paseto/v4: allow empty Footer and empty data in Payload

If the footer is empty then the message will be unpacked with its own
public key, instead of sender public key.

5 files changed, 85 insertions, 11 deletions

diff --git a/lib/paseto/footer.go b/lib/paseto/footer.go
index acaa3714..ae4fff09 100644
--- a/lib/paseto/footer.go
+++ b/lib/paseto/footer.go
@@ -8,5 +8,5 @@ package paseto
 // MUST NOT include sensitive information.
 type Footer struct {
 	Data   any    `json:"data,omitempty"`
-	PeerID string `json:"peer_id"`
+	PeerID string `json:"peer_id,omitempty"`
 }
diff --git a/lib/paseto/message_test.go b/lib/paseto/message_test.go
index aa4f7a23..a3d21420 100644
--- a/lib/paseto/message_test.go
+++ b/lib/paseto/message_test.go
@@ -31,7 +31,6 @@ func TestNewMessage(t *testing.T) {
     "peer_id": "sender"
   },
   "Payload": {
-    "data": null,
     "iss": "sender",
     "sub": "test",
     "aud": "receiver",
diff --git a/lib/paseto/payload.go b/lib/paseto/payload.go
index af889d77..346356f7 100644
--- a/lib/paseto/payload.go
+++ b/lib/paseto/payload.go
@@ -29,9 +29,9 @@ var (
 // The claims follow RFC 7519 that includes issuer, subject, audience,
 // expiration time, not-before time, issued-at, and ID.
 type Payload struct {
-	// Data defines actual information to be send in message.
+	// Data defines additional information to be send in message.
 	// Data must be JSON encodable.
-	Data any `json:"data"`
+	Data any `json:"data,omitempty"`
 
 	// Issuer defines the peer ID that issued the payload.
 	Issuer string `json:"iss,omitempty"`
diff --git a/lib/paseto/v4/public_mode.go b/lib/paseto/v4/public_mode.go
index e4b281d7..7e54d505 100644
--- a/lib/paseto/v4/public_mode.go
+++ b/lib/paseto/v4/public_mode.go
@@ -95,6 +95,9 @@ func (pmode *PublicMode) Pack(msg paseto.Message, implicit []byte) (
 	if err != nil {
 		return ``, fmt.Errorf(`%s: %w`, logp, err)
 	}
+	if bytes.Equal(msg.RawFooter, []byte(`{}`)) {
+		msg.RawFooter = nil
+	}
 	token, err = pmode.Sign(msg.RawPayload, msg.RawFooter, implicit)
 	if err != nil {
 		return ``, fmt.Errorf(`%s: %w`, logp, err)
@@ -166,14 +169,20 @@ func (pmode *PublicMode) Unpack(token string, implicit []byte, msg *paseto.Messa
 		return fmt.Errorf(`%s: %w`, logp, err)
 	}
 
-	err = json.Unmarshal(msg.RawFooter, &msg.Footer)
-	if err != nil {
-		return fmt.Errorf(`%w: %w`, paseto.ErrTokenFooter, err)
-	}
+	var sender paseto.Peer
+	if msg.RawFooter != nil {
+		err = json.Unmarshal(msg.RawFooter, &msg.Footer)
+		if err != nil {
+			return fmt.Errorf(`%w: %w`, paseto.ErrTokenFooter, err)
+		}
 
-	sender, ok := pmode.GetPeer(msg.Footer.PeerID)
-	if !ok {
-		return fmt.Errorf(`%s: %w %s`, logp, ErrPeerID, msg.Footer.PeerID)
+		var ok bool
+		sender, ok = pmode.GetPeer(msg.Footer.PeerID)
+		if !ok {
+			return fmt.Errorf(`%s: %w %s`, logp, ErrPeerID, msg.Footer.PeerID)
+		}
+	} else {
+		sender = pmode.Peer
 	}
 
 	if !ed25519.Verify(sender.PublicKey, msg.PAE, msg.Sig) {
diff --git a/lib/paseto/v4/public_mode_test.go b/lib/paseto/v4/public_mode_test.go
index 658facb8..3e060e8a 100644
--- a/lib/paseto/v4/public_mode_test.go
+++ b/lib/paseto/v4/public_mode_test.go
@@ -9,7 +9,10 @@ import (
 	"log"
 	"os"
 	"testing"
+	"testing/cryptotest"
+	"testing/synctest"
 
