json: Decode into native Go data structures

This patch adds an ability to convert JSON-encoded data into
a hierarchy of Go's native data types.

R=rsc
CC=golang-dev
https://golang.org/cl/161060

src/pkg/expvar/expvar_test.go

@@ -61,18 +61,20 @@ func TestMapCounter(t *testing.T) {
 	// colours.String() should be '{"red":3, "blue":4}',
 	// though the order of red and blue could vary.
 	s := colours.String();
-	j, ok, errtok := json.StringToJson(s);
-	if !ok {
-		t.Errorf("colours.String() isn't valid JSON: %v", errtok)
+	j, err := json.Decode(s);
+	if err != nil {
+		t.Errorf("colours.String() isn't valid JSON: %v", err)
 	}
-	if j.Kind() != json.MapKind {
+	m, ok := j.(map[string]interface{});
+	if !ok {
 		t.Error("colours.String() didn't produce a map.")
 	}
-	red := j.Get("red");
-	if red.Kind() != json.NumberKind {
-		t.Error("red.Kind() is not a NumberKind.")
+	red := m["red"];
+	x, ok := red.(float64);
+	if !ok {
+		t.Error("red.Kind() is not a number.")
 	}
-	if x := red.Number(); x != 3 {
+	if x != 3 {
 		t.Error("red = %v, want 3", x)
 	}
 }

src/pkg/json/Makefile

@@ -6,7 +6,8 @@ include ../../Make.$(GOARCH)
 
 TARG=json
 GOFILES=\
-	generic.go\
+	decode.go\
+	error.go\
 	parse.go\
 	struct.go\
 

src/pkg/json/decode.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Represents JSON data structure using native Go types: booleans, floats,
+// strings, arrays, and maps.
+
+package json
+
+import (
+	"container/vector";
+	"os";
+)
+
+// Decode a JSON string
+
+// Decode parses the string s as a JSON-syntax string and returns the
+// generic JSON object representation.  The object representation is a tree
+// of Go data types.  The data return value may be one of float64, string,
+// bool, nil, []interface{} or map[string]interface{}.  The array and map
+// elements may in turn contain any of the types listed above and so on.
+
+// If Decode encounters a syntax error, it returns with err set to an
+// instance of ParseError.  See ParseError documentation for details.
+func Decode(s string) (data interface{}, err os.Error) {
+	jb := newDecoder(nil, nil);
+	ok, errPos, errTok := Parse(s, jb);
+	if ok {
+		data = jb.Data()
+	} else {
+		err = &ParseError{Index: errPos, Token: errTok}
+	}
+	return;
+}
+
+type decoder struct {
+	// A value being constructed.
+	value	interface{};
+	// Container entity to flush into.  Can be either vector.Vector or
+	// map[string]interface{}.
+	container	interface{};
+	// The index into the container interface.  Either int or string.
+	index	interface{};
+}
+
+func newDecoder(container interface{}, key interface{}) *decoder {
+	return &decoder{container: container, index: key}
+}
+
+func (j *decoder) Int64(i int64)	{ j.value = float64(i) }
+
+func (j *decoder) Uint64(i uint64)	{ j.value = float64(i) }
+
+func (j *decoder) Float64(f float64) {
+	j.value = float64(f)
+}
+
+func (j *decoder) String(s string)	{ j.value = s }
+
+func (j *decoder) Bool(b bool)	{ j.value = b }
+
+func (j *decoder) Null()	{ j.value = nil }
+
+func (j *decoder) Array()	{ j.value = new(vector.Vector) }
+
+func (j *decoder) Map()	{ j.value = make(map[string]interface{}) }
+
+func (j *decoder) Elem(i int) Builder {
+	v, ok := j.value.(*vector.Vector);
+	if !ok {
+		v = new(vector.Vector);
+		j.value = v;
+	}
+	if v.Len() <= i {
+		v.Resize(i+1, (i+1)*2)
+	}
+	return newDecoder(v, i);
+}
+
+func (j *decoder) Key(s string) Builder {
+	m, ok := j.value.(map[string]interface{});
+	if !ok {
+		m = make(map[string]interface{});
+		j.value = m;
+	}
+	return newDecoder(m, s);
+}
+
+func (j *decoder) Flush() {
+	switch c := j.container.(type) {
+	case *vector.Vector:
+		index := j.index.(int);
+		c.Set(index, j.Data());
+	case map[string]interface{}:
+		index := j.index.(string);
+		c[index] = j.Data();
+	}
+}
+
+// Get the value built by this builder.
+func (j *decoder) Data() interface{} {
+	switch v := j.value.(type) {
+	case *vector.Vector:
+		return v.Data()
+	}
+	return j.value;
+}

