Merge pull request #16 from ucan-wg/policy-serial

policy: IPLD encode/decode

capability/policy/ipld.go

@@ -0,0 +1,262 @@
+package policy
+
+import (
+	"fmt"
+
+	"github.com/ipld/go-ipld-prime"
+	"github.com/ipld/go-ipld-prime/codec/dagjson"
+	"github.com/ipld/go-ipld-prime/datamodel"
+	"github.com/ipld/go-ipld-prime/must"
+	"github.com/ipld/go-ipld-prime/node/basicnode"
+
+	"github.com/ucan-wg/go-ucan/v1/capability/policy/selector"
+)
+
+func FromIPLD(node datamodel.Node) (Policy, error) {
+	return statementsFromIPLD("/", node)
+}
+
+func FromDagJson(json string) (Policy, error) {
+	nodes, err := ipld.Decode([]byte(json), dagjson.Decode)
+	if err != nil {
+		return nil, err
+	}
+	return FromIPLD(nodes)
+}
+
+func statementFromIPLD(path string, node datamodel.Node) (Statement, error) {
+	// sanity checks
+	if node.Kind() != datamodel.Kind_List {
+		return nil, ErrNotATuple(path)
+	}
+	if node.Length() != 2 && node.Length() != 3 {
+		return nil, ErrUnrecognizedShape(path)
+	}
+
+	// extract operator
+	opNode, _ := node.LookupByIndex(0)
+	if opNode.Kind() != datamodel.Kind_String {
+		return nil, ErrNotAString(path)
+	}
+	op := must.String(opNode)
+
+	arg2AsSelector := func() (selector.Selector, error) {
+		nd, _ := node.LookupByIndex(1)
+		if nd.Kind() != datamodel.Kind_String {
+			return nil, ErrNotAString(path + "1/")
+		}
+		sel, err := selector.Parse(must.String(nd))
+		if err != nil {
+			return nil, ErrInvalidSelector(path+"1/", err)
+		}
+		return sel, nil
+	}
+
+	switch node.Length() {
+	case 2:
+		switch op {
+		case KindNot:
+			arg2, _ := node.LookupByIndex(1)
+			statement, err := statementFromIPLD(path+"1/", arg2)
+			if err != nil {
+				return nil, err
+			}
+			return Not(statement), nil
+
+		case KindAnd, KindOr:
+			arg2, _ := node.LookupByIndex(1)
+			statement, err := statementsFromIPLD(path+"1/", arg2)
+			if err != nil {
+				return nil, err
+			}
+			return connective{kind: op, statements: statement}, nil
+
+		default:
+			return nil, ErrUnrecognizedOperator(path, op)
+		}
+	case 3:
+		switch op {
+		case KindEqual, KindLessThan, KindLessThanOrEqual, KindGreaterThan, KindGreaterThanOrEqual:
+			sel, err := arg2AsSelector()
+			if err != nil {
+				return nil, err
+			}
+			arg3, _ := node.LookupByIndex(2)
+			return equality{kind: op, selector: sel, value: arg3}, nil
+
+		case KindLike:
+			sel, err := arg2AsSelector()
+			if err != nil {
+				return nil, err
+			}
+			pattern, _ := node.LookupByIndex(2)
+			if pattern.Kind() != datamodel.Kind_String {
+				return nil, ErrNotAString(path + "2/")
+			}
+			res, err := Like(sel, must.String(pattern))
+			if err != nil {
+				return nil, ErrInvalidPattern(path+"2/", err)
+			}
+			return res, nil
+
+		case KindAll, KindAny:
+			sel, err := arg2AsSelector()
+			if err != nil {
+				return nil, err
+			}
+			statementsNodes, _ := node.LookupByIndex(2)
+			statements, err := statementsFromIPLD(path+"1/", statementsNodes)
+			return quantifier{kind: op, selector: sel, statements: statements}, nil
+
+		default:
+			return nil, ErrUnrecognizedOperator(path, op)
+		}
+
+	default:
+		return nil, ErrUnrecognizedShape(path)
+	}
+}
+
+func statementsFromIPLD(path string, node datamodel.Node) ([]Statement, error) {
+	// sanity checks
+	if node.Kind() != datamodel.Kind_List {
+		return nil, ErrNotATuple(path)
+	}
+	if node.Length() == 0 {
+		return nil, ErrEmptyList(path)
+	}
+
+	res := make([]Statement, node.Length())
+
+	for i := int64(0); i < node.Length(); i++ {
+		nd, _ := node.LookupByIndex(i)
+		statement, err := statementFromIPLD(fmt.Sprintf("%s%d/", path, i), nd)
+		if err != nil {
+			return nil, err
+		}
+		res[i] = statement
+	}
+
+	return res, nil
+}
+
+func (p Policy) ToIPLD() (datamodel.Node, error) {
+	return statementsToIPLD(p)
+}
+
+func statementsToIPLD(statements []Statement) (datamodel.Node, error) {
+	list := basicnode.Prototype.List.NewBuilder()
+	// can't error, we have the right builder.
+	listBuilder, _ := list.BeginList(int64(len(statements)))
+	for _, argStatement := range statements {
+		node, err := statementToIPLD(argStatement)
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignNode(node)
+		if err != nil {
+			return nil, err
+		}
+	}
+	err := listBuilder.Finish()
+	if err != nil {
+		return nil, err
+	}
+	return list.Build(), nil
+}
+
+func statementToIPLD(statement Statement) (datamodel.Node, error) {
+	list := basicnode.Prototype.List.NewBuilder()
+
+	length := int64(3)
+	switch statement.(type) {
+	case negation, connective:
+		length = 2
+	}
+
+	// can't error, we have the right builder.
+	listBuilder, _ := list.BeginList(length)
+
+	switch statement := statement.(type) {
+	case equality:
+		err := listBuilder.AssembleValue().AssignString(statement.kind)
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignString(statement.selector.String())
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignNode(statement.value)
+		if err != nil {
+			return nil, err
+		}
+
+	case negation:
+		err := listBuilder.AssembleValue().AssignString(statement.Kind())
+		if err != nil {
+			return nil, err
+		}
+		node, err := statementToIPLD(statement.statement)
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignNode(node)
+		if err != nil {
+			return nil, err
+		}
+
+	case connective:
+		err := listBuilder.AssembleValue().AssignString(statement.kind)
+		if err != nil {
+			return nil, err
+		}
+		args, err := statementsToIPLD(statement.statements)
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignNode(args)
+		if err != nil {
+			return nil, err
+		}
+
+	case wildcard:
+		err := listBuilder.AssembleValue().AssignString(statement.Kind())
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignString(statement.selector.String())
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignString(statement.pattern)
+		if err != nil {
+			return nil, err
+		}
+
+	case quantifier:
+		err := listBuilder.AssembleValue().AssignString(statement.kind)
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignString(statement.selector.String())
+		if err != nil {
+			return nil, err
+		}
+		args, err := statementsToIPLD(statement.statements)
+		if err != nil {
+			return nil, err
+		}
+		err = listBuilder.AssembleValue().AssignNode(args)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	err := listBuilder.Finish()
+	if err != nil {
+		return nil, err
+	}
+
+	return list.Build(), nil
+}

capability/policy/ipld_errors.go

@@ -0,0 +1,47 @@
+package policy
+
+import "fmt"
+
+type errWithPath struct {
+	path string
+	msg  string
+}
+
+func (e errWithPath) Error() string {
+	return fmt.Sprintf("IPLD path '%s': %s", e.path, e.msg)
+}
+
+func ErrInvalidSelector(path string, err error) error {
+	return errWithPath{path: path, msg: fmt.Sprintf("invalid selector: %s", err)}
+}
+
+func ErrInvalidPattern(path string, err error) error {
+	return errWithPath{path: path, msg: fmt.Sprintf("invalid pattern: %s", err)}
+}
+
+func ErrNotAString(path string) error {
+	return errWithPath{path: path, msg: ""}
+}
+
+func ErrUnrecognizedOperator(path string, op string) error {
+	return errWithPath{path: path, msg: fmt.Sprintf("unrecognized operator '%s'", safeStr(op))}
+}
+
+func ErrUnrecognizedShape(path string) error {
+	return errWithPath{path: path, msg: "unrecognized shape"}
+}
+
+func ErrNotATuple(path string) error {
+	return errWithPath{path: path, msg: "not a tuple"}
+}
+
+func ErrEmptyList(path string) error {
+	return errWithPath{path: path, msg: "empty list"}
+}
+
+func safeStr(str string) string {
+	if len(str) > 10 {
+		return str[:10]
+	}
+	return str
+}

