Make ECChain opaque [][]byte in GBPFT

cmd/f3sim/f3sim.go

@@ -40,7 +40,7 @@ func main() {
 		sm := sim.NewSimulation(simConfig, graniteConfig, *traceLevel)
 
 		// Same chain for everyone.
-		candidate := sm.Base(0).Extend(sm.CIDGen.Sample())
+		candidate := sm.Base(0).Extend(sm.TipGen.Sample())
 		sm.SetChains(sim.ChainCount{Count: *participantCount, Chain: candidate})
 
 		err := sm.Run(1, *maxRounds)

gen/main.go

@@ -15,7 +15,6 @@ func main() {
 		gpbft.GMessage{},
 		gpbft.Payload{},
 		gpbft.Justification{},
-		gpbft.TipSet{},
 	)
 	if err != nil {
 		fmt.Println(err)

gpbft/chain.go

@@ -1,61 +1,31 @@
 package gpbft
 
 import (
-	"encoding/binary"
+	"bytes"
+	"encoding/hex"
 	"errors"
-	"io"
-	"strconv"
 	"strings"
 )
 
-// Information about a tipset that is relevant to the F3 protocol.
-// This is a lightweight value type comprising 3 machine words.
-// Fields are exported for CBOR generation, but are opqaue and should not be accessed
-// within the protocol implementation.
-type TipSet struct {
-	// The epoch of the blocks in the tipset.
-	Epoch int64
-	// The CID of the tipset.
-	CID TipSetID
-}
-
-// Creates a new tipset.
-func NewTipSet(epoch int64, cid TipSetID) TipSet {
-	return TipSet{
-		Epoch: epoch,
-		CID:   cid,
-	}
-}
-
-// Returns a zero value tipset.
-// The zero value is not a meaningful tipset and may be used to represent bottom.
-func ZeroTipSet() TipSet {
-	return TipSet{}
-}
-
-func (t TipSet) IsZero() bool {
-	return t.Epoch == 0 && t.CID.IsZero()
-}
-
-func (t TipSet) String() string {
-	var b strings.Builder
-	b.Write(t.CID.Bytes())
-	b.WriteString("@")
-	b.WriteString(strconv.FormatInt(t.Epoch, 10))
-	return b.String()
-}
-
-func (t TipSet) MarshalForSigning(w io.Writer) {
-	_ = binary.Write(w, binary.BigEndian, t.Epoch)
-	_, _ = w.Write(t.CID.Bytes())
-}
+// Opaque type representing a tipset.
+// This is expected to be:
+// - a canonical sequence of CIDs of block headers identifying a tipset,
+// - a commitment to the resulting power table,
+// - a commitment to additional derived values.
+// However, GossipPBFT doesn't need to know anything about that structure.
+type TipSet = []byte
 
 // A chain of tipsets comprising a base (the last finalised tipset from which the chain extends).
 // and (possibly empty) suffix.
-// Tipsets are assumed to be built contiguously on each other, though epochs may be missing due to null rounds.
-// The zero value is not a valid chain, and represents a "bottom" value when used in a Granite message.
+// Tipsets are assumed to be built contiguously on each other,
+// though epochs may be missing due to null rounds.
+// The zero value is not a valid chain, and represents a "bottom" value
+// when used in a Granite message.
 type ECChain []TipSet
 
+// A map key for a chain. The zero value means "bottom".
+type ChainKey string
+
 // Creates a new chain.
 func NewChain(base TipSet, suffix ...TipSet) (ECChain, error) {
 	var chain ECChain = []TipSet{base}
@@ -91,27 +61,14 @@ func (c ECChain) Head() TipSet {
 	return c[len(c)-1]
 }
 
-// Returns the CID of the head tipset, or empty string for a zero value
-func (c ECChain) HeadOrZero() TipSet {
-	if c.IsZero() {
-		return ZeroTipSet()
-	}
-	return c.Head()
-}
-
 // Returns a new chain with the same base and no suffix.
 // Invalid for a zero value.
 func (c ECChain) BaseChain() ECChain {
 	return ECChain{c[0]}
 }
 
-// Returns a new chain extending this chain with one tipset.
-// The new tipset is given an epoch and weight one greater than the previous head.
-func (c ECChain) Extend(cid TipSetID) ECChain {
-	return append(c, TipSet{
-		Epoch: c.Head().Epoch + 1,
-		CID:   cid,
-	})
+func (c ECChain) Extend(tip TipSet) ECChain {
+	return append(c, tip)
 }
 
 // Returns a chain with suffix (after the base) truncated to a maximum length.
@@ -127,7 +84,7 @@ func (c ECChain) Eq(other ECChain) bool {
 		return false
 	}
 	for i := range c {
-		if c[i] != other[i] {
+		if !bytes.Equal(c[i], other[i]) {
 			return false
 		}
 	}
@@ -140,16 +97,16 @@ func (c ECChain) SameBase(other ECChain) bool {
 	if c.IsZero() || other.IsZero() {
 		return false
 	}
-	return c.Base() == other.Base()
+	return bytes.Equal(c.Base(), other.Base())
 }
 
 // Check whether a chain has a specific base tipset.
 // Always false for a zero value.
 func (c ECChain) HasBase(t TipSet) bool {
-	if c.IsZero() || t.IsZero() {
+	if c.IsZero() || len(t) == 0 {
 		return false
 	}
-	return c[0] == t
+	return bytes.Equal(c[0], t)
 }
 
 // Checks whether a chain has some prefix (including the base).
@@ -162,7 +119,7 @@ func (c ECChain) HasPrefix(other ECChain) bool {
 		return false
 	}
 	for i := range other {
-		if c[i] != other[i] {
+		if !bytes.Equal(c[i], other[i]) {
 			return false
 		}
 	}
@@ -171,12 +128,12 @@ func (c ECChain) HasPrefix(other ECChain) bool {
 
 // Checks whether a chain has some tipset (including as its base).
 func (c ECChain) HasTipset(t TipSet) bool {
-	if t.IsZero() {
+	if len(t) == 0 {
 		// Chain can never contain zero-valued TipSet.
 		return false
 	}
 	for _, t2 := range c {
-		if t2 == t {
+		if bytes.Equal(t, t2) {
 			return true
 		}
 	}
@@ -192,25 +149,29 @@ func (c ECChain) Validate() error {
 	if c.IsZero() {
 		return nil
 	}
-	var epochSoFar int64
 	for _, tipSet := range c {
-		switch {
-		case tipSet.IsZero():
+		if len(tipSet) == 0 {
 			return errors.New("chain cannot contain zero-valued tip sets")
-		case tipSet.Epoch <= epochSoFar:
-			return errors.New("chain epoch must be in order and unique")
-		default:
-			epochSoFar = tipSet.Epoch
 		}
 	}
 	return nil
 }
 
+// Returns an identifier for the chain suitable for use as a map key.
+// This must completely determine the sequence of tipsets in the chain.
+func (c ECChain) Key() ChainKey {
+	buf := bytes.Buffer{}
+	for _, t := range c {
+		buf.Write(t)
+	}
+	return ChainKey(buf.String())
+}
+
 func (c ECChain) String() string {
 	var b strings.Builder
 	b.WriteString("[")
 	for i, t := range c {
-		b.WriteString(t.String())
+		b.WriteString(hex.EncodeToString(t))
 		if i < len(c)-1 {
 			b.WriteString(", ")
 		}