core.rst

Go Protocol buffers

rules_go provides rules that generate Go packages from .proto files. These packages can be imported like regular Go libraries.

Contents

• Overview
• Avoiding conflicts
  • Option 1: Use go_proto_library exclusively
  • Option 2: Use pre-generated .pb.go files
  • A note on vendored .proto files
• API
  • go_proto_library
  • go_proto_compiler
• Predefined plugins
• Providers
  • GoProtoCompiler
• Dependencies

---

Overview

Protocol buffers are built with the three rules below. go_proto_library and go_proto_compiler may be loaded from @io_bazel_rules_go//proto:def.bzl.

• proto_library: This is a Bazel built-in rule. It lists a set of .proto files in its srcs attribute and lists other proto_library dependencies in its deps attribute. proto_library rules may be referenced by language-specific code generation rules like java_proto_library and go_proto_library.
• go_proto_library: Generates Go code from .proto files using one or more proto plugins, then builds that code into a Go library. go_proto_library references proto_library sources via the proto attribute. They may reference other go_proto_library and go_library dependencies via the deps attributes. go_proto_library rules can be depended on or embedded directly by go_library and go_binary.
• go_proto_compiler: Defines a protoc plugin. By default, go_proto_library generates Go code with the default Go plugin, but other plugins can be used by setting the compilers attribute. A few common plugins are provided in @io_bazel_rules_go//proto.

The go_proto_compiler rule produces a GoProtoCompiler provider. If you need a greater degree of customization (for example, if you don't want to use protoc), you can implement a compatible rule that returns one of these.

The go_proto_library rule produces the normal set of Go providers. This makes it compatible with other Go rules for use in deps and embed attributes.

Avoiding conflicts

When linking programs that depend on protos, care must be taken to ensure that the same proto isn't registered by more than one package. This may happen if you depend on a go_proto_library and a vendored go_library generated from the same .proto files. You may see compile-time, link-time, or run-time errors as a result of this.

There are two main ways to avoid conflicts.

Option 1: Use go_proto_library exclusively

You can avoid proto conflicts by using go_proto_library to generate code at build time and avoiding go_library rules based on pre-generated .pb.go files.

Gazelle generates rules in this mode by default. When .proto files are present, it will generate go_proto_library rules and go_library rules that embed them (which are safe to use). Gazelle will automatically exclude .pb.go files that correspond to .proto files. If you have .proto files belonging to multiple packages in the same directory, add the following directives to your root build file:

# gazelle:proto package
# gazelle:proto_group go_package

rules_go provides go_proto_library rules for commonly used proto libraries. The Well Known Types can be found in the @io_bazel_rules_go//proto/wkt package. There are implicit dependencies of go_proto_library rules that use the default compiler, so they don't need to be written explicitly in deps. You can also find rules for Google APIs and gRPC in @go_googleapis//. You can list these rules with the commands:

$ bazel query 'kind(go_proto_library, @io_bazel_rules_go//proto/wkt:all)'
$ bazel query 'kind(go_proto_library, @go_googleapis//...)'

Some commonly used Go libraries, such as github.com/golang/protobuf/ptypes, depend on the Well Known Types. In order to avoid conflicts when using these libraries, separate versions of these libraries are provided with go_proto_library dependencies. Gazelle resolves imports of these libraries automatically. For example, it will resolve ptypes as @com_github_golang_protobuf//ptypes:go_default_library_gen.

Option 2: Use pre-generated .pb.go files

You can also avoid conflicts by generating .pb.go files ahead of time and using those exclusively instead of using go_proto_library. This may be a better option for established Go projects that also need to build with go build.

Gazelle can generate rules for projects built in this mode. Add the following comment to your root build file:

# gazelle:proto disable_global

This prevents Gazelle from generating go_proto_library rules. .pb.go files won't be excluded, and all special cases for imports (such as ptypes) are disabled.

If you have go_repository rules in your WORKSPACE file that may have protos, you'll also need to add build_file_proto_mode = "disable_global" to those as well.

go_repository(
    name = "com_example_some_project",
    importpath = "example.com/some/project",
    tag = "v0.1.2",
    build_file_proto_mode = "disable_global",
)

A note on vendored .proto files

By default, Bazel assumes imports in .proto files are relative to a repository root directory. This means, for example, if you import "foo/bar/baz.proto", that file must be in the directory foo/bar, not vendor/example.com/repo/foo/bar.

To deal with this, use the strip_import_prefix option in the proto_library for the vendored file.

