Try the Buf CLI

The Buf CLI is the ultimate tool for modern, fast, and efficient Protobuf API management. With features such as formatting, linting, breaking change detection and code generation, Buf offers a comprehensive solution for Protobuf development and maintenance. Buf is designed to integrate seamlessly with your existing workflow, so you can focus on what matters most: writing great APIs. Whether you are working with a small, focused project or a massive, complex system, Buf is the perfect choice. In the next 10 minutes, you will learn how to use the Buf CLI to easily build, lint, format and generate code for your project.

Prerequisites

• Install the Buf CLI if you haven't already. You need version 1.32.0 or higher to do the tour, so if you previously installed the Buf CLI, check the version and update if necessary:

  $ buf --version
  

• Have git and go installed and in your $PATH.

• Clone the buf-tour repo:

  $ git clone git@github.com:bufbuild/buf-tour.git
  

The repository contains a start directory and a finish directory. During this tour you'll work on files in the start/getting-started-with-buf-cli directory, and at the end they should match the files in the finish/getting-started-with-buf-cli directory.

1. Configure and build

We'll start our tour by configuring the Buf CLI and building the .proto files that define the pet store API, which specifies a way to create, get, and delete pets in the store.

$ cd buf-tour/start/getting-started-with-buf-cli

Configure the workspace

You configure a Buf CLI workspace with a buf.yaml file, which defines the list of Protobuf file directories that you want to treat as logical units, or modules. Create the file with this command:

$ buf config init

After you run the command, there's a buf.yaml in the workspace directory with the following content:

version: v2
lint:
  use:
    - DEFAULT
breaking:
  use:
    - FILE

The buf.yaml file sits at the root of your workspace, and the workspace it defines is the default input for all Buf operations.

Update directory path and build module

The generated buf.yaml file behaves like a workspace with one module with its path set to the current directory. To explicitly define the modules within your workspace, provide the paths to the directories containing your .proto files. Add the proto directory to the buf.yaml file using the modules key:

version: v2
+modules:
+  - path: proto
lint:
  use:
    - DEFAULT
breaking:
  use:
    - FILE

Before you continue, verify that everything is set up properly and the module builds. If there are no errors, you know that you've set up a Buf module correctly:

$ buf build
$ echo $?
Output
0

2. Generate code

The Buf CLI provides a user-friendly experience for generating code locally that's compatible with any reasonable existing usage of protoc, so let's jump in and generate some code.

Configure a buf.gen.yaml file

Now that the module is configured, we'll create a buf.gen.yaml file to configure local code generation. It controls how the buf generate command executes protoc plugins on a given module. You can use it to configure where each protoc plugin writes its results and specify options for each plugin.

Create a buf.gen.yaml file in the current directory:

$ touch buf.gen.yaml

Update the contents of your buf.gen.yaml to generate code using the Go and Connect-Go plugins:

version: v2
managed:
  enabled: true
  override:
    - file_option: go_package_prefix
      value: github.com/bufbuild/buf-tour/gen
plugins:
  - remote: buf.build/protocolbuffers/go
    out: gen
    opt: paths=source_relative
  - remote: buf.build/connectrpc/go
    out: gen
    opt: paths=source_relative
inputs:
  - directory: proto

Given this config, the Buf CLI does two things:

• It executes the protocolbuffers/go plugin to generate Go-specific code for your .proto files and places its output in the gen directory.
• It executes the connectrpc/go plugin to generate client and server stubs for Connect-Go into the gen directory.

There are a few things to note in this configuration:

• Managed mode

  Managed mode is a configuration option that tells the Buf CLI to set all the file options in your workspace according to an opinionated set of values suitable for each of the supported Protobuf languages. The file options have long been a source of confusion and frustration for Protobuf users, so managed mode sets them on the fly per the configuration, allowing you to remove them from your .proto files.

• Remote plugins

  The plugins specified here are remote plugins hosted on the Buf Schema Registry. Using them removes the need to download, maintain, or run plugins on your local machine.

• Inputs

  The buf generate command can accept many types of input, such as Buf modules, GitHub repositories, and tarball/zip archives. The example code points to the proto subdirectory in the workspace.

Generate Go and Connect RPC stubs

Now that you have a buf.gen.yaml file configured, you can generate the Connect RPC and Go code associated with the PetStoreService API. Run this command:

$ buf generate

If successful, you'll notice a few new files in the gen directory—they're your generated code stubs:

getting-started-with-buf-cli
├── buf.gen.yaml
├── buf.yaml
├── gen
│   ├── google
│   │   └── type
│   │       └── datetime.pb.go
│   └── pet
│       └── v1
│           ├── pet.pb.go
│           └── petv1connect
│               └── pet.connect.go
└── proto
    ├── google
    │   └── type
    │       └── datetime.proto
    └── pet
        └── v1
            └── pet.proto

3. Lint your API

Though the Buf CLI is a great drop-in replacement for protoc, it's far more than a just a Protobuf compiler. It also provides linting functionality through the buf lint command. When you run buf lint, it checks all of the modules listed in the buf.yaml file against the specified set of lint rules.

Run this command to check all .proto files in the tour workspace for lint errors:

$ buf lint
Output
proto/google/type/datetime.proto:17:1:Package name "google.type" should be suffixed with a correctly formed version, such as "google.type.v1".
proto/pet/v1/pet.proto:42:10:Field name "petID" should be lower_snake_case, such as "pet_id".
proto/pet/v1/pet.proto:47:9:Service name "PetStore" should be suffixed with "Service".

The current pet store API has a few lint failures across both of its files. These failures break rules in the DEFAULT category that's configured in the buf.yaml file.

Fix lint failures

Start by fixing the lint failures for the pet/v1/pet.proto file, which stem from the FIELD_LOWER_SNAKE_CASE and SERVICE_SUFFIX rules. The results indicate exactly what you need to change to fix the errors, so update the pet.proto file:

syntax = "proto3";

package pet.v1;

...

message DeletePetRequest {
-  string petID = 1;
+  string pet_id = 1;
}

message DeletePetResponse {}

-service PetStore {
+service PetStoreService {
  rpc GetPet(GetPetRequest) returns (GetPetResponse) {}
  rpc PutPet(PutPetRequest) returns (PutPetResponse) {}
  rpc DeletePet(DeletePetRequest) returns (DeletePetResponse) {}
}

Run buf lint again to verify that two of the failures are resolved:

$ buf lint
Output
google/type/datetime.proto:17:1:Package name "google.type" should be suffixed with a correctly formed version, such as "google.type.v1".

Because you changed the name of the petID field and the service, you need to regenerate the code stubs:

$ buf generate

Ignore lint failures

The google/type/datetime.proto isn't actually a file in your local project. Instead, it's one of your dependencies, provided by googleapis, so you can't change its package declaration to fix the lint failure. Instead, you can tell the Buf CLI to ignore the google/type/datetime.proto file with this configuration change:

version: v2
modules:
  - path: proto
lint:
  use:
    - DEFAULT
+  ignore:
+    - proto/google/type/datetime.proto
breaking:
  use:
    - FILE

Run buf lint one final time and there should be no more errors.

For more info on lint rules and configuration, check out the lint documentation.

4. Detect breaking changes

The Buf CLI also enables you to detect breaking changes between different versions of your API. The buf breaking command checks all of the modules listed in the buf.yaml file against the specified set of breaking rules in comparison to a past version of your Protobuf schema. The rules are selectable and are split up into logical categories depending on the type of breaking changes you care about:

• FILE: Detects changes that move generated code between files, breaking generated source code on a per-file basis.
• PACKAGE: Detects changes that break generated source code changes on a per-package basis. It detects changes that would break the generated stubs, but only accounting for package-level changes.
• WIRE_JSON: Detects changes that break wire (binary) or JSON encoding. Because JSON is ubiquitous, we recommend this as the minimum level.
• WIRE: Detects changes that break wire (binary) encoding.

The default value is FILE, which we recommend to guarantee maximum compatibility across consumers of your APIs. We generally suggest choosing only one of these options rather than including/excluding specific breaking change rules, as you would when specifying a linting configuration. Your buf.yaml file currently has the FILE option configured:

version: v2
modules:
  - path: proto
lint:
  use:
    - DEFAULT
  ignore:
    - proto/google/type/datetime.proto
breaking:
  use:
    - FILE

Break your API

To see the feature in action, you'll need to introduce a breaking change. First, make a change that's breaking at the WIRE level. This is the most fundamental type of breaking change, as it changes how the Protobuf messages are encoded in transit ("on the wire"). This type of breaking change affects all users in all languages.

