diff --git a/vendor/github.com/golang/protobuf/jsonpb/jsonpb.go b/vendor/github.com/golang/protobuf/jsonpb/jsonpb.go
new file mode 100644
index 0000000..e9cc202
--- /dev/null
+++ b/vendor/github.com/golang/protobuf/jsonpb/jsonpb.go
@@ -0,0 +1,1284 @@
+// Go support for Protocol Buffers - Google's data interchange format
+//
+// Copyright 2015 The Go Authors.  All rights reserved.
+// https://github.com/golang/protobuf
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+/*
+Package jsonpb provides marshaling and unmarshaling between protocol buffers and JSON.
+It follows the specification at https://developers.google.com/protocol-buffers/docs/proto3#json.
+
+This package produces a different output than the standard "encoding/json" package,
+which does not operate correctly on protocol buffers.
+*/
+package jsonpb
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"reflect"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/golang/protobuf/proto"
+
+	stpb "github.com/golang/protobuf/ptypes/struct"
+)
+
+const secondInNanos = int64(time.Second / time.Nanosecond)
+const maxSecondsInDuration = 315576000000
+
+// Marshaler is a configurable object for converting between
+// protocol buffer objects and a JSON representation for them.
+type Marshaler struct {
+	// Whether to render enum values as integers, as opposed to string values.
+	EnumsAsInts bool
+
+	// Whether to render fields with zero values.
+	EmitDefaults bool
+
+	// A string to indent each level by. The presence of this field will
+	// also cause a space to appear between the field separator and
+	// value, and for newlines to be appear between fields and array
+	// elements.
+	Indent string
+
+	// Whether to use the original (.proto) name for fields.
+	OrigName bool
+
+	// A custom URL resolver to use when marshaling Any messages to JSON.
+	// If unset, the default resolution strategy is to extract the
+	// fully-qualified type name from the type URL and pass that to
+	// proto.MessageType(string).
+	AnyResolver AnyResolver
+}
+
+// AnyResolver takes a type URL, present in an Any message, and resolves it into
+// an instance of the associated message.
+type AnyResolver interface {
+	Resolve(typeUrl string) (proto.Message, error)
+}
+
+func defaultResolveAny(typeUrl string) (proto.Message, error) {
+	// Only the part of typeUrl after the last slash is relevant.
+	mname := typeUrl
+	if slash := strings.LastIndex(mname, "/"); slash >= 0 {
+		mname = mname[slash+1:]
+	}
+	mt := proto.MessageType(mname)
+	if mt == nil {
+		return nil, fmt.Errorf("unknown message type %q", mname)
+	}
+	return reflect.New(mt.Elem()).Interface().(proto.Message), nil
+}
+
+// JSONPBMarshaler is implemented by protobuf messages that customize the
+// way they are marshaled to JSON. Messages that implement this should
+// also implement JSONPBUnmarshaler so that the custom format can be
+// parsed.
+//
+// The JSON marshaling must follow the proto to JSON specification:
+//	https://developers.google.com/protocol-buffers/docs/proto3#json
+type JSONPBMarshaler interface {
+	MarshalJSONPB(*Marshaler) ([]byte, error)
+}
+
+// JSONPBUnmarshaler is implemented by protobuf messages that customize
+// the way they are unmarshaled from JSON. Messages that implement this
+// should also implement JSONPBMarshaler so that the custom format can be
+// produced.
+//
+// The JSON unmarshaling must follow the JSON to proto specification:
+//	https://developers.google.com/protocol-buffers/docs/proto3#json
+type JSONPBUnmarshaler interface {
+	UnmarshalJSONPB(*Unmarshaler, []byte) error
+}
+
+// Marshal marshals a protocol buffer into JSON.
+func (m *Marshaler) Marshal(out io.Writer, pb proto.Message) error {
+	v := reflect.ValueOf(pb)
+	if pb == nil || (v.Kind() == reflect.Ptr && v.IsNil()) {
+		return errors.New("Marshal called with nil")
+	}
+	// Check for unset required fields first.
+	if err := checkRequiredFields(pb); err != nil {
+		return err
+	}
+	writer := &errWriter{writer: out}
+	return m.marshalObject(writer, pb, "", "")
+}
+
+// MarshalToString converts a protocol buffer object to JSON string.
+func (m *Marshaler) MarshalToString(pb proto.Message) (string, error) {
+	var buf bytes.Buffer
+	if err := m.Marshal(&buf, pb); err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}
+
+type int32Slice []int32
+
+var nonFinite = map[string]float64{
+	`"NaN"`:       math.NaN(),
+	`"Infinity"`:  math.Inf(1),
+	`"-Infinity"`: math.Inf(-1),
+}
+
+// For sorting extensions ids to ensure stable output.
+func (s int32Slice) Len() int           { return len(s) }
+func (s int32Slice) Less(i, j int) bool { return s[i] < s[j] }
+func (s int32Slice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+
+type wkt interface {
+	XXX_WellKnownType() string
+}
+
+// marshalObject writes a struct to the Writer.
+func (m *Marshaler) marshalObject(out *errWriter, v proto.Message, indent, typeURL string) error {
+	if jsm, ok := v.(JSONPBMarshaler); ok {
+		b, err := jsm.MarshalJSONPB(m)
+		if err != nil {
+			return err
+		}
+		if typeURL != "" {
+			// we are marshaling this object to an Any type
+			var js map[string]*json.RawMessage
+			if err = json.Unmarshal(b, &js); err != nil {
+				return fmt.Errorf("type %T produced invalid JSON: %v", v, err)
+			}
+			turl, err := json.Marshal(typeURL)
+			if err != nil {
+				return fmt.Errorf("failed to marshal type URL %q to JSON: %v", typeURL, err)
+			}
+			js["@type"] = (*json.RawMessage)(&turl)
+			if m.Indent != "" {
+				b, err = json.MarshalIndent(js, indent, m.Indent)
+			} else {
+				b, err = json.Marshal(js)
+			}
+			if err != nil {
+				return err
+			}
+		}
+
+		out.write(string(b))
+		return out.err
+	}
+
+	s := reflect.ValueOf(v).Elem()
+
+	// Handle well-known types.
+	if wkt, ok := v.(wkt); ok {
+		switch wkt.XXX_WellKnownType() {
+		case "DoubleValue", "FloatValue", "Int64Value", "UInt64Value",
+			"Int32Value", "UInt32Value", "BoolValue", "StringValue", "BytesValue":
+			// "Wrappers use the same representation in JSON
+			//  as the wrapped primitive type, ..."
+			sprop := proto.GetProperties(s.Type())
+			return m.marshalValue(out, sprop.Prop[0], s.Field(0), indent)
+		case "Any":
+			// Any is a bit more involved.
+			return m.marshalAny(out, v, indent)
+		case "Duration":
+			s, ns := s.Field(0).Int(), s.Field(1).Int()
+			if s < -maxSecondsInDuration || s > maxSecondsInDuration {
+				return fmt.Errorf("seconds out of range %v", s)
+			}
+			if ns <= -secondInNanos || ns >= secondInNanos {
+				return fmt.Errorf("ns out of range (%v, %v)", -secondInNanos, secondInNanos)
+			}
+			if (s > 0 && ns < 0) || (s < 0 && ns > 0) {
+				return errors.New("signs of seconds and nanos do not match")
+			}
+			// Generated output always contains 0, 3, 6, or 9 fractional digits,
+			// depending on required precision, followed by the suffix "s".
+			f := "%d.%09d"
+			if ns < 0 {
+				ns = -ns
+				if s == 0 {
+					f = "-%d.%09d"
+				}
+			}
+			x := fmt.Sprintf(f, s, ns)
+			x = strings.TrimSuffix(x, "000")
+			x = strings.TrimSuffix(x, "000")
+			x = strings.TrimSuffix(x, ".000")
+			out.write(`"`)
+			out.write(x)
+			out.write(`s"`)
+			return out.err
+		case "Struct", "ListValue":
+			// Let marshalValue handle the `Struct.fields` map or the `ListValue.values` slice.
+			// TODO: pass the correct Properties if needed.
+			return m.marshalValue(out, &proto.Properties{}, s.Field(0), indent)
+		case "Timestamp":
+			// "RFC 3339, where generated output will always be Z-normalized
+			//  and uses 0, 3, 6 or 9 fractional digits."
+			s, ns := s.Field(0).Int(), s.Field(1).Int()
+			if ns < 0 || ns >= secondInNanos {
+				return fmt.Errorf("ns out of range [0, %v)", secondInNanos)
+			}
+			t := time.Unix(s, ns).UTC()
+			// time.RFC3339Nano isn't exactly right (we need to get 3/6/9 fractional digits).
+			x := t.Format("2006-01-02T15:04:05.000000000")
+			x = strings.TrimSuffix(x, "000")
+			x = strings.TrimSuffix(x, "000")
+			x = strings.TrimSuffix(x, ".000")
+			out.write(`"`)
+			out.write(x)
+			out.write(`Z"`)
+			return out.err
+		case "Value":
+			// Value has a single oneof.
+			kind := s.Field(0)
+			if kind.IsNil() {
+				// "absence of any variant indicates an error"
+				return errors.New("nil Value")
+			}
+			// oneof -> *T -> T -> T.F
+			x := kind.Elem().Elem().Field(0)
+			// TODO: pass the correct Properties if needed.
+			return m.marshalValue(out, &proto.Properties{}, x, indent)
+		}
+	}
+
+	out.write("{")
+	if m.Indent != "" {
+		out.write("\n")
+	}
+
+	firstField := true
+
+	if typeURL != "" {
+		if err := m.marshalTypeURL(out, indent, typeURL); err != nil {
+			return err
+		}
+		firstField = false
+	}
+
+	for i := 0; i < s.NumField(); i++ {
+		value := s.Field(i)
+		valueField := s.Type().Field(i)
+		if strings.HasPrefix(valueField.Name, "XXX_") {
+			continue
+		}
+
+		// IsNil will panic on most value kinds.
+		switch value.Kind() {
+		case reflect.Chan, reflect.Func, reflect.Interface:
+			if value.IsNil() {
+				continue
+			}
+		}
+
+		if !m.EmitDefaults {
+			switch value.Kind() {
+			case reflect.Bool:
+				if !value.Bool() {
+					continue
+				}
+			case reflect.Int32, reflect.Int64:
+				if value.Int() == 0 {
+					continue
+				}
+			case reflect.Uint32, reflect.Uint64:
+				if value.Uint() == 0 {
+					continue
+				}
+			case reflect.Float32, reflect.Float64:
+				if value.Float() == 0 {
+					continue
+				}
+			case reflect.String:
+				if value.Len() == 0 {
+					continue
+				}
+			case reflect.Map, reflect.Ptr, reflect.Slice:
+				if value.IsNil() {
+					continue
+				}
+			}
+		}
+
+		// Oneof fields need special handling.
+		if valueField.Tag.Get("protobuf_oneof") != "" {
+			// value is an interface containing &T{real_value}.
+			sv := value.Elem().Elem() // interface -> *T -> T
+			value = sv.Field(0)
+			valueField = sv.Type().Field(0)
+		}
+		prop := jsonProperties(valueField, m.OrigName)
+		if !firstField {
+			m.writeSep(out)
+		}
+		if err := m.marshalField(out, prop, value, indent); err != nil {
+			return err
+		}
+		firstField = false
+	}
+
+	// Handle proto2 extensions.
+	if ep, ok := v.(proto.Message); ok {
+		extensions := proto.RegisteredExtensions(v)
+		// Sort extensions for stable output.
+		ids := make([]int32, 0, len(extensions))
+		for id, desc := range extensions {
+			if !proto.HasExtension(ep, desc) {
+				continue
+			}
+			ids = append(ids, id)
+		}
+		sort.Sort(int32Slice(ids))
+		for _, id := range ids {
+			desc := extensions[id]
+			if desc == nil {
+				// unknown extension
+				continue
+			}
+			ext, extErr := proto.GetExtension(ep, desc)
+			if extErr != nil {
+				return extErr
+			}
+			value := reflect.ValueOf(ext)
+			var prop proto.Properties
+			prop.Parse(desc.Tag)
+			prop.JSONName = fmt.Sprintf("[%s]", desc.Name)
+			if !firstField {
+				m.writeSep(out)
+			}
+			if err := m.marshalField(out, &prop, value, indent); err != nil {
+				return err
+			}
+			firstField = false
+		}
+
+	}
+
+	if m.Indent != "" {
+		out.write("\n")
+		out.write(indent)
+	}
+	out.write("}")
+	return out.err
+}
+
+func (m *Marshaler) writeSep(out *errWriter) {
+	if m.Indent != "" {
+		out.write(",\n")
+	} else {
+		out.write(",")
+	}
+}
+
+func (m *Marshaler) marshalAny(out *errWriter, any proto.Message, indent string) error {
+	// "If the Any contains a value that has a special JSON mapping,
+	//  it will be converted as follows: {"@type": xxx, "value": yyy}.
+	//  Otherwise, the value will be converted into a JSON object,
+	//  and the "@type" field will be inserted to indicate the actual data type."
+	v := reflect.ValueOf(any).Elem()
+	turl := v.Field(0).String()
+	val := v.Field(1).Bytes()
+
+	var msg proto.Message
+	var err error
+	if m.AnyResolver != nil {
+		msg, err = m.AnyResolver.Resolve(turl)
+	} else {
+		msg, err = defaultResolveAny(turl)
+	}
+	if err != nil {
+		return err
+	}
+
+	if err := proto.Unmarshal(val, msg); err != nil {
+		return err
+	}
+
+	if _, ok := msg.(wkt); ok {
+		out.write("{")
+		if m.Indent != "" {
+			out.write("\n")
+		}
+		if err := m.marshalTypeURL(out, indent, turl); err != nil {
+			return err
+		}
+		m.writeSep(out)
+		if m.Indent != "" {
+			out.write(indent)
+			out.write(m.Indent)
+			out.write(`"value": `)
+		} else {
+			out.write(`"value":`)
+		}
+		if err := m.marshalObject(out, msg, indent+m.Indent, ""); err != nil {
+			return err
+		}
+		if m.Indent != "" {
+			out.write("\n")
+			out.write(indent)
+		}
+		out.write("}")
+		return out.err
+	}
+
+	return m.marshalObject(out, msg, indent, turl)
+}
+
+func (m *Marshaler) marshalTypeURL(out *errWriter, indent, typeURL string) error {
+	if m.Indent != "" {
+		out.write(indent)
+		out.write(m.Indent)
+	}
+	out.write(`"@type":`)
+	if m.Indent != "" {
+		out.write(" ")
+	}
+	b, err := json.Marshal(typeURL)
+	if err != nil {
+		return err
+	}
+	out.write(string(b))
+	return out.err
+}
+
+// marshalField writes field description and value to the Writer.
+func (m *Marshaler) marshalField(out *errWriter, prop *proto.Properties, v reflect.Value, indent string) error {
+	if m.Indent != "" {
+		out.write(indent)
+		out.write(m.Indent)
+	}
+	out.write(`"`)
+	out.write(prop.JSONName)
+	out.write(`":`)
+	if m.Indent != "" {
+		out.write(" ")
+	}
+	if err := m.marshalValue(out, prop, v, indent); err != nil {
+		return err
+	}
+	return nil
+}
+
+// marshalValue writes the value to the Writer.
+func (m *Marshaler) marshalValue(out *errWriter, prop *proto.Properties, v reflect.Value, indent string) error {
+	var err error
+	v = reflect.Indirect(v)
+
+	// Handle nil pointer
+	if v.Kind() == reflect.Invalid {
+		out.write("null")
+		return out.err
+	}
+
+	// Handle repeated elements.
+	if v.Kind() == reflect.Slice && v.Type().Elem().Kind() != reflect.Uint8 {
+		out.write("[")
+		comma := ""
+		for i := 0; i < v.Len(); i++ {
+			sliceVal := v.Index(i)
+			out.write(comma)
+			if m.Indent != "" {
+				out.write("\n")
+				out.write(indent)
+				out.write(m.Indent)
+				out.write(m.Indent)
+			}
+			if err := m.marshalValue(out, prop, sliceVal, indent+m.Indent); err != nil {
+				return err
+			}
+			comma = ","
+		}
+		if m.Indent != "" {
+			out.write("\n")
+			out.write(indent)
+			out.write(m.Indent)
+		}
+		out.write("]")
+		return out.err
+	}
+
+	// Handle well-known types.
+	// Most are handled up in marshalObject (because 99% are messages).
+	if wkt, ok := v.Interface().(wkt); ok {
+		switch wkt.XXX_WellKnownType() {
+		case "NullValue":
+			out.write("null")
+			return out.err
+		}
+	}
+
+	// Handle enumerations.
+	if !m.EnumsAsInts && prop.Enum != "" {
+		// Unknown enum values will are stringified by the proto library as their
+		// value. Such values should _not_ be quoted or they will be interpreted
+		// as an enum string instead of their value.
+		enumStr := v.Interface().(fmt.Stringer).String()
+		var valStr string
+		if v.Kind() == reflect.Ptr {
+			valStr = strconv.Itoa(int(v.Elem().Int()))
+		} else {
+			valStr = strconv.Itoa(int(v.Int()))
+		}
+		isKnownEnum := enumStr != valStr
+		if isKnownEnum {
+			out.write(`"`)
+		}
+		out.write(enumStr)
+		if isKnownEnum {
+			out.write(`"`)
+		}
+		return out.err
+	}
+
+	// Handle nested messages.
+	if v.Kind() == reflect.Struct {
+		return m.marshalObject(out, v.Addr().Interface().(proto.Message), indent+m.Indent, "")
+	}
+
+	// Handle maps.
+	// Since Go randomizes map iteration, we sort keys for stable output.
+	if v.Kind() == reflect.Map {
+		out.write(`{`)
+		keys := v.MapKeys()
+		sort.Sort(mapKeys(keys))
+		for i, k := range keys {
+			if i > 0 {
+				out.write(`,`)
+			}
+			if m.Indent != "" {
+				out.write("\n")
+				out.write(indent)
+				out.write(m.Indent)
+				out.write(m.Indent)
+			}
+
+			// TODO handle map key prop properly
+			b, err := json.Marshal(k.Interface())
+			if err != nil {
+				return err
+			}
+			s := string(b)
+
+			// If the JSON is not a string value, encode it again to make it one.
+			if !strings.HasPrefix(s, `"`) {
+				b, err := json.Marshal(s)
+				if err != nil {
+					return err
+				}
+				s = string(b)
+			}
+
+			out.write(s)
+			out.write(`:`)
+			if m.Indent != "" {
+				out.write(` `)
+			}
+
+			vprop := prop
+			if prop != nil && prop.MapValProp != nil {
+				vprop = prop.MapValProp
+			}
+			if err := m.marshalValue(out, vprop, v.MapIndex(k), indent+m.Indent); err != nil {
+				return err
+			}
+		}
+		if m.Indent != "" {
+			out.write("\n")
+			out.write(indent)
+			out.write(m.Indent)
+		}
+		out.write(`}`)
+		return out.err
+	}
+
+	// Handle non-finite floats, e.g. NaN, Infinity and -Infinity.
+	if v.Kind() == reflect.Float32 || v.Kind() == reflect.Float64 {
+		f := v.Float()
+		var sval string
+		switch {
+		case math.IsInf(f, 1):
+			sval = `"Infinity"`
+		case math.IsInf(f, -1):
+			sval = `"-Infinity"`
+		case math.IsNaN(f):
+			sval = `"NaN"`
+		}
+		if sval != "" {
+			out.write(sval)
+			return out.err
+		}
+	}
+
+	// Default handling defers to the encoding/json library.
+	b, err := json.Marshal(v.Interface())
+	if err != nil {
+		return err
+	}
+	needToQuote := string(b[0]) != `"` && (v.Kind() == reflect.Int64 || v.Kind() == reflect.Uint64)
+	if needToQuote {
+		out.write(`"`)
+	}
+	out.write(string(b))
+	if needToQuote {
+		out.write(`"`)
+	}
+	return out.err
+}
+
+// Unmarshaler is a configurable object for converting from a JSON
+// representation to a protocol buffer object.
+type Unmarshaler struct {
+	// Whether to allow messages to contain unknown fields, as opposed to
+	// failing to unmarshal.
+	AllowUnknownFields bool
+
+	// A custom URL resolver to use when unmarshaling Any messages from JSON.
+	// If unset, the default resolution strategy is to extract the
+	// fully-qualified type name from the type URL and pass that to
+	// proto.MessageType(string).
+	AnyResolver AnyResolver
+}
+
+// UnmarshalNext unmarshals the next protocol buffer from a JSON object stream.
+// This function is lenient and will decode any options permutations of the
+// related Marshaler.
+func (u *Unmarshaler) UnmarshalNext(dec *json.Decoder, pb proto.Message) error {
+	inputValue := json.RawMessage{}
+	if err := dec.Decode(&inputValue); err != nil {
+		return err
+	}
+	if err := u.unmarshalValue(reflect.ValueOf(pb).Elem(), inputValue, nil); err != nil {
+		return err
+	}
+	return checkRequiredFields(pb)
+}
+
+// Unmarshal unmarshals a JSON object stream into a protocol
+// buffer. This function is lenient and will decode any options
+// permutations of the related Marshaler.
+func (u *Unmarshaler) Unmarshal(r io.Reader, pb proto.Message) error {
+	dec := json.NewDecoder(r)
+	return u.UnmarshalNext(dec, pb)
+}
+
+// UnmarshalNext unmarshals the next protocol buffer from a JSON object stream.
+// This function is lenient and will decode any options permutations of the
+// related Marshaler.
+func UnmarshalNext(dec *json.Decoder, pb proto.Message) error {
+	return new(Unmarshaler).UnmarshalNext(dec, pb)
+}
+
+// Unmarshal unmarshals a JSON object stream into a protocol
+// buffer. This function is lenient and will decode any options
+// permutations of the related Marshaler.
+func Unmarshal(r io.Reader, pb proto.Message) error {
+	return new(Unmarshaler).Unmarshal(r, pb)
+}
+
+// UnmarshalString will populate the fields of a protocol buffer based
+// on a JSON string. This function is lenient and will decode any options
+// permutations of the related Marshaler.
+func UnmarshalString(str string, pb proto.Message) error {
+	return new(Unmarshaler).Unmarshal(strings.NewReader(str), pb)
+}
+
+// unmarshalValue converts/copies a value into the target.
+// prop may be nil.
+func (u *Unmarshaler) unmarshalValue(target reflect.Value, inputValue json.RawMessage, prop *proto.Properties) error {
+	targetType := target.Type()
+
+	// Allocate memory for pointer fields.
+	if targetType.Kind() == reflect.Ptr {
+		// If input value is "null" and target is a pointer type, then the field should be treated as not set
+		// UNLESS the target is structpb.Value, in which case it should be set to structpb.NullValue.
+		_, isJSONPBUnmarshaler := target.Interface().(JSONPBUnmarshaler)
+		if string(inputValue) == "null" && targetType != reflect.TypeOf(&stpb.Value{}) && !isJSONPBUnmarshaler {
+			return nil
+		}
+		target.Set(reflect.New(targetType.Elem()))
+
+		return u.unmarshalValue(target.Elem(), inputValue, prop)
+	}
+
+	if jsu, ok := target.Addr().Interface().(JSONPBUnmarshaler); ok {
+		return jsu.UnmarshalJSONPB(u, []byte(inputValue))
+	}
+
+	// Handle well-known types that are not pointers.
+	if w, ok := target.Addr().Interface().(wkt); ok {
+		switch w.XXX_WellKnownType() {
+		case "DoubleValue", "FloatValue", "Int64Value", "UInt64Value",
+			"Int32Value", "UInt32Value", "BoolValue", "StringValue", "BytesValue":
+			return u.unmarshalValue(target.Field(0), inputValue, prop)
+		case "Any":
+			// Use json.RawMessage pointer type instead of value to support pre-1.8 version.
+			// 1.8 changed RawMessage.MarshalJSON from pointer type to value type, see
+			// https://github.com/golang/go/issues/14493
+			var jsonFields map[string]*json.RawMessage
+			if err := json.Unmarshal(inputValue, &jsonFields); err != nil {
+				return err
+			}
+
+			val, ok := jsonFields["@type"]
+			if !ok || val == nil {
+				return errors.New("Any JSON doesn't have '@type'")
+			}
+
+			var turl string
+			if err := json.Unmarshal([]byte(*val), &turl); err != nil {
+				return fmt.Errorf("can't unmarshal Any's '@type': %q", *val)
+			}
+			target.Field(0).SetString(turl)
+
+			var m proto.Message
+			var err error
+			if u.AnyResolver != nil {
+				m, err = u.AnyResolver.Resolve(turl)
+			} else {
+				m, err = defaultResolveAny(turl)
+			}
+			if err != nil {
+				return err
+			}
+
+			if _, ok := m.(wkt); ok {
+				val, ok := jsonFields["value"]
+				if !ok {
+					return errors.New("Any JSON doesn't have 'value'")
+				}
+
+				if err := u.unmarshalValue(reflect.ValueOf(m).Elem(), *val, nil); err != nil {
+					return fmt.Errorf("can't unmarshal Any nested proto %T: %v", m, err)
+				}
+			} else {
+				delete(jsonFields, "@type")
+				nestedProto, err := json.Marshal(jsonFields)
+				if err != nil {
+					return fmt.Errorf("can't generate JSON for Any's nested proto to be unmarshaled: %v", err)
+				}
+
+				if err = u.unmarshalValue(reflect.ValueOf(m).Elem(), nestedProto, nil); err != nil {
+					return fmt.Errorf("can't unmarshal Any nested proto %T: %v", m, err)
+				}
+			}
+
+			b, err := proto.Marshal(m)
+			if err != nil {
+				return fmt.Errorf("can't marshal proto %T into Any.Value: %v", m, err)
+			}
+			target.Field(1).SetBytes(b)
+
+			return nil
+		case "Duration":
+			unq, err := unquote(string(inputValue))
+			if err != nil {
+				return err
+			}
+
+			d, err := time.ParseDuration(unq)
+			if err != nil {
+				return fmt.Errorf("bad Duration: %v", err)
+			}
+
+			ns := d.Nanoseconds()
+			s := ns / 1e9
+			ns %= 1e9
+			target.Field(0).SetInt(s)
+			target.Field(1).SetInt(ns)
+			return nil
+		case "Timestamp":
+			unq, err := unquote(string(inputValue))