src/pkg/json/decode_test.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+	"container/vector";
+	"reflect";
+	"testing";
+)
+
+func TestDecodeInt64(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Int64(-15);
+	assertResult(t, nb.Data(), float64(-15));
+}
+
+func TestDecodeUint64(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Uint64(15);
+	assertResult(t, nb.Data(), float64(15));
+}
+
+func TestDecodeFloat64(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Float64(3.14159);
+	assertResult(t, nb.Data(), float64(3.14159));
+}
+
+func TestDecodeString(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.String("Some string");
+	assertResult(t, nb.Data(), "Some string");
+}
+
+func TestDecodeBool(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Bool(true);
+	assertResult(t, nb.Data(), true);
+}
+
+func TestDecodeNull(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Null();
+	assertResult(t, nb.Data(), nil);
+}
+
+func TestDecodeEmptyArray(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Array();
+	assertResult(t, nb.Data(), []interface{}{});
+}
+
+func TestDecodeEmptyMap(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Map();
+	assertResult(t, nb.Data(), map[string]interface{}{});
+}
+
+func TestDecodeFlushElem(t *testing.T) {
+	testVec := new(vector.Vector).Resize(2, 2);
+	nb := newDecoder(testVec, 1);
+	nb.Float64(3.14159);
+	nb.Flush();
+	assertResult(t, testVec.Data(), []interface{}{nil, float64(3.14159)});
+}
+
+func TestDecodeFlushKey(t *testing.T) {
+	testMap := make(map[string]interface{});
+	nb := newDecoder(testMap, "key");
+	nb.Float64(3.14159);
+	nb.Flush();
+	assertResult(t, testMap, map[string]interface{}{"key": float64(3.14159)});
+}
+
+// Elem() and Key() are hard to test in isolation because all they do
+// is create a new, properly initialized, decoder, and modify state of
+// the underlying decoder.  I'm testing them through already tested
+// Array(), String(), and Flush().
+
+func TestDecodeElem(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Array();
+	var b Builder = nb.Elem(0);
+	b.String("0");
+	b.Flush();
+	assertResult(t, nb.Data(), []interface{}{"0"});
+}
+
+func TestDecodeKey(t *testing.T) {
+	nb := newDecoder(nil, nil);
+	nb.Map();
+	var b Builder = nb.Key("a");
+	b.String("0");
+	b.Flush();
+	assertResult(t, nb.Data(), map[string]interface{}{"a": "0"});
+}
+
+func assertResult(t *testing.T, results, expected interface{}) {
+	if !reflect.DeepEqual(results, expected) {
+		t.Fatalf("have %T(%#v) want %T(%#v)", results, results, expected, expected)
+	}
+}
+
+type decodeTest struct {
+	s string;
+	r interface{};
+}
+
+var tests = []decodeTest{
+	decodeTest{`null`, nil},
+	decodeTest{`true`, true},
+	decodeTest{`false`, false},
+	decodeTest{`"abc"`, "abc"},
+	decodeTest{`123`, float64(123)},
+	decodeTest{`0.1`, float64(0.1)},
+	decodeTest{`1e-10`, float64(1e-10)},
+	decodeTest{`[]`, []interface{}{}},
+	decodeTest{`[1,2,3,4]`, []interface{}{float64(1), float64(2), float64(3), float64(4)}},
+	decodeTest{`[1,2,"abc",null,true,false]`, []interface{}{float64(1), float64(2), "abc", nil, true, false}},
+	decodeTest{`{}`, map[string]interface{}{}},
+	decodeTest{`{"a":1}`, map[string]interface{}{"a": float64(1)}},
+	decodeTest{`"q\u0302"`, "q\u0302"},
+}
+
+func TestDecode(t *testing.T) {
+	for _, test := range tests {
+		if val, err := Decode(test.s); err != nil || !reflect.DeepEqual(val, test.r) {
+			t.Errorf("Decode(%#q) = %v, %v want %v, nil", test.s, val, err, test.r)
+		}
+	}
+}

