options-gen

Codegen for functional options in go projects

Programming language: Go

License: MIT License

Tags: Go Generate Tools    

README

options-gen

Generate the options for your service/client/etc. All that you need is to define a struct with fields, that can be applied as Option then embed this struct into yours.

Installation

go install github.com/kazhuravlev/options-gen/cmd/options-gen

Usage

package mypkg

import (
  "io"
  "log"
)

//go:generate options-gen -out-filename=options_generated.go -from-struct=Options
type Options struct {
  logger     log.Logger `option:"mandatory"`
  listenAddr string     `option:"mandatory" validate:"required,hostname_port"`
  closer     io.Closer  `validate:"required"`
}

go generate ./...

This will generate out-filename file with options constructor. Like this:

// options_generated.go
package mypkg

import (
  "log"
)

func NewOptions( 
  // mandatory options. you cannot ignore or forget them because they are arguments.
  logger log.Logger, 
  listenAddr string,
  // optional: you can leave them empty or not.
  other ...Option,
) {
  ...
}

// Validate will check that all options are in desired state
func (o *Options) Validate() error {
  ...
}

And you can use generated options as follows:

package mypkg

import "fmt"

type Component struct {
  opts Options // struct that you define as struct with options 
}

func New(opts Options) (*Component, error) { // constructor of your service/client/component
  if err := opts.Validate(); err != nil {  // always add only these lines for all your constructors
    return nil, fmt.Errorf("cannot validate options: %w", err)
  }

  return &Component{opts: opts}, nil // embed options into your component
}

And after that you can use new constructor in (for ex.) main.go:

package main

func main() {
  c, err := mypkg.New(mypkg.NewOptions( /* ... */))
  if err != nil {
    panic(err)
  }
}

Examples

See an [examples](./examples) to get real-world examples.

Configuration

To configure this tool you should know two things: how to work with cli tool and how to define options in your Options struct.

CLI tool

All the tool needs is the information about source and target files and packages. Tool can be invoked by options-gen (after Installation) and it will have the following arguments:

• filename - is a source filename that contains Options struct relative to the current dir. For example ./pkg/github-client/options.go. Default: $GOFILE (file where you placed //go:generate).
• pkg - name of output filename package. In most cases we can just use the same package as the filename file. For example githubclient. Default: $GOPACKAGE. Package name same as file where you placed //go:generate.
• from-struct - name of structure that contains our options. For example Options.
• out-filename - specifies an output filename. This filename will be rewritten with options-gen specific content. For example ./pkg/github-client/options_generated.go.

See an Examples.

Option tag

You can control two important things. The first is about the options constructor

• how options-gen will generate NewOptions constructor. The second is about how to validate data, that has been passed as value for this field.

Control the constructor

options-gen can generate a constructor that can receive all option fields as separate arguments. It will force the user to pass each (or someone) option field to the constructor. Like this:

// Mark Field1 as mandatory
type Options struct {
  Field1 string `option:"mandatory"`
}

// options-gen will generate constructor like this
func NewOptions(field1 string, otherOptions ...option)...

But, if we do not want to force the user to pass each argument - we can remove the option:"mandatory" feature for this field and get something like this:

// Do not mark Field1 as mandatory
type Options struct {
  Field1 string
}

// options-gen will generate constructor like this
func NewOptions(otherOptions ...option)...

So, this allows setting only those options fields that user is want to set.

Validate field data

After we define the fields, we want to restrict the values of these fields. To do that we can use a well-known library validator

Just read the docs for validator library and add tag to fields like this:

type Options struct {
  maxDbConn int `validate:"required,min=1,max=16"`
}

Contributing

The development process is pretty simple:

• Fork the repo on GitHub
• Clone your copy of the repo
• Create a new branch for your goals
• Install the Task. It's like Make, but simple
• Check that your working copy is ready to start development by running task check in repo workdir
• Reach your goals!
• Check that all is ok by task check
• Create a Pull Request