclient/client.go

@@ -1093,7 +1093,7 @@ func (c *Client) run(ctx context.Context, ps *pairedSessions, madePairing *bool)
 		rcv.KEs = make([]*wire.MsgMixKeyExchange, 0, len(sesRun.prs))
 		ctx, cancel := context.WithDeadline(ctx, d.recvKE)
 		defer cancel()
-		err = mp.Receive(ctx, len(sesRun.prs), rcv)
+		err = mp.Receive(ctx, rcv)
 		if ctx.Err() != nil {
 			err = fmt.Errorf("session %x KE receive context cancelled: %w",
 				sesRun.sid[:], ctx.Err())
@@ -1264,7 +1264,7 @@ func (c *Client) run(ctx context.Context, ps *pairedSessions, madePairing *bool)
 	rcv.KEs = nil
 	rcv.CTs = make([]*wire.MsgMixCiphertexts, 0, len(prs))
 	rcvCtx, rcvCtxCancel := context.WithDeadline(ctx, d.recvCT)
-	err = mp.Receive(rcvCtx, len(prs), rcv)
+	err = mp.Receive(rcvCtx, rcv)
 	rcvCtxCancel()
 	cts := rcv.CTs
 	for _, ct := range cts {
@@ -1350,7 +1350,7 @@ func (c *Client) run(ctx context.Context, ps *pairedSessions, madePairing *bool)
 	rcv.CTs = nil
 	rcv.SRs = make([]*wire.MsgMixSlotReserve, 0, len(prs))
 	rcvCtx, rcvCtxCancel = context.WithDeadline(ctx, d.recvSR)
-	err = mp.Receive(rcvCtx, len(prs), rcv)
+	err = mp.Receive(rcvCtx, rcv)
 	rcvCtxCancel()
 	srs := rcv.SRs
 	for _, sr := range srs {
@@ -1428,7 +1428,7 @@ func (c *Client) run(ctx context.Context, ps *pairedSessions, madePairing *bool)
 	rcv.SRs = nil
 	rcv.DCs = make([]*wire.MsgMixDCNet, 0, len(prs))
 	rcvCtx, rcvCtxCancel = context.WithDeadline(ctx, d.recvDC)
-	err = mp.Receive(rcvCtx, len(prs), rcv)
+	err = mp.Receive(rcvCtx, rcv)
 	rcvCtxCancel()
 	dcs := rcv.DCs
 	for _, dc := range dcs {
@@ -1508,7 +1508,7 @@ func (c *Client) run(ctx context.Context, ps *pairedSessions, madePairing *bool)
 	rcv.DCs = nil
 	rcv.CMs = make([]*wire.MsgMixConfirm, 0, len(prs))
 	rcvCtx, rcvCtxCancel = context.WithDeadline(ctx, d.recvCM)
-	err = mp.Receive(rcvCtx, len(prs), rcv)
+	err = mp.Receive(rcvCtx, rcv)
 	rcvCtxCancel()
 	cms := rcv.CMs
 	for _, cm := range cms {
@@ -1612,16 +1612,15 @@ func (c *Client) roots(ctx context.Context, seenSRs []chainhash.Hash,
 	// We can return a result as soon as we read any valid factored
 	// polynomial message that provides the solutions for this SR
 	// polynomial.
-	expectedMessages := 1
 	rcv := &mixpool.Received{
 		Sid: sesRun.sid,
-		FPs: make([]*wire.MsgMixFactoredPoly, 0, sesRun.mtot),
+		FPs: make([]*wire.MsgMixFactoredPoly, 0, 1),
 	}
 	roots := make([]*big.Int, 0, len(a)-1)
 	checkedFPByIdentity := make(map[identity]struct{})
 	for {
 		rcv.FPs = rcv.FPs[:0]
-		err := c.mixpool.Receive(ctx, expectedMessages, rcv)
+		err := c.mixpool.Receive(ctx, rcv)
 		if err != nil {
 			return nil, err
 		}
@@ -1663,7 +1662,7 @@ func (c *Client) roots(ctx context.Context, seenSRs []chainhash.Hash,
 			checkedFPByIdentity[fp.Identity] = struct{}{}
 		}
 
-		expectedMessages = len(rcv.FPs) + 1
+		rcv.FPs = make([]*wire.MsgMixFactoredPoly, 0, len(rcv.FPs)+1)
 	}
 }
 

mixing/mixpool/mixpool.go

@@ -595,8 +595,9 @@ PRLoop:
 
 // Received is a parameter for Pool.Receive describing the session and run to
 // receive messages for, and slices for returning results.  A single non-nil
-// slice is required and indicates which message slice will be will be
-// appended to.  Received messages are unsorted.
+// slice with capacity of the expected number of messages is required and
+// indicates which message slice will be will be appended to.  Received
+// messages are unsorted.
 type Received struct {
 	Sid [32]byte
 	KEs []*wire.MsgMixKeyExchange
@@ -620,7 +621,7 @@ type Received struct {
 // r.RSs is nil, Receive immediately returns ErrSecretsRevealed.  An
 // additional call to Receive with a non-nil RSs can be used to receive all of
 // the secrets after each peer publishes their own revealed secrets.
-func (p *Pool) Receive(ctx context.Context, expectedMessages int, r *Received) error {
+func (p *Pool) Receive(ctx context.Context, r *Received) error {
 	sid := r.Sid
 	var bc *broadcast
 
@@ -632,30 +633,37 @@ func (p *Pool) Receive(ctx context.Context, expectedMessages int, r *Received) e
 	}
 	bc = &ses.bc
 
-	nonNilSlices := 0
-	if r.KEs != nil {
-		nonNilSlices++
+	var capSlices, expectedMessages int
+	if cap(r.KEs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.KEs)
 	}
-	if r.CTs != nil {
-		nonNilSlices++
+	if cap(r.CTs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.CTs)
 	}
-	if r.SRs != nil {
-		nonNilSlices++
+	if cap(r.SRs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.SRs)
 	}
-	if r.DCs != nil {
-		nonNilSlices++
+	if cap(r.DCs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.DCs)
 	}
-	if r.CMs != nil {
-		nonNilSlices++
+	if cap(r.CMs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.CMs)
 	}
-	if r.FPs != nil {
-		nonNilSlices++
+	if cap(r.FPs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.FPs)
 	}
-	if r.RSs != nil {
-		nonNilSlices++
+	if cap(r.RSs) != 0 {
+		capSlices++
+		expectedMessages = cap(r.RSs)
 	}
-	if nonNilSlices != 1 {
-		return fmt.Errorf("mixpool: exactly one Received slice must be non-nil")
+	if capSlices != 1 {
+		return fmt.Errorf("mixpool: exactly one Received slice must have non-zero capacity")
 	}
 
 Loop: