Go driven rpc code generation tool for right now.

• 100% Go
• Describe services with Go interfaces (with structs, methods, comments, etc.)
• Generate server and client code
• Production ready templates (or copy and modify)

• Grafana Labs, IRM tool
• Pace.dev
• Firesearch.dev

These templates are already being used in production.

• There are some official Oto templates
• The Pace CLI tool is generated from an open-source CLI template

• VIDEO: Mat Ryer gives an overview of Oto at the Belfast Gophers meetup

• BLOG: How code generation wrote our API and CLI

Install the project:

go install github.com/pacedotdev/oto@latest

Create a project folder, and write your service definition as a Go interface:

// definitions/definitons.go
package definitions

// GreeterService makes nice greetings.
type GreeterService interface {
    // Greet makes a greeting.
    Greet(GreetRequest) GreetResponse
}

// GreetRequest is the request object for GreeterService.Greet.
type GreetRequest struct {
    // Name is the person to greet.
    // example: "Mat Ryer"
    Name string
}

// GreetResponse is the response object containing a
// person's greeting.
type GreetResponse struct {
    // Greeting is the greeting that was generated.
    // example: "Hello Mat Ryer"
    Greeting string
}

Download templates from otohttp

mkdir templates \
    && wget https://raw.githubusercontent.com/pacedotdev/oto/master/otohttp/templates/server.go.plush -q -O ./templates/server.go.plush \
    && wget https://raw.githubusercontent.com/pacedotdev/oto/master/otohttp/templates/client.js.plush -q -O ./templates/client.js.plush

Use the oto tool to generate a client and server:

mkdir generated
oto -template ./templates/server.go.plush \
    -out ./generated/oto.gen.go \
    -ignore Ignorer \
    -pkg generated \
    ./definitions
gofmt -w ./generated/oto.gen.go ./generated/oto.gen.go
oto -template ./templates/client.js.plush \
    -out ./generated/oto.gen.js \
    -ignore Ignorer \
    ./definitions

• Run oto -help for more information about these flags

Implement the service in Go:

// greeter_service.go
package main

// GreeterService makes nice greetings.
type GreeterService struct{}

// Greet makes a greeting.
func (GreeterService) Greet(ctx context.Context, r GreetRequest) (*GreetResponse, error) {
    resp := &GreetResponse{
        Greeting: "Hello " + r.Name,
    }
    return resp, nil
}

Use the generated Go code to write a main.go that exposes the server:

// main.go
package main

func main() {
    g := GreeterService{}
    server := otohttp.NewServer()
    server.Basepath = "/oto/"
    generated.RegisterGreeterService(server, g)
    http.Handle(server.Basepath, server)
    log.Fatal(http.ListenAndServe(":8080", nil))
}

• The otohttp.Server performs its own routing and so has a Basepath field which you should use when you route the handler.

Use the generated client to access the service in JavaScript:

import { GreeterService } from "oto.gen.js";

const greeterService = new GreeterService();

greeterService
  .greet({
    name: "Mat",
  })
  .then((response) => alert(response.greeting))
  .catch((e) => alert(e));

You can control the name of the field in JSON and in front-end code using json tags:

// Thing does something.
type Thing struct {
    SomeField string `json:"some_field"
}

• The SomeField field will appear as some_field in json and front-end code
• The name must be a valid JavaScript field name

You can provide strings to your templates via the -params flag:

oto \
    -template ./templates/server.go.plush \
    -out ./oto.gen.go \
    -params "key1:value1,key2:value2" \
    ./path/to/definition

Within your templates, you may access these strings with <%= params["key1"] %>.

It's possible to include additional metadata for services, methods, objects, and fields in the comments.

// Thing does something.
// field: "value"
type Thing struct {
    //...
}

The Metadata["field"] value will be the string value.

• The value must be valid JSON (for strings, use quotes)

Examples are officially supported, but all data is available via the Metadata map fields.

To provide an example value for a field, you may use the example: prefix line in a comment.

// GreetRequest is the request object for GreeterService.Greet.
type GreetRequest struct {
    // Name is the person to greet.
    // example: "Mat Ryer"
    Name string
}

• The example must be valid JSON

The example is extracted and made available via the Field.Example field.

### Open API

To work on the Open API spec, you might find this command helpful:

oto -template ./otohttp/templates/openapi.yaml.plush -out openapi.yaml -v -ignore Ignorer ./parser/testdata/services/pleasantries

Special thank you to:

• @mgutz - for struct tag support
• @sethcenterbar - for comment metadata support