proto: ignore unknown fields in map entries (#561)

A proto map entry is conceptually a message with two fields.
In the same way that unknown fields don't cause a parsing error,
map parsing should ignore unknown fields and tags.
Similarly, it treats a missing field as the zero value.

Fixes #403

proto/map_test.go

@@ -2,12 +2,36 @@ package proto_test
 
 import (
  "fmt"
+ "reflect"
  "testing"
 
  "github.com/golang/protobuf/proto"
  ppb "github.com/golang/protobuf/proto/proto3_proto"
 )
 
+func TestMap(t *testing.T) {
+ var b []byte
+ fmt.Sscanf("a2010c0a044b657931120456616c31a201130a044b657932120556616c3261120456616c32a201240a044b6579330d05000000120556616c33621a0556616c3361120456616c331505000000a20100a201260a044b657934130a07536f6d6555524c1209536f6d655469746c651a08536e69707065743114", "%x", &b)
+
+ var m ppb.Message
+ if err := proto.Unmarshal(b, &m); err != nil {
+ t.Fatalf("proto.Unmarshal error: %v", err)
+ }
+
+ got := m.StringMap
+ want := map[string]string{
+ "": "",
+ "Key1": "Val1",
+ "Key2": "Val2",
+ "Key3": "Val3",
+ "Key4": "",
+ }
+
+ if !reflect.DeepEqual(got, want) {
+ t.Errorf("maps differ:\ngot %#v\nwant %#v", got, want)
+ }
+}
+
 func marshalled() []byte {
  m := &ppb.IntMaps{}
  for i := 0; i < 1000; i++ {

proto/proto3_proto/proto3.proto

@@ -66,6 +66,8 @@ message Message {
 
  Message submessage = 17;
  repeated Message children = 18;
+
+ map<string, string> string_map = 20;
 }
 
 message Nested {