streamline int overflow check for token timestamps

token/delegation/delegation.go

@@ -18,7 +18,6 @@ import (
 	"github.com/ucan-wg/go-ucan/pkg/command"
 	"github.com/ucan-wg/go-ucan/pkg/meta"
 	"github.com/ucan-wg/go-ucan/pkg/policy"
-	"github.com/ucan-wg/go-ucan/pkg/policy/limits"
 	"github.com/ucan-wg/go-ucan/token/internal/nonce"
 	"github.com/ucan-wg/go-ucan/token/internal/parse"
 )
@@ -177,18 +176,6 @@ func (t *Token) validate() error {
 		errs = errors.Join(errs, fmt.Errorf("token nonce too small"))
 	}
 
-	if t.notBefore != nil {
-		if err := validateTimestamp(t.notBefore.Unix(), "nbf"); err != nil {
-			errs = errors.Join(errs, err)
-		}
-	}
-
-	if t.expiration != nil {
-		if err := validateTimestamp(t.expiration.Unix(), "exp"); err != nil {
-			errs = errors.Join(errs, err)
-		}
-	}
-
 	return errs
 }
 
@@ -228,8 +215,15 @@ func tokenFromModel(m tokenPayloadModel) (*Token, error) {
 
 	tkn.meta = m.Meta
 
-	tkn.notBefore = parse.OptionalTimestamp(m.Nbf)
+	tkn.notBefore, err = parse.OptionalTimestamp(m.Nbf)
-	tkn.expiration = parse.OptionalTimestamp(m.Exp)
+	if err != nil {
+		return nil, fmt.Errorf("parse notBefore: %w", err)
+	}
+
+	tkn.expiration, err = parse.OptionalTimestamp(m.Exp)
+	if err != nil {
+		return nil, fmt.Errorf("parse expiration: %w", err)
+	}
 
 	if err := tkn.validate(); err != nil {
 		return nil, err
@@ -237,11 +231,3 @@ func tokenFromModel(m tokenPayloadModel) (*Token, error) {
 
 	return &tkn, nil
 }
-
-func validateTimestamp(ts int64, field string) error {
-	if ts > limits.MaxInt53 || ts < limits.MinInt53 {
-		return fmt.Errorf("token %s timestamp %d exceeds safe integer bounds", field, ts)
-	}
-
-	return nil
-}

token/internal/parse/parse.go

@@ -1,9 +1,11 @@
 package parse
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/ucan-wg/go-ucan/did"
+	"github.com/ucan-wg/go-ucan/pkg/policy/limits"
 )
 
 func OptionalDID(s *string) (did.DID, error) {
@@ -13,10 +15,15 @@ func OptionalDID(s *string) (did.DID, error) {
 	return did.Parse(*s)
 }
 
-func OptionalTimestamp(sec *int64) *time.Time {
+func OptionalTimestamp(sec *int64) (*time.Time, error) {
 	if sec == nil {
-		return nil
+		return nil, nil
 	}
+
+	if *sec > limits.MaxInt53 || *sec < limits.MinInt53 {
+		return nil, fmt.Errorf("timestamp value %d exceeds safe integer bounds", *sec)
+	}
+
 	t := time.Unix(*sec, 0)
-	return &t
+	return &t, nil
 }

token/invocation/invocation.go

@@ -275,8 +275,15 @@ func tokenFromModel(m tokenPayloadModel) (*Token, error) {
 	tkn.proof = m.Prf
 	tkn.meta = m.Meta
 
-	tkn.expiration = parse.OptionalTimestamp(m.Exp)
+	tkn.expiration, err = parse.OptionalTimestamp(m.Exp)
-	tkn.invokedAt = parse.OptionalTimestamp(m.Iat)
+	if err != nil {
+		return nil, fmt.Errorf("parse expiration: %w", err)
+	}
+
+	tkn.invokedAt, err = parse.OptionalTimestamp(m.Iat)
+	if err != nil {
+		return nil, fmt.Errorf("parse invokedAt: %w", err)
+	}
 
 	tkn.cause = m.Cause