Add built-ins to un/marshal JSON

ast/builtins.go

@@ -47,6 +47,9 @@ var DefaultBuiltins = [...]*Builtin{
 
 	// Strings
 	Concat, FormatInt, IndexOf, Substring, Lower, Upper, Contains, StartsWith, EndsWith,
+
+	// JSON
+	JSONMarshal, JSONUnmarshal,
 }
 
 // BuiltinMap provides a convenient mapping of built-in names to
@@ -290,6 +293,24 @@ var Upper = &Builtin{
 	TargetPos: []int{1},
 }
 
+/**
+ * JSON
+ */
+
+// JSONMarshal serializes the input term.
+var JSONMarshal = &Builtin{
+	Name:      Var("json_marshal"),
+	NumArgs:   2,
+	TargetPos: []int{1},
+}
+
+// JSONUnmarshal deserializes the input string.
+var JSONUnmarshal = &Builtin{
+	Name:      Var("json_unmarshal"),
+	NumArgs:   2,
+	TargetPos: []int{1},
+}
+
 /**
  * Deprecated built-ins.
  */

topdown/json.go

@@ -0,0 +1,49 @@
+// Copyright 2017 The OPA Authors.  All rights reserved.
+// Use of this source code is governed by an Apache2
+// license that can be found in the LICENSE file.
+
+package topdown
+
+import (
+	"encoding/json"
+
+	"github.com/open-policy-agent/opa/ast"
+	"github.com/open-policy-agent/opa/topdown/builtins"
+	"github.com/open-policy-agent/opa/util"
+)
+
+func builtinJSONMarshal(a ast.Value) (ast.Value, error) {
+
+	asJSON, err := ast.JSON(a)
+	if err != nil {
+		return nil, err
+	}
+
+	bs, err := json.Marshal(asJSON)
+	if err != nil {
+		return nil, err
+	}
+
+	return ast.String(string(bs)), nil
+}
+
+func builtinJSONUnmarshal(a ast.Value) (ast.Value, error) {
+
+	str, err := builtins.StringOperand(a, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	var x interface{}
+
+	if err := util.UnmarshalJSON([]byte(str), &x); err != nil {
+		return nil, err
+	}
+
+	return ast.InterfaceToValue(x)
+}
+
+func init() {
+	RegisterFunctionalBuiltin1(ast.JSONMarshal.Name, builtinJSONMarshal)
+	RegisterFunctionalBuiltin1(ast.JSONUnmarshal.Name, builtinJSONUnmarshal)
+}

topdown/topdown_test.go

@@ -1144,6 +1144,26 @@ func TestTopDownStrings(t *testing.T) {
 	}
 }
 
+func TestTopDownJSONBuiltins(t *testing.T) {
+
+	tests := []struct {
+		note     string
+		rules    []string
+		expected interface{}
+	}{
+		{"marshal", []string{`p = x { json_marshal([{"foo": {1,2,3}}], x) }`}, `"[{\"foo\":[1,2,3]}]"`},
+		{"unmarshal", []string{`p = x { json_unmarshal("[{\"foo\":[1,2,3]}]", x) }`}, `[{"foo": [1,2,3]}]"`},
+		{"unmarshal-non-string", []string{`p = x { json_unmarshal(data.a[0], x) }`}, fmt.Errorf("operand 1 must be string but got number")},
+	}
+
+	data := loadSmallTestData()
+
+	for _, tc := range tests {
+		runTopDownTestCase(t, data, tc.note, tc.rules, tc.expected)
+	}
+
+}
+
 func TestTopDownEmbeddedVirtualDoc(t *testing.T) {
 
 	compiler := compileModules([]string{