gogoprotobuf使用(上)
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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 (this *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.
摘自：https://godoc.org/code.google.com/p/gogoprotobuf/gogoproto
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)
}
由于oschina对博文长度有限制，剩余部分转下文《gogoprotobuf使用(下)》。