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 1.9. 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 `$GOPATH/bin` 30 unless `$GOBIN` is set. It must be in your `$PATH` for the protocol 31 compiler, `protoc`, to find it. 32- If you need a particular version of `protoc-gen-go` (e.g., to match your 33 `proto` package version), one option is 34 ```shell 35 GIT_TAG="v1.2.0" # change as needed 36 go get -d -u github.com/golang/protobuf/protoc-gen-go 37 git -C "$(go env GOPATH)"/src/github.com/golang/protobuf checkout $GIT_TAG 38 go install github.com/golang/protobuf/protoc-gen-go 39 ``` 40 41This software has two parts: a 'protocol compiler plugin' that 42generates Go source files that, once compiled, can access and manage 43protocol buffers; and a library that implements run-time support for 44encoding (marshaling), decoding (unmarshaling), and accessing protocol 45buffers. 46 47There is support for gRPC in Go using protocol buffers. 48See the note at the bottom of this file for details. 49 50There are no insertion points in the plugin. 51 52 53## Using protocol buffers with Go ## 54 55Once the software is installed, there are two steps to using it. 56First you must compile the protocol buffer definitions and then import 57them, with the support library, into your program. 58 59To compile the protocol buffer definition, run protoc with the --go_out 60parameter set to the directory you want to output the Go code to. 61 62 protoc --go_out=. *.proto 63 64The generated files will be suffixed .pb.go. See the Test code below 65for an example using such a file. 66 67## Packages and input paths ## 68 69The protocol buffer language has a concept of "packages" which does not 70correspond well to the Go notion of packages. In generated Go code, 71each source `.proto` file is associated with a single Go package. The 72name and import path for this package is specified with the `go_package` 73proto option: 74 75 option go_package = "github.com/golang/protobuf/ptypes/any"; 76 77The protocol buffer compiler will attempt to derive a package name and 78import path if a `go_package` option is not present, but it is 79best to always specify one explicitly. 80 81There is a one-to-one relationship between source `.proto` files and 82generated `.pb.go` files, but any number of `.pb.go` files may be 83contained in the same Go package. 84 85The output name of a generated file is produced by replacing the 86`.proto` suffix with `.pb.go` (e.g., `foo.proto` produces `foo.pb.go`). 87However, the output directory is selected in one of two ways. Let 88us say we have `inputs/x.proto` with a `go_package` option of 89`github.com/golang/protobuf/p`. The corresponding output file may 90be: 91 92- Relative to the import path: 93 94```shell 95 protoc --go_out=. inputs/x.proto 96 # writes ./github.com/golang/protobuf/p/x.pb.go 97``` 98 99 (This can work well with `--go_out=$GOPATH`.) 100 101- Relative to the input file: 102 103```shell 104protoc --go_out=paths=source_relative:. inputs/x.proto 105# generate ./inputs/x.pb.go 106``` 107 108## Generated code ## 109 110The package comment for the proto library contains text describing 111the interface provided in Go for protocol buffers. Here is an edited 112version. 113 114The proto package converts data structures to and from the 115wire format of protocol buffers. It works in concert with the 116Go source code generated for .proto files by the protocol compiler. 117 118A summary of the properties of the protocol buffer interface 119for a protocol buffer variable v: 120 121 - Names are turned from camel_case to CamelCase for export. 122 - There are no methods on v to set fields; just treat 123 them as structure fields. 124 - There are getters that return a field's value if set, 125 and return the field's default value if unset. 126 The getters work even if the receiver is a nil message. 127 - The zero value for a struct is its correct initialization state. 128 All desired fields must be set before marshaling. 129 - A Reset() method will restore a protobuf struct to its zero state. 130 - Non-repeated fields are pointers to the values; nil means unset. 131 That is, optional or required field int32 f becomes F *int32. 132 - Repeated fields are slices. 133 - Helper functions are available to aid the setting of fields. 134 Helpers for getting values are superseded by the 135 GetFoo methods and their use is deprecated. 136 msg.Foo = proto.String("hello") // set field 137 - Constants are defined to hold the default values of all fields that 138 have them. They have the form Default_StructName_FieldName. 139 Because the getter methods handle defaulted values, 140 direct use of these constants should be rare. 141 - Enums are given type names and maps from names to values. 142 Enum values are prefixed with the enum's type name. Enum types have 143 a String method, and a Enum method to assist in message construction. 144 - Nested groups and enums have type names prefixed with the name of 145 the surrounding message type. 146 - Extensions are given descriptor names that start with E_, 147 followed by an underscore-delimited list of the nested messages 148 that contain it (if any) followed by the CamelCased name of the 149 extension field itself. HasExtension, ClearExtension, GetExtension 150 and SetExtension are functions for manipulating extensions. 151 - Oneof field sets are given a single field in their message, 152 with distinguished wrapper types for each possible field value. 153 - Marshal and Unmarshal are functions to encode and decode the wire format. 