capability/policy/ipld_test.go

@@ -0,0 +1,45 @@
+package policy
+
+import (
+	"testing"
+
+	"github.com/ipld/go-ipld-prime"
+	"github.com/ipld/go-ipld-prime/codec/dagjson"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIpldRoundTrip(t *testing.T) {
+	const illustrativeExample = `
+[
+    ["==", ".status", "draft"],
+    ["all", ".reviewer", [
+		["like", ".email", "*@example.com"]]
+	],
+    ["any", ".tags", [ 
+		["or", [
+			["==", ".", "news"], 
+			["==", ".", "press"]]
+      ]]
+	]
+]`
+
+	for _, tc := range []struct {
+		name, dagJsonStr string
+	}{
+		{"illustrativeExample", illustrativeExample},
+	} {
+		nodes, err := ipld.Decode([]byte(tc.dagJsonStr), dagjson.Decode)
+		require.NoError(t, err)
+
+		pol, err := FromIPLD(nodes)
+		require.NoError(t, err)
+
+		wroteIpld, err := pol.ToIPLD()
+		require.NoError(t, err)
+
+		wroteAsDagJson, err := ipld.Encode(wroteIpld, dagjson.Encode)
+		require.NoError(t, err)
+
+		require.JSONEq(t, tc.dagJsonStr, string(wroteAsDagJson))
+	}
+}

capability/policy/match.go

@@ -25,52 +25,52 @@ func Match(policy Policy, node ipld.Node) bool {
 func matchStatement(statement Statement, node ipld.Node) bool {
 	switch statement.Kind() {
 	case KindEqual:
-		if s, ok := statement.(EqualityStatement); ok {
-			one, _, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(equality); ok {
+			one, _, err := selector.Select(s.selector, node)
 			if err != nil || one == nil {
 				return false
 			}
-			return datamodel.DeepEqual(s.Value(), one)
+			return datamodel.DeepEqual(s.value, one)
 		}
 	case KindGreaterThan:
-		if s, ok := statement.(InequalityStatement); ok {
-			one, _, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(equality); ok {
+			one, _, err := selector.Select(s.selector, node)
 			if err != nil || one == nil {
 				return false
 			}
-			return isOrdered(s.Value(), one, gt)
+			return isOrdered(s.value, one, gt)
 		}
 	case KindGreaterThanOrEqual:
-		if s, ok := statement.(InequalityStatement); ok {
-			one, _, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(equality); ok {
+			one, _, err := selector.Select(s.selector, node)
 			if err != nil || one == nil {
 				return false
 			}
-			return isOrdered(s.Value(), one, gte)
+			return isOrdered(s.value, one, gte)
 		}
 	case KindLessThan:
-		if s, ok := statement.(InequalityStatement); ok {
-			one, _, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(equality); ok {
+			one, _, err := selector.Select(s.selector, node)
 			if err != nil || one == nil {
 				return false
 			}
-			return isOrdered(s.Value(), one, lt)
+			return isOrdered(s.value, one, lt)
 		}
 	case KindLessThanOrEqual:
-		if s, ok := statement.(InequalityStatement); ok {
-			one, _, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(equality); ok {
+			one, _, err := selector.Select(s.selector, node)
 			if err != nil || one == nil {
 				return false
 			}
-			return isOrdered(s.Value(), one, lte)
+			return isOrdered(s.value, one, lte)
 		}
 	case KindNot:
-		if s, ok := statement.(NegationStatement); ok {
-			return !matchStatement(s.Value(), node)
+		if s, ok := statement.(negation); ok {
+			return !matchStatement(s.statement, node)
 		}
 	case KindAnd:
-		if s, ok := statement.(ConjunctionStatement); ok {
-			for _, cs := range s.Value() {
+		if s, ok := statement.(connective); ok {
+			for _, cs := range s.statements {
 				r := matchStatement(cs, node)
 				if !r {
 					return false
@@ -79,11 +79,11 @@ func matchStatement(statement Statement, node ipld.Node) bool {
 			return true
 		}
 	case KindOr:
-		if s, ok := statement.(DisjunctionStatement); ok {
-			if len(s.Value()) == 0 {
+		if s, ok := statement.(connective); ok {
+			if len(s.statements) == 0 {
 				return true
 			}
-			for _, cs := range s.Value() {
+			for _, cs := range s.statements {
 				r := matchStatement(cs, node)
 				if r {
 					return true
@@ -92,8 +92,8 @@ func matchStatement(statement Statement, node ipld.Node) bool {
 			return false
 		}
 	case KindLike:
-		if s, ok := statement.(WildcardStatement); ok {
-			one, _, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(wildcard); ok {
+			one, _, err := selector.Select(s.selector, node)
 			if err != nil || one == nil {
 				return false
 			}
@@ -101,16 +101,16 @@ func matchStatement(statement Statement, node ipld.Node) bool {
 			if err != nil {
 				return false
 			}
-			return s.Value().Match(v)
+			return s.glob.Match(v)
 		}
 	case KindAll:
-		if s, ok := statement.(QuantifierStatement); ok {
-			_, many, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(quantifier); ok {
+			_, many, err := selector.Select(s.selector, node)
 			if err != nil || many == nil {
 				return false
 			}
 			for _, n := range many {
-				ok := Match(s.Value(), n)
+				ok := Match(s.statements, n)
 				if !ok {
 					return false
 				}
@@ -118,13 +118,13 @@ func matchStatement(statement Statement, node ipld.Node) bool {
 			return true
 		}
 	case KindAny:
-		if s, ok := statement.(QuantifierStatement); ok {
-			_, many, err := selector.Select(s.Selector(), node)
+		if s, ok := statement.(quantifier); ok {
+			_, many, err := selector.Select(s.selector, node)
 			if err != nil || many == nil {
 				return false
 			}
 			for _, n := range many {
-				ok := Match(s.Value(), n)
+				ok := Match(s.statements, n)
 				if ok {
 					return true
 				}

