libgo: Update to weekly 2011-11-09.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@182073 138bc75d-0d04-0410-961f-82ee72b054a4

12 files changed, 3595 insertions, 0 deletions

diff --git a/libgo/go/encoding/json/decode.go b/libgo/go/encoding/json/decode.go
new file mode 100644
index 00000000000..41295d2d241
--- /dev/null
+++ b/libgo/go/encoding/json/decode.go
@@ -0,0 +1,939 @@
+// Copyright 2010 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 (
+	"encoding/base64"
+	"errors"
+	"reflect"
+	"runtime"
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf16"
+	"unicode/utf8"
+)
+
+// Unmarshal parses the JSON-encoded data and stores the result
+// in the value pointed to by v.
+//
+// Unmarshal uses the inverse of the encodings that
+// Marshal uses, allocating maps, slices, and pointers as necessary,
+// with the following additional rules:
+//
+// To unmarshal JSON into a pointer, Unmarshal first handles the case of
+// the JSON being the JSON literal null.  In that case, Unmarshal sets
+// the pointer to nil.  Otherwise, Unmarshal unmarshals the JSON into
+// the value pointed at by the pointer.  If the pointer is nil, Unmarshal
+// allocates a new value for it to point to.
+//
+// To unmarshal JSON into an interface value, Unmarshal unmarshals
+// the JSON into the concrete value contained in the interface value.
+// If the interface value is nil, that is, has no concrete value stored in it,
+// Unmarshal stores one of these in the interface value:
+//
+//	bool, for JSON booleans
+//	float64, for JSON numbers
+//	string, for JSON strings
+//	[]interface{}, for JSON arrays
+//	map[string]interface{}, for JSON objects
+//	nil for JSON null
+//
+// If a JSON value is not appropriate for a given target type,
+// or if a JSON number overflows the target type, Unmarshal
+// skips that field and completes the unmarshalling as best it can.
+// If no more serious errors are encountered, Unmarshal returns
+// an UnmarshalTypeError describing the earliest such error.
+//
+func Unmarshal(data []byte, v interface{}) error {
+	d := new(decodeState).init(data)
+
+	// Quick check for well-formedness.
+	// Avoids filling out half a data structure
+	// before discovering a JSON syntax error.
+	err := checkValid(data, &d.scan)
+	if err != nil {
+		return err
+	}
+
+	return d.unmarshal(v)
+}
+
+// Unmarshaler is the interface implemented by objects
+// that can unmarshal a JSON description of themselves.
+// The input can be assumed to be a valid JSON object
+// encoding.  UnmarshalJSON must copy the JSON data
+// if it wishes to retain the data after returning.
+type Unmarshaler interface {
+	UnmarshalJSON([]byte) error
+}
+
+// An UnmarshalTypeError describes a JSON value that was
+// not appropriate for a value of a specific Go type.
+type UnmarshalTypeError struct {
+	Value string       // description of JSON value - "bool", "array", "number -5"
+	Type  reflect.Type // type of Go value it could not be assigned to
+}
+
+func (e *UnmarshalTypeError) Error() string {
+	return "json: cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String()
+}
+
+// An UnmarshalFieldError describes a JSON object key that
+// led to an unexported (and therefore unwritable) struct field.
+type UnmarshalFieldError struct {
+	Key   string
+	Type  reflect.Type
+	Field reflect.StructField
+}
+
+func (e *UnmarshalFieldError) Error() string {
+	return "json: cannot unmarshal object key " + strconv.Quote(e.Key) + " into unexported field " + e.Field.Name + " of type " + e.Type.String()
+}
+
+// An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
+// (The argument to Unmarshal must be a non-nil pointer.)
+type InvalidUnmarshalError struct {
+	Type reflect.Type
+}
+
+func (e *InvalidUnmarshalError) Error() string {
+	if e.Type == nil {
+		return "json: Unmarshal(nil)"
+	}
+
+	if e.Type.Kind() != reflect.Ptr {
+		return "json: Unmarshal(non-pointer " + e.Type.String() + ")"
+	}
+	return "json: Unmarshal(nil " + e.Type.String() + ")"
+}
+
+func (d *decodeState) unmarshal(v interface{}) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if _, ok := r.(runtime.Error); ok {
+				panic(r)
+			}
+			err = r.(error)
+		}
+	}()
+
+	rv := reflect.ValueOf(v)
+	pv := rv
+	if pv.Kind() != reflect.Ptr || pv.IsNil() {
+		return &InvalidUnmarshalError{reflect.TypeOf(v)}
+	}
+
+	d.scan.reset()
+	// We decode rv not pv.Elem because the Unmarshaler interface
+	// test must be applied at the top level of the value.
+	d.value(rv)
+	return d.savedError
+}
+
+// decodeState represents the state while decoding a JSON value.
+type decodeState struct {
+	data       []byte
+	off        int // read offset in data
+	scan       scanner
+	nextscan   scanner // for calls to nextValue
+	savedError error
+	tempstr    string // scratch space to avoid some allocations
+}
+
+// errPhase is used for errors that should not happen unless
+// there is a bug in the JSON decoder or something is editing
+// the data slice while the decoder executes.
+var errPhase = errors.New("JSON decoder out of sync - data changing underfoot?")
+
+func (d *decodeState) init(data []byte) *decodeState {
+	d.data = data
+	d.off = 0
+	d.savedError = nil
+	return d
+}
+
+// error aborts the decoding by panicking with err.
+func (d *decodeState) error(err error) {
+	panic(err)
+}
+
+// saveError saves the first err it is called with,
+// for reporting at the end of the unmarshal.
+func (d *decodeState) saveError(err error) {
+	if d.savedError == nil {
+		d.savedError = err
+	}
+}
+
+// next cuts off and returns the next full JSON value in d.data[d.off:].
+// The next value is known to be an object or array, not a literal.
+func (d *decodeState) next() []byte {
+	c := d.data[d.off]
+	item, rest, err := nextValue(d.data[d.off:], &d.nextscan)
+	if err != nil {
+		d.error(err)
+	}
+	d.off = len(d.data) - len(rest)
+
+	// Our scanner has seen the opening brace/bracket
+	// and thinks we're still in the middle of the object.
+	// invent a closing brace/bracket to get it out.
+	if c == '{' {
+		d.scan.step(&d.scan, '}')
+	} else {
+		d.scan.step(&d.scan, ']')
+	}
+
+	return item
+}
+
+// scanWhile processes bytes in d.data[d.off:] until it
+// receives a scan code not equal to op.
+// It updates d.off and returns the new scan code.
+func (d *decodeState) scanWhile(op int) int {
+	var newOp int
+	for {
+		if d.off >= len(d.data) {
+			newOp = d.scan.eof()
+			d.off = len(d.data) + 1 // mark processed EOF with len+1
+		} else {
+			c := int(d.data[d.off])
+			d.off++
+			newOp = d.scan.step(&d.scan, c)
+		}
+		if newOp != op {
+			break
+		}
+	}
+	return newOp
+}
+
+// value decodes a JSON value from d.data[d.off:] into the value.
+// it updates d.off to point past the decoded value.
+func (d *decodeState) value(v reflect.Value) {
+	if !v.IsValid() {
+		_, rest, err := nextValue(d.data[d.off:], &d.nextscan)
+		if err != nil {
+			d.error(err)
+		}
+		d.off = len(d.data) - len(rest)
+
+		// d.scan thinks we're still at the beginning of the item.
+		// Feed in an empty string - the shortest, simplest value -
+		// so that it knows we got to the end of the value.
+		if d.scan.step == stateRedo {
+			panic("redo")
+		}
+		d.scan.step(&d.scan, '"')
+		d.scan.step(&d.scan, '"')
+		return
+	}
+
+	switch op := d.scanWhile(scanSkipSpace); op {
+	default:
+		d.error(errPhase)
+
+	case scanBeginArray:
+		d.array(v)
+
+	case scanBeginObject:
+		d.object(v)
+
+	case scanBeginLiteral:
+		d.literal(v)
+	}
+}
+
+// indirect walks down v allocating pointers as needed,
+// until it gets to a non-pointer.
+// if it encounters an Unmarshaler, indirect stops and returns that.
+// if decodingNull is true, indirect stops at the last pointer so it can be set to nil.
+func (d *decodeState) indirect(v reflect.Value, decodingNull bool) (Unmarshaler, reflect.Value) {
+	// If v is a named type and is addressable,
+	// start with its address, so that if the type has pointer methods,
+	// we find them.
+	if v.Kind() != reflect.Ptr && v.Type().Name() != "" && v.CanAddr() {
+		v = v.Addr()
+	}
+	for {
+		var isUnmarshaler bool
+		if v.Type().NumMethod() > 0 {
+			// Remember that this is an unmarshaler,
+			// but wait to return it until after allocating
+			// the pointer (if necessary).
+			_, isUnmarshaler = v.Interface().(Unmarshaler)
+		}
+
+		if iv := v; iv.Kind() == reflect.Interface && !iv.IsNil() {
+			v = iv.Elem()
+			continue
+		}
+
+		pv := v
+		if pv.Kind() != reflect.Ptr {
+			break
+		}
+
+		if pv.Elem().Kind() != reflect.Ptr && decodingNull && pv.CanSet() {
+			return nil, pv
+		}
+		if pv.IsNil() {
+			pv.Set(reflect.New(pv.Type().Elem()))
+		}
+		if isUnmarshaler {
+			// Using v.Interface().(Unmarshaler)
+			// here means that we have to use a pointer
+			// as the struct field.  We cannot use a value inside
+			// a pointer to a struct, because in that case
+			// v.Interface() is the value (x.f) not the pointer (&x.f).
+			// This is an unfortunate consequence of reflect.
+			// An alternative would be to look up the
+			// UnmarshalJSON method and return a FuncValue.
+			return v.Interface().(Unmarshaler), reflect.Value{}
+		}
+		v = pv.Elem()
+	}
+	return nil, v
+}
+
+// array consumes an array from d.data[d.off-1:], decoding into the value v.
+// the first byte of the array ('[') has been read already.
+func (d *decodeState) array(v reflect.Value) {
+	// Check for unmarshaler.
+	unmarshaler, pv := d.indirect(v, false)
+	if unmarshaler != nil {
+		d.off--
+		err := unmarshaler.UnmarshalJSON(d.next())
+		if err != nil {
+			d.error(err)
+		}
+		return
+	}
+	v = pv
+
+	// Decoding into nil interface?  Switch to non-reflect code.
+	iv := v
+	ok := iv.Kind() == reflect.Interface
+	if ok {
+		iv.Set(reflect.ValueOf(d.arrayInterface()))
+		return
+	}
+
+	// Check type of target.
+	av := v
+	if av.Kind() != reflect.Array && av.Kind() != reflect.Slice {
+		d.saveError(&UnmarshalTypeError{"array", v.Type()})
+		d.off--
+		d.next()
+		return
+	}
+
+	sv := v
+
+	i := 0
+	for {
+		// Look ahead for ] - can only happen on first iteration.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+
+		// Back up so d.value can have the byte we just read.
+		d.off--
+		d.scan.undo(op)
+
+		// Get element of array, growing if necessary.
+		if i >= av.Cap() && sv.IsValid() {
+			newcap := sv.Cap() + sv.Cap()/2
+			if newcap < 4 {
+				newcap = 4
+			}
+			newv := reflect.MakeSlice(sv.Type(), sv.Len(), newcap)
+			reflect.Copy(newv, sv)
+			sv.Set(newv)
+		}
+		if i >= av.Len() && sv.IsValid() {
+			// Must be slice; gave up on array during i >= av.Cap().
+			sv.SetLen(i + 1)
+		}
+
+		// Decode into element.
+		if i < av.Len() {
+			d.value(av.Index(i))
+		} else {
+			// Ran out of fixed array: skip.
+			d.value(reflect.Value{})
+		}
+		i++
+
+		// Next token must be , or ].
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+		if op != scanArrayValue {
+			d.error(errPhase)
+		}
+	}
+	if i < av.Len() {
+		if !sv.IsValid() {
+			// Array.  Zero the rest.
+			z := reflect.Zero(av.Type().Elem())
+			for ; i < av.Len(); i++ {
+				av.Index(i).Set(z)
+			}
+		} else {
+			sv.SetLen(i)
+		}
+	}
+}
+
+// object consumes an object from d.data[d.off-1:], decoding into the value v.
+// the first byte of the object ('{') has been read already.
+func (d *decodeState) object(v reflect.Value) {
+	// Check for unmarshaler.
+	unmarshaler, pv := d.indirect(v, false)
+	if unmarshaler != nil {
+		d.off--
+		err := unmarshaler.UnmarshalJSON(d.next())
+		if err != nil {
+			d.error(err)
+		}
+		return
+	}
+	v = pv
+
+	// Decoding into nil interface?  Switch to non-reflect code.
