Getting Started with 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.

By the end of this Getting Started guide you will have a strong understanding of the core components of the Buf CLI, including:

• Buf Modules and how to create & configure them
• Plugins and how to use them to generate code
• How to use the Buf CLI to lint & format your API schemas
• Detect and prevent breaking changes in your APIs

Before you begin

Let's check the version of buf you'll be using is up-to-date.

$ buf --version
Output
1.15.1

Clone the Git repository

First, clone the Git repository that contains the starter code for the PetStore service. From the development directory of your choice, run this command:

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

You'll notice that the repository contains a start directory and a finish directory. During this guide 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 buf 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

1.1. Configure buf

buf is configured with a buf.yaml file, create your own with this command:

$ cd proto
$ buf mod init

After you run this command, you'll notice a buf.yaml in the current directory with the following content:

version: v1
breaking:
  use:
    - FILE
lint:
  use:
    - DEFAULT

buf assumes there is a buf.yaml in your current directory by default, or uses a default value in lieu of a buf.yaml file. We recommend always having a buf.yaml file at the root of your .proto files hierarchy, as this is how .proto import paths are resolved.

Before we continue, let's verify that everything is set up properly, and we can build our module. If there are no errors, we know that we've set up a buf module correctly:

$ buf build
$ echo $?
Output
0

2. Generate Code

buf 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.

Move back to the getting-started-with-buf-cli directory with this command:

$ cd ..
$ ls
Output
proto

2.1. Configure a buf.gen.yaml

Previously you created a buf.yaml in the proto directory this denotes the root of the buf module. A module is a collection of Protobuf files that are configured, built, and versioned as a logical unit. By moving away from individual .proto files, the module simplifies file discovery. Now, we will create a buf.gen.yaml.

The buf.gen.yaml file controls how the buf generate command executes protoc plugins on a given module. With a buf.gen.yaml, you can configure where each protoc plugin writes its result and specify options for each plugin.

Create a buf.gen.yaml file in the getting-started-with-buf-cli directory:

$ touch buf.gen.yaml
$ ls
Output
buf.gen.yaml
proto

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

version: v1
managed:
  enabled: true
  go_package_prefix:
    default: github.com/bufbuild/buf-tour/gen
plugins:
  - plugin: buf.build/protocolbuffers/go
    out: gen
    opt: paths=source_relative
  - plugin: buf.build/bufbuild/connect-go
    out: gen
    opt: paths=source_relative

Given this config, buf 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 bufbuild/connect-go plugin to generates client and server stubs for connect-go. Compatible with the gRPC, gRPC-Web, and Connect RPC protocols into the gen directory.

Connect is an RPC protocol which supports gRPC — including streaming! They interoperate seamlessly with Envoy, grpcurl, gRPC Gateway, and every other gRPC implementation. Connect servers handle gRPC-Web requests natively, without a translating proxy. Learn more here.

2.2. Generate Go and Connect stubs

Now that you have a buf.gen.yaml with the plugins configured, you can generate the Connect and Go code associated with thePetStoreService API.

Run this command, targeting the input defined in the proto directory:

$ buf generate proto
---

If successful, you'll notice a few new files in the gen directory (as configured by the buf.gen.yaml created above):

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

That's how easy it is to generate code using buf. There's no need to build up a set of complicated protoc commands; your configuration is contained within the buf.gen.yaml. Don't stop here though, we are just getting started!

3. Lint Your API

Whilst buf is a great, simplified, drop-in replacement of protoc it's far more than a just a Protobuf compiler. The buf CLI provides linting functionality through the buf lint command. When you run buf lint, buf runs a set of lint rules across all the Protobuf files covered by a buf.yaml configuration file.

Run all the configured lint rules by running this command:

$ buf lint proto
Output
google/type/datetime.proto:17:1:Package name "google.type" should be suffixed with a correctly formed version, such as "google.type.v1".
pet/v1/pet.proto:44:10:Field name "petID" should be lower_snake_case, such as "pet_id".
pet/v1/pet.proto:49:9:Service name "PetStore" should be suffixed with "Service".

As you can see, the current pet store API has a few lint failures across both of its files. These failures belong to the DEFAULT lint category configured in the buf.yaml:

version: v1
breaking:
  use:
    - FILE
lint:
  use:
    - DEFAULT

3.1. 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. buf indicates exactly what you need to change to fix the errors, so you can fix the failures with these updates:

Take a look at the full set of lint rules here.

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) {}
}

Verify that two of the failures are resolved by linting again and seeing only one remaining error:

$ 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".

3.2. 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 satisfy buf's lint requirements. ignore the google/type/datetime.proto file from buf lint like with this config update:

 version: v1
 breaking:
   use:
     - FILE
 lint:
   use:
     - DEFAULT
+  ignore:
+    - google/type/datetime.proto

$ buf lint proto --error-format=config-ignore-yaml
Output
version: v1
lint:
  ignore_only:
    PACKAGE_DIRECTORY_MATCH:
      - proto/pet/v1/pet.proto
    SERVICE_SUFFIX:
      - proto/pet/v1/pet.proto

4. Detect breaking changes

Detect breaking changes between different versions of your API. buf breaking runs a set of breaking rules across the current version of your entire Protobuf schema in comparison to a past version of your Protobuf schema. The rules are selectable, and split up into logical categories depending on the nature of breaking changes you care about:

• FILE: Generated source code breaking changes on a per-file basis, that is changes that would break the generated stubs where definitions cannot be moved across files.
• PACKAGE: Generated source code breaking changes on a per-package basis, that is changes that would break the generated stubs, but only accounting for package-level changes.
• WIRE: Wire breaking changes, that is changes that would break wire compatibility, including checks to make sure you reserve deleted types of which re-use in the future could cause wire incompatibilities.
• WIRE_JSON: Wire breaking changes and JSON breaking changes, that is changes that would break either wire compatibility or JSON compatibility.

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: v1
breaking:
  use:
    - FILE
lint:
  use:
    - DEFAULT
  ignore:
    - google/type/datetime.proto

4.1. Break Your API

Next, 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.

For example, 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;
}

4.2. Run buf breaking

Now, verify that this is a breaking change against the local main branch. You'll also notice errors related to the changes you made in the previous step:

$ buf breaking proto --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:35:3:Field "1" on message "PutPetRequest" changed type from "enum" to "string".
proto/pet/v1/pet.proto:44:3:Field "1" with name "pet_id" on message "DeletePetRequest" changed option "json_name" from "petID" to "petId".
proto/pet/v1/pet.proto:44:10:Field "1" on message "DeletePetRequest" changed name from "petID" to "pet_id".

You can run buf breaking on your module by specifying the filepath to the directory containing the buf.yaml and choosing an input to compare it against. In the above example, you can target the input defined in the current directory and compare it against the remote in the same subdirectory.

4.3. 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;
}

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.

5.1. Initialize a go.mod

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 config file, the go.mod file tracks your code's Go dependencies.

5.2. 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"
	"github.com/bufbuild/connect-go"
	"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
}

5.3. 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

5.4. Call PutPet

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

First, run the server:

... Listening on 127.0.0.1:8080

In a separate terminal, in the root working directory, hit the API with a buf curl command:

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

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 formatting, and generate code as a drop in replacement for protoc. We hope that this tutorial has helped you understand the benefits of using the Buf CLI and how to use it effectively in your own projects.

Find out more about building with Buf:

• Getting Started with the Buf Schema Registry