gogoprotobuf使用(上)

摘要: 着重说明gogoprotobuf的一些选项

声明：版权所有，谢绝转载。

在go中使用google protobuf，有两个可选用的包: goprotobuf（go官方出品）和gogoprotobuf(gogo组织出品^_^)。

gogoprotobuf能够完全兼容google protobuf。而且经过我一些测试，它生成大代码质量确实要比goprotobuf高一些，主要是它在goprotobuf之上extend了一些option。这些option也是有级别区分的，有的option只能修饰field，有的可以修饰enum，有的可以修饰message，有的是修饰package（即对整个文件都有效）。下面一一说明其一些选项的意义。

另外，本文的所有proto示例都是proto v3格式。

1 gogoproto.goproto_enum_prefix

如果选项为false，则生成的代码中不加"E_"。

pb code:
enum E {
// option (gogoproto.goproto_enum_prefix) = false;
A = 0;
B = 2;
}
go code:
const (
// option (gogoproto.goproto_enum_prefix) = false;
E_A E = 0
E_B E = 2
)

or
pb code:
enum E {
// option (gogoproto.goproto_enum_prefix) = false;
A = 0;
B = 2;
}
go code:
const (
A E = 0
B E = 2
)

2 gogoproto.goproto_getters

如果选项为false，则不会为message的每个field生成一个Get函数。

pb code:
message test {
// option (gogoproto.goproto_getters) = false;
E e = 1;
}
go code:
type Test struct {
E                *E     `protobuf:"varint,1,opt,name=e,enum=test.E" json:"e,omitempty"`
XXX_unrecognized []byte `json:"-"`
}

func (m *Test) GetE() E {
if m != nil && m.E != nil {
return *m.E
}
return A
}

or

pb code:
message test {
option (gogoproto.goproto_getters) = false;
E e = 1;
}

go code:
type Test struct {
E                *E     `protobuf:"varint,1,opt,name=e,enum=test.E" json:"e,omitempty"`
XXX_unrecognized []byte `json:"-"`
}

3 gogoproto.face

当这个选项为true的时候，会为message生成相应的interface。

message test {
option (gogoproto.goproto_getters) = false;
option (gogoproto.face) = true;
string msg = 1;
}

type Test struct {
Msg              *string `protobuf:"bytes,1,opt,name=msg" json:"msg,omitempty"`
XXX_unrecognized []byte  `json:"-"`
}

func (m *Test) Reset()         { *m = Test{} }
func (m *Test) String() string { return proto.CompactTextString(m) }
func (*Test) ProtoMessage()    {}

func init() {
proto.RegisterEnum("test.E", E_name, E_value)
}

type TestFace interface {
Proto() github_com_gogo_protobuf_proto.Message
GetMsg() *string
}

func (th
8000
is *Test) Proto() github_com_gogo_protobuf_proto.Message {
return this
}

func (this *Test) TestProto() github_com_gogo_protobuf_proto.Message {
return NewTestFromFace(this)
}

func (this *Test) GetMsg() *string {
return this.Msg
}

func NewTestFromFace(that TestFace) *Test {
this := &Test{}
this.Msg = that.GetMsg()
return this
}

这个选项要求goproto_getters选项为false，即只生成interface相应的method。否则，你会收到如下error：

panic: face requires getters to be disabled please use gogoproto.getters or gogoproto.getters_all and set it to false

goroutine 1 [running]:
github.com/gogo/protobuf/plugin/face.(*plugin).Generate(0x2086c00a0, 0x20870b780)
/Users/Alex/bin/go/src/github.com/gogo/protobuf/plugin/face/face.go:164 +0x37d
github.com/gogo/protobuf/protoc-gen-gogo/generator.(*Generator).runPlugins(0x2087001c0, 0x20870b780)
/Users/Alex/bin/go/src/github.com/gogo/protobuf/protoc-gen-gogo/generator/generator.go:1008 +0x91
github.com/gogo/protobuf/protoc-gen-gogo/generator.(*Generator).generate(0x2087001c0, 0x20870b780)
/Users/Alex/bin/go/src/github.com/gogo/protobuf/protoc-gen-gogo/generator/generator.go:1047 +0x3e1
github.com/gogo/protobuf/protoc-gen-gogo/generator.(*Generator).GenerateAllFiles(0x2087001c0)
/Users/Alex/bin/go/src/github.com/gogo/protobuf/protoc-gen-gogo/generator/generator.go:994 +0x249
main.main()
/Users/Alex/bin/go/src/github.com/gogo/protobuf/protoc-gen-gogo/main.go:96 +0x31d
--gogo_out: protoc-gen-gogo: Plugin failed with status code 2.

4 gogoproto.nullable

有没有注意到上面的示例中Test的成员msg类型为string*，当你要向它赋值的时候，可能要写出如下代码：

var test Test
test.Msg = new(string)
*test.Msg = "test.msg"

or

test := Test{Msg:proto.String("hello")}

是不是感觉很麻烦？而且生成一堆临时对象，不利于gc。此时如果nullable选项为false，就不用这么麻烦了

pb code:
message test {
string msg = 1 [(gogoproto.nullable) = false];
}
go code:
type Test struct {
Msg              string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

严格地说，nullable这个option是违背protobuf的初衷的。使用了它之后，message序列化的时候，gogo会为message的每个field设置一个值，而google protobuf则是要求如果一个option的field没有被赋值，则序列化的时候不会把这个成员序列化进最终结果的。gogo官方的详尽解释是：

The protocol buffer specification states, somewhere, that you should be able to tell whether a field is set or unset. With the option nullable=false this feature is lost, since your non-nullable fields will always be set. It can be seen as a layer on top of protocol buffers, where before and after marshalling all non-nullable fields are set and they cannot be unset.