+	iv := v
+	if iv.Kind() == reflect.Interface {
+		iv.Set(reflect.ValueOf(d.objectInterface()))
+		return
+	}
+
+	// Check type of target: struct or map[string]T
+	var (
+		mv reflect.Value
+		sv reflect.Value
+	)
+	switch v.Kind() {
+	case reflect.Map:
+		// map must have string type
+		t := v.Type()
+		if t.Key() != reflect.TypeOf("") {
+			d.saveError(&UnmarshalTypeError{"object", v.Type()})
+			break
+		}
+		mv = v
+		if mv.IsNil() {
+			mv.Set(reflect.MakeMap(t))
+		}
+	case reflect.Struct:
+		sv = v
+	default:
+		d.saveError(&UnmarshalTypeError{"object", v.Type()})
+	}
+
+	if !mv.IsValid() && !sv.IsValid() {
+		d.off--
+		d.next() // skip over { } in input
+		return
+	}
+
+	var mapElem reflect.Value
+
+	for {
+		// Read opening " of string key or closing }.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			// closing } - can only happen on first iteration.
+			break
+		}
+		if op != scanBeginLiteral {
+			d.error(errPhase)
+		}
+
+		// Read string key.
+		start := d.off - 1
+		op = d.scanWhile(scanContinue)
+		item := d.data[start : d.off-1]
+		key, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+
+		// Figure out field corresponding to key.
+		var subv reflect.Value
+		destring := false // whether the value is wrapped in a string to be decoded first
+
+		if mv.IsValid() {
+			elemType := mv.Type().Elem()
+			if !mapElem.IsValid() {
+				mapElem = reflect.New(elemType).Elem()
+			} else {
+				mapElem.Set(reflect.Zero(elemType))
+			}
+			subv = mapElem
+		} else {
+			var f reflect.StructField
+			var ok bool
+			st := sv.Type()
+			for i := 0; i < sv.NumField(); i++ {
+				sf := st.Field(i)
+				tag := sf.Tag.Get("json")
+				if tag == "-" {
+					// Pretend this field doesn't exist.
+					continue
+				}
+				// First, tag match
+				tagName, _ := parseTag(tag)
+				if tagName == key {
+					f = sf
+					ok = true
+					break // no better match possible
+				}
+				// Second, exact field name match
+				if sf.Name == key {
+					f = sf
+					ok = true
+				}
+				// Third, case-insensitive field name match,
+				// but only if a better match hasn't already been seen
+				if !ok && strings.EqualFold(sf.Name, key) {
+					f = sf
+					ok = true
+				}
+			}
+
+			// Extract value; name must be exported.
+			if ok {
+				if f.PkgPath != "" {
+					d.saveError(&UnmarshalFieldError{key, st, f})
+				} else {
+					subv = sv.FieldByIndex(f.Index)
+				}
+				_, opts := parseTag(f.Tag.Get("json"))
+				destring = opts.Contains("string")
+			}
+		}
+
+		// Read : before value.
+		if op == scanSkipSpace {
+			op = d.scanWhile(scanSkipSpace)
+		}
+		if op != scanObjectKey {
+			d.error(errPhase)
+		}
+
+		// Read value.
+		if destring {
+			d.value(reflect.ValueOf(&d.tempstr))
+			d.literalStore([]byte(d.tempstr), subv)
+		} else {
+			d.value(subv)
+		}
+		// Write value back to map;
+		// if using struct, subv points into struct already.
+		if mv.IsValid() {
+			mv.SetMapIndex(reflect.ValueOf(key), subv)
+		}
+
+		// Next token must be , or }.
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			break
+		}
+		if op != scanObjectValue {
+			d.error(errPhase)
+		}
+	}
+}
+
+// literal consumes a literal from d.data[d.off-1:], decoding into the value v.
+// The first byte of the literal has been read already
+// (that's how the caller knows it's a literal).
+func (d *decodeState) literal(v reflect.Value) {
+	// All bytes inside literal return scanContinue op code.
+	start := d.off - 1
+	op := d.scanWhile(scanContinue)
+
+	// Scan read one byte too far; back up.
+	d.off--
+	d.scan.undo(op)
+
+	d.literalStore(d.data[start:d.off], v)
+}
+
+// literalStore decodes a literal stored in item into v.
+func (d *decodeState) literalStore(item []byte, v reflect.Value) {
+	// Check for unmarshaler.
+	wantptr := item[0] == 'n' // null
+	unmarshaler, pv := d.indirect(v, wantptr)
+	if unmarshaler != nil {
+		err := unmarshaler.UnmarshalJSON(item)
+		if err != nil {
+			d.error(err)
+		}
+		return
+	}
+	v = pv
+
+	switch c := item[0]; c {
+	case 'n': // null
+		switch v.Kind() {
+		default:
+			d.saveError(&UnmarshalTypeError{"null", v.Type()})
+		case reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
+			v.Set(reflect.Zero(v.Type()))
+		}
+
+	case 't', 'f': // true, false
+		value := c == 't'
+		switch v.Kind() {
+		default:
+			d.saveError(&UnmarshalTypeError{"bool", v.Type()})
+		case reflect.Bool:
+			v.SetBool(value)
+		case reflect.Interface:
+			v.Set(reflect.ValueOf(value))
+		}
+
+	case '"': // string
+		s, ok := unquoteBytes(item)
+		if !ok {
+			d.error(errPhase)
+		}
+		switch v.Kind() {
+		default:
+			d.saveError(&UnmarshalTypeError{"string", v.Type()})
+		case reflect.Slice:
+			if v.Type() != byteSliceType {
+				d.saveError(&UnmarshalTypeError{"string", v.Type()})
+				break
+			}
+			b := make([]byte, base64.StdEncoding.DecodedLen(len(s)))
+			n, err := base64.StdEncoding.Decode(b, s)
+			if err != nil {
+				d.saveError(err)
+				break
+			}
+			v.Set(reflect.ValueOf(b[0:n]))
+		case reflect.String:
+			v.SetString(string(s))
+		case reflect.Interface:
+			v.Set(reflect.ValueOf(string(s)))
+		}
+
+	default: // number
+		if c != '-' && (c < '0' || c > '9') {
+			d.error(errPhase)
+		}
+		s := string(item)
+		switch v.Kind() {
+		default:
+			d.error(&UnmarshalTypeError{"number", v.Type()})
+		case reflect.Interface:
+			n, err := strconv.Atof64(s)
+			if err != nil {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.Set(reflect.ValueOf(n))
+
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			n, err := strconv.Atoi64(s)
+			if err != nil || v.OverflowInt(n) {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.SetInt(n)
+
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+			n, err := strconv.Atoui64(s)
+			if err != nil || v.OverflowUint(n) {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.SetUint(n)
+
+		case reflect.Float32, reflect.Float64:
+			n, err := strconv.AtofN(s, v.Type().Bits())
+			if err != nil || v.OverflowFloat(n) {
+				d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
+				break
+			}
+			v.SetFloat(n)
+		}
+	}
+}
+
+// The xxxInterface routines build up a value to be stored
+// in an empty interface.  They are not strictly necessary,
+// but they avoid the weight of reflection in this common case.
+
+// valueInterface is like value but returns interface{}
+func (d *decodeState) valueInterface() interface{} {
+	switch d.scanWhile(scanSkipSpace) {
+	default:
+		d.error(errPhase)
+	case scanBeginArray:
+		return d.arrayInterface()
+	case scanBeginObject:
+		return d.objectInterface()
+	case scanBeginLiteral:
+		return d.literalInterface()
+	}
+	panic("unreachable")
+}
+
+// arrayInterface is like array but returns []interface{}.
+func (d *decodeState) arrayInterface() []interface{} {
+	var v []interface{}
+	for {
+		// Look ahead for ] - can only happen on first iteration.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+
+		// Back up so d.value can have the byte we just read.
+		d.off--
+		d.scan.undo(op)
+
+		v = append(v, d.valueInterface())
+
+		// Next token must be , or ].
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndArray {
+			break
+		}
+		if op != scanArrayValue {
+			d.error(errPhase)
+		}
+	}
+	return v
+}
+
+// objectInterface is like object but returns map[string]interface{}.
+func (d *decodeState) objectInterface() map[string]interface{} {
+	m := make(map[string]interface{})
+	for {
+		// Read opening " of string key or closing }.
+		op := d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			// closing } - can only happen on first iteration.
+			break
+		}
+		if op != scanBeginLiteral {
+			d.error(errPhase)
+		}
+
+		// Read string key.
+		start := d.off - 1
+		op = d.scanWhile(scanContinue)
+		item := d.data[start : d.off-1]
+		key, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+
+		// Read : before value.
+		if op == scanSkipSpace {
+			op = d.scanWhile(scanSkipSpace)
+		}
+		if op != scanObjectKey {
+			d.error(errPhase)
+		}
+
+		// Read value.
+		m[key] = d.valueInterface()
+
+		// Next token must be , or }.
+		op = d.scanWhile(scanSkipSpace)
+		if op == scanEndObject {
+			break
+		}
+		if op != scanObjectValue {
+			d.error(errPhase)
+		}
+	}
+	return m
+}
+
+// literalInterface is like literal but returns an interface value.
+func (d *decodeState) literalInterface() interface{} {
+	// All bytes inside literal return scanContinue op code.
+	start := d.off - 1
+	op := d.scanWhile(scanContinue)
+
+	// Scan read one byte too far; back up.
+	d.off--
+	d.scan.undo(op)
+	item := d.data[start:d.off]
+
+	switch c := item[0]; c {
+	case 'n': // null
+		return nil
+
+	case 't', 'f': // true, false
+		return c == 't'
+
+	case '"': // string
+		s, ok := unquote(item)
+		if !ok {
+			d.error(errPhase)
+		}
+		return s
+
+	default: // number
+		if c != '-' && (c < '0' || c > '9') {
+			d.error(errPhase)
+		}
+		n, err := strconv.Atof64(string(item))
+		if err != nil {
+			d.saveError(&UnmarshalTypeError{"number " + string(item), reflect.TypeOf(0.0)})
+		}
+		return n
+	}
+	panic("unreachable")
+}
+
+// getu4 decodes \uXXXX from the beginning of s, returning the hex value,
+// or it returns -1.
+func getu4(s []byte) rune {
+	if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
+		return -1
+	}
+	r, err := strconv.Btoui64(string(s[2:6]), 16)
+	if err != nil {
+		return -1
+	}
+	return rune(r)
+}
+
+// unquote converts a quoted JSON string literal s into an actual string t.
+// The rules are different than for Go, so cannot use strconv.Unquote.
+func unquote(s []byte) (t string, ok bool) {
+	s, ok = unquoteBytes(s)
+	t = string(s)
+	return
+}
+
+func unquoteBytes(s []byte) (t []byte, ok bool) {
+	if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
+		return
+	}
+	s = s[1 : len(s)-1]
+
+	// Check for unusual characters. If there are none,
+	// then no unquoting is needed, so return a slice of the
+	// original bytes.
+	r := 0
+	for r < len(s) {
+		c := s[r]
+		if c == '\\' || c == '"' || c < ' ' {
+			break
+		}
+		if c < utf8.RuneSelf {
+			r++
+			continue
+		}
+		rr, size := utf8.DecodeRune(s[r:])
+		if rr == utf8.RuneError && size == 1 {
+			break
+		}
+		r += size
+	}
+	if r == len(s) {
+		return s, true
+	}
+
+	b := make([]byte, len(s)+2*utf8.UTFMax)
+	w := copy(b, s[0:r])
+	for r < len(s) {
+		// Out of room?  Can only happen if s is full of
+		// malformed UTF-8 and we're replacing each
+		// byte with RuneError.
+		if w >= len(b)-2*utf8.UTFMax {
+			nb := make([]byte, (len(b)+utf8.UTFMax)*2)
+			copy(nb, b[0:w])
+			b = nb
+		}
+		switch c := s[r]; {
+		case c == '\\':
+			r++
+			if r >= len(s) {
+				return
+			}
+			switch s[r] {
+			default:
+				return
+			case '"', '\\', '/', '\'':
+				b[w] = s[r]
+				r++
+				w++
+			case 'b':
+				b[w] = '\b'
+				r++
+				w++
+			case 'f':
+				b[w] = '\f'
+				r++
+				w++
+			case 'n':
+				b[w] = '\n'
+				r++
+				w++
+			case 'r':
+				b[w] = '\r'
+				r++
+				w++
+			case 't':
+				b[w] = '\t'
+				r++
+				w++
+			case 'u':
+				r--
+				rr := getu4(s[r:])
+				if rr < 0 {
+					return
+				}
+				r += 6
+				if utf16.IsSurrogate(rr) {
+					rr1 := getu4(s[r:])
+					if dec := utf16.DecodeRune(rr, rr1); dec != unicode.ReplacementChar {
+						// A valid pair; consume.
+						r += 6
+						w += utf8.EncodeRune(b[w:], dec)
+						break
+					}
+					// Invalid surrogate; fall back to replacement rune.
+					rr = unicode.ReplacementChar
+				}
+				w += utf8.EncodeRune(b[w:], rr)
+			}
+
+		// Quote, control characters are invalid.
+		case c == '"', c < ' ':
+			return
+
+		// ASCII
+		case c < utf8.RuneSelf:
+			b[w] = c
+			r++
+			w++
+
+		// Coerce to well-formed UTF-8.
