refactor: remove explicit closures. expose rego fns (#170)

policy/rego.go

@@ -88,10 +88,7 @@ func (re *regoEvaluator) Evaluate(ctx context.Context, resolver attestation.Reso
 		rego.Store(store),
 		rego.GenerateJSON(jsonGenerator[Result]()),
 	)
-	regoFnOpts := &regoFnOpts{
-		attestationResolver: resolver,
-		attestationVerifier: re.attestationVerifier,
-	}
+	regoFnOpts := NewRegoFunctionOptions(resolver, re.attestationVerifier)
 	for _, custom := range RegoFunctions(regoFnOpts) {
 		regoOpts = append(regoOpts, custom.Func)
 	}
@@ -175,7 +172,7 @@ func handleErrors2(f func(rCtx rego.BuiltinContext, a, b *ast.Term) (*ast.Term,
 	}
 }
 
-func RegoFunctions(regoOpts *regoFnOpts) []*tester.Builtin {
+func RegoFunctions(regoOpts *RegoFnOpts) []*tester.Builtin {
 	return []*tester.Builtin{
 		{
 			Decl: verifyDecl,
@@ -186,7 +183,7 @@ func RegoFunctions(regoOpts *regoFnOpts) []*tester.Builtin {
 					Memoize:          true,
 					Nondeterministic: verifyDecl.Nondeterministic,
 				},
-				handleErrors2(verifyInTotoEnvelope(regoOpts))),
+				handleErrors2(regoOpts.verifyInTotoEnvelope)),
 		},
 		{
 			Decl: attestDecl,
@@ -197,89 +194,97 @@ func RegoFunctions(regoOpts *regoFnOpts) []*tester.Builtin {
 					Memoize:          true,
 					Nondeterministic: attestDecl.Nondeterministic,
 				},
-				handleErrors1(fetchInTotoAttestations(regoOpts))),
+				handleErrors1(regoOpts.fetchInTotoAttestations)),
 		},
 	}
 }
 
-func fetchInTotoAttestations(regoOpts *regoFnOpts) rego.Builtin1 {
-	return func(rCtx rego.BuiltinContext, predicateTypeTerm *ast.Term) (*ast.Term, error) {
-		predicateTypeStr, ok := predicateTypeTerm.Value.(ast.String)
-		if !ok {
-			return nil, fmt.Errorf("predicateTypeTerm is not a string")
-		}
-		predicateType := string(predicateTypeStr)
+// because we don't control the signature here (blame rego)
+// nolint:gocritic
+func (regoOpts *RegoFnOpts) fetchInTotoAttestations(rCtx rego.BuiltinContext, predicateTypeTerm *ast.Term) (*ast.Term, error) {
+	predicateTypeStr, ok := predicateTypeTerm.Value.(ast.String)
+	if !ok {
+		return nil, fmt.Errorf("predicateTypeTerm is not a string")
+	}
+	predicateType := string(predicateTypeStr)
 
-		envelopes, err := regoOpts.attestationResolver.Attestations(rCtx.Context, predicateType)
+	envelopes, err := regoOpts.attestationResolver.Attestations(rCtx.Context, predicateType)
+	if err != nil {
+		return nil, err
+	}
+
+	// Convert each envelope to an ast.Value.
+	values := make([]*ast.Term, len(envelopes))
+	for i, envelope := range envelopes {
+		value, err := ast.InterfaceToValue(envelope)
 		if err != nil {
 			return nil, err
 		}
-
-		// Convert each envelope to an ast.Value.
-		values := make([]*ast.Term, len(envelopes))
-		for i, envelope := range envelopes {
-			value, err := ast.InterfaceToValue(envelope)
-			if err != nil {
-				return nil, err
-			}
-			values[i] = ast.NewTerm(value)
-		}
-
-		// Wrap the values in an ast.Set and convert it to an ast.Term.
-		set := ast.NewTerm(ast.NewSet(values...))
-
-		return set, nil
+		values[i] = ast.NewTerm(value)
 	}
+
+	// Wrap the values in an ast.Set and convert it to an ast.Term.
+	set := ast.NewTerm(ast.NewSet(values...))
+
+	return set, nil
 }
 
