delegation,invocation: proper String() function

did/did.go

@@ -102,6 +102,9 @@ func (d DID) PubKey() (crypto.PubKey, error) {
 
 // String formats the decentralized identity document (DID) as a string.
 func (d DID) String() string {
+	if d == Undef {
+		return "(undefined)"
+	}
 	key, _ := mbase.Encode(mbase.Base58BTC, []byte(d.bytes))
 	return "did:key:" + key
 }

token/delegation/delegation.go

@@ -10,8 +10,10 @@ package delegation
 // TODO: change the "delegation" link above when the specification is merged
 
 import (
+	"encoding/base64"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/ucan-wg/go-ucan/did"
@@ -170,6 +172,32 @@ func (t *Token) IsValidAt(ti time.Time) bool {
 	return true
 }
 
+func (t *Token) String() string {
+	var res strings.Builder
+
+	var kind string
+	switch {
+	case t.issuer == t.subject:
+		kind = " (root delegation)"
+	case t.subject == did.Undef:
+		kind = " (powerline delegation)"
+	default:
+		kind = " (normal delegation)"
+	}
+
+	res.WriteString(fmt.Sprintf("Issuer: %s\n", t.Issuer()))
+	res.WriteString(fmt.Sprintf("Audience: %s\n", t.Audience()))
+	res.WriteString(fmt.Sprintf("Subject: %s%s\n", t.Subject(), kind))
+	res.WriteString(fmt.Sprintf("Command: %s\n", t.Command()))
+	res.WriteString(fmt.Sprintf("Policy: %s\n", t.Policy()))
+	res.WriteString(fmt.Sprintf("Nonce: %s\n", base64.StdEncoding.EncodeToString(t.Nonce())))
+	res.WriteString(fmt.Sprintf("Meta: %s\n", t.Meta()))
+	res.WriteString(fmt.Sprintf("NotBefore: %v\n", t.NotBefore()))
+	res.WriteString(fmt.Sprintf("Expiration: %v", t.Expiration()))
+
+	return res.String()
+}
+
 func (t *Token) validate() error {
 	var errs error
 

token/invocation/invocation.go

@@ -8,8 +8,10 @@
 package invocation
 
 import (
+	"encoding/base64"
 	"errors"
 	"fmt"
+	"strings"
 	"time"
 
 	"github.com/ipfs/go-cid"
@@ -214,6 +216,24 @@ func (t *Token) IsValidAt(ti time.Time) bool {
 	return true
 }
 
+func (t *Token) String() string {
+	var res strings.Builder
+
+	res.WriteString(fmt.Sprintf("Issuer: %s\n", t.Issuer()))
+	res.WriteString(fmt.Sprintf("Audience: %s\n", t.Audience()))
+	res.WriteString(fmt.Sprintf("Subject: %v\n", t.Subject()))
+	res.WriteString(fmt.Sprintf("Command: %s\n", t.Command()))
+	res.WriteString(fmt.Sprintf("Args: %s\n", t.Arguments()))
+	res.WriteString(fmt.Sprintf("Proof: %v\n", t.Proof()))
+	res.WriteString(fmt.Sprintf("Nonce: %s\n", base64.StdEncoding.EncodeToString(t.Nonce())))
+	res.WriteString(fmt.Sprintf("Meta: %s\n", t.Meta()))
+	res.WriteString(fmt.Sprintf("Expiration: %v\n", t.Expiration()))
+	res.WriteString(fmt.Sprintf("Invoked At: %v\n", t.InvokedAt()))
+	res.WriteString(fmt.Sprintf("Cause: %v", t.Cause()))
+
+	return res.String()
+}
+
 func (t *Token) validate() error {
 	var errs error