+		default:
+			rr, size := utf8.DecodeRune(s[r:])
+			r += size
+			w += utf8.EncodeRune(b[w:], rr)
+		}
+	}
+	return b[0:w], true
+}
diff --git a/libgo/go/encoding/json/decode_test.go b/libgo/go/encoding/json/decode_test.go
new file mode 100644
index 00000000000..bd4326a0cd7
--- /dev/null
+++ b/libgo/go/encoding/json/decode_test.go
@@ -0,0 +1,564 @@
+// Copyright 2010 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 (
+	"bytes"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+type T struct {
+	X string
+	Y int
+	Z int `json:"-"`
+}
+
+type tx struct {
+	x int
+}
+
+var txType = reflect.TypeOf((*tx)(nil)).Elem()
+
+// A type that can unmarshal itself.
+
+type unmarshaler struct {
+	T bool
+}
+
+func (u *unmarshaler) UnmarshalJSON(b []byte) error {
+	*u = unmarshaler{true} // All we need to see that UnmarshalJson is called.
+	return nil
+}
+
+type ustruct struct {
+	M unmarshaler
+}
+
+var (
+	um0, um1 unmarshaler // target2 of unmarshaling
+	ump      = &um1
+	umtrue   = unmarshaler{true}
+	umslice  = []unmarshaler{{true}}
+	umslicep = new([]unmarshaler)
+	umstruct = ustruct{unmarshaler{true}}
+)
+
+type unmarshalTest struct {
+	in  string
+	ptr interface{}
+	out interface{}
+	err error
+}
+
+var unmarshalTests = []unmarshalTest{
+	// basic types
+	{`true`, new(bool), true, nil},
+	{`1`, new(int), 1, nil},
+	{`1.2`, new(float64), 1.2, nil},
+	{`-5`, new(int16), int16(-5), nil},
+	{`"a\u1234"`, new(string), "a\u1234", nil},
+	{`"http:\/\/"`, new(string), "http://", nil},
+	{`"g-clef: \uD834\uDD1E"`, new(string), "g-clef: \U0001D11E", nil},
+	{`"invalid: \uD834x\uDD1E"`, new(string), "invalid: \uFFFDx\uFFFD", nil},
+	{"null", new(interface{}), nil, nil},
+	{`{"X": [1,2,3], "Y": 4}`, new(T), T{Y: 4}, &UnmarshalTypeError{"array", reflect.TypeOf("")}},
+	{`{"x": 1}`, new(tx), tx{}, &UnmarshalFieldError{"x", txType, txType.Field(0)}},
+
+	// Z has a "-" tag.
+	{`{"Y": 1, "Z": 2}`, new(T), T{Y: 1}, nil},
+
+	// syntax errors
+	{`{"X": "foo", "Y"}`, nil, nil, &SyntaxError{"invalid character '}' after object key", 17}},
+
+	// composite tests
+	{allValueIndent, new(All), allValue, nil},
+	{allValueCompact, new(All), allValue, nil},
+	{allValueIndent, new(*All), &allValue, nil},
+	{allValueCompact, new(*All), &allValue, nil},
+	{pallValueIndent, new(All), pallValue, nil},
+	{pallValueCompact, new(All), pallValue, nil},
+	{pallValueIndent, new(*All), &pallValue, nil},
+	{pallValueCompact, new(*All), &pallValue, nil},
+
+	// unmarshal interface test
+	{`{"T":false}`, &um0, umtrue, nil}, // use "false" so test will fail if custom unmarshaler is not called
+	{`{"T":false}`, &ump, &umtrue, nil},
+	{`[{"T":false}]`, &umslice, umslice, nil},
+	{`[{"T":false}]`, &umslicep, &umslice, nil},
+	{`{"M":{"T":false}}`, &umstruct, umstruct, nil},
+}
+
+func TestMarshal(t *testing.T) {
+	b, err := Marshal(allValue)
+	if err != nil {
+		t.Fatalf("Marshal allValue: %v", err)
+	}
+	if string(b) != allValueCompact {
+		t.Errorf("Marshal allValueCompact")
+		diff(t, b, []byte(allValueCompact))
+		return
+	}
+
+	b, err = Marshal(pallValue)
+	if err != nil {
+		t.Fatalf("Marshal pallValue: %v", err)
+	}
+	if string(b) != pallValueCompact {
+		t.Errorf("Marshal pallValueCompact")
+		diff(t, b, []byte(pallValueCompact))
+		return
+	}
+}
+
+func TestMarshalBadUTF8(t *testing.T) {
+	s := "hello\xffworld"
+	b, err := Marshal(s)
+	if err == nil {
+		t.Fatal("Marshal bad UTF8: no error")
+	}
+	if len(b) != 0 {
+		t.Fatal("Marshal returned data")
+	}
+	if _, ok := err.(*InvalidUTF8Error); !ok {
+		t.Fatalf("Marshal did not return InvalidUTF8Error: %T %v", err, err)
+	}
+}
+
+func TestUnmarshal(t *testing.T) {
+	for i, tt := range unmarshalTests {
+		var scan scanner
+		in := []byte(tt.in)
+		if err := checkValid(in, &scan); err != nil {
+			if !reflect.DeepEqual(err, tt.err) {
+				t.Errorf("#%d: checkValid: %#v", i, err)
+				continue
+			}
+		}
+		if tt.ptr == nil {
+			continue
+		}
+		// v = new(right-type)
+		v := reflect.New(reflect.TypeOf(tt.ptr).Elem())
+		if err := Unmarshal([]byte(in), v.Interface()); !reflect.DeepEqual(err, tt.err) {
+			t.Errorf("#%d: %v want %v", i, err, tt.err)
+			continue
+		}
+		if !reflect.DeepEqual(v.Elem().Interface(), tt.out) {
+			t.Errorf("#%d: mismatch\nhave: %#+v\nwant: %#+v", i, v.Elem().Interface(), tt.out)
+			data, _ := Marshal(v.Elem().Interface())
+			println(string(data))
+			data, _ = Marshal(tt.out)
+			println(string(data))
+			continue
+		}
+	}
+}
+
+func TestUnmarshalMarshal(t *testing.T) {
+	initBig()
+	var v interface{}
+	if err := Unmarshal(jsonBig, &v); err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	b, err := Marshal(v)
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	if bytes.Compare(jsonBig, b) != 0 {
+		t.Errorf("Marshal jsonBig")
+		diff(t, b, jsonBig)
+		return
+	}
+}
+
+func TestLargeByteSlice(t *testing.T) {
+	s0 := make([]byte, 2000)
+	for i := range s0 {
+		s0[i] = byte(i)
+	}
+	b, err := Marshal(s0)
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	var s1 []byte
+	if err := Unmarshal(b, &s1); err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if bytes.Compare(s0, s1) != 0 {
+		t.Errorf("Marshal large byte slice")
+		diff(t, s0, s1)
+	}
+}
+
+type Xint struct {
+	X int
+}
+
+func TestUnmarshalInterface(t *testing.T) {
+	var xint Xint
+	var i interface{} = &xint
+	if err := Unmarshal([]byte(`{"X":1}`), &i); err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if xint.X != 1 {
+		t.Fatalf("Did not write to xint")
+	}
+}
+
+func TestUnmarshalPtrPtr(t *testing.T) {
+	var xint Xint
+	pxint := &xint
+	if err := Unmarshal([]byte(`{"X":1}`), &pxint); err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if xint.X != 1 {
+		t.Fatalf("Did not write to xint")
+	}
+}
+
+func TestEscape(t *testing.T) {
+	const input = `"foobar"<html>`
+	const expected = `"\"foobar\"\u003chtml\u003e"`
+	b, err := Marshal(input)
+	if err != nil {
+		t.Fatalf("Marshal error: %v", err)
+	}
+	if s := string(b); s != expected {
+		t.Errorf("Encoding of [%s] was [%s], want [%s]", input, s, expected)
+	}
+}
+
+func TestHTMLEscape(t *testing.T) {
+	b, err := MarshalForHTML("foobarbaz<>&quux")
+	if err != nil {
+		t.Fatalf("MarshalForHTML error: %v", err)
+	}
+	if !bytes.Equal(b, []byte(`"foobarbaz\u003c\u003e\u0026quux"`)) {
+		t.Fatalf("Unexpected encoding of \"<>&\": %s", b)
+	}
+}
+
+func noSpace(c rune) rune {
+	if isSpace(c) {
+		return -1
+	}
+	return c
+}
+
+type All struct {
+	Bool    bool
+	Int     int
+	Int8    int8
+	Int16   int16
+	Int32   int32
+	Int64   int64
+	Uint    uint
+	Uint8   uint8
+	Uint16  uint16
+	Uint32  uint32
+	Uint64  uint64
+	Uintptr uintptr
+	Float32 float32
+	Float64 float64
+
+	Foo  string `json:"bar"`
+	Foo2 string `json:"bar2,dummyopt"`
+
+	IntStr int64 `json:",string"`
+
+	PBool    *bool
+	PInt     *int
+	PInt8    *int8
+	PInt16   *int16
+	PInt32   *int32
+	PInt64   *int64
+	PUint    *uint
+	PUint8   *uint8
+	PUint16  *uint16
+	PUint32  *uint32
+	PUint64  *uint64
+	PUintptr *uintptr
+	PFloat32 *float32
+	PFloat64 *float64
+
+	String  string
+	PString *string
+
+	Map   map[string]Small
+	MapP  map[string]*Small
+	PMap  *map[string]Small
+	PMapP *map[string]*Small
+
+	EmptyMap map[string]Small
+	NilMap   map[string]Small
+
+	Slice   []Small
+	SliceP  []*Small
+	PSlice  *[]Small
+	PSliceP *[]*Small
+
+	EmptySlice []Small
+	NilSlice   []Small
+
+	StringSlice []string
+	ByteSlice   []byte
+
+	Small   Small
+	PSmall  *Small
+	PPSmall **Small
+
+	Interface  interface{}
+	PInterface *interface{}
+
+	unexported int
+}
+
+type Small struct {
+	Tag string
+}
+
+var allValue = All{
+	Bool:    true,
+	Int:     2,
+	Int8:    3,
+	Int16:   4,
+	Int32:   5,
+	Int64:   6,
+	Uint:    7,
+	Uint8:   8,
+	Uint16:  9,
+	Uint32:  10,
+	Uint64:  11,
+	Uintptr: 12,
+	Float32: 14.1,
+	Float64: 15.1,
+	Foo:     "foo",
+	Foo2:    "foo2",
+	IntStr:  42,
+	String:  "16",
+	Map: map[string]Small{
+		"17": {Tag: "tag17"},
+		"18": {Tag: "tag18"},
+	},
+	MapP: map[string]*Small{
+		"19": &Small{Tag: "tag19"},
+		"20": nil,
+	},
+	EmptyMap:    map[string]Small{},
+	Slice:       []Small{{Tag: "tag20"}, {Tag: "tag21"}},
+	SliceP:      []*Small{&Small{Tag: "tag22"}, nil, &Small{Tag: "tag23"}},
+	EmptySlice:  []Small{},
+	StringSlice: []string{"str24", "str25", "str26"},
+	ByteSlice:   []byte{27, 28, 29},
+	Small:       Small{Tag: "tag30"},
+	PSmall:      &Small{Tag: "tag31"},
+	Interface:   5.2,
+}
+
+var pallValue = All{
+	PBool:      &allValue.Bool,
+	PInt:       &allValue.Int,
+	PInt8:      &allValue.Int8,
+	PInt16:     &allValue.Int16,
+	PInt32:     &allValue.Int32,
+	PInt64:     &allValue.Int64,
+	PUint:      &allValue.Uint,
+	PUint8:     &allValue.Uint8,
+	PUint16:    &allValue.Uint16,
+	PUint32:    &allValue.Uint32,
+	PUint64:    &allValue.Uint64,
+	PUintptr:   &allValue.Uintptr,
+	PFloat32:   &allValue.Float32,
+	PFloat64:   &allValue.Float64,
+	PString:    &allValue.String,
+	PMap:       &allValue.Map,
+	PMapP:      &allValue.MapP,
+	PSlice:     &allValue.Slice,
+	PSliceP:    &allValue.SliceP,
+	PPSmall:    &allValue.PSmall,
+	PInterface: &allValue.Interface,
+}
+
+var allValueIndent = `{
+	"Bool": true,
+	"Int": 2,
+	"Int8": 3,
+	"Int16": 4,
+	"Int32": 5,
+	"Int64": 6,
+	"Uint": 7,
+	"Uint8": 8,
+	"Uint16": 9,
+	"Uint32": 10,
+	"Uint64": 11,
+	"Uintptr": 12,
+	"Float32": 14.1,
+	"Float64": 15.1,
+	"bar": "foo",
+	"bar2": "foo2",
+	"IntStr": "42",
+	"PBool": null,
+	"PInt": null,
+	"PInt8": null,
+	"PInt16": null,
+	"PInt32": null,
+	"PInt64": null,
+	"PUint": null,
+	"PUint8": null,
+	"PUint16": null,
+	"PUint32": null,
+	"PUint64": null,
+	"PUintptr": null,
+	"PFloat32": null,
+	"PFloat64": null,
+	"String": "16",
+	"PString": null,
+	"Map": {
+		"17": {
+			"Tag": "tag17"
+		},
+		"18": {
+			"Tag": "tag18"
+		}
+	},
+	"MapP": {
+		"19": {
+			"Tag": "tag19"
+		},
+		"20": null
+	},
+	"PMap": null,
+	"PMapP": null,
+	"EmptyMap": {},
+	"NilMap": null,
+	"Slice": [
+		{
+			"Tag": "tag20"
+		},
+		{
+			"Tag": "tag21"
+		}
+	],
+	"SliceP": [
+		{
+			"Tag": "tag22"
+		},
+		null,
+		{
+			"Tag": "tag23"
+		}
+	],
+	"PSlice": null,
+	"PSliceP": null,
+	"EmptySlice": [],
+	"NilSlice": null,
+	"StringSlice": [
+		"str24",
+		"str25",
+		"str26"
+	],
+	"ByteSlice": "Gxwd",
+	"Small": {
+		"Tag": "tag30"
+	},
+	"PSmall": {
+		"Tag": "tag31"
+	},
+	"PPSmall": null,
+	"Interface": 5.2,
+	"PInterface": null
+}`
+
+var allValueCompact = strings.Map(noSpace, allValueIndent)
+
+var pallValueIndent = `{
+	"Bool": false,
+	"Int": 0,
+	"Int8": 0,
+	"Int16": 0,
+	"Int32": 0,
+	"Int64": 0,
+	"Uint": 0,
+	"Uint8": 0,
+	"Uint16": 0,
+	"Uint32": 0,
+	"Uint64": 0,
+	"Uintptr": 0,
+	"Float32": 0,
+	"Float64": 0,
+	"bar": "",
+	"bar2": "",
+        "IntStr": "0",
+	"PBool": true,
+	"PInt": 2,
+	"PInt8": 3,
+	"PInt16": 4,
+	"PInt32": 5,
+	"PInt64": 6,
+	"PUint": 7,
+	"PUint8": 8,
+	"PUint16": 9,
+	"PUint32": 10,
+	"PUint64": 11,
+	"PUintptr": 12,
+	"PFloat32": 14.1,
+	"PFloat64": 15.1,
+	"String": "",
+	"PString": "16",
+	"Map": null,
+	"MapP": null,
+	"PMap": {
+		"17": {
+			"Tag": "tag17"
+		},
+		"18": {
+			"Tag": "tag18"
+		}
+	},
+	"PMapP": {
+		"19": {
+			"Tag": "tag19"
+		},
+		"20": null
+	},
+	"EmptyMap": null,
+	"NilMap": null,
+	"Slice": null,
+	"SliceP": null,
+	"PSlice": [
+		{
+			"Tag": "tag20"
+		},
+		{
+			"Tag": "tag21"
+		}
+	],
+	"PSliceP": [
+		{
+			"Tag": "tag22"
+		},
+		null,
+		{
+			"Tag": "tag23"
+		}
+	],
+	"EmptySlice": null,
+	"NilSlice": null,
+	"StringSlice": null,
+	"ByteSlice": null,
+	"Small": {
+		"Tag": ""
+	},
+	"PSmall": null,
+	"PPSmall": {
+		"Tag": "tag31"
+	},
+	"Interface": null,
+	"PInterface": 5.2
+}`
+
+var pallValueCompact = strings.Map(noSpace, pallValueIndent)
diff --git a/libgo/go/encoding/json/encode.go b/libgo/go/encoding/json/encode.go
new file mode 100644
index 00000000000..35964c5d9c2
--- /dev/null
+++ b/libgo/go/encoding/json/encode.go
@@ -0,0 +1,472 @@
+// Copyright 2010 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 implements encoding and decoding of JSON objects as defined in
+// RFC 4627.
+//
+// See "JSON and Go" for an introduction to this package:
+// http://blog.golang.org/2011/01/json-and-go.html
+package json
+
+import (
+	"bytes"
+	"encoding/base64"
+	"reflect"
+	"runtime"
+	"sort"
+	"strconv"
+	"unicode"
+	"unicode/utf8"
+)
+
+// Marshal returns the JSON encoding of v.
+//
+// Marshal traverses the value v recursively.
+// If an encountered value implements the Marshaler interface
+// and is not a nil pointer, Marshal calls its MarshalJSON method
+// to produce JSON.  The nil pointer exception is not strictly necessary
+// but mimics a similar, necessary exception in the behavior of
+// UnmarshalJSON.
+//
+// Otherwise, Marshal uses the following type-dependent default encodings:
+//
+// Boolean values encode as JSON booleans.
+//
+// Floating point and integer values encode as JSON numbers.
+//
+// String values encode as JSON strings, with each invalid UTF-8 sequence
+// replaced by the encoding of the Unicode replacement character U+FFFD.
+//
+// Array and slice values encode as JSON arrays, except that
+// []byte encodes as a base64-encoded string.
+//
+// Struct values encode as JSON objects. Each exported struct field
+// becomes a member of the object unless
+//   - the field's tag is "-", or
+//   - the field is empty and its tag specifies the "omitempty" option.
+// The empty values are false, 0, any
+// nil pointer or interface value, and any array, slice, map, or string of
+// length zero. The object's default key string is the struct field name
+// but can be specified in the struct field's tag value. The "json" key in
+// struct field's tag value is the key name, followed by an optional comma
+// and options. Examples:
+//
+//   // Field is ignored by this package.
+//   Field int `json:"-"`
+//
+//   // Field appears in JSON as key "myName".
+//   Field int `json:"myName"`
+//
+//   // Field appears in JSON as key "myName" and
+//   // the field is omitted from the object if its value is empty,
+//   // as defined above.
+//   Field int `json:"myName,omitempty"`
+//
+//   // Field appears in JSON as key "Field" (the default), but
+//   // the field is skipped if empty.
+//   // Note the leading comma.
+//   Field int `json:",omitempty"`
+//
+// The "string" option signals that a field is stored as JSON inside a
+// JSON-encoded string.  This extra level of encoding is sometimes
+// used when communicating with JavaScript programs:
+//
+//    Int64String int64 `json:",string"`
+//
+// The key name will be used if it's a non-empty string consisting of
+// only Unicode letters, digits, dollar signs, hyphens, and underscores.
+//
+// Map values encode as JSON objects.
+// The map's key type must be string; the object keys are used directly
+// as map keys.
+//
+// Pointer values encode as the value pointed to.
+// A nil pointer encodes as the null JSON object.
+//
+// Interface values encode as the value contained in the interface.
+// A nil interface value encodes as the null JSON object.
+//
+// Channel, complex, and function values cannot be encoded in JSON.
+// Attempting to encode such a value causes Marshal to return
+// an InvalidTypeError.
+//
+// JSON cannot represent cyclic data structures and Marshal does not
+// handle them.  Passing cyclic structures to Marshal will result in
+// an infinite recursion.
+//
+func Marshal(v interface{}) ([]byte, error) {
+	e := &encodeState{}
+	err := e.marshal(v)
+	if err != nil {
+		return nil, err
+	}
+	return e.Bytes(), nil
+}
+
+// MarshalIndent is like Marshal but applies Indent to format the output.
+func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
+	b, err := Marshal(v)
+	if err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	err = Indent(&buf, b, prefix, indent)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+// MarshalForHTML is like Marshal but applies HTMLEscape to the output.
+func MarshalForHTML(v interface{}) ([]byte, error) {
+	b, err := Marshal(v)
+	if err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	HTMLEscape(&buf, b)
+	return buf.Bytes(), nil
+}
+
+// HTMLEscape appends to dst the JSON-encoded src with <, >, and &
+// characters inside string literals changed to \u003c, \u003e, \u0026
+// so that the JSON will be safe to embed inside HTML <script> tags.
+// For historical reasons, web browsers don't honor standard HTML
+// escaping within <script> tags, so an alternative JSON encoding must
+// be used.
+func HTMLEscape(dst *bytes.Buffer, src []byte) {
+	// < > & can only appear in string literals,
+	// so just scan the string one byte at a time.
+	start := 0
+	for i, c := range src {
+		if c == '<' || c == '>' || c == '&' {
+			if start < i {
+				dst.Write(src[start:i])
+			}
+			dst.WriteString(`\u00`)
+			dst.WriteByte(hex[c>>4])
+			dst.WriteByte(hex[c&0xF])
+			start = i + 1
+		}
+	}
+	if start < len(src) {
+		dst.Write(src[start:])
+	}
+}
+
+// Marshaler is the interface implemented by objects that
+// can marshal themselves into valid JSON.
+type Marshaler interface {
+	MarshalJSON() ([]byte, error)
+}
+
+type UnsupportedTypeError struct {
+	Type reflect.Type
+}
+
+func (e *UnsupportedTypeError) Error() string {
+	return "json: unsupported type: " + e.Type.String()
+}
+
+type InvalidUTF8Error struct {
+	S string
+}
+
+func (e *InvalidUTF8Error) Error() string {
+	return "json: invalid UTF-8 in string: " + strconv.Quote(e.S)
+}
+
+type MarshalerError struct {
+	Type reflect.Type
+	Err  error
+}
+
+func (e *MarshalerError) Error() string {
+	return "json: error calling MarshalJSON for type " + e.Type.String() + ": " + e.Err.Error()
+}
+
+type interfaceOrPtrValue interface {
+	IsNil() bool
+	Elem() reflect.Value
+}
+
+var hex = "0123456789abcdef"
+
+// An encodeState encodes JSON into a bytes.Buffer.
+type encodeState struct {
+	bytes.Buffer // accumulated output
+}
+
+func (e *encodeState) marshal(v interface{}) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if _, ok := r.(runtime.Error); ok {
+				panic(r)
+			}
+			err = r.(error)
+		}
+	}()
+	e.reflectValue(reflect.ValueOf(v))
+	return nil
+}
+
+func (e *encodeState) error(err error) {
+	panic(err)
+}
+
+var byteSliceType = reflect.TypeOf([]byte(nil))
+
+func isEmptyValue(v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
+		return v.Len() == 0
+	case reflect.Bool:
+		return !v.Bool()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return v.Int() == 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return v.Uint() == 0
+	case reflect.Float32, reflect.Float64:
+		return v.Float() == 0
+	case reflect.Interface, reflect.Ptr:
+		return v.IsNil()
+	}
+	return false
+}
+
+func (e *encodeState) reflectValue(v reflect.Value) {
+	e.reflectValueQuoted(v, false)
+}
+
+// reflectValueQuoted writes the value in v to the output.
+// If quoted is true, the serialization is wrapped in a JSON string.
+func (e *encodeState) reflectValueQuoted(v reflect.Value, quoted bool) {
+	if !v.IsValid() {
+		e.WriteString("null")
+		return
+	}
+
+	if j, ok := v.Interface().(Marshaler); ok && (v.Kind() != reflect.Ptr || !v.IsNil()) {
+		b, err := j.MarshalJSON()
+		if err == nil {
+			// copy JSON into buffer, checking validity.
+			err = Compact(&e.Buffer, b)
+		}
+		if err != nil {
+			e.error(&MarshalerError{v.Type(), err})
+		}
+		return
+	}
+
+	writeString := (*encodeState).WriteString
+	if quoted {
+		writeString = (*encodeState).string
+	}
+
+	switch v.Kind() {
+	case reflect.Bool:
+		x := v.Bool()
+		if x {
+			writeString(e, "true")
+		} else {
+			writeString(e, "false")
+		}
+
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		writeString(e, strconv.Itoa64(v.Int()))
+
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		writeString(e, strconv.Uitoa64(v.Uint()))
+
+	case reflect.Float32, reflect.Float64:
+		writeString(e, strconv.FtoaN(v.Float(), 'g', -1, v.Type().Bits()))
+
+	case reflect.String:
+		if quoted {
+			sb, err := Marshal(v.String())
+			if err != nil {
+				e.error(err)
+			}
+			e.string(string(sb))
+		} else {
+			e.string(v.String())
+		}
+
+	case reflect.Struct:
+		e.WriteByte('{')
+		t := v.Type()
+		n := v.NumField()
+		first := true
+		for i := 0; i < n; i++ {
+			f := t.Field(i)
+			if f.PkgPath != "" {
+				continue
+			}
+			tag, omitEmpty, quoted := f.Name, false, false
+			if tv := f.Tag.Get("json"); tv != "" {
+				if tv == "-" {
+					continue
+				}
+				name, opts := parseTag(tv)
+				if isValidTag(name) {
+					tag = name
+				}
+				omitEmpty = opts.Contains("omitempty")
+				quoted = opts.Contains("string")
+			}
+			fieldValue := v.Field(i)
+			if omitEmpty && isEmptyValue(fieldValue) {
+				continue
+			}
+			if first {
+				first = false
+			} else {
+				e.WriteByte(',')
+			}
+			e.string(tag)
+			e.WriteByte(':')
+			e.reflectValueQuoted(fieldValue, quoted)
+		}
+		e.WriteByte('}')
+
+	case reflect.Map:
+		if v.Type().Key().Kind() != reflect.String {
+			e.error(&UnsupportedTypeError{v.Type()})
+		}
+		if v.IsNil() {
+			e.WriteString("null")
+			break
+		}
+		e.WriteByte('{')
+		var sv stringValues = v.MapKeys()
+		sort.Sort(sv)
+		for i, k := range sv {
+			if i > 0 {
+				e.WriteByte(',')
+			}
+			e.string(k.String())
+			e.WriteByte(':')
+			e.reflectValue(v.MapIndex(k))
+		}
+		e.WriteByte('}')
+
+	case reflect.Slice:
+		if v.IsNil() {
+			e.WriteString("null")
+			break
+		}
+		// Slices can be marshalled as nil, but otherwise are handled
+		// as arrays.