capability/policy/match_test.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"testing"
 
-	"github.com/gobwas/glob"
 	"github.com/ipfs/go-cid"
 	"github.com/ipld/go-ipld-prime"
 	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
@@ -294,8 +293,7 @@ func TestMatch(t *testing.T) {
 	})
 
 	t.Run("wildcard", func(t *testing.T) {
-		glb, err := glob.Compile(`Alice\*, Bob*, Carol.`)
-		require.NoError(t, err)
+		pattern := `Alice\*, Bob*, Carol.`
 
 		for _, s := range []string{
 			"Alice*, Bob, Carol.",
@@ -310,7 +308,10 @@ func TestMatch(t *testing.T) {
 					nb.AssignString(s)
 					nd := nb.Build()
 
-					pol := Policy{Like(selector.MustParse("."), glb)}
+					statement, err := Like(selector.MustParse("."), pattern)
+					require.NoError(t, err)
+
+					pol := Policy{statement}
 					ok := Match(pol, nd)
 					require.True(t, ok)
 				})
@@ -331,7 +332,10 @@ func TestMatch(t *testing.T) {
 					nb.AssignString(s)
 					nd := nb.Build()
 
-					pol := Policy{Like(selector.MustParse("."), glb)}
+					statement, err := Like(selector.MustParse("."), pattern)
+					require.NoError(t, err)
+
+					pol := Policy{statement}
 					ok := Match(pol, nd)
 					require.False(t, ok)
 				})

capability/policy/policy.go

@@ -10,68 +10,25 @@ import (
 )
 