src/pkg/json/error.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import "fmt"
+
+// ParseError aggregates information about a JSON parse error.  It is
+// compatible with the os.Error interface.
+type ParseError struct {
+	Index	int;	// A byte index in JSON string where the error occurred
+	Token	string;	// An offending token
+}
+
+// Produce a string representation of this ParseError.
+func (pe *ParseError) String() string {
+	return fmt.Sprintf("Unexpected JSON token at position %d: %q.", pe.Index, pe.Token)
+}

src/pkg/json/generic.go

-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Generic representation of JSON objects.
-
-package json
-
-import (
-	"container/vector";
-	"fmt";
-	"math";
-	"strconv";
-	"strings";
-)
-
-// Integers identifying the data type in the Json interface.
-const (
-	StringKind	= iota;
-	NumberKind;
-	MapKind;	// JSON term is "Object", but in Go, it's a map
-	ArrayKind;
-	BoolKind;
-	NullKind;
-)
-
-// The Json interface is implemented by all JSON objects.
-type Json interface {
-	Kind() int;		// StringKind, NumberKind, etc.
-	String() string;	// a string form (any kind)
-	Number() float64;	// numeric form (NumberKind)
-	Bool() bool;		// boolean (BoolKind)
-	Get(s string) Json;	// field lookup (MapKind)
-	Elem(i int) Json;	// element lookup (ArrayKind)
-	Len() int;		// length (ArrayKind, MapKind)
-	Map() map[string]Json;	// map form (MapKind)
-}
-
-// JsonToString returns the textual JSON syntax representation
-// for the JSON object j.
-//
-// JsonToString differs from j.String() in the handling
-// of string objects.  If j represents the string abc,
-// j.String() == `abc`, but JsonToString(j) == `"abc"`.
-func JsonToString(j Json) string {
-	if j == nil {
-		return "null"
-	}
-	if j.Kind() == StringKind {
-		return Quote(j.String())
-	}
-	return j.String();
-}
-
-type _Null struct{}
-
-// Null is the JSON object representing the null data object.
-var Null Json = &_Null{}
-
-func (*_Null) Kind() int		{ return NullKind }
-func (*_Null) String() string		{ return "null" }
-func (*_Null) Number() float64		{ return 0 }
-func (*_Null) Bool() bool		{ return false }
-func (*_Null) Get(s string) Json	{ return Null }
-func (*_Null) Elem(int) Json		{ return Null }
-func (*_Null) Len() int			{ return 0 }
-func (*_Null) Map() map[string]Json	{ return nil }
-
-type _String struct {
-	s	string;
-	_Null;
-}
-
-func (j *_String) Kind() int		{ return StringKind }
-func (j *_String) String() string	{ return j.s }
-
-type _Number struct {
-	f	float64;
-	_Null;
-}
-
-func (j *_Number) Kind() int		{ return NumberKind }
-func (j *_Number) Number() float64	{ return j.f }
-func (j *_Number) String() string {
-	if math.Floor(j.f) == j.f {
-		return fmt.Sprintf("%.0f", j.f)
-	}
-	return fmt.Sprintf("%g", j.f);
-}
-
-type _Array struct {
-	a	*vector.Vector;
-	_Null;
-}
-
-func (j *_Array) Kind() int	{ return ArrayKind }
-func (j *_Array) Len() int	{ return j.a.Len() }
-func (j *_Array) Elem(i int) Json {
-	if i < 0 || i >= j.a.Len() {
-		return Null
-	}
-	return j.a.At(i).(Json);
-}
-func (j *_Array) String() string {
-	s := "[";
-	for i := 0; i < j.a.Len(); i++ {
-		if i > 0 {
-			s += ","
-		}
-		s += JsonToString(j.a.At(i).(Json));
-	}
-	s += "]";
-	return s;
-}
-
-type _Bool struct {
-	b	bool;
-	_Null;
-}
-
-func (j *_Bool) Kind() int	{ return BoolKind }
-func (j *_Bool) Bool() bool	{ return j.b }
-func (j *_Bool) String() string {
-	if j.b {
-		return "true"
-	}
-	return "false";
-}
-
-type _Map struct {
-	m	map[string]Json;
-	_Null;
-}
-
-func (j *_Map) Kind() int	{ return MapKind }
-func (j *_Map) Len() int	{ return len(j.m) }
-func (j *_Map) Get(s string) Json {
-	if j.m == nil {
-		return Null
-	}
-	v, ok := j.m[s];
-	if !ok {
-		return Null
-	}
-	return v;
-}
-func (j *_Map) String() string {
-	s := "{";
-	first := true;
-	for k, v := range j.m {
-		if first {
-			first = false
-		} else {
-			s += ","
-		}
-		s += Quote(k);
-		s += ":";
-		s += JsonToString(v);