+		fallthrough
+	case reflect.Array:
+		if v.Type() == byteSliceType {
+			e.WriteByte('"')
+			s := v.Interface().([]byte)
+			if len(s) < 1024 {
+				// for small buffers, using Encode directly is much faster.
+				dst := make([]byte, base64.StdEncoding.EncodedLen(len(s)))
+				base64.StdEncoding.Encode(dst, s)
+				e.Write(dst)
+			} else {
+				// for large buffers, avoid unnecessary extra temporary
+				// buffer space.
+				enc := base64.NewEncoder(base64.StdEncoding, e)
+				enc.Write(s)
+				enc.Close()
+			}
+			e.WriteByte('"')
+			break
+		}
+		e.WriteByte('[')
+		n := v.Len()
+		for i := 0; i < n; i++ {
+			if i > 0 {
+				e.WriteByte(',')
+			}
+			e.reflectValue(v.Index(i))
+		}
+		e.WriteByte(']')
+
+	case reflect.Interface, reflect.Ptr:
+		if v.IsNil() {
+			e.WriteString("null")
+			return
+		}
+		e.reflectValue(v.Elem())
+
+	default:
+		e.error(&UnsupportedTypeError{v.Type()})
+	}
+	return
+}
+
+func isValidTag(s string) bool {
+	if s == "" {
+		return false
+	}
+	for _, c := range s {
+		if c != '$' && c != '-' && c != '_' && !unicode.IsLetter(c) && !unicode.IsDigit(c) {
+			return false
+		}
+	}
+	return true
+}
+
+// stringValues is a slice of reflect.Value holding *reflect.StringValue.
+// It implements the methods to sort by string.
+type stringValues []reflect.Value
+
+func (sv stringValues) Len() int           { return len(sv) }
+func (sv stringValues) Swap(i, j int)      { sv[i], sv[j] = sv[j], sv[i] }
+func (sv stringValues) Less(i, j int) bool { return sv.get(i) < sv.get(j) }
+func (sv stringValues) get(i int) string   { return sv[i].String() }
+
+func (e *encodeState) string(s string) (int, error) {
+	len0 := e.Len()
+	e.WriteByte('"')
+	start := 0
+	for i := 0; i < len(s); {
+		if b := s[i]; b < utf8.RuneSelf {
+			if 0x20 <= b && b != '\\' && b != '"' && b != '<' && b != '>' {
+				i++
+				continue
+			}
+			if start < i {
+				e.WriteString(s[start:i])
+			}
+			switch b {
+			case '\\', '"':
+				e.WriteByte('\\')
+				e.WriteByte(b)
+			case '\n':
+				e.WriteByte('\\')
+				e.WriteByte('n')
+			case '\r':
+				e.WriteByte('\\')
+				e.WriteByte('r')
+			default:
+				// This encodes bytes < 0x20 except for \n and \r,
+				// as well as < and >. The latter are escaped because they
+				// can lead to security holes when user-controlled strings
+				// are rendered into JSON and served to some browsers.
+				e.WriteString(`\u00`)
+				e.WriteByte(hex[b>>4])
+				e.WriteByte(hex[b&0xF])
+			}
+			i++
+			start = i
+			continue
+		}
+		c, size := utf8.DecodeRuneInString(s[i:])
+		if c == utf8.RuneError && size == 1 {
+			e.error(&InvalidUTF8Error{s})
+		}
+		i += size
+	}
+	if start < len(s) {
+		e.WriteString(s[start:])
+	}
+	e.WriteByte('"')
+	return e.Len() - len0, nil
+}
diff --git a/libgo/go/encoding/json/encode_test.go b/libgo/go/encoding/json/encode_test.go
new file mode 100644
index 00000000000..92f266aba63
--- /dev/null
+++ b/libgo/go/encoding/json/encode_test.go
@@ -0,0 +1,84 @@
+// Copyright 2011 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 (
+	"bytes"
+	"reflect"
+	"testing"
+)
+
+type Optionals struct {
+	Sr string `json:"sr"`
+	So string `json:"so,omitempty"`
+	Sw string `json:"-"`
+
+	Ir int `json:"omitempty"` // actually named omitempty, not an option
+	Io int `json:"io,omitempty"`
+
+	Slr []string `json:"slr,random"`
+	Slo []string `json:"slo,omitempty"`
+
+	Mr map[string]interface{} `json:"mr"`
+	Mo map[string]interface{} `json:",omitempty"`
+}
+
+var optionalsExpected = `{
+ "sr": "",
+ "omitempty": 0,
+ "slr": null,
+ "mr": {}
+}`
+
+func TestOmitEmpty(t *testing.T) {
+	var o Optionals
+	o.Sw = "something"
+	o.Mr = map[string]interface{}{}
+	o.Mo = map[string]interface{}{}
+
+	got, err := MarshalIndent(&o, "", " ")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := string(got); got != optionalsExpected {
+		t.Errorf(" got: %s\nwant: %s\n", got, optionalsExpected)
+	}
+}
+
+type StringTag struct {
+	BoolStr bool   `json:",string"`
+	IntStr  int64  `json:",string"`
+	StrStr  string `json:",string"`
+}
+
+var stringTagExpected = `{
+ "BoolStr": "true",
+ "IntStr": "42",
+ "StrStr": "\"xzbit\""
+}`
+
+func TestStringTag(t *testing.T) {
+	var s StringTag
+	s.BoolStr = true
+	s.IntStr = 42
+	s.StrStr = "xzbit"
+	got, err := MarshalIndent(&s, "", " ")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := string(got); got != stringTagExpected {
+		t.Fatalf(" got: %s\nwant: %s\n", got, stringTagExpected)
+	}
+
+	// Verify that it round-trips.
+	var s2 StringTag
+	err = NewDecoder(bytes.NewBuffer(got)).Decode(&s2)
+	if err != nil {
+		t.Fatalf("Decode: %v", err)
+	}
+	if !reflect.DeepEqual(s, s2) {
+		t.Fatalf("decode didn't match.\nsource: %#v\nEncoded as:\n%s\ndecode: %#v", s, string(got), s2)
+	}
+}
diff --git a/libgo/go/encoding/json/indent.go b/libgo/go/encoding/json/indent.go
new file mode 100644
index 00000000000..5ba19b07ac6
--- /dev/null
+++ b/libgo/go/encoding/json/indent.go
@@ -0,0 +1,114 @@
+// Copyright 2010 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 "bytes"
+
+// Compact appends to dst the JSON-encoded src with
+// insignificant space characters elided.
+func Compact(dst *bytes.Buffer, src []byte) error {
+	origLen := dst.Len()
+	var scan scanner
+	scan.reset()
+	start := 0
+	for i, c := range src {
+		v := scan.step(&scan, int(c))
+		if v >= scanSkipSpace {
+			if v == scanError {
+				break
+			}
+			if start < i {
+				dst.Write(src[start:i])
+			}
+			start = i + 1
+		}
+	}
+	if scan.eof() == scanError {
+		dst.Truncate(origLen)
+		return scan.err
+	}
+	if start < len(src) {
+		dst.Write(src[start:])
+	}
+	return nil
+}
+
+func newline(dst *bytes.Buffer, prefix, indent string, depth int) {
+	dst.WriteByte('\n')
+	dst.WriteString(prefix)
+	for i := 0; i < depth; i++ {
+		dst.WriteString(indent)
+	}
+}
+
+// Indent appends to dst an indented form of the JSON-encoded src.
+// Each element in a JSON object or array begins on a new,
+// indented line beginning with prefix followed by one or more
+// copies of indent according to the indentation nesting.
+// The data appended to dst has no trailing newline, to make it easier
+// to embed inside other formatted JSON data.
+func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
+	origLen := dst.Len()
+	var scan scanner
+	scan.reset()
+	needIndent := false
+	depth := 0
+	for _, c := range src {
+		scan.bytes++
+		v := scan.step(&scan, int(c))
+		if v == scanSkipSpace {
+			continue
+		}
+		if v == scanError {
+			break
+		}
+		if needIndent && v != scanEndObject && v != scanEndArray {
+			needIndent = false
+			depth++
+			newline(dst, prefix, indent, depth)
+		}
+
+		// Emit semantically uninteresting bytes
+		// (in particular, punctuation in strings) unmodified.
+		if v == scanContinue {
+			dst.WriteByte(c)
+			continue
+		}
+
+		// Add spacing around real punctuation.
+		switch c {
+		case '{', '[':
+			// delay indent so that empty object and array are formatted as {} and [].
+			needIndent = true
+			dst.WriteByte(c)
+
+		case ',':
+			dst.WriteByte(c)
+			newline(dst, prefix, indent, depth)
+
+		case ':':
+			dst.WriteByte(c)
+			dst.WriteByte(' ')
+
+		case '}', ']':
+			if needIndent {
+				// suppress indent in empty object/array
+				needIndent = false
+			} else {
+				depth--
+				newline(dst, prefix, indent, depth)
+			}
+			dst.WriteByte(c)
+
+		default:
+			dst.WriteByte(c)
+		}
+	}
+	if scan.eof() == scanError {
+		dst.Truncate(origLen)
+		return scan.err
+	}
+	return nil
+}
diff --git a/libgo/go/encoding/json/scanner.go b/libgo/go/encoding/json/scanner.go
new file mode 100644
index 00000000000..179690464b9
--- /dev/null
+++ b/libgo/go/encoding/json/scanner.go
@@ -0,0 +1,621 @@
+// Copyright 2010 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
+
+// JSON value parser state machine.
+// Just about at the limit of what is reasonable to write by hand.
+// Some parts are a bit tedious, but overall it nicely factors out the
+// otherwise common code from the multiple scanning functions
+// in this package (Compact, Indent, checkValid, nextValue, etc).
+//
+// This file starts with two simple examples using the scanner
+// before diving into the scanner itself.
+
+import "strconv"
+
+// checkValid verifies that data is valid JSON-encoded data.
+// scan is passed in for use by checkValid to avoid an allocation.
+func checkValid(data []byte, scan *scanner) error {
+	scan.reset()
+	for _, c := range data {
+		scan.bytes++
+		if scan.step(scan, int(c)) == scanError {
+			return scan.err
+		}
+	}
+	if scan.eof() == scanError {
+		return scan.err
+	}
+	return nil
+}
+
+// nextValue splits data after the next whole JSON value,
+// returning that value and the bytes that follow it as separate slices.
+// scan is passed in for use by nextValue to avoid an allocation.
+func nextValue(data []byte, scan *scanner) (value, rest []byte, err error) {
+	scan.reset()
+	for i, c := range data {
+		v := scan.step(scan, int(c))
+		if v >= scanEnd {
+			switch v {
+			case scanError:
+				return nil, nil, scan.err
+			case scanEnd:
+				return data[0:i], data[i:], nil
+			}
+		}
+	}
+	if scan.eof() == scanError {
+		return nil, nil, scan.err
+	}
+	return data, nil, nil
+}
+
+// A SyntaxError is a description of a JSON syntax error.
+type SyntaxError struct {
+	msg    string // description of error
+	Offset int64  // error occurred after reading Offset bytes
+}
+
+func (e *SyntaxError) Error() string { return e.msg }
+
+// A scanner is a JSON scanning state machine.
+// Callers call scan.reset() and then pass bytes in one at a time
+// by calling scan.step(&scan, c) for each byte.
+// The return value, referred to as an opcode, tells the
+// caller about significant parsing events like beginning
+// and ending literals, objects, and arrays, so that the
+// caller can follow along if it wishes.
+// The return value scanEnd indicates that a single top-level
+// JSON value has been completed, *before* the byte that
+// just got passed in.  (The indication must be delayed in order
+// to recognize the end of numbers: is 123 a whole value or
+// the beginning of 12345e+6?).
+type scanner struct {
+	// The step is a func to be called to execute the next transition.
+	// Also tried using an integer constant and a single func
+	// with a switch, but using the func directly was 10% faster
+	// on a 64-bit Mac Mini, and it's nicer to read.
+	step func(*scanner, int) int
+
+	// Stack of what we're in the middle of - array values, object keys, object values.
+	parseState []int
+
+	// Error that happened, if any.