 const (
-	KindEqual              = "=="
-	KindGreaterThan        = ">"
-	KindGreaterThanOrEqual = ">="
-	KindLessThan           = "<"
-	KindLessThanOrEqual    = "<="
-	KindNot                = "not"
-	KindAnd                = "and"
-	KindOr                 = "or"
-	KindLike               = "like"
-	KindAll                = "all"
-	KindAny                = "any"
+	KindEqual              = "=="   // implemented by equality
+	KindGreaterThan        = ">"    // implemented by equality
+	KindGreaterThanOrEqual = ">="   // implemented by equality
+	KindLessThan           = "<"    // implemented by equality
+	KindLessThanOrEqual    = "<="   // implemented by equality
+	KindNot                = "not"  // implemented by negation
+	KindAnd                = "and"  // implemented by connective
+	KindOr                 = "or"   // implemented by connective
+	KindLike               = "like" // implemented by wildcard
+	KindAll                = "all"  // implemented by quantifier
+	KindAny                = "any"  // implemented by quantifier
 )
 
-type Policy = []Statement
+type Policy []Statement
 
 type Statement interface {
 	Kind() string
 }
 
-type EqualityStatement interface {
-	Statement
-	Selector() selector.Selector
-	Value() ipld.Node
-}
-
-type InequalityStatement interface {
-	Statement
-	Selector() selector.Selector
-	Value() ipld.Node
-}
-
-type WildcardStatement interface {
-	Statement
-	Selector() selector.Selector
-	Value() glob.Glob
-}
-
-type ConnectiveStatement interface {
-	Statement
-}
-
-type NegationStatement interface {
-	ConnectiveStatement
-	Value() Statement
-}
-
-type ConjunctionStatement interface {
-	ConnectiveStatement
-	Value() []Statement
-}
-
-type DisjunctionStatement interface {
-	ConnectiveStatement
-	Value() []Statement
-}
-
-type QuantifierStatement interface {
-	Statement
-	Selector() selector.Selector
-	Value() Policy
-}
-
 type equality struct {
 	kind     string
 	selector selector.Selector
@@ -82,31 +39,23 @@ func (e equality) Kind() string {
 	return e.kind
 }
 
-func (e equality) Value() ipld.Node {
-	return e.value
-}
-
-func (e equality) Selector() selector.Selector {
-	return e.selector
-}
-
-func Equal(selector selector.Selector, value ipld.Node) EqualityStatement {
+func Equal(selector selector.Selector, value ipld.Node) Statement {
 	return equality{KindEqual, selector, value}
 }
 
-func GreaterThan(selector selector.Selector, value ipld.Node) InequalityStatement {
+func GreaterThan(selector selector.Selector, value ipld.Node) Statement {
 	return equality{KindGreaterThan, selector, value}
 }
 
-func GreaterThanOrEqual(selector selector.Selector, value ipld.Node) InequalityStatement {
+func GreaterThanOrEqual(selector selector.Selector, value ipld.Node) Statement {
 	return equality{KindGreaterThanOrEqual, selector, value}
 }
 
-func LessThan(selector selector.Selector, value ipld.Node) InequalityStatement {
+func LessThan(selector selector.Selector, value ipld.Node) Statement {
 	return equality{KindLessThan, selector, value}
 }
 
-func LessThanOrEqual(selector selector.Selector, value ipld.Node) InequalityStatement {
+func LessThanOrEqual(selector selector.Selector, value ipld.Node) Statement {
 	return equality{KindLessThanOrEqual, selector, value}
 }
 
@@ -118,89 +67,59 @@ func (n negation) Kind() string {
 	return KindNot
 }
 
-func (n negation) Value() Statement {
-	return n.statement
-}
-
-func Not(stmt Statement) NegationStatement {
+func Not(stmt Statement) Statement {
 	return negation{stmt}
 }
 
-type conjunction struct {
+type connective struct {
+	kind       string
 	statements []Statement
 }
 
-func (n conjunction) Kind() string {
-	return KindAnd
+func (c connective) Kind() string {
+	return c.kind
 }
 
-func (n conjunction) Value() []Statement {
-	return n.statements
+func And(stmts ...Statement) Statement {
+	return connective{KindAnd, stmts}
 }
 
-func And(stmts ...Statement) ConjunctionStatement {
-	return conjunction{stmts}
-}
-
-type disjunction struct {
-	statements []Statement
-}
-
-func (n disjunction) Kind() string {
-	return KindOr
-}
-
-func (n disjunction) Value() []Statement {
-	return n.statements
-}
-
-func Or(stmts ...Statement) DisjunctionStatement {
-	return disjunction{stmts}
+func Or(stmts ...Statement) Statement {
+	return connective{KindOr, stmts}
 }
 
 type wildcard struct {
 	selector selector.Selector
-	glob     glob.Glob
+	pattern  string
+	glob     glob.Glob // not serialized
 }
 
 func (n wildcard) Kind() string {
 	return KindLike
 }
 
-func (n wildcard) Selector() selector.Selector {
-	return n.selector
-}
-
-func (n wildcard) Value() glob.Glob {
-	return n.glob
-}
-
-func Like(selector selector.Selector, glob glob.Glob) WildcardStatement {
-	return wildcard{selector, glob}
+func Like(selector selector.Selector, pattern string) (Statement, error) {
+	g, err := glob.Compile(pattern)
+	if err != nil {
+		return nil, err
+	}
+	return wildcard{selector, pattern, g}, nil
 }
 
 type quantifier struct {
-	kind     string
-	selector selector.Selector
-	policy   Policy
+	kind       string
+	selector   selector.Selector
+	statements []Statement
 }
 
 func (n quantifier) Kind() string {
 	return n.kind
 }
 
-func (n quantifier) Selector() selector.Selector {
-	return n.selector
-}
-
-func (n quantifier) Value() Policy {
-	return n.policy
-}
-
-func All(selector selector.Selector, policy ...Statement) QuantifierStatement {
+func All(selector selector.Selector, policy ...Statement) Statement {
 	return quantifier{KindAll, selector, policy}
 }
 
-func Any(selector selector.Selector, policy ...Statement) QuantifierStatement {
+func Any(selector selector.Selector, policy ...Statement) Statement {
 	return quantifier{KindAny, selector, policy}
 }

delegation/delegation.ipldsch

@@ -13,7 +13,8 @@ type Payload struct {
     cmd String
 
     # The delegation policy
-    pol Policy
+    # It doesn't seem possible to represent it with a schema.
+    pol Any
 
     # A unique, random nonce
     nonce Bytes
@@ -26,7 +27,3 @@ type Payload struct {
     # The timestamp at which the Invocation becomes invalid
     exp nullable Int
 }
-
-type Policy struct {
-
-}

delegation/schema.go

@@ -46,7 +46,7 @@ type PayloadModel struct {
 	Cmd string
 
 	// The delegation policy
-	Pol PolicyModel
+	Pol datamodel.Node
 
 	// A unique, random nonce
 	Nonce []byte
@@ -67,10 +67,3 @@ type MetaModel struct {
 	Keys   []string
 	Values map[string]datamodel.Node
 }
-
-type PolicyModel struct {
-}
-
-func PointerTo[T any](v T) *T {
-	return &v
-}

delegation/schema_test.go

@@ -5,51 +5,62 @@ import (
 	"testing"
 
 	"github.com/ipld/go-ipld-prime"
-	"github.com/ipld/go-ipld-prime/datamodel"
-	"github.com/ipld/go-ipld-prime/node/bindnode"
 	"github.com/stretchr/testify/require"
 )
 
 func TestSchemaRoundTrip(t *testing.T) {
-	p := &PayloadModel{
-		Iss:   "did:key:abc123",
-		Aud:   "did:key:def456",
-		Sub:   PointerTo(""),
-		Cmd:   "/foo/bar",
-		Pol:   PolicyModel{}, // TODO: have something here
-		Nonce: []byte("super-random"),
-		Meta: MetaModel{
-			Keys: []string{"foo", "bar"},
-			Values: map[string]datamodel.Node{
-				"foo": bindnode.Wrap(PointerTo("fooo"), nil),
-				"bar": bindnode.Wrap(PointerTo("baaar"), nil),
-			},
-		},
-		Nbf: PointerTo(int64(123456)),
-		Exp: PointerTo(int64(123456)),
-	}
+	const delegationJson = `
+{
+  "aud":"did:key:def456",
+  "cmd":"/foo/bar",
+  "exp":123456,
+  "iss":"did:key:abc123",
+  "meta":{
+    "bar":"baaar",
+    "foo":"fooo"
+  },
+  "nbf":123456,
+  "nonce":{
+    "/":{
+      "bytes":"c3VwZXItcmFuZG9t"
+    }
+  },
+  "pol":[
+    ["==", ".status", "draft"],
+    ["all", ".reviewer", [
+		["like", ".email", "*@example.com"]]
+	],
+    ["any", ".tags", [ 
+		["or", [
+			["==", ".", "news"], 
+			["==", ".", "press"]]
+      ]]
+	]
+  ],
+  "sub":""
+}
+`
+	// format:    dagJson   -->   PayloadModel   -->   dagCbor   -->   PayloadModel   -->   dagJson
+	// function:      DecodeDagJson()      EncodeDagCbor()   DecodeDagCbor()     EncodeDagJson()
 