Change the type of the Pet.pet_type field from PetType to string:

 message Pet {
- PetType pet_type = 1;
+ string pet_type = 1;
  string pet_id = 2;
  string name = 3;
}

Run buf breaking

Now, verify that this is a breaking change by running buf breaking on your workspace, by choosing an input to compare it against. In this example, you'll compare against your local main Git branch:

# Compare against the 'proto' subdirectory in the Git repo because 'proto' is defined as the module in buf.yaml
$ buf breaking --against "../../.git#subdir=start/getting-started-with-buf-cli/proto"
Output
proto/pet/v1/pet.proto:1:1:Previously present service "PetStore" was deleted from file.
proto/pet/v1/pet.proto:18:3:Field "1" on message "Pet" changed type from "enum" to "string".
proto/pet/v1/pet.proto:42:3:Field "1" with name "pet_id" on message "DeletePetRequest" changed option "json_name" from "petID" to "petId".
proto/pet/v1/pet.proto:42:10:Field "1" on message "DeletePetRequest" changed name from "petID" to "pet_id".

Revert changes

Once you've determined that your change is breaking, revert it:

 message Pet {
- string pet_type = 1;
+ PetType pet_type = 1;
  string pet_id = 2;
  string name = 3;
}

The other changes you made to fix lint errors are also breaking changes and would normally need to be addressed. However, for the purpose of this tutorial assume they are approved and leave them in place.

5. Implement an API

In this section, you'll implement a PetStoreService client and server, both of which you can run on the command line.

Initialize a go.mod file

Before you write Go code, initialize a go.mod file with the go mod init command:

$ go mod init github.com/bufbuild/buf-tour

Similar to the buf.yaml file, the go.mod file tracks your code's Go dependencies.

Implement the server

Start implementing a server by creating a server/main.go file:

$ mkdir server
$ touch server/main.go

Copy and paste this content into that file:

package main

import (
  "context"
  "fmt"
  "log"
  "net/http"
  petv1 "github.com/bufbuild/buf-tour/gen/pet/v1"
  "github.com/bufbuild/buf-tour/gen/pet/v1/petv1connect"
  connect "connectrpc.com/connect"
  "golang.org/x/net/http2"
  "golang.org/x/net/http2/h2c"
)

const address = "localhost:8080"

func main() {
  mux := http.NewServeMux()
  path, handler := petv1connect.NewPetStoreServiceHandler(&petStoreServiceServer{})
  mux.Handle(path, handler)
  fmt.Println("... Listening on", address)
  http.ListenAndServe(
    address,
    // Use h2c so we can serve HTTP/2 without TLS.
    h2c.NewHandler(mux, &http2.Server{}),
  )
}

// petStoreServiceServer implements the PetStoreService API.
type petStoreServiceServer struct {
  petv1connect.UnimplementedPetStoreServiceHandler
}

// PutPet adds the pet associated with the given request into the PetStore.
func (s *petStoreServiceServer) PutPet(
  ctx context.Context,
  req *connect.Request[petv1.PutPetRequest],
) (*connect.Response[petv1.PutPetResponse], error) {
  name := req.Msg.GetName()
  petType := req.Msg.GetPetType()
  log.Printf("Got a request to create a %v named %s", petType, name)
  return connect.NewResponse(&petv1.PutPetResponse{}), nil
}

Resolve Go dependencies

Now that you have code for a server, run this command to resolve the dependencies you need to build the code:

$ go mod tidy

Call the API

With the server/main.go implementation shown above, run the server and call the PutPet endpoint from the buf CLI.

First, run the server:

$ go run server/main.go
Output
... Listening on 127.0.0.1:8080

In a separate terminal, in the workspace root, add a pet to the store by calling the API with buf curl:

$ buf curl \
  --schema . \
  --data '{"pet_type": "PET_TYPE_SNAKE", "name": "Ekans"}' \
  http://localhost:8080/pet.v1.PetStoreService/PutPet
Output
{}

Go back to the server terminal window, and a snake should have been added to the store:

2024/04/23 14:23:35 Got a request to create a PET_TYPE_SNAKE named Ekans

The Buf CLI is a powerful tool that streamlines the workflow for protocol buffer development. It provides a simple way to manage your .proto files, perform linting and breaking change detection, and generate code as a drop-in replacement for protoc. To see how you can more effectively work with Protobuf schemas in larger organizations, try the Buf Schema Registry tour next.

Related docs

• Learn about modules and workspaces in more detail.
• Read the buf.yaml and buf.gen.yaml configuration file reference pages.