+			if err != nil {
+				return err
+			}
+
+			t, err := time.Parse(time.RFC3339Nano, unq)
+			if err != nil {
+				return fmt.Errorf("bad Timestamp: %v", err)
+			}
+
+			target.Field(0).SetInt(t.Unix())
+			target.Field(1).SetInt(int64(t.Nanosecond()))
+			return nil
+		case "Struct":
+			var m map[string]json.RawMessage
+			if err := json.Unmarshal(inputValue, &m); err != nil {
+				return fmt.Errorf("bad StructValue: %v", err)
+			}
+
+			target.Field(0).Set(reflect.ValueOf(map[string]*stpb.Value{}))
+			for k, jv := range m {
+				pv := &stpb.Value{}
+				if err := u.unmarshalValue(reflect.ValueOf(pv).Elem(), jv, prop); err != nil {
+					return fmt.Errorf("bad value in StructValue for key %q: %v", k, err)
+				}
+				target.Field(0).SetMapIndex(reflect.ValueOf(k), reflect.ValueOf(pv))
+			}
+			return nil
+		case "ListValue":
+			var s []json.RawMessage
+			if err := json.Unmarshal(inputValue, &s); err != nil {
+				return fmt.Errorf("bad ListValue: %v", err)
+			}
+
+			target.Field(0).Set(reflect.ValueOf(make([]*stpb.Value, len(s))))
+			for i, sv := range s {
+				if err := u.unmarshalValue(target.Field(0).Index(i), sv, prop); err != nil {
+					return err
+				}
+			}
+			return nil
+		case "Value":
+			ivStr := string(inputValue)
+			if ivStr == "null" {
+				target.Field(0).Set(reflect.ValueOf(&stpb.Value_NullValue{}))
+			} else if v, err := strconv.ParseFloat(ivStr, 0); err == nil {
+				target.Field(0).Set(reflect.ValueOf(&stpb.Value_NumberValue{v}))
+			} else if v, err := unquote(ivStr); err == nil {
+				target.Field(0).Set(reflect.ValueOf(&stpb.Value_StringValue{v}))
+			} else if v, err := strconv.ParseBool(ivStr); err == nil {
+				target.Field(0).Set(reflect.ValueOf(&stpb.Value_BoolValue{v}))
+			} else if err := json.Unmarshal(inputValue, &[]json.RawMessage{}); err == nil {
+				lv := &stpb.ListValue{}
+				target.Field(0).Set(reflect.ValueOf(&stpb.Value_ListValue{lv}))
+				return u.unmarshalValue(reflect.ValueOf(lv).Elem(), inputValue, prop)
+			} else if err := json.Unmarshal(inputValue, &map[string]json.RawMessage{}); err == nil {
+				sv := &stpb.Struct{}
+				target.Field(0).Set(reflect.ValueOf(&stpb.Value_StructValue{sv}))
+				return u.unmarshalValue(reflect.ValueOf(sv).Elem(), inputValue, prop)
+			} else {
+				return fmt.Errorf("unrecognized type for Value %q", ivStr)
+			}
+			return nil
+		}
+	}
+
+	// Handle enums, which have an underlying type of int32,
+	// and may appear as strings.
+	// The case of an enum appearing as a number is handled
+	// at the bottom of this function.
+	if inputValue[0] == '"' && prop != nil && prop.Enum != "" {
+		vmap := proto.EnumValueMap(prop.Enum)
+		// Don't need to do unquoting; valid enum names
+		// are from a limited character set.
+		s := inputValue[1 : len(inputValue)-1]
+		n, ok := vmap[string(s)]
+		if !ok {
+			return fmt.Errorf("unknown value %q for enum %s", s, prop.Enum)
+		}
+		if target.Kind() == reflect.Ptr { // proto2
+			target.Set(reflect.New(targetType.Elem()))
+			target = target.Elem()
+		}
+		if targetType.Kind() != reflect.Int32 {
+			return fmt.Errorf("invalid target %q for enum %s", targetType.Kind(), prop.Enum)
+		}
+		target.SetInt(int64(n))
+		return nil
+	}
+
+	// Handle nested messages.
+	if targetType.Kind() == reflect.Struct {
+		var jsonFields map[string]json.RawMessage
+		if err := json.Unmarshal(inputValue, &jsonFields); err != nil {
+			return err
+		}
+
+		consumeField := func(prop *proto.Properties) (json.RawMessage, bool) {
+			// Be liberal in what names we accept; both orig_name and camelName are okay.
+			fieldNames := acceptedJSONFieldNames(prop)
+
+			vOrig, okOrig := jsonFields[fieldNames.orig]
+			vCamel, okCamel := jsonFields[fieldNames.camel]
+			if !okOrig && !okCamel {
+				return nil, false
+			}
+			// If, for some reason, both are present in the data, favour the camelName.
+			var raw json.RawMessage
+			if okOrig {
+				raw = vOrig
+				delete(jsonFields, fieldNames.orig)
+			}
+			if okCamel {
+				raw = vCamel
+				delete(jsonFields, fieldNames.camel)
+			}
+			return raw, true
+		}
+
+		sprops := proto.GetProperties(targetType)
+		for i := 0; i < target.NumField(); i++ {
+			ft := target.Type().Field(i)
+			if strings.HasPrefix(ft.Name, "XXX_") {
+				continue
+			}
+
+			valueForField, ok := consumeField(sprops.Prop[i])
+			if !ok {
+				continue
+			}
+
+			if err := u.unmarshalValue(target.Field(i), valueForField, sprops.Prop[i]); err != nil {
+				return err
+			}
+		}
+		// Check for any oneof fields.