-	}
-	s += "}";
-	return s;
-}
-func (j *_Map) Map() map[string]Json	{ return j.m }
-
-// Walk evaluates path relative to the JSON object j.
-// Path is taken as a sequence of slash-separated field names
-// or numbers that can be used to index into JSON map and
-// array objects.
-//
-// For example, if j is the JSON object for
-// {"abc": [true, false]}, then Walk(j, "abc/1") returns the
-// JSON object for true.
-func Walk(j Json, path string) Json {
-	for len(path) > 0 {
-		var elem string;
-		if i := strings.Index(path, "/"); i >= 0 {
-			elem = path[0:i];
-			path = path[i+1:];
-		} else {
-			elem = path;
-			path = "";
-		}
-		switch j.Kind() {
-		case ArrayKind:
-			indx, err := strconv.Atoi(elem);
-			if err != nil {
-				return Null
-			}
-			j = j.Elem(indx);
-		case MapKind:
-			j = j.Get(elem)
-		default:
-			return Null
-		}
-	}
-	return j;
-}
-
-// Equal returns whether a and b are indistinguishable JSON objects.
-func Equal(a, b Json) bool {
-	switch {
-	case a == nil && b == nil:
-		return true
-	case a == nil || b == nil:
-		return false
-	case a.Kind() != b.Kind():
-		return false
-	}
-
-	switch a.Kind() {
-	case NullKind:
-		return true
-	case StringKind:
-		return a.String() == b.String()
-	case NumberKind:
-		return a.Number() == b.Number()
-	case BoolKind:
-		return a.Bool() == b.Bool()
-	case ArrayKind:
-		if a.Len() != b.Len() {
-			return false
-		}
-		for i := 0; i < a.Len(); i++ {
-			if !Equal(a.Elem(i), b.Elem(i)) {
-				return false
-			}
-		}
-		return true;
-	case MapKind:
-		m := a.(*_Map).m;
-		if len(m) != len(b.(*_Map).m) {
-			return false
-		}
-		for k, v := range m {
-			if !Equal(v, b.Get(k)) {
-				return false
-			}
-		}
-		return true;
-	}
-
-	// invalid kind
-	return false;
-}
-
-
-// Parse builder for JSON objects.
-
-type _JsonBuilder struct {
-	// either writing to *ptr
-	ptr	*Json;
-
-	// or to a[i] (can't set ptr = &a[i])
-	a	*vector.Vector;
-	i	int;
-
-	// or to m[k] (can't set ptr = &m[k])
-	m	map[string]Json;
-	k	string;
-}
-
-func (b *_JsonBuilder) Put(j Json) {
-	switch {
-	case b.ptr != nil:
-		*b.ptr = j
-	case b.a != nil:
-		b.a.Set(b.i, j)
-	case b.m != nil:
-		b.m[b.k] = j
-	}
-}
-
-func (b *_JsonBuilder) Get() Json {
-	switch {
-	case b.ptr != nil:
-		return *b.ptr
-	case b.a != nil:
-		return b.a.At(b.i).(Json)
-	case b.m != nil:
-		return b.m[b.k]
-	}
-	return nil;
-}
-
-func (b *_JsonBuilder) Float64(f float64)	{ b.Put(&_Number{f, _Null{}}) }
-
-func (b *_JsonBuilder) Int64(i int64)	{ b.Float64(float64(i)) }
-
-func (b *_JsonBuilder) Uint64(i uint64)	{ b.Float64(float64(i)) }
-
-func (b *_JsonBuilder) Bool(tf bool)	{ b.Put(&_Bool{tf, _Null{}}) }
-
-func (b *_JsonBuilder) Null()	{ b.Put(Null) }
-
-func (b *_JsonBuilder) String(s string)	{ b.Put(&_String{s, _Null{}}) }
-
-
-func (b *_JsonBuilder) Array()	{ b.Put(&_Array{new(vector.Vector), _Null{}}) }
-
-func (b *_JsonBuilder) Map()	{ b.Put(&_Map{make(map[string]Json), _Null{}}) }
-
-func (b *_JsonBuilder) Elem(i int) Builder {
-	bb := new(_JsonBuilder);
-	bb.a = b.Get().(*_Array).a;
-	bb.i = i;
-	for i >= bb.a.Len() {
-		bb.a.Push(Null)
-	}
-	return bb;
-}
-
-func (b *_JsonBuilder) Key(k string) Builder {
-	bb := new(_JsonBuilder);
-	bb.m = b.Get().(*_Map).m;
-	bb.k = k;
-	bb.m[k] = Null;
-	return bb;
-}
-
-func (b *_JsonBuilder) Flush()	{}
-
-// StringToJson parses the string s as a JSON-syntax string
-// and returns the generic JSON object representation.
-// On success, StringToJson returns with ok set to true and errtok empty.
-// If StringToJson encounters a syntax error, it returns with
-// ok set to false and errtok set to a fragment of the offending syntax.
-func StringToJson(s string) (json Json, ok bool, errtok string) {
-	var j Json;
-	b := new(_JsonBuilder);
-	b.ptr = &j;
-	ok, _, errtok = Parse(s, b);
-	if !ok {
-		return nil, false, errtok
-	}
-	return j, true, "";
-}
-
-// BUG(rsc): StringToJson should return an os.Error instead of a bool.

