1# Go support for Protocol Buffers - Google's data interchange format 2 3[](https://travis-ci.org/golang/protobuf) 4[](https://godoc.org/github.com/golang/protobuf) 5 6Google's data interchange format. 7Copyright 2010 The Go Authors. 8https://github.com/golang/protobuf 9 10This package and the code it generates requires at least Go 1.6. 11 12This software implements Go bindings for protocol buffers. For 13information about protocol buffers themselves, see 14 https://developers.google.com/protocol-buffers/ 15 16## Installation ## 17 18To use this software, you must: 19- Install the standard C++ implementation of protocol buffers from 20 https://developers.google.com/protocol-buffers/ 21- Of course, install the Go compiler and tools from 22 https://golang.org/ 23 See 24 https://golang.org/doc/install 25 for details or, if you are using gccgo, follow the instructions at 26 https://golang.org/doc/install/gccgo 27- Grab the code from the repository and install the proto package. 28 The simplest way is to run `go get -u github.com/golang/protobuf/protoc-gen-go`. 29 The compiler plugin, protoc-gen-go, will be installed in $GOBIN, 30 defaulting to $GOPATH/bin. It must be in your $PATH for the protocol 31 compiler, protoc, to find it. 32 33This software has two parts: a 'protocol compiler plugin' that 34generates Go source files that, once compiled, can access and manage 35protocol buffers; and a library that implements run-time support for 36encoding (marshaling), decoding (unmarshaling), and accessing protocol 37buffers. 38 39There is support for gRPC in Go using protocol buffers. 40See the note at the bottom of this file for details. 41 42There are no insertion points in the plugin. 43 44 45## Using protocol buffers with Go ## 46 47Once the software is installed, there are two steps to using it. 48First you must compile the protocol buffer definitions and then import 49them, with the support library, into your program. 50 51To compile the protocol buffer definition, run protoc with the --go_out 52parameter set to the directory you want to output the Go code to. 53 54 protoc --go_out=. *.proto 55 56The generated files will be suffixed .pb.go. See the Test code below 57for an example using such a file. 58 59## Packages and input paths ## 60 61The protocol buffer language has a concept of "packages" which does not 62correspond well to the Go notion of packages. In generated Go code, 63each source `.proto` file is associated with a single Go package. The 64name and import path for this package is specified with the `go_package` 65proto option: 66 67 option go_package = "github.com/golang/protobuf/ptypes/any"; 68 69The protocol buffer compiler will attempt to derive a package name and 70import path if a `go_package` option is not present, but it is 71best to always specify one explicitly. 72 73There is a one-to-one relationship between source `.proto` files and 74generated `.pb.go` files, but any number of `.pb.go` files may be 75contained in the same Go package. 76 77The output name of a generated file is produced by replacing the 78`.proto` suffix with `.pb.go` (e.g., `foo.proto` produces `foo.pb.go`). 79However, the output directory is selected in one of two ways. Let 80us say we have `inputs/x.proto` with a `go_package` option of 81`github.com/golang/protobuf/p`. The corresponding output file may 82be: 83 84- Relative to the import path: 85 86```shell 87 protoc --go_out=. inputs/x.proto 88 # writes ./github.com/golang/protobuf/p/x.pb.go 89``` 90 91 (This can work well with `--go_out=$GOPATH`.) 92 93- Relative to the input file: 94 95```shell 96protoc --go_out=paths=source_relative:. inputs/x.proto 97# generate ./inputs/x.pb.go 98``` 99 100## Generated code ## 101 102The package comment for the proto library contains text describing 103the interface provided in Go for protocol buffers. Here is an edited 104version. 105 106The proto package converts data structures to and from the 107wire format of protocol buffers. It works in concert with the 108Go source code generated for .proto files by the protocol compiler. 109 110A summary of the properties of the protocol buffer interface 111for a protocol buffer variable v: 112 113 - Names are turned from camel_case to CamelCase for export. 114 - There are no methods on v to set fields; just treat 115 them as structure fields. 116 - There are getters that return a field's value if set, 117 and return the field's default value if unset. 118 The getters work even if the receiver is a nil message. 119 - The zero value for a struct is its correct initialization state. 120 All desired fields must be set before marshaling. 121 - A Reset() method will restore a protobuf struct to its zero state. 122 - Non-repeated fields are pointers to the values; nil means unset. 123 That is, optional or required field int32 f becomes F *int32. 124 - Repeated fields are slices. 125 - Helper functions are available to aid the setting of fields. 126 Helpers for getting values are superseded by the 127 GetFoo methods and their use is deprecated. 128 msg.Foo = proto.String("hello") // set field 129 - Constants are defined to hold the default values of all fields that 130 have them. They have the form Default_StructName_FieldName. 131 Because the getter methods handle defaulted values, 132 direct use of these constants should be rare. 133 - Enums are given type names and maps from names to values. 134 Enum values are prefixed with the enum's type name. Enum types have 135 a String method, and a Enum method to assist in message construction. 136 - Nested groups and enums have type names prefixed with the name of 137 the surrounding message type. 138 - Extensions are given descriptor names that start with E_, 139 followed by an underscore-delimited list of the nested messages 140 that contain it (if any) followed by the CamelCased name of the 141 extension field itself. HasExtension, ClearExtension, GetExtension 142 and SetExtension are functions for manipulating extensions. 