+		if len(jsonFields) > 0 {
+			for _, oop := range sprops.OneofTypes {
+				raw, ok := consumeField(oop.Prop)
+				if !ok {
+					continue
+				}
+				nv := reflect.New(oop.Type.Elem())
+				target.Field(oop.Field).Set(nv)
+				if err := u.unmarshalValue(nv.Elem().Field(0), raw, oop.Prop); err != nil {
+					return err
+				}
+			}
+		}
+		// Handle proto2 extensions.
+		if len(jsonFields) > 0 {
+			if ep, ok := target.Addr().Interface().(proto.Message); ok {
+				for _, ext := range proto.RegisteredExtensions(ep) {
+					name := fmt.Sprintf("[%s]", ext.Name)
+					raw, ok := jsonFields[name]
+					if !ok {
+						continue
+					}
+					delete(jsonFields, name)
+					nv := reflect.New(reflect.TypeOf(ext.ExtensionType).Elem())
+					if err := u.unmarshalValue(nv.Elem(), raw, nil); err != nil {
+						return err
+					}
+					if err := proto.SetExtension(ep, ext, nv.Interface()); err != nil {
+						return err
+					}
+				}
+			}
+		}
+		if !u.AllowUnknownFields && len(jsonFields) > 0 {
+			// Pick any field to be the scapegoat.
+			var f string
+			for fname := range jsonFields {
+				f = fname
+				break
+			}
+			return fmt.Errorf("unknown field %q in %v", f, targetType)
+		}
+		return nil
+	}
+
+	// Handle arrays (which aren't encoded bytes)
+	if targetType.Kind() == reflect.Slice && targetType.Elem().Kind() != reflect.Uint8 {
+		var slc []json.RawMessage
+		if err := json.Unmarshal(inputValue, &slc); err != nil {
+			return err
+		}
+		if slc != nil {
+			l := len(slc)
+			target.Set(reflect.MakeSlice(targetType, l, l))
+			for i := 0; i < l; i++ {
+				if err := u.unmarshalValue(target.Index(i), slc[i], prop); err != nil {
+					return err
+				}
+			}
+		}
+		return nil
+	}
+
+	// Handle maps (whose keys are always strings)
+	if targetType.Kind() == reflect.Map {
+		var mp map[string]json.RawMessage
+		if err := json.Unmarshal(inputValue, &mp); err != nil {
+			return err
+		}
+		if mp != nil {
+			target.Set(reflect.MakeMap(targetType))
+			for ks, raw := range mp {
+				// Unmarshal map key. The core json library already decoded the key into a
+				// string, so we handle that specially. Other types were quoted post-serialization.
+				var k reflect.Value
+				if targetType.Key().Kind() == reflect.String {
+					k = reflect.ValueOf(ks)
+				} else {
+					k = reflect.New(targetType.Key()).Elem()
+					var kprop *proto.Properties
+					if prop != nil && prop.MapKeyProp != nil {
+						kprop = prop.MapKeyProp
+					}
+					if err := u.unmarshalValue(k, json.RawMessage(ks), kprop); err != nil {
+						return err
+					}
+				}
+
+				// Unmarshal map value.
+				v := reflect.New(targetType.Elem()).Elem()
+				var vprop *proto.Properties
+				if prop != nil && prop.MapValProp != nil {
+					vprop = prop.MapValProp
+				}
+				if err := u.unmarshalValue(v, raw, vprop); err != nil {
+					return err
+				}
+				target.SetMapIndex(k, v)
+			}
+		}
+		return nil
+	}
+
+	// Non-finite numbers can be encoded as strings.
+	isFloat := targetType.Kind() == reflect.Float32 || targetType.Kind() == reflect.Float64
+	if isFloat {
+		if num, ok := nonFinite[string(inputValue)]; ok {
+			target.SetFloat(num)
+			return nil
+		}
+	}
+
+	// integers & floats can be encoded as strings. In this case we drop
+	// the quotes and proceed as normal.
+	isNum := targetType.Kind() == reflect.Int64 || targetType.Kind() == reflect.Uint64 ||
+		targetType.Kind() == reflect.Int32 || targetType.Kind() == reflect.Uint32 ||
+		targetType.Kind() == reflect.Float32 || targetType.Kind() == reflect.Float64
+	if isNum && strings.HasPrefix(string(inputValue), `"`) {
+		inputValue = inputValue[1 : len(inputValue)-1]
+	}
+
+	// Use the encoding/json for parsing other value types.
+	return json.Unmarshal(inputValue, target.Addr().Interface())
+}
+
+func unquote(s string) (string, error) {
+	var ret string
+	err := json.Unmarshal([]byte(s), &ret)
+	return ret, err
+}
+
+// jsonProperties returns parsed proto.Properties for the field and corrects JSONName attribute.
+func jsonProperties(f reflect.StructField, origName bool) *proto.Properties {
+	var prop proto.Properties
+	prop.Init(f.Type, f.Name, f.Tag.Get("protobuf"), &f)
+	if origName || prop.JSONName == "" {
+		prop.JSONName = prop.OrigName
+	}
+	return &prop
+}
+
+type fieldNames struct {
+	orig, camel string
+}
+
+func acceptedJSONFieldNames(prop *proto.Properties) fieldNames {
+	opts := fieldNames{orig: prop.OrigName, camel: prop.OrigName}
+	if prop.JSONName != "" {
+		opts.camel = prop.JSONName
+	}
+	return opts
+}
+
+// Writer wrapper inspired by https://blog.golang.org/errors-are-values
+type errWriter struct {
+	writer io.Writer
+	err    error
+}
+
+func (w *errWriter) write(str string) {
+	if w.err != nil {
+		return
+	}
+	_, w.err = w.writer.Write([]byte(str))
+}
+
+// Map fields may have key types of non-float scalars, strings and enums.
