simplify codebase.

verifier.go

@@ -0,0 +1,86 @@
+package opentimestamps
+
+import (
+	"fmt"
+	"math"
+	"time"
+
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/wire"
+)
+
+type Bitcoin interface {
+	GetBlockHash(height int64) (*chainhash.Hash, error)
+	GetBlockHeader(hash *chainhash.Hash) (*wire.BlockHeader, error)
+}
+
+// VerifyAttestation checks a BitcoinAttestation using a given hash digest. It
+// returns the time of the block if the verification succeeds, an error
+// otherwise.
+func VerifyAttestation(bitcoinInterface Bitcoin, digest []byte, a *BitcoinAttestation) (*time.Time, error) {
+	if a.Height > math.MaxInt64 {
+		return nil, fmt.Errorf("illegal block height")
+	}
+	blockHash, err := bitcoinInterface.GetBlockHash(int64(a.Height))
+	if err != nil {
+		return nil, err
+	}
+	h, err := bitcoinInterface.GetBlockHeader(blockHash)
+	if err != nil {
+		return nil, err
+	}
+
+	merkleRootBytes := h.MerkleRoot[:]
+	err = a.VerifyAgainstBlockHash(digest, merkleRootBytes)
+	if err != nil {
+		return nil, err
+	}
+	utc := h.Timestamp.UTC()
+
+	return &utc, nil
+}
+
+// A BitcoinVerification is the result of verifying a BitcoinAttestation
+type BitcoinVerification struct {
+	Timestamp       *Timestamp
+	Attestation     *BitcoinAttestation
+	AttestationTime *time.Time
+	Error           error
+}
+
+// BitcoinVerifications returns the all bitcoin attestation results for the
+// timestamp.
+func BitcoinVerifications(bitcoinInterface Bitcoin, t *Timestamp) (res []BitcoinVerification) {
+	t.Walk(func(ts *Timestamp) {
+		for _, att := range ts.Attestations {
+			btcAtt, ok := att.(*BitcoinAttestation)
+			if !ok {
+				continue
+			}
+			attTime, err := VerifyAttestation(bitcoinInterface, ts.Message, btcAtt)
+			res = append(res, BitcoinVerification{
+				Timestamp:       ts,
+				Attestation:     btcAtt,
+				AttestationTime: attTime,
+				Error:           err,
+			})
+		}
+	})
+	return res
+}
+
+// Verify returns the earliest bitcoin-attested time, or nil if none can be
+// found or verified successfully.
+func Verify(bitcoinInterface Bitcoin, t *Timestamp) (ret *time.Time, err error) {
+	res := BitcoinVerifications(bitcoinInterface, t)
+	for _, r := range res {
+		if r.Error != nil {
+			err = r.Error
+			continue
+		}
+		if ret == nil || r.AttestationTime.Before(*ret) {
+			ret = r.AttestationTime
+		}
+	}
+	return
+}