+	err error
+
+	// 1-byte redo (see undo method)
+	redoCode  int
+	redoState func(*scanner, int) int
+
+	// total bytes consumed, updated by decoder.Decode
+	bytes int64
+}
+
+// These values are returned by the state transition functions
+// assigned to scanner.state and the method scanner.eof.
+// They give details about the current state of the scan that
+// callers might be interested to know about.
+// It is okay to ignore the return value of any particular
+// call to scanner.state: if one call returns scanError,
+// every subsequent call will return scanError too.
+const (
+	// Continue.
+	scanContinue     = iota // uninteresting byte
+	scanBeginLiteral        // end implied by next result != scanContinue
+	scanBeginObject         // begin object
+	scanObjectKey           // just finished object key (string)
+	scanObjectValue         // just finished non-last object value
+	scanEndObject           // end object (implies scanObjectValue if possible)
+	scanBeginArray          // begin array
+	scanArrayValue          // just finished array value
+	scanEndArray            // end array (implies scanArrayValue if possible)
+	scanSkipSpace           // space byte; can skip; known to be last "continue" result
+
+	// Stop.
+	scanEnd   // top-level value ended *before* this byte; known to be first "stop" result
+	scanError // hit an error, scanner.err.
+)
+
+// These values are stored in the parseState stack.
+// They give the current state of a composite value
+// being scanned.  If the parser is inside a nested value
+// the parseState describes the nested state, outermost at entry 0.
+const (
+	parseObjectKey   = iota // parsing object key (before colon)
+	parseObjectValue        // parsing object value (after colon)
+	parseArrayValue         // parsing array value
+)
+
+// reset prepares the scanner for use.
+// It must be called before calling s.step.
+func (s *scanner) reset() {
+	s.step = stateBeginValue
+	s.parseState = s.parseState[0:0]
+	s.err = nil
+}
+
+// eof tells the scanner that the end of input has been reached.
+// It returns a scan status just as s.step does.
+func (s *scanner) eof() int {
+	if s.err != nil {
+		return scanError
+	}
+	if s.step == stateEndTop {
+		return scanEnd
+	}
+	s.step(s, ' ')
+	if s.step == stateEndTop {
+		return scanEnd
+	}
+	if s.err == nil {
+		s.err = &SyntaxError{"unexpected end of JSON input", s.bytes}
+	}
+	return scanError
+}
+
+// pushParseState pushes a new parse state p onto the parse stack.
+func (s *scanner) pushParseState(p int) {
+	s.parseState = append(s.parseState, p)
+}
+
+// popParseState pops a parse state (already obtained) off the stack
+// and updates s.step accordingly.
+func (s *scanner) popParseState() {
+	n := len(s.parseState) - 1
+	s.parseState = s.parseState[0:n]
+	if n == 0 {
+		s.step = stateEndTop
+	} else {
+		s.step = stateEndValue
+	}
+}
+
+func isSpace(c rune) bool {
+	return c == ' ' || c == '\t' || c == '\r' || c == '\n'
+}
+
+// NOTE(rsc): The various instances of
+//
+//	if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n')
+//
+// below should all be if c <= ' ' && isSpace(c), but inlining
+// the checks makes a significant difference (>10%) in tight loops
+// such as nextValue.  These should be rewritten with the clearer
+// function call once 6g knows to inline the call.
+
+// stateBeginValueOrEmpty is the state after reading `[`.
+func stateBeginValueOrEmpty(s *scanner, c int) int {
+	if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+		return scanSkipSpace
+	}
+	if c == ']' {
+		return stateEndValue(s, c)
+	}
+	return stateBeginValue(s, c)
+}
+
+// stateBeginValue is the state at the beginning of the input.
+func stateBeginValue(s *scanner, c int) int {
+	if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+		return scanSkipSpace
+	}
+	switch c {
+	case '{':
+		s.step = stateBeginStringOrEmpty
+		s.pushParseState(parseObjectKey)
+		return scanBeginObject
+	case '[':
+		s.step = stateBeginValueOrEmpty
+		s.pushParseState(parseArrayValue)
+		return scanBeginArray
+	case '"':
+		s.step = stateInString
+		return scanBeginLiteral
+	case '-':
+		s.step = stateNeg
+		return scanBeginLiteral
+	case '0': // beginning of 0.123
+		s.step = state0
+		return scanBeginLiteral
+	case 't': // beginning of true
+		s.step = stateT
+		return scanBeginLiteral
+	case 'f': // beginning of false
+		s.step = stateF
+		return scanBeginLiteral
+	case 'n': // beginning of null
+		s.step = stateN
+		return scanBeginLiteral
+	}
+	if '1' <= c && c <= '9' { // beginning of 1234.5
+		s.step = state1
+		return scanBeginLiteral
+	}
+	return s.error(c, "looking for beginning of value")
+}
+
+// stateBeginStringOrEmpty is the state after reading `{`.
+func stateBeginStringOrEmpty(s *scanner, c int) int {
+	if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+		return scanSkipSpace
+	}
+	if c == '}' {
+		n := len(s.parseState)
+		s.parseState[n-1] = parseObjectValue
+		return stateEndValue(s, c)
+	}
+	return stateBeginString(s, c)
+}
+
+// stateBeginString is the state after reading `{"key": value,`.
+func stateBeginString(s *scanner, c int) int {
+	if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+		return scanSkipSpace
+	}
+	if c == '"' {
+		s.step = stateInString
+		return scanBeginLiteral
+	}
+	return s.error(c, "looking for beginning of object key string")
+}
+
+// stateEndValue is the state after completing a value,
+// such as after reading `{}` or `true` or `["x"`.
+func stateEndValue(s *scanner, c int) int {
+	n := len(s.parseState)
+	if n == 0 {
+		// Completed top-level before the current byte.
+		s.step = stateEndTop
+		return stateEndTop(s, c)
+	}
+	if c <= ' ' && (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
+		s.step = stateEndValue
+		return scanSkipSpace
+	}
+	ps := s.parseState[n-1]
+	switch ps {
+	case parseObjectKey:
+		if c == ':' {
+			s.parseState[n-1] = parseObjectValue
+			s.step = stateBeginValue
+			return scanObjectKey
+		}
+		return s.error(c, "after object key")
+	case parseObjectValue:
+		if c == ',' {
+			s.parseState[n-1] = parseObjectKey
+			s.step = stateBeginString
+			return scanObjectValue
+		}
+		if c == '}' {
+			s.popParseState()
+			return scanEndObject
+		}
+		return s.error(c, "after object key:value pair")
+	case parseArrayValue:
+		if c == ',' {
+			s.step = stateBeginValue
+			return scanArrayValue
+		}
+		if c == ']' {
+			s.popParseState()
+			return scanEndArray
+		}
+		return s.error(c, "after array element")
+	}
+	return s.error(c, "")
+}
+
+// stateEndTop is the state after finishing the top-level value,
+// such as after reading `{}` or `[1,2,3]`.
+// Only space characters should be seen now.
+func stateEndTop(s *scanner, c int) int {
+	if c != ' ' && c != '\t' && c != '\r' && c != '\n' {
+		// Complain about non-space byte on next call.
+		s.error(c, "after top-level value")
+	}
+	return scanEnd
+}
+
+// stateInString is the state after reading `"`.
+func stateInString(s *scanner, c int) int {
+	if c == '"' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	if c == '\\' {
+		s.step = stateInStringEsc
+		return scanContinue
+	}
+	if c < 0x20 {
+		return s.error(c, "in string literal")
+	}
+	return scanContinue
+}
+
+// stateInStringEsc is the state after reading `"\` during a quoted string.
+func stateInStringEsc(s *scanner, c int) int {
+	switch c {
+	case 'b', 'f', 'n', 'r', 't', '\\', '/', '"':
+		s.step = stateInString
+		return scanContinue
+	}
+	if c == 'u' {
+		s.step = stateInStringEscU
+		return scanContinue
+	}
+	return s.error(c, "in string escape code")
+}
+
+// stateInStringEscU is the state after reading `"\u` during a quoted string.
+func stateInStringEscU(s *scanner, c int) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInStringEscU1
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU1 is the state after reading `"\u1` during a quoted string.
+func stateInStringEscU1(s *scanner, c int) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInStringEscU12
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU12 is the state after reading `"\u12` during a quoted string.
+func stateInStringEscU12(s *scanner, c int) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInStringEscU123
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU123 is the state after reading `"\u123` during a quoted string.
+func stateInStringEscU123(s *scanner, c int) int {
+	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
+		s.step = stateInString
+		return scanContinue
+	}
+	// numbers
+	return s.error(c, "in \\u hexadecimal character escape")
+}
+
+// stateInStringEscU123 is the state after reading `-` during a number.
+func stateNeg(s *scanner, c int) int {
+	if c == '0' {
+		s.step = state0
+		return scanContinue
+	}
+	if '1' <= c && c <= '9' {
+		s.step = state1
+		return scanContinue
+	}
+	return s.error(c, "in numeric literal")
+}
+
+// state1 is the state after reading a non-zero integer during a number,
+// such as after reading `1` or `100` but not `0`.
+func state1(s *scanner, c int) int {
+	if '0' <= c && c <= '9' {
+		s.step = state1
+		return scanContinue
+	}
+	return state0(s, c)
+}
+
+// state0 is the state after reading `0` during a number.
+func state0(s *scanner, c int) int {
+	if c == '.' {
+		s.step = stateDot
+		return scanContinue
+	}
+	if c == 'e' || c == 'E' {
+		s.step = stateE
+		return scanContinue
+	}
+	return stateEndValue(s, c)
+}
+
+// stateDot is the state after reading the integer and decimal point in a number,
+// such as after reading `1.`.
+func stateDot(s *scanner, c int) int {
+	if '0' <= c && c <= '9' {
+		s.step = stateDot0
+		return scanContinue
+	}
+	return s.error(c, "after decimal point in numeric literal")
+}
+
+// stateDot0 is the state after reading the integer, decimal point, and subsequent
+// digits of a number, such as after reading `3.14`.
+func stateDot0(s *scanner, c int) int {
+	if '0' <= c && c <= '9' {
+		s.step = stateDot0
+		return scanContinue
+	}
+	if c == 'e' || c == 'E' {
+		s.step = stateE
+		return scanContinue
+	}
+	return stateEndValue(s, c)
+}
+
+// stateE is the state after reading the mantissa and e in a number,
+// such as after reading `314e` or `0.314e`.
+func stateE(s *scanner, c int) int {
+	if c == '+' {
+		s.step = stateESign
+		return scanContinue
+	}
+	if c == '-' {
+		s.step = stateESign
+		return scanContinue
+	}
+	return stateESign(s, c)
+}
+
+// stateESign is the state after reading the mantissa, e, and sign in a number,
+// such as after reading `314e-` or `0.314e+`.
+func stateESign(s *scanner, c int) int {
+	if '0' <= c && c <= '9' {
+		s.step = stateE0
+		return scanContinue
+	}
+	return s.error(c, "in exponent of numeric literal")
+}
+
+// stateE0 is the state after reading the mantissa, e, optional sign,
+// and at least one digit of the exponent in a number,
+// such as after reading `314e-2` or `0.314e+1` or `3.14e0`.
+func stateE0(s *scanner, c int) int {
+	if '0' <= c && c <= '9' {
+		s.step = stateE0
+		return scanContinue
+	}
+	return stateEndValue(s, c)
+}
+
+// stateT is the state after reading `t`.
+func stateT(s *scanner, c int) int {
+	if c == 'r' {
+		s.step = stateTr
+		return scanContinue
+	}
+	return s.error(c, "in literal true (expecting 'r')")
+}
+
+// stateTr is the state after reading `tr`.
+func stateTr(s *scanner, c int) int {
+	if c == 'u' {
+		s.step = stateTru
+		return scanContinue
+	}
+	return s.error(c, "in literal true (expecting 'u')")
+}
+
+// stateTru is the state after reading `tru`.
+func stateTru(s *scanner, c int) int {
+	if c == 'e' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	return s.error(c, "in literal true (expecting 'e')")
+}
+
+// stateF is the state after reading `f`.
+func stateF(s *scanner, c int) int {
+	if c == 'a' {
+		s.step = stateFa
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 'a')")
+}
+
+// stateFa is the state after reading `fa`.
+func stateFa(s *scanner, c int) int {
+	if c == 'l' {
+		s.step = stateFal
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 'l')")
+}
+
+// stateFal is the state after reading `fal`.
+func stateFal(s *scanner, c int) int {
+	if c == 's' {
+		s.step = stateFals
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 's')")
+}
+
+// stateFals is the state after reading `fals`.
+func stateFals(s *scanner, c int) int {
+	if c == 'e' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	return s.error(c, "in literal false (expecting 'e')")
+}
+
+// stateN is the state after reading `n`.
+func stateN(s *scanner, c int) int {
+	if c == 'u' {
+		s.step = stateNu
+		return scanContinue
+	}
+	return s.error(c, "in literal null (expecting 'u')")
+}
+
+// stateNu is the state after reading `nu`.
+func stateNu(s *scanner, c int) int {
+	if c == 'l' {
+		s.step = stateNul
+		return scanContinue
+	}
+	return s.error(c, "in literal null (expecting 'l')")
+}
+
+// stateNul is the state after reading `nul`.