+// The easiest way to sort them in some deterministic order is to use fmt.
+// If this turns out to be inefficient we can always consider other options,
+// such as doing a Schwartzian transform.
+//
+// Numeric keys are sorted in numeric order per
+// https://developers.google.com/protocol-buffers/docs/proto#maps.
+type mapKeys []reflect.Value
+
+func (s mapKeys) Len() int      { return len(s) }
+func (s mapKeys) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+func (s mapKeys) Less(i, j int) bool {
+	if k := s[i].Kind(); k == s[j].Kind() {
+		switch k {
+		case reflect.String:
+			return s[i].String() < s[j].String()
+		case reflect.Int32, reflect.Int64:
+			return s[i].Int() < s[j].Int()
+		case reflect.Uint32, reflect.Uint64:
+			return s[i].Uint() < s[j].Uint()
+		}
+	}
+	return fmt.Sprint(s[i].Interface()) < fmt.Sprint(s[j].Interface())
+}
+
+// checkRequiredFields returns an error if any required field in the given proto message is not set.
+// This function is used by both Marshal and Unmarshal.  While required fields only exist in a
+// proto2 message, a proto3 message can contain proto2 message(s).
+func checkRequiredFields(pb proto.Message) error {
+	// Most well-known type messages do not contain required fields.  The "Any" type may contain
+	// a message that has required fields.
+	//
+	// When an Any message is being marshaled, the code will invoked proto.Unmarshal on Any.Value
+	// field in order to transform that into JSON, and that should have returned an error if a
+	// required field is not set in the embedded message.
+	//
+	// When an Any message is being unmarshaled, the code will have invoked proto.Marshal on the
+	// embedded message to store the serialized message in Any.Value field, and that should have
+	// returned an error if a required field is not set.
+	if _, ok := pb.(wkt); ok {
+		return nil
+	}
+
+	v := reflect.ValueOf(pb)
+	// Skip message if it is not a struct pointer.
+	if v.Kind() != reflect.Ptr {
+		return nil
+	}
+	v = v.Elem()
+	if v.Kind() != reflect.Struct {
+		return nil
+	}
+
+	for i := 0; i < v.NumField(); i++ {
+		field := v.Field(i)
+		sfield := v.Type().Field(i)
+
+		if sfield.PkgPath != "" {
+			// blank PkgPath means the field is exported; skip if not exported
+			continue
+		}
+
+		if strings.HasPrefix(sfield.Name, "XXX_") {
+			continue
+		}
+
+		// Oneof field is an interface implemented by wrapper structs containing the actual oneof
+		// field, i.e. an interface containing &T{real_value}.
+		if sfield.Tag.Get("protobuf_oneof") != "" {
+			if field.Kind() != reflect.Interface {
+				continue
+			}
+			v := field.Elem()
+			if v.Kind() != reflect.Ptr || v.IsNil() {
+				continue
+			}
+			v = v.Elem()
+			if v.Kind() != reflect.Struct || v.NumField() < 1 {
+				continue
+			}
+			field = v.Field(0)
+			sfield = v.Type().Field(0)
+		}
+
+		protoTag := sfield.Tag.Get("protobuf")
+		if protoTag == "" {
+			continue
+		}
+		var prop proto.Properties
+		prop.Init(sfield.Type, sfield.Name, protoTag, &sfield)
+
+		switch field.Kind() {
+		case reflect.Map:
+			if field.IsNil() {
+				continue
+			}
+			// Check each map value.
+			keys := field.MapKeys()
+			for _, k := range keys {
+				v := field.MapIndex(k)
+				if err := checkRequiredFieldsInValue(v); err != nil {
+					return err
+				}
+			}
+		case reflect.Slice:
+			// Handle non-repeated type, e.g. bytes.
+			if !prop.Repeated {
+				if prop.Required && field.IsNil() {
+					return fmt.Errorf("required field %q is not set", prop.Name)
+				}
+				continue
+			}
+
+			// Handle repeated type.
+			if field.IsNil() {
+				continue
+			}
+			// Check each slice item.
+			for i := 0; i < field.Len(); i++ {
+				v := field.Index(i)
+				if err := checkRequiredFieldsInValue(v); err != nil {
+					return err
+				}
+			}
+		case reflect.Ptr:
+			if field.IsNil() {
+				if prop.Required {
+					return fmt.Errorf("required field %q is not set", prop.Name)
+				}
+				continue
+			}
+			if err := checkRequiredFieldsInValue(field); err != nil {
+				return err
+			}
+		}
+	}
+
+	// Handle proto2 extensions.
+	for _, ext := range proto.RegisteredExtensions(pb) {
+		if !proto.HasExtension(pb, ext) {
+			continue
+		}
+		ep, err := proto.GetExtension(pb, ext)
+		if err != nil {
+			return err
+		}
+		err = checkRequiredFieldsInValue(reflect.ValueOf(ep))
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func checkRequiredFieldsInValue(v reflect.Value) error {
+	if pm, ok := v.Interface().(proto.Message); ok {
+		return checkRequiredFields(pm)
+	}
+	return nil
+}