ref: https://godoc.org/code.google.com/p/gogoprotobuf/gogoproto

注意: bytes成员不要使用这个option，否则会收到编译警告“WARNING: field Message.Data is a non-nullable bytes type, nullable=false has no effect”

5 gogoproto.customname

在生成的代码中修改成员的名称，这个选项在这种情况下非常有用：field的名称与message的method的名称一样。

pb code:
message test {
option (gogoproto.goproto_getters) = false;
string msg = 1 [(gogoproto.nullable) = false, (gogoproto.customname) = "MyMsg"];
}
go code:
type Test struct {
MyMsg            string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

类似的选项还有gogoproto.customtype，不再赘述。

6 gogoproto.goproto_stringer

此选项不设置的时候，其为true。当这个选项为false的时候，gogo不再为message对一个的struct生成String()方法。这个选项建议不要设置为false。

pb code:
message test {
option (gogoproto.goproto_stringer) = true;
string msg = 1 [(gogoproto.nullable) = false, (gogoproto.customname) = "MyMsg"];
}
go code:
type Test struct {
MyMsg            string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

func (m *Test) Reset()         { *m = Test{} }
func (m *Test) String() string { return proto.CompactTextString(m) }
func (*Test) ProtoMessage()    {}

or
pb code:
option (gogoproto.goproto_getters_all) = false;

message test {
option (gogoproto.goproto_stringer) = false;
string msg = 1 [(gogoproto.nullable) = false, (gogoproto.customname) = "MyMsg"];
}
go code:
type Test struct {
MyMsg            string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

func (m *Test) Reset()      { *m = Test{} }
func (*Test) ProtoMessage() {}

7 gogoproto.gostring

这个选项为message级别，为true的时候，gogo会为相应的message生成GoString()方法。如果想为所有的message生成之类函数，可以设置package级别的gogoproto.stringer_all为true。

pb code:
option (gogoproto.goproto_getters_all) = false;

message test {
option (gogoproto.gostring) = true;
string msg = 1 [(gogoproto.nullable) = false, (gogoproto.customname) = "MyMsg"];
}
go code:
type Test struct {
MyMsg            string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

func (m *Test) Reset()         { *m = Test{} }
func (m *Test) String() string { return proto.CompactTextString(m) }
func (*Test) ProtoMessage()    {}

func init() {
proto.RegisterEnum("test.E", E_name, E_value)
}
func (this *Test) GoString() string {
if this == nil {
return "nil"
}
s := strings.Join([]string{`&test.Test{` +
`MyMsg:` + fmt.Sprintf("%#v", this.MyMsg),
`XXX_unrecognized:` + fmt.Sprintf("%#v", this.XXX_unrecognized) + `}`}, ", ")
return s
}

gogoproto.stringer_all

pb code:
option (gogoproto.goproto_getters_all) = false;
option (gogoproto.gostring_all) = true;

message test {
string msg = 1 [(gogoproto.nullable) = false, (gogoproto.customname) = "MyMsg"];
}
go code:
type Test struct {
MyMsg            string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

func (m *Test) Reset()         { *m = Test{} }
func (m *Test) String() string { return proto.CompactTextString(m) }
func (*Test) ProtoMessage()    {}

func init() {
proto.RegisterEnum("test.E", E_name, E_value)
}
func (this *Test) GoString() string {
if this == nil {
return "nil"
}
s := strings.Join([]string{`&test.Test{` +
`MyMsg:` + fmt.Sprintf("%#v", this.MyMsg),
`XXX_unrecognized:` + fmt.Sprintf("%#v", this.XXX_unrecognized) + `}`}, ", ")
return s
}

测试用例：

package main

import (
"fmt"
"strings"
)

type Test struct {
MyMsg            string `protobuf:"bytes,1,opt,name=msg" json:"msg"`
XXX_unrecognized []byte `json:"-"`
}

func (this *Test) GoString() string {
if this == nil {
return "nil"
}
s := strings.Join([]string{`&test.Test{` +
`MyMsg:` + fmt.Sprintf("%#v", this.MyMsg),
`XXX_unrecognized:` + fmt.Sprintf("%#v", this.XXX_unrecognized) + `}`}, ", ")
return s
}

func main() {
var test Test
test.MyMsg = "hello, world!"
fmt.Printf("%#v\n", test)
}

8 populate & populate_all

这个选项为message级别，当设置其值为true的时候，gogo会为每个message生成一个NewPopulated函数。

pb code:
option (gogoproto.populate_all) = true;

message B {
optional A A = 1 [(gogoproto.nullable) = false, (gogoproto.embed) = true];
repeated bytes G = 2 [(gogoproto.customtype) = "github.com/gogo/protobuf/test/custom.Uint128", (gogoproto.nullable) = false];
}

go code:

func NewPopulatedB(r randyExample, easy bool) *B {
this := &B{}
v2 := NewPopulatedA(r, easy)
this.A = *v2
if r.Intn(10) != 0 {
v3 := r.Intn(10)
this.G = make([]github_com_gogo_protobuf_test_custom.Uint128, v3)
for i := 0; i < v3; i++ {
v4 := github_com_gogo_protobuf_test_custom.NewPopulatedUint128(r)
this.G[i] = *v4
}
}
if !easy && r.Intn(10) != 0 {
this.XXX_unrecognized = randUnrecognizedExample(r, 3)
}
return this
}

如果gogo为message生成了test函数，这些函数就会调用NewPopulated函数。如果用户没有使用这个选项但是使用了test选项，则用户需自定义NewPopulated函数。

由于oschina对博文长度有限制，剩余部分转下文《gogoprotobuf使用(下)》。