+func stateNul(s *scanner, c int) int {
+	if c == 'l' {
+		s.step = stateEndValue
+		return scanContinue
+	}
+	return s.error(c, "in literal null (expecting 'l')")
+}
+
+// stateError is the state after reaching a syntax error,
+// such as after reading `[1}` or `5.1.2`.
+func stateError(s *scanner, c int) int {
+	return scanError
+}
+
+// error records an error and switches to the error state.
+func (s *scanner) error(c int, context string) int {
+	s.step = stateError
+	s.err = &SyntaxError{"invalid character " + quoteChar(c) + " " + context, s.bytes}
+	return scanError
+}
+
+// quoteChar formats c as a quoted character literal
+func quoteChar(c int) string {
+	// special cases - different from quoted strings
+	if c == '\'' {
+		return `'\''`
+	}
+	if c == '"' {
+		return `'"'`
+	}
+
+	// use quoted string with different quotation marks
+	s := strconv.Quote(string(c))
+	return "'" + s[1:len(s)-1] + "'"
+}
+
+// undo causes the scanner to return scanCode from the next state transition.
+// This gives callers a simple 1-byte undo mechanism.
+func (s *scanner) undo(scanCode int) {
+	if s.step == stateRedo {
+		panic("invalid use of scanner")
+	}
+	s.redoCode = scanCode
+	s.redoState = s.step
+	s.step = stateRedo
+}
+
+// stateRedo helps implement the scanner's 1-byte undo.
+func stateRedo(s *scanner, c int) int {
+	s.step = s.redoState
+	return s.redoCode
+}
diff --git a/libgo/go/encoding/json/scanner_test.go b/libgo/go/encoding/json/scanner_test.go
new file mode 100644
index 00000000000..a0a5995af8f
--- /dev/null
+++ b/libgo/go/encoding/json/scanner_test.go
@@ -0,0 +1,302 @@
+// Copyright 2010 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 (
+	"bytes"
+	"math"
+	"math/rand"
+	"reflect"
+	"testing"
+)
+
+// Tests of simple examples.
+
+type example struct {
+	compact string
+	indent  string
+}
+
+var examples = []example{
+	{`1`, `1`},
+	{`{}`, `{}`},
+	{`[]`, `[]`},
+	{`{"":2}`, "{\n\t\"\": 2\n}"},
+	{`[3]`, "[\n\t3\n]"},
+	{`[1,2,3]`, "[\n\t1,\n\t2,\n\t3\n]"},
+	{`{"x":1}`, "{\n\t\"x\": 1\n}"},
+	{ex1, ex1i},
+}
+
+var ex1 = `[true,false,null,"x",1,1.5,0,-5e+2]`
+
+var ex1i = `[
+	true,
+	false,
+	null,
+	"x",
+	1,
+	1.5,
+	0,
+	-5e+2
+]`
+
+func TestCompact(t *testing.T) {
+	var buf bytes.Buffer
+	for _, tt := range examples {
+		buf.Reset()
+		if err := Compact(&buf, []byte(tt.compact)); err != nil {
+			t.Errorf("Compact(%#q): %v", tt.compact, err)
+		} else if s := buf.String(); s != tt.compact {
+			t.Errorf("Compact(%#q) = %#q, want original", tt.compact, s)
+		}
+
+		buf.Reset()
+		if err := Compact(&buf, []byte(tt.indent)); err != nil {
+			t.Errorf("Compact(%#q): %v", tt.indent, err)
+			continue
+		} else if s := buf.String(); s != tt.compact {
+			t.Errorf("Compact(%#q) = %#q, want %#q", tt.indent, s, tt.compact)
+		}
+	}
+}
+
+func TestIndent(t *testing.T) {
+	var buf bytes.Buffer
+	for _, tt := range examples {
+		buf.Reset()
+		if err := Indent(&buf, []byte(tt.indent), "", "\t"); err != nil {
+			t.Errorf("Indent(%#q): %v", tt.indent, err)
+		} else if s := buf.String(); s != tt.indent {
+			t.Errorf("Indent(%#q) = %#q, want original", tt.indent, s)
+		}
+
+		buf.Reset()
+		if err := Indent(&buf, []byte(tt.compact), "", "\t"); err != nil {
+			t.Errorf("Indent(%#q): %v", tt.compact, err)
+			continue
+		} else if s := buf.String(); s != tt.indent {
+			t.Errorf("Indent(%#q) = %#q, want %#q", tt.compact, s, tt.indent)
+		}
+	}
+}
+
+// Tests of a large random structure.
+
+func TestCompactBig(t *testing.T) {
+	initBig()
+	var buf bytes.Buffer
+	if err := Compact(&buf, jsonBig); err != nil {
+		t.Fatalf("Compact: %v", err)
+	}
+	b := buf.Bytes()
+	if bytes.Compare(b, jsonBig) != 0 {
+		t.Error("Compact(jsonBig) != jsonBig")
+		diff(t, b, jsonBig)
+		return
+	}
+}
+
+func TestIndentBig(t *testing.T) {
+	initBig()
+	var buf bytes.Buffer
+	if err := Indent(&buf, jsonBig, "", "\t"); err != nil {
+		t.Fatalf("Indent1: %v", err)
+	}
+	b := buf.Bytes()
+	if len(b) == len(jsonBig) {
+		// jsonBig is compact (no unnecessary spaces);
+		// indenting should make it bigger
+		t.Fatalf("Indent(jsonBig) did not get bigger")
+	}
+
+	// should be idempotent
+	var buf1 bytes.Buffer
+	if err := Indent(&buf1, b, "", "\t"); err != nil {
+		t.Fatalf("Indent2: %v", err)
+	}
+	b1 := buf1.Bytes()
+	if bytes.Compare(b1, b) != 0 {
+		t.Error("Indent(Indent(jsonBig)) != Indent(jsonBig)")
+		diff(t, b1, b)
+		return
+	}
+
+	// should get back to original
+	buf1.Reset()
+	if err := Compact(&buf1, b); err != nil {
+		t.Fatalf("Compact: %v", err)
+	}
+	b1 = buf1.Bytes()
+	if bytes.Compare(b1, jsonBig) != 0 {
+		t.Error("Compact(Indent(jsonBig)) != jsonBig")
+		diff(t, b1, jsonBig)
+		return
+	}
+}
+
+type indentErrorTest struct {
+	in  string
+	err error
+}
+
+var indentErrorTests = []indentErrorTest{
+	{`{"X": "foo", "Y"}`, &SyntaxError{"invalid character '}' after object key", 17}},
+	{`{"X": "foo" "Y": "bar"}`, &SyntaxError{"invalid character '\"' after object key:value pair", 13}},
+}
+
+func TestIndentErrors(t *testing.T) {
+	for i, tt := range indentErrorTests {
+		slice := make([]uint8, 0)
+		buf := bytes.NewBuffer(slice)
+		if err := Indent(buf, []uint8(tt.in), "", ""); err != nil {
+			if !reflect.DeepEqual(err, tt.err) {
+				t.Errorf("#%d: Indent: %#v", i, err)
+				continue
+			}
+		}
+	}
+}
+
+func TestNextValueBig(t *testing.T) {
+	initBig()
+	var scan scanner
+	item, rest, err := nextValue(jsonBig, &scan)
+	if err != nil {
+		t.Fatalf("nextValue: %s", err)
+	}
+	if len(item) != len(jsonBig) || &item[0] != &jsonBig[0] {
+		t.Errorf("invalid item: %d %d", len(item), len(jsonBig))
+	}
+	if len(rest) != 0 {
+		t.Errorf("invalid rest: %d", len(rest))
+	}
+
+	item, rest, err = nextValue(append(jsonBig, "HELLO WORLD"...), &scan)
+	if err != nil {
+		t.Fatalf("nextValue extra: %s", err)
+	}
+	if len(item) != len(jsonBig) {
+		t.Errorf("invalid item: %d %d", len(item), len(jsonBig))
+	}
+	if string(rest) != "HELLO WORLD" {
+		t.Errorf("invalid rest: %d", len(rest))
+	}
+}
+
+func BenchmarkSkipValue(b *testing.B) {
+	initBig()
+	var scan scanner
+	for i := 0; i < b.N; i++ {
+		nextValue(jsonBig, &scan)
+	}
+	b.SetBytes(int64(len(jsonBig)))
+}
+
+func diff(t *testing.T, a, b []byte) {
+	for i := 0; ; i++ {
+		if i >= len(a) || i >= len(b) || a[i] != b[i] {
+			j := i - 10
+			if j < 0 {
+				j = 0
+			}
+			t.Errorf("diverge at %d: «%s» vs «%s»", i, trim(a[j:]), trim(b[j:]))
+			return
+		}
+	}
+}
+
+func trim(b []byte) []byte {
+	if len(b) > 20 {
+		return b[0:20]
+	}
+	return b
+}
+
+// Generate a random JSON object.
+
+var jsonBig []byte
+
+const (
+	big   = 10000
+	small = 100
+)
+
+func initBig() {
+	n := big
+	if testing.Short() {
+		n = small
+	}
+	if len(jsonBig) != n {
+		b, err := Marshal(genValue(n))
+		if err != nil {
+			panic(err)
+		}
+		jsonBig = b
+	}
+}
+
+func genValue(n int) interface{} {
+	if n > 1 {
+		switch rand.Intn(2) {
+		case 0:
+			return genArray(n)
+		case 1:
+			return genMap(n)
+		}
+	}
+	switch rand.Intn(3) {
+	case 0:
+		return rand.Intn(2) == 0
+	case 1:
+		return rand.NormFloat64()
+	case 2:
+		return genString(30)
+	}
+	panic("unreachable")
+}
+
+func genString(stddev float64) string {
+	n := int(math.Abs(rand.NormFloat64()*stddev + stddev/2))
+	c := make([]rune, n)
+	for i := range c {
+		f := math.Abs(rand.NormFloat64()*64 + 32)
+		if f > 0x10ffff {
+			f = 0x10ffff
+		}
+		c[i] = rune(f)
+	}
+	return string(c)
+}
+
+func genArray(n int) []interface{} {
+	f := int(math.Abs(rand.NormFloat64()) * math.Min(10, float64(n/2)))
+	if f > n {
+		f = n
+	}
+	if n > 0 && f == 0 {
+		f = 1
+	}
+	x := make([]interface{}, f)
+	for i := range x {
+		x[i] = genValue(((i+1)*n)/f - (i*n)/f)
+	}
+	return x
+}
+
+func genMap(n int) map[string]interface{} {
+	f := int(math.Abs(rand.NormFloat64()) * math.Min(10, float64(n/2)))
+	if f > n {
+		f = n
+	}
+	if n > 0 && f == 0 {
+		f = 1
+	}
+	x := make(map[string]interface{})
+	for i := 0; i < f; i++ {
+		x[genString(10)] = genValue(((i+1)*n)/f - (i*n)/f)
+	}
+	return x
+}
diff --git a/libgo/go/encoding/json/stream.go b/libgo/go/encoding/json/stream.go
new file mode 100644
index 00000000000..f2476395023
--- /dev/null
+++ b/libgo/go/encoding/json/stream.go
@@ -0,0 +1,185 @@
+// Copyright 2010 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 (
+	"errors"
+	"io"
+)
+
+// A Decoder reads and decodes JSON objects from an input stream.
+type Decoder struct {
+	r    io.Reader
+	buf  []byte
+	d    decodeState
+	scan scanner
+	err  error
+}
+
+// NewDecoder returns a new decoder that reads from r.
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{r: r}
+}
+
+// Decode reads the next JSON-encoded value from its
+// input and stores it in the value pointed to by v.
+//
+// See the documentation for Unmarshal for details about
+// the conversion of JSON into a Go value.
+func (dec *Decoder) Decode(v interface{}) error {
+	if dec.err != nil {
+		return dec.err
+	}
+
+	n, err := dec.readValue()
+	if err != nil {
+		return err
+	}
+
+	// Don't save err from unmarshal into dec.err:
+	// the connection is still usable since we read a complete JSON
+	// object from it before the error happened.
+	dec.d.init(dec.buf[0:n])
+	err = dec.d.unmarshal(v)
+
+	// Slide rest of data down.
+	rest := copy(dec.buf, dec.buf[n:])
+	dec.buf = dec.buf[0:rest]
+
+	return err
+}
+
+// readValue reads a JSON value into dec.buf.
+// It returns the length of the encoding.
+func (dec *Decoder) readValue() (int, error) {
+	dec.scan.reset()
+
+	scanp := 0
+	var err error
+Input:
+	for {
+		// Look in the buffer for a new value.
+		for i, c := range dec.buf[scanp:] {
+			dec.scan.bytes++
+			v := dec.scan.step(&dec.scan, int(c))
+			if v == scanEnd {
+				scanp += i
+				break Input
+			}
+			// scanEnd is delayed one byte.
+			// We might block trying to get that byte from src,
+			// so instead invent a space byte.
