Add TimestampTime() to ct.SignedTreeHead

ct/types.go

@@ -6,6 +6,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"time"
 )
 
 const (
@@ -289,6 +290,10 @@ type SignedTreeHead struct {
 	LogID             SHA256Hash      `json:"log_id"`              // The SHA256 hash of the log's public key
 }
 
+func (sth *SignedTreeHead) TimestampTime() time.Time {
+	return time.Unix(int64(sth.Timestamp/1000), int64(sth.Timestamp%1000)*1_000_000).UTC()
+}
+
 // SignedCertificateTimestamp represents the structure returned by the
 // add-chain and add-pre-chain methods after base64 decoding. (see RFC sections
 // 3.2 ,4.1 and 4.2)