API

go_proto_library

go_proto_library generates a set of .go files from a set of .proto files (specified in a proto_library rule), then builds a Go library from those files. go_proto_library can be imported like any go_library rule.

Providers

• GoLibrary
• GoSource
• GoArchive

Attributes

Name	Type	Default value
name	string	mandatory value
A unique name for this rule. By convention, and in order to interoperate cleanly with Gazelle, this should be a name like foo_go_proto, where foo is the Go package name or the last component of the proto package name (hopefully the same). The proto_library referenced by proto should be named foo_proto.
proto	label	mandatory value
Points to the proto_library containing the .proto sources this rule should generate code from. Avoid using this argument, use protos instead.
protos	label	mandatory value
List of proto_library targets containing the .proto sources this rule should generate code from. This argument should be used instead of proto argument.
deps	label_list	[]
List of Go libraries this library depends on directly. Usually, this will be a list of go_proto_library rules that correspond to the deps of the proto_library rule referenced by proto. Additional dependencies may be added by the proto compiler. For example, the default compiler implicitly adds dependencies on the go_proto_library rules for the Well Known Types.
importpath	string	mandatory value
The source import path of this library. Other libraries can import this library using this path. This must be specified in go_proto_library or inherited from one of the targets in embed. importpath must match the import path specified in .proto files using option go_package. The option determines how .pb.go files generated for protos importing this proto will import this package.
importmap	string	""
The Go package path of this library. This is mostly only visible to the compiler and linker, but it may also be seen in stack traces. This may be set to prevent a binary from linking multiple packages with the same import path, e.g., from different vendor directories.
embed	label_list	[]
List of Go libraries that should be combined with this library. The srcs and deps from these libraries will be incorporated into this library when it is compiled. Embedded libraries must have the same importpath and Go package name.
gc_goopts	string_list	[]
List of flags to add to the Go compilation command when using the gc compiler. Subject to Make variable substitution and Bourne shell tokenization.
compiler	label	None
Equivalent to compilers with a single label.
compilers	label_list	["@io_bazel_rules_go//proto:go_proto"]
List of rules producing GoProtoCompiler providers (normally go_proto_compiler rules). This is usually understood to be a list of protoc plugins used to generate Go code. See Predefined plugins for some options.

Example: Basic proto

Suppose you have two .proto files in separate packages: foo/foo.proto and bar/bar.proto. foo/foo.proto looks like this:

syntax = "proto3";

option go_package = "example.com/repo/foo";

import "google/protobuf/any.proto";
import "bar/bar.proto";

message Foo {
  bar.Bar x = 1;
  google.protobuf.Any y = 2;
};

In foo/BUILD.bazel, we need to declare a proto_library rule that lists foo.proto in its srcs attribute. Since we import some other protos, we also need a label in deps for each imported package. We will need to create another proto_library in bar/BUILD.bazel, but we can use an existing library for any.proto, since it's one of the Well Known Types.

proto_library(
    name = "foo_proto",
    srcs = ["foo.proto"],
    deps = [
        "//bar:bar_proto",
        "@com_google_protobuf//:any_proto",
    ],
    visibility = ["//visibility:public"],
)

In order to these this proto in Go, we need to declare a go_proto_library that references to proto_library to be built via the proto attribute. Like go_library, an importpath attribute needs to be declared. Ideally, this should match the option go_package declaration in the .proto file, but this is not required. We also need to list Go packages that the generated Go code imports in the deps attributes. Generally, deps in go_proto_library will correspond with deps in proto_library, but the Well Known Types don't need to be listed (they are added automatically by the compiler in use).

load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")

go_proto_library(
    name = "foo_go_proto",
    importpath = "example.com/repo/foo",
    proto = ":foo_proto",
    visibility = ["//visibility:public"],
    deps = ["//bar:bar_go_proto"],
)

This library can be imported like a regular Go library by other rules.

load("@io_bazel_rules_go//go:def.bzl", "go_binary")

go_binary(
    name = "main",
    srcs = ["main.go"],
    deps = ["//foo:foo_go_proto"],
)

If you need to add additional source files to a package built from protos, you can do so with a separate go_library that embeds the go_proto_library.

load("@io_bazel_rules_go//go:def.bzl", "go_library")

go_library(
    name = "foo",
    srcs = ["extra.go"],
    embed = [":foo_go_proto"],
    importpath = "example.com/repo/foo",
    visibility = ["//visibility:public"],
)

For convenience, proto_library, go_proto_library, and go_binary can all be generated by Gazelle.

Example: gRPC

To compile protos that contain service definitions, just use the go_grpc plugin.

load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")

proto_library(
    name = "foo_proto",
    srcs = ["foo.proto"],
    visibility = ["//visibility:public"],
)

go_proto_library(
    name = "foo_go_proto",
    compilers = ["@io_bazel_rules_go//proto:go_grpc"],
    importpath = "example.com/repo/foo",
    proto = ":foo_proto",
    visibility = ["//visibility:public"],
    deps = ["//bar:bar_go_proto"],
)

go_proto_compiler

go_proto_compiler describes a plugin for protoc, the proto compiler. Different plugins will generate different Go code from the same protos. Compilers may be chosen through the compilers attribute of go_proto_library.

Several instances of this rule are listed in Predefined plugins. You will only need to use this rule directly if you need a plugin which is not there.

Providers

• GoProtoCompiler
• GoLibrary
• GoSource

Attributes

Name	Type	Default value
name	string	mandatory value
A unique name for this rule.
deps	label_list	[]
List of Go libraries that Go code generated by this compiler depends on implicitly. Rules in this list must produce the GoLibrary provider. This should contain libraries for the Well Known Types at least.
options	string_list	[]
List of command line options to be passed to the compiler. Each option will be preceded by --option.
suffix	string	.pb.go
File name suffix of generated Go files. go_proto_compiler assumes that one Go file will be generated for each input .proto file. Output file names will have the .proto suffix removed and this suffix appended. For example, foo.proto will become foo.pb.go.
valid_archive	bool	True
Whether code generated by this compiler can be compiled into a standalone archive file without additional sources.
import_path_option	bool	True
When true, the importpath attribute from go_proto_library rules using this compiler will be passed to the compiler on the command line as --option import_path={}.
plugin	label	@com_github_golang_protobuf//protoc-gen-go
The plugin to use with protoc via the --plugin option. This rule must produce an executable file.

Predefined plugins

Several go_proto_compiler rules are predefined in @io_bazel_rules_go//proto.

• go_proto: default plugin from github.com/golang/protobuf.
• go_grpc: default gRPC plugin.
• go_proto_validate: validator plugin from github.com/mwitkow/go-proto-validators. Generates Validate methods.
• gogoprotobuf plugins for the variants combo, gofast, gogo, gogofast, gogofaster, gogoslick, gogotypes, gostring. For each variant, there is a regular version (e.g., gogo_proto) and a gRPC version (e.g., gogo_grpc).

Providers

Providers are objects produced by Bazel rules and consumed by other rules that depend on them. See Go providers for information about Go providers, specifically GoLibrary, GoSource, and GoArchive.

GoProtoCompiler

GoProtoCompiler is the provider returned by the go_proto_compiler rule and anything compatible with it. The go_proto_library rule expects any rule listed in its compilers attribute to provide GoProtoCompiler. If the go_proto_compiler rule doesn't do what you need (e.g., you don't want to use protoc), you can write a new rule that produces this.

GoProtoCompiler is loaded from @io_bazel_rules_go//proto:def.bzl.

GoProtoCompiler has the fields described below. Additional fields may be added to pass information to the compile function. This interface is not final and may change in the future.

Name	Type
deps	Target list
A list of Go libraries to be added as dependencies to any go_proto_library compiled with this compiler. Each target must provide GoLibrary, GoSource, and GoArchive. This list should include libraries for the Well Known Types and anything else considered "standard".
compile	Function
A function which declares output files and actions when called. See compiler.bzl for details.
valid_archive	bool
Whether the compiler produces a complete Go library. Compilers that just add methods to structs produced by other compilers will set this to false.

Dependencies

In order to support protocol buffers, rules_go declares the external repositories listed below in go_rules_dependencies(). These repositories will only be downloaded if proto rules are used.

• @com_google_protobuf (github.com/google/protobuf): Well Known Types and general proto support.
• @com_github_golang_protobuf (github.com/golang/protobuf): standard Go proto plugin.
• @com_github_mwitkow_go_proto_validators (github.com/mwitkow/go-proto-validators): validator plugin.
• @com_github_gogo_protobuf (github.com/gogo/protobuf): gogoprotobuf plugins.
• @org_golang_google_grpc (github.com/grpc/grpc-go: gRPC support.
• gRPC dependencies
  • @org_golang_x_net (golang.org/x/net)
  • @org_golang_x_text (golang.org/x/text)
  • @org_golang_google_genproto (google.golang.org/genproto)