+			if v == scanEndObject && dec.scan.step(&dec.scan, ' ') == scanEnd {
+				scanp += i + 1
+				break Input
+			}
+			if v == scanError {
+				dec.err = dec.scan.err
+				return 0, dec.scan.err
+			}
+		}
+		scanp = len(dec.buf)
+
+		// Did the last read have an error?
+		// Delayed until now to allow buffer scan.
+		if err != nil {
+			if err == io.EOF {
+				if dec.scan.step(&dec.scan, ' ') == scanEnd {
+					break Input
+				}
+				if nonSpace(dec.buf) {
+					err = io.ErrUnexpectedEOF
+				}
+			}
+			dec.err = err
+			return 0, err
+		}
+
+		// Make room to read more into the buffer.
+		const minRead = 512
+		if cap(dec.buf)-len(dec.buf) < minRead {
+			newBuf := make([]byte, len(dec.buf), 2*cap(dec.buf)+minRead)
+			copy(newBuf, dec.buf)
+			dec.buf = newBuf
+		}
+
+		// Read.  Delay error for next iteration (after scan).
+		var n int
+		n, err = dec.r.Read(dec.buf[len(dec.buf):cap(dec.buf)])
+		dec.buf = dec.buf[0 : len(dec.buf)+n]
+	}
+	return scanp, nil
+}
+
+func nonSpace(b []byte) bool {
+	for _, c := range b {
+		if !isSpace(rune(c)) {
+			return true
+		}
+	}
+	return false
+}
+
+// An Encoder writes JSON objects to an output stream.
+type Encoder struct {
+	w   io.Writer
+	e   encodeState
+	err error
+}
+
+// NewEncoder returns a new encoder that writes to w.
+func NewEncoder(w io.Writer) *Encoder {
+	return &Encoder{w: w}
+}
+
+// Encode writes the JSON encoding of v to the connection.
+//
+// See the documentation for Marshal for details about the
+// conversion of Go values to JSON.
+func (enc *Encoder) Encode(v interface{}) error {
+	if enc.err != nil {
+		return enc.err
+	}
+	enc.e.Reset()
+	err := enc.e.marshal(v)
+	if err != nil {
+		return err
+	}
+
+	// Terminate each value with a newline.
+	// This makes the output look a little nicer
+	// when debugging, and some kind of space
+	// is required if the encoded value was a number,
+	// so that the reader knows there aren't more
+	// digits coming.
+	enc.e.WriteByte('\n')
+
+	if _, err = enc.w.Write(enc.e.Bytes()); err != nil {
+		enc.err = err
+	}
+	return err
+}
+
+// RawMessage is a raw encoded JSON object.
+// It implements Marshaler and Unmarshaler and can
+// be used to delay JSON decoding or precompute a JSON encoding.
+type RawMessage []byte
+
+// MarshalJSON returns *m as the JSON encoding of m.
+func (m *RawMessage) MarshalJSON() ([]byte, error) {
+	return *m, nil
+}
+
+// UnmarshalJSON sets *m to a copy of data.
+func (m *RawMessage) UnmarshalJSON(data []byte) error {
+	if m == nil {
+		return errors.New("json.RawMessage: UnmarshalJSON on nil pointer")
+	}
+	*m = append((*m)[0:0], data...)
+	return nil
+}
+
+var _ Marshaler = (*RawMessage)(nil)
+var _ Unmarshaler = (*RawMessage)(nil)
diff --git a/libgo/go/encoding/json/stream_test.go b/libgo/go/encoding/json/stream_test.go
new file mode 100644
index 00000000000..ce5a7e6d656
--- /dev/null
+++ b/libgo/go/encoding/json/stream_test.go
@@ -0,0 +1,147 @@
+// Copyright 2010 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 (
+	"bytes"
+	"reflect"
+	"testing"
+)
+
+// Test values for the stream test.
+// One of each JSON kind.
+var streamTest = []interface{}{
+	0.1,
+	"hello",
+	nil,
+	true,
+	false,
+	[]interface{}{"a", "b", "c"},
+	map[string]interface{}{"K": "Kelvin", "ß": "long s"},
+	3.14, // another value to make sure something can follow map
+}
+
+var streamEncoded = `0.1
+"hello"
+null
+true
+false
+["a","b","c"]
+{"ß":"long s","K":"Kelvin"}
+3.14
+`
+
+func TestEncoder(t *testing.T) {
+	for i := 0; i <= len(streamTest); i++ {
+		var buf bytes.Buffer
+		enc := NewEncoder(&buf)
+		for j, v := range streamTest[0:i] {
+			if err := enc.Encode(v); err != nil {
+				t.Fatalf("encode #%d: %v", j, err)
+			}
+		}
+		if have, want := buf.String(), nlines(streamEncoded, i); have != want {
+			t.Errorf("encoding %d items: mismatch", i)
+			diff(t, []byte(have), []byte(want))
+			break
+		}
+	}
+}
+
+func TestDecoder(t *testing.T) {
+	for i := 0; i <= len(streamTest); i++ {
+		// Use stream without newlines as input,
+		// just to stress the decoder even more.
+		// Our test input does not include back-to-back numbers.
+		// Otherwise stripping the newlines would
+		// merge two adjacent JSON values.
+		var buf bytes.Buffer
+		for _, c := range nlines(streamEncoded, i) {
+			if c != '\n' {
+				buf.WriteRune(c)
+			}
+		}
+		out := make([]interface{}, i)
+		dec := NewDecoder(&buf)
+		for j := range out {
+			if err := dec.Decode(&out[j]); err != nil {
+				t.Fatalf("decode #%d/%d: %v", j, i, err)
+			}
+		}
+		if !reflect.DeepEqual(out, streamTest[0:i]) {
+			t.Errorf("decoding %d items: mismatch", i)
+			for j := range out {
+				if !reflect.DeepEqual(out[j], streamTest[j]) {
+					t.Errorf("#%d: have %v want %v", j, out[j], streamTest[j])
+				}
+			}
+			break
+		}
+	}
+}
+
+func nlines(s string, n int) string {
+	if n <= 0 {
+		return ""
+	}
+	for i, c := range s {
+		if c == '\n' {
+			if n--; n == 0 {
+				return s[0 : i+1]
+			}
+		}
+	}
+	return s
+}
+
+func TestRawMessage(t *testing.T) {
+	// TODO(rsc): Should not need the * in *RawMessage
+	var data struct {
+		X  float64
+		Id *RawMessage
+		Y  float32
+	}
+	const raw = `["\u0056",null]`
+	const msg = `{"X":0.1,"Id":["\u0056",null],"Y":0.2}`
+	err := Unmarshal([]byte(msg), &data)
+	if err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if string([]byte(*data.Id)) != raw {
+		t.Fatalf("Raw mismatch: have %#q want %#q", []byte(*data.Id), raw)
+	}
+	b, err := Marshal(&data)
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	if string(b) != msg {
+		t.Fatalf("Marshal: have %#q want %#q", b, msg)
+	}
+}
+
+func TestNullRawMessage(t *testing.T) {
+	// TODO(rsc): Should not need the * in *RawMessage
+	var data struct {
+		X  float64
+		Id *RawMessage
+		Y  float32
+	}
+	data.Id = new(RawMessage)
+	const msg = `{"X":0.1,"Id":null,"Y":0.2}`
+	err := Unmarshal([]byte(msg), &data)
+	if err != nil {
+		t.Fatalf("Unmarshal: %v", err)
+	}
+	if data.Id != nil {
+		t.Fatalf("Raw mismatch: have non-nil, want nil")
+	}
+	b, err := Marshal(&data)
+	if err != nil {
+		t.Fatalf("Marshal: %v", err)
+	}
+	if string(b) != msg {
+		t.Fatalf("Marshal: have %#q want %#q", b, msg)
+	}
+}
diff --git a/libgo/go/encoding/json/tagkey_test.go b/libgo/go/encoding/json/tagkey_test.go
new file mode 100644
index 00000000000..31fe2be3621
--- /dev/null
+++ b/libgo/go/encoding/json/tagkey_test.go
@@ -0,0 +1,95 @@
+// Copyright 2011 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 (
+	"testing"
+)
+
+type basicLatin2xTag struct {
+	V string `json:"$-"`
+}
+
+type basicLatin3xTag struct {
+	V string `json:"0123456789"`
+}
+
+type basicLatin4xTag struct {
+	V string `json:"ABCDEFGHIJKLMO"`
+}
+
+type basicLatin5xTag struct {
+	V string `json:"PQRSTUVWXYZ_"`
+}
+
+type basicLatin6xTag struct {
+	V string `json:"abcdefghijklmno"`
+}
+
+type basicLatin7xTag struct {
+	V string `json:"pqrstuvwxyz"`
+}
+
+type miscPlaneTag struct {
+	V string `json:"色は匂へど"`
+}
+
+type emptyTag struct {
+	W string
+}
+
+type misnamedTag struct {
+	X string `jsom:"Misnamed"`
+}
+
+type badFormatTag struct {
+	Y string `:"BadFormat"`
+}
+
+type badCodeTag struct {
+	Z string `json:" !\"#%&'()*+,./"`
+}
+
+var structTagObjectKeyTests = []struct {
+	raw   interface{}
+	value string
+	key   string
+}{
+	{basicLatin2xTag{"2x"}, "2x", "$-"},
+	{basicLatin3xTag{"3x"}, "3x", "0123456789"},
+	{basicLatin4xTag{"4x"}, "4x", "ABCDEFGHIJKLMO"},
+	{basicLatin5xTag{"5x"}, "5x", "PQRSTUVWXYZ_"},
+	{basicLatin6xTag{"6x"}, "6x", "abcdefghijklmno"},
+	{basicLatin7xTag{"7x"}, "7x", "pqrstuvwxyz"},
+	{miscPlaneTag{"いろはにほへと"}, "いろはにほへと", "色は匂へど"},
+	{emptyTag{"Pour Moi"}, "Pour Moi", "W"},
+	{misnamedTag{"Animal Kingdom"}, "Animal Kingdom", "X"},
+	{badFormatTag{"Orfevre"}, "Orfevre", "Y"},
+	{badCodeTag{"Reliable Man"}, "Reliable Man", "Z"},
+}
+
+func TestStructTagObjectKey(t *testing.T) {
+	for _, tt := range structTagObjectKeyTests {
+		b, err := Marshal(tt.raw)
+		if err != nil {
+			t.Fatalf("Marshal(%#q) failed: %v", tt.raw, err)
+		}
+		var f interface{}
+		err = Unmarshal(b, &f)
+		if err != nil {
+			t.Fatalf("Unmarshal(%#q) failed: %v", b, err)
+		}
+		for i, v := range f.(map[string]interface{}) {
+			switch i {
+			case tt.key:
+				if s, ok := v.(string); !ok || s != tt.value {
+					t.Fatalf("Unexpected value: %#q, want %v", s, tt.value)
+				}
+			default:
+				t.Fatalf("Unexpected key: %#q", i)
+			}
+		}
+	}
+}
diff --git a/libgo/go/encoding/json/tags.go b/libgo/go/encoding/json/tags.go
new file mode 100644
index 00000000000..58cda2027c6
--- /dev/null
+++ b/libgo/go/encoding/json/tags.go
@@ -0,0 +1,44 @@
+// Copyright 2011 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 (
+	"strings"
+)
+
+// tagOptions is the string following a comma in a struct field's "json"
+// tag, or the empty string. It does not include the leading comma.
+type tagOptions string
+
+// parseTag splits a struct field's json tag into its name and
+// comma-separated options.
+func parseTag(tag string) (string, tagOptions) {
+	if idx := strings.Index(tag, ","); idx != -1 {
+		return tag[:idx], tagOptions(tag[idx+1:])
+	}
+	return tag, tagOptions("")
+}
+
+// Contains returns whether checks that a comma-separated list of options
+// contains a particular substr flag. substr must be surrounded by a
+// string boundary or commas.
+func (o tagOptions) Contains(optionName string) bool {
+	if len(o) == 0 {
+		return false
+	}
+	s := string(o)
+	for s != "" {
+		var next string
+		i := strings.Index(s, ",")
+		if i >= 0 {
+			s, next = s[:i], s[i+1:]
+		}
+		if s == optionName {
+			return true
+		}
+		s = next
+	}
+	return false
+}
diff --git a/libgo/go/encoding/json/tags_test.go b/libgo/go/encoding/json/tags_test.go
new file mode 100644
index 00000000000..91fb18831e2
--- /dev/null
+++ b/libgo/go/encoding/json/tags_test.go
@@ -0,0 +1,28 @@
+// Copyright 2011 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 (
+	"testing"
+)
+
+func TestTagParsing(t *testing.T) {
+	name, opts := parseTag("field,foobar,foo")
+	if name != "field" {
+		t.Fatalf("name = %q, want field", name)
+	}
+	for _, tt := range []struct {
+		opt  string
+		want bool
+	}{
+		{"foobar", true},
+		{"foo", true},
+		{"bar", false},
+	} {
+		if opts.Contains(tt.opt) != tt.want {
+			t.Errorf("Contains(%q) = %v", tt.opt, !tt.want)
+		}
+	}
+}