-	cborBytes, err := p.EncodeDagCbor()
+	p1, err := DecodeDagJson([]byte(delegationJson))
+	require.NoError(t, err)
+
+	cborBytes, err := p1.EncodeDagCbor()
 	require.NoError(t, err)
 	fmt.Println("cborBytes length", len(cborBytes))
 	fmt.Println("cbor", string(cborBytes))
 
-	jsonBytes, err := p.EncodeDagJson()
+	p2, err := DecodeDagCbor(cborBytes)
 	require.NoError(t, err)
-	fmt.Println("jsonBytes length", len(jsonBytes))
-	fmt.Println("json: ", string(jsonBytes))
+	fmt.Println("read Cbor", p2)
 
-	fmt.Println()
-
-	readCbor, err := DecodeDagCbor(cborBytes)
+	readJson, err := p2.EncodeDagJson()
 	require.NoError(t, err)
-	fmt.Println("readCbor", readCbor)
-	require.Equal(t, p, readCbor)
+	fmt.Println("readJson length", len(readJson))
+	fmt.Println("json: ", string(readJson))
 
-	readJson, err := DecodeDagJson(jsonBytes)
-	require.NoError(t, err)
-	fmt.Println("readJson", readJson)
-	require.Equal(t, p, readJson)
+	require.JSONEq(t, delegationJson, string(readJson))
 }
 
 func BenchmarkSchemaLoad(b *testing.B) {

delegation/view.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/ipld/go-ipld-prime/datamodel"
 
+	"github.com/ucan-wg/go-ucan/v1/capability/command"
 	"github.com/ucan-wg/go-ucan/v1/capability/policy"
 	"github.com/ucan-wg/go-ucan/v1/did"
 )
@@ -18,7 +19,7 @@ type View struct {
 	// Principal that the chain is about (the Subject)
 	Subject did.DID
 	// The Command to eventually invoke
-	Command string
+	Command *command.Command
 	// The delegation policy
 	Policy policy.Policy
 	// A unique, random nonce
@@ -56,11 +57,15 @@ func ViewFromModel(m PayloadModel) (*View, error) {
 		view.Subject = did.Undef
 	}
 
-	// TODO: make that a Command object, and validate it
-	view.Command = m.Cmd
+	view.Command, err = command.Parse(m.Cmd)
+	if err != nil {
+		return nil, fmt.Errorf("parse command: %w", err)
+	}
 
-	// TODO: parsing + validation
-	view.Policy = policy.Policy{}
+	view.Policy, err = policy.FromIPLD(m.Pol)
+	if err != nil {
+		return nil, fmt.Errorf("parse policy: %w", err)
+	}
 
 	if len(m.Nonce) == 0 {
 		return nil, fmt.Errorf("nonce is required")
@@ -80,22 +85,3 @@ func ViewFromModel(m PayloadModel) (*View, error) {
 
 	return &view, nil
 }
-
-func (view *View) Capability() *Capability {
-	return &Capability{
-		Subject: view.Subject,
-		Command: view.Command,
-		Policy:  view.Policy,
-	}
-}
-
-// Capability is a subset of a delegation formed by the triple (subject, command, policy).
-// TODO: useful?
-type Capability struct {
-	// Principal that the chain is about (the Subject)
-	Subject did.DID
-	// The Command to eventually invoke
-	Command string
-	// The delegation policy
-	Policy policy.Policy
-}