+	"git.sr.ht/~shulhan/pakakeh.go/lib/paseto"
 	"git.sr.ht/~shulhan/pakakeh.go/lib/test"
 )
 
@@ -36,6 +39,69 @@ func (tvp *testVectorPublic) init() {
 	}
 }
 
+func TestPublicMode_Pack(t *testing.T) {
+	cryptotest.SetGlobalRandom(t, 1)
+
+	listcase := []struct {
+		msg           paseto.Message
+		desc          string
+		expToken      string
+		expRawPayload string
+		expRawFooter  string
+	}{{
+		desc:          `Empty`,
+		expToken:      `v4.public.e316aAoBcV59pCXGKmxwuKl050jOA9gP9F5qCFWllfEHUzzEWqRtZDK29vC07QoCJZEd-6T_65tybe4uJRuErwwE`,
+		expRawPayload: `{}`,
+	}, {
+		desc: `FooterOnly`,
+		msg: paseto.Message{
+			Footer: paseto.Footer{
+				Data: `footer.data`,
+			},
+		},
+		expToken:      `v4.public.e32fZEGqzzkbqRiMbrlQnsacHTa1RjMBuE5cgciyHTEQiUIwh67S106_rGBROlkJKu71axKQURDKqjLMS1E6liQF.eyJkYXRhIjoiZm9vdGVyLmRhdGEifQ`,
+		expRawPayload: `{}`,
+		expRawFooter:  `{"data":"footer.data"}`,
+	}, {
+		desc: `PayloadAndFooter`,
+		msg: paseto.Message{
+			Payload: paseto.Payload{
+				Data: []byte{0x73, 0x68, 0x75, 0x6c},
+			},
+			Footer: paseto.Footer{
+				Data: `footer.data`,
+			},
+		},
+		expToken:      `v4.public.eyJkYXRhIjoiYzJoMWJBPT0ifXIYsFygQyakjTQ2j500FIxcPKrE3B3G1Sid7NAvvZ9_yqAZgIhhMu4ojqiewIPw81G-ZvX7GO321Ofgvv8_Zgw.eyJkYXRhIjoiZm9vdGVyLmRhdGEifQ`,
+		expRawPayload: `{"data":"c2h1bA=="}`,
+		expRawFooter:  `{"data":"footer.data"}`,
+	}}
+
+	seed, err := hex.DecodeString(`b4cbfb43df4ce210727d953e4a713307fa19bb7d9f85041438d9e11b942a3774`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	pmode := NewPublicMode(``, [32]byte(seed))
+
+	synctest.Test(t, func(t *testing.T) {
+		for _, tc := range listcase {
+			gotToken, err := pmode.Pack(tc.msg, nil)
+			if err != nil {
+				t.Fatalf(`%s: %s`, tc.desc, err)
+			}
+			test.Assert(t, tc.desc, tc.expToken, gotToken)
+
+			msg := paseto.Message{}
+			err = UnpackPublicToken(&msg, gotToken, nil)
+			if err != nil {
+				t.Fatalf(`%s: %s`, tc.desc, err)
+			}
+			test.Assert(t, `RawPayload`, tc.expRawPayload, string(msg.RawPayload))
+			test.Assert(t, `RawFooter`, tc.expRawFooter, string(msg.RawFooter))
+		}
+	})
+}
+
 func TestPublicMode_Sign(t *testing.T) {
 	logp := `TestPublicMode_Sign`