143 - Oneof field sets are given a single field in their message, 144 with distinguished wrapper types for each possible field value. 145 - Marshal and Unmarshal are functions to encode and decode the wire format. 146 147When the .proto file specifies `syntax="proto3"`, there are some differences: 148 149 - Non-repeated fields of non-message type are values instead of pointers. 150 - Enum types do not get an Enum method. 151 152Consider file test.proto, containing 153 154```proto 155 syntax = "proto2"; 156 package example; 157 158 enum FOO { X = 17; }; 159 160 message Test { 161 required string label = 1; 162 optional int32 type = 2 [default=77]; 163 repeated int64 reps = 3; 164 optional group OptionalGroup = 4 { 165 required string RequiredField = 5; 166 } 167 } 168``` 169 170To create and play with a Test object from the example package, 171 172```go 173 package main 174 175 import ( 176 "log" 177 178 "github.com/golang/protobuf/proto" 179 "path/to/example" 180 ) 181 182 func main() { 183 test := &example.Test { 184 Label: proto.String("hello"), 185 Type: proto.Int32(17), 186 Reps: []int64{1, 2, 3}, 187 Optionalgroup: &example.Test_OptionalGroup { 188 RequiredField: proto.String("good bye"), 189 }, 190 } 191 data, err := proto.Marshal(test) 192 if err != nil { 193 log.Fatal("marshaling error: ", err) 194 } 195 newTest := &example.Test{} 196 err = proto.Unmarshal(data, newTest) 197 if err != nil { 198 log.Fatal("unmarshaling error: ", err) 199 } 200 // Now test and newTest contain the same data. 201 if test.GetLabel() != newTest.GetLabel() { 202 log.Fatalf("data mismatch %q != %q", test.GetLabel(), newTest.GetLabel()) 203 } 204 // etc. 205 } 206``` 207 208## Parameters ## 209 210To pass extra parameters to the plugin, use a comma-separated 211parameter list separated from the output directory by a colon: 212 213 protoc --go_out=plugins=grpc,import_path=mypackage:. *.proto 214 215- `paths=(import | source_relative)` - specifies how the paths of 216 generated files are structured. See the "Packages and imports paths" 217 section above. The default is `import`. 218- `plugins=plugin1+plugin2` - specifies the list of sub-plugins to 219 load. The only plugin in this repo is `grpc`. 220- `Mfoo/bar.proto=quux/shme` - declares that foo/bar.proto is 221 associated with Go package quux/shme. This is subject to the 222 import_prefix parameter. 223 224The following parameters are deprecated and should not be used: 225 226- `import_prefix=xxx` - a prefix that is added onto the beginning of 227 all imports. 228- `import_path=foo/bar` - used as the package if no input files 229 declare `go_package`. If it contains slashes, everything up to the 230 rightmost slash is ignored. 231 232## gRPC Support ## 233 234If a proto file specifies RPC services, protoc-gen-go can be instructed to 235generate code compatible with gRPC (http://www.grpc.io/). To do this, pass 236the `plugins` parameter to protoc-gen-go; the usual way is to insert it into 237the --go_out argument to protoc: 238 239 protoc --go_out=plugins=grpc:. *.proto 240 241## Compatibility ## 242 243The library and the generated code are expected to be stable over time. 244However, we reserve the right to make breaking changes without notice for the 245following reasons: 246 247- Security. A security issue in the specification or implementation may come to 248 light whose resolution requires breaking compatibility. We reserve the right 249 to address such security issues. 250- Unspecified behavior. There are some aspects of the Protocol Buffers 251 specification that are undefined. Programs that depend on such unspecified 252 behavior may break in future releases. 253- Specification errors or changes. If it becomes necessary to address an 254 inconsistency, incompleteness, or change in the Protocol Buffers 255 specification, resolving the issue could affect the meaning or legality of 256 existing programs. We reserve the right to address such issues, including 257 updating the implementations. 258- Bugs. If the library has a bug that violates the specification, a program 259 that depends on the buggy behavior may break if the bug is fixed. We reserve 260 the right to fix such bugs. 261- Adding methods or fields to generated structs. These may conflict with field 262 names that already exist in a schema, causing applications to break. When the 263 code generator encounters a field in the schema that would collide with a 264 generated field or method name, the code generator will append an underscore 265 to the generated field or method name. 266- Adding, removing, or changing methods or fields in generated structs that 267 start with `XXX`. These parts of the generated code are exported out of 268 necessity, but should not be considered part of the public API. 269- Adding, removing, or changing unexported symbols in generated code. 270 271Any breaking changes outside of these will be announced 6 months in advance to 272protobuf@googlegroups.com. 273 274You should, whenever possible, use generated code created by the `protoc-gen-go` 275tool built at the same commit as the `proto` package. The `proto` package 276declares package-level constants in the form `ProtoPackageIsVersionX`. 277Application code and generated code may depend on one of these constants to 278ensure that compilation will fail if the available version of the proto library 279is too old. Whenever we make a change to the generated code that requires newer 280library support, in the same commit we will increment the version number of the 281generated code and declare a new package-level constant whose name incorporates 282the latest version number. Removing a compatibility constant is considered a 283breaking change and would be subject to the announcement policy stated above. 284 285The `protoc-gen-go/generator` package exposes a plugin interface, 286which is used by the gRPC code generation. This interface is not 287supported and is subject to incompatible changes without notice. 288
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