src/pkg/json/generic_test.go

-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package json
-
-import (
-	"reflect";
-	"testing";
-)
-
-var jsontests = []string{
-	`null`,
-	`true`,
-	`false`,
-	`"abc"`,
-	`123`,
-	`0.1`,
-	`1e-10`,
-	`[]`,
-	`[1,2,3,4]`,
-	`[1,2,"abc",null,true,false]`,
-	`{}`,
-	`{"a":1}`,
-	`"q\u0302"`,
-}
-
-func TestJson(t *testing.T) {
-	for i := 0; i < len(jsontests); i++ {
-		val, ok, errtok := StringToJson(jsontests[i]);
-		if !ok {
-			t.Errorf("StringToJson(%#q) => error near %v", jsontests[i], errtok);
-			continue;
-		}
-		str := JsonToString(val);
-		if str != jsontests[i] {
-			t.Errorf("JsonToString(StringToJson(%#q)) = %#q", jsontests[i], str);
-			continue;
-		}
-	}
-}
-
-func TestJsonMap(t *testing.T) {
-	values := make(map[string]Json);
-	mapstr := "{";
-	for i := 0; i < len(jsontests); i++ {
-		val, ok, errtok := StringToJson(jsontests[i]);
-		if !ok {
-			t.Errorf("StringToJson(%#q) => error near %v", jsontests[i], errtok)
-		}
-		if i > 0 {
-			mapstr += ","
-		}
-		values[jsontests[i]] = val;
-		mapstr += Quote(jsontests[i]);
-		mapstr += ":";
-		mapstr += JsonToString(val);
-	}
-	mapstr += "}";
-
-	mapv, ok, errtok := StringToJson(mapstr);
-	if !ok {
-		t.Fatalf("StringToJson(%#q) => error near %v", mapstr, errtok)
-	}
-	if mapv == nil {
-		t.Fatalf("StringToJson(%#q) => nil, %v, %v", mapstr, ok, errtok)
-	}
-	if cnt := mapv.Len(); cnt != len(jsontests) {
-		t.Errorf("StringToJson(%#q).Len() => %v, want %v", mapstr, cnt,
-			len(jsontests))
-	}
-	for k, v := range values {
-		if v1 := mapv.Get(k); !Equal(v1, v) {
-			t.Errorf("MapTest: Walk(%#q) => %v, want %v", k, v1, v)
-		}
-	}
-	if !reflect.DeepEqual(values, mapv.Map()) {
-		t.Errorf("DeepEqual(values, mapv.Map()) failed")
-	}
-}