-type regoFnOpts struct {
+type RegoFnOpts struct {
 	attestationResolver attestation.Resolver
 	attestationVerifier attestation.Verifier
 }
 
-func verifyInTotoEnvelope(regoOpts *regoFnOpts) rego.Builtin2 {
-	return func(rCtx rego.BuiltinContext, envTerm, optsTerm *ast.Term) (*ast.Term, error) {
-		env := new(attestation.Envelope)
-		opts := new(attestation.VerifyOptions)
-		err := ast.As(envTerm.Value, env)
-		if err != nil {
-			return nil, fmt.Errorf("failed to cast envelope: %w", err)
-		}
-		err = ast.As(optsTerm.Value, &opts)
-		if err != nil {
-			return nil, fmt.Errorf("failed to cast verifier options: %w", err)
-		}
-		payload, err := attestation.VerifyDSSE(rCtx.Context, regoOpts.attestationVerifier, env, opts)
-		if err != nil {
-			return nil, fmt.Errorf("failed to verify envelope: %w", err)
-		}
-
-		statement := new(intoto.Statement)
-
-		switch env.PayloadType {
-		case intoto.PayloadType:
-			err = json.Unmarshal(payload, statement)
-			if err != nil {
-				return nil, fmt.Errorf("failed to unmarshal statement: %w", err)
-			}
-			// TODO: implement other types of envelope
-		default:
-			return nil, fmt.Errorf("unsupported payload type: %s", env.PayloadType)
-		}
-
-		err = VerifySubject(rCtx.Context, statement.Subject, regoOpts.attestationResolver)
-		if err != nil {
-			return nil, fmt.Errorf("failed to verify subject: %w", err)
-		}
-
-		value, err := ast.InterfaceToValue(statement)
-		if err != nil {
-			return nil, err
-		}
-		return ast.NewTerm(value), nil
+// this is exported for testing here and in clients of the library.
+func NewRegoFunctionOptions(resolver attestation.Resolver, verifier attestation.Verifier) *RegoFnOpts {
+	return &RegoFnOpts{
+		attestationResolver: resolver,
+		attestationVerifier: verifier,
 	}
 }
 
+// because we don't control the signature here (blame rego)
+// nolint:gocritic
+func (regoOpts *RegoFnOpts) verifyInTotoEnvelope(rCtx rego.BuiltinContext, envTerm, optsTerm *ast.Term) (*ast.Term, error) {
+	env := new(attestation.Envelope)
+	opts := new(attestation.VerifyOptions)
+	err := ast.As(envTerm.Value, env)
+	if err != nil {
+		return nil, fmt.Errorf("failed to cast envelope: %w", err)
+	}
+	err = ast.As(optsTerm.Value, &opts)
+	if err != nil {
+		return nil, fmt.Errorf("failed to cast verifier options: %w", err)
+	}
+	payload, err := attestation.VerifyDSSE(rCtx.Context, regoOpts.attestationVerifier, env, opts)
+	if err != nil {
+		return nil, fmt.Errorf("failed to verify envelope: %w", err)
+	}
+
+	statement := new(intoto.Statement)
+
+	switch env.PayloadType {
+	case intoto.PayloadType:
+		err = json.Unmarshal(payload, statement)
+		if err != nil {
+			return nil, fmt.Errorf("failed to unmarshal statement: %w", err)
+		}
+		// TODO: implement other types of envelope
+	default:
+		return nil, fmt.Errorf("unsupported payload type: %s", env.PayloadType)
+	}
+
+	err = VerifySubject(rCtx.Context, statement.Subject, regoOpts.attestationResolver)
+	if err != nil {
+		return nil, fmt.Errorf("failed to verify subject: %w", err)
+	}
+
+	value, err := ast.InterfaceToValue(statement)
+	if err != nil {
+		return nil, err
+	}
+	return ast.NewTerm(value), nil
+}
+
 func loadYAML(path string, bs []byte) (interface{}, error) {
 	var x interface{}
 	bs, err := yaml.YAMLToJSON(bs)