154 155When the .proto file specifies `syntax="proto3"`, there are some differences: 156 157 - Non-repeated fields of non-message type are values instead of pointers. 158 - Enum types do not get an Enum method. 159 160Consider file test.proto, containing 161 162```proto 163 syntax = "proto2"; 164 package example; 165 166 enum FOO { X = 17; }; 167 168 message Test { 169 required string label = 1; 170 optional int32 type = 2 [default=77]; 171 repeated int64 reps = 3; 172 } 173``` 174 175To create and play with a Test object from the example package, 176 177```go 178 package main 179 180 import ( 181 "log" 182 183 "github.com/golang/protobuf/proto" 184 "path/to/example" 185 ) 186 187 func main() { 188 test := &example.Test{ 189 Label: proto.String("hello"), 190 Type: proto.Int32(17), 191 Reps: []int64{1, 2, 3}, 192 } 193 data, err := proto.Marshal(test) 194 if err != nil { 195 log.Fatal("marshaling error: ", err) 196 } 197 newTest := &example.Test{} 198 err = proto.Unmarshal(data, newTest) 199 if err != nil { 200 log.Fatal("unmarshaling error: ", err) 201 } 202 // Now test and newTest contain the same data. 203 if test.GetLabel() != newTest.GetLabel() { 204 log.Fatalf("data mismatch %q != %q", test.GetLabel(), newTest.GetLabel()) 205 } 206 // etc. 207 } 208``` 209 210## Parameters ## 211 212To pass extra parameters to the plugin, use a comma-separated 213parameter list separated from the output directory by a colon: 214 215 protoc --go_out=plugins=grpc,import_path=mypackage:. *.proto 216 217- `paths=(import | source_relative)` - specifies how the paths of 218 generated files are structured. See the "Packages and imports paths" 219 section above. The default is `import`. 220- `plugins=plugin1+plugin2` - specifies the list of sub-plugins to 221 load. The only plugin in this repo is `grpc`. 222- `Mfoo/bar.proto=quux/shme` - declares that foo/bar.proto is 223 associated with Go package quux/shme. This is subject to the 224 import_prefix parameter. 225 226The following parameters are deprecated and should not be used: 227 228- `import_prefix=xxx` - a prefix that is added onto the beginning of 229 all imports. 230- `import_path=foo/bar` - used as the package if no input files 231 declare `go_package`. If it contains slashes, everything up to the 232 rightmost slash is ignored. 233 234## gRPC Support ## 235 236If a proto file specifies RPC services, protoc-gen-go can be instructed to 237generate code compatible with gRPC (http://www.grpc.io/). To do this, pass 238the `plugins` parameter to protoc-gen-go; the usual way is to insert it into 239the --go_out argument to protoc: 240 241 protoc --go_out=plugins=grpc:. *.proto 242 243## Compatibility ## 244 245The library and the generated code are expected to be stable over time. 246However, we reserve the right to make breaking changes without notice for the 247following reasons: 248 249- Security. A security issue in the specification or implementation may come to 250 light whose resolution requires breaking compatibility. We reserve the right 251 to address such security issues. 252- Unspecified behavior. There are some aspects of the Protocol Buffers 253 specification that are undefined. Programs that depend on such unspecified 254 behavior may break in future releases. 255- Specification errors or changes. If it becomes necessary to address an 256 inconsistency, incompleteness, or change in the Protocol Buffers 257 specification, resolving the issue could affect the meaning or legality of 258 existing programs. We reserve the right to address such issues, including 259 updating the implementations. 260- Bugs. If the library has a bug that violates the specification, a program 261 that depends on the buggy behavior may break if the bug is fixed. We reserve 262 the right to fix such bugs. 263- Adding methods or fields to generated structs. These may conflict with field 264 names that already exist in a schema, causing applications to break. When the 265 code generator encounters a field in the schema that would collide with a 266 generated field or method name, the code generator will append an underscore 267 to the generated field or method name. 268- Adding, removing, or changing methods or fields in generated structs that 269 start with `XXX`. These parts of the generated code are exported out of 270 necessity, but should not be considered part of the public API. 271- Adding, removing, or changing unexported symbols in generated code. 272 273Any breaking changes outside of these will be announced 6 months in advance to 274protobuf@googlegroups.com. 275 276You should, whenever possible, use generated code created by the `protoc-gen-go` 277tool built at the same commit as the `proto` package. The `proto` package 278declares package-level constants in the form `ProtoPackageIsVersionX`. 279Application code and generated code may depend on one of these constants to 280ensure that compilation will fail if the available version of the proto library 281is too old. Whenever we make a change to the generated code that requires newer 282library support, in the same commit we will increment the version number of the 283generated code and declare a new package-level constant whose name incorporates 284the latest version number. Removing a compatibility constant is considered a 285breaking change and would be subject to the announcement policy stated above. 286 287The `protoc-gen-go/generator` package exposes a plugin interface, 288which is used by the gRPC code generation. This interface is not 289supported and is subject to incompatible changes without notice. 290
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