rebuild-aio

Watch, rebuild, bundle, all-in-one

Usage

Usage:
    rebuild \ 
    --watch <glob> \ 
    [--transform <glob>] \ 
    [--using <file.js>] \
    --output <dir> \
    [--fork <string>] \
    [--spawn <string>] \ 
    [--kill <number>] \
    [--wait <number>] \
    [--debug]
    
Example:
    rebuild --watch src --transform 'src/*/src/**/*.{js,mjs}' --transform 'src/web/node_modules/**/*.{js,mjs}' --using transformer.js --output build --fork server.js -k 3000 --wait 500

Options:
    --watch -w        A glob. All watched files go to the output, but some are transformed along the way. At least one required.
    --transform -t    Files matching this glob are passed through the transformer. Multiple allowed.
    --using -u        The transformer. A JS file. Default: `default export async (inputPath, outputPath, contents) => {return contents}`. Optional.
    --output -o       The output directory. Required.
    --fork -f         The restart command. Optional. If omitted, then rebuild will exit after the first build.
    --spawn -s        The restart command. Optional. If omitted, no rebuilding or monitoring happens.
    --cleanup -c      A JS file. Signature: `default export async (child, spawnerType, signal) => {}`. Optional.
    --kill -k         A port to kill on ctrl+c. Optional. Multiple allowed.
    --wait            How long to wait on file changes and termination before forcefully stopping the process. Default is 3000.
    --debug -d        Log statements about node_modules are excluded by default.

Overview

1. Visit all files in watch tree.
2. For each file, if it matches the --transform glob, then pass it through the transformer specified using --using.
3. Pass the transformed (or original if no transform was performed) file to the --output dir.
4. If --fork or --spawn are defined, run the command. Changes are watched, passed through the transform again, and the exec command re-executed.
   1. While running as a change watcher, ctrl+c interrupt will cause the ports listed by --kill to be killed. Port killing does not happen on change restarts.
   2. While running as a change watcher, the optional function passed by --cleanup is awaited. This provides a way to implement custom restart logic. For example, you might want to utilize the fork's IPC connection to send a message using childProcess.send(), allowing the server to gracefully handle restarts.
5. If --fork or --spawn are not defined, then stop after the initial build instead of watching and rebuilding.

--transform --using

This package supports a customizable transform step during the build process. Here is an example transformer:

// transformer.js
import flowRemoveTypes from "flow-remove-types"
import convertJsx from "jsx-to-hyperscript"
import {transformImports} from "web-imports"
import fs from "fs"
import path from "path"

const clientPath = path.resolve('src/web')

function isUnder(filepath, dir) {
  return filepath.startsWith(dir)
}

// filepath and outputPath are absolute paths.
export default async function transform(filepath, outputPath, contents) {
  const filename = path.relative(path.resolve(outputPath, "../"), outputPath)

  // Remove type annotations, and possibly generate sourcemaps:
  const flowOut = flowRemoveTypes(contents)
  const flowConverted = flowOut.toString()
  const flowMap = flowOut.generateMap()
  fs.writeFileSync(
    path.resolve(outputPath, "../", `${filename}.map`),
    JSON.stringify(flowMap),
    { encoding: "utf-8" },
  )

  // Transform JSX:
  const jsxConverted = convertJsx(flowConverted)

  // Transform import statements in client:
  if (isUnder(filepath, clientPath)) {
    const importsConverted = await transformImports(jsxConverted, filepath)
    return importsConverted
  } else {
    return jsxConverted
  }
}

--fork, --spawn, --exec

--fork causes the child process to be created using fork. This is useful for implementing graceful restarts.

The argument passed to --fork must be an ES module, I.E. a JS file. It cannot run CLI commands directly.

--spawn causes the child process to be created using spawn, but restarts terminate the process abruptly.

--exec uses execSync to run the specified command. This is useful for running CLI commands directly on restarts.

SIGTERM

When using --spawn, restarts use child.kill(), which sends SIGTERM in non-Windows environments. In all environments, using child.kill(), the child process is ended abruptly, and on Linux, any of their subprocesses will not be terminated.

Because of these issues, it is recommended to use --fork and to implement a SIGRES handler in your code.

SIGRES

SIGRES is sent during a restart. It is used for implementing graceful restarting.

A handler for it should be placed at the beginning of the script forked by --fork.

// forked_process.js
process.on('message', (m) => {
  if (m === 'SIGRES') {
    process.exit() // must exit eventually.
  }
})

Note that SIGRES is made up, and it not a POSIX signal.

SIGINT

The built-in POSIX signal SIGINT can be handled like this:

process.on('SIGINT', () => {
  process.exit() // must exit eventually.
})

--kill

--kill is used to kill processes behind ports on ctrl+c, but not on restarts.

If you need to kill ports on restarts, use a custom --cleanup function.

--cleanup

Similar to --transform, this is a JS file which has a default export.

Cleanup is called on ctrl+c interrupts and restarts.

The cleanup(child, spawnerType, signal) function takes in the child which is a child process obtained from spawn or fork, and a signal whose value is either SIGINT or SIGRES.

The function should either send a kill signal to the child and wait for it to exit itself, or abruptly kill the process using child.kill().

You can send a kill signal to the child, with cross-platform support, using --fork and child.send('SIGRES'). This will cause the child to be a forked process, which allows messages between the parent and child to be passed using IPC.

This is the default cleanup function:

// cleanup.js
// import {kill} from "cross-port-killer"

async (child, spawnerType, signal) => {
   if (signal === 'SIGINT') {
      child.kill('SIGINT') // child is expected to exit on its own
   } else {
      // SIGRES signal handling:
      if (spawnerType === 'spawn') {
         // await kill(4000)
         child.kill()
      } else if (spawnerType === 'fork') {
         child.send('SIGRES') // child is expected to exit on its own
      }
   }
}

Pause and Resume Forking

If you have multiple --fork commands, by default, they will be forked in order with minimal delay between them. This can be problematic if one child process depends on another to have completed startup.

A service can tell the monitor to pause and resume forking. This is done using these IPC messages:

• process.send({pauseForking: true}) - To be placed at the beginning of your startup script.
• process.send({resumeForking: true}) - To be placed at the end of your startup script.

Here is an example:

process.send({
  pauseForking: true // Tell rebuild-aio to pause forking.
})

import {start, stop} from './localMysqlServer.js'
const port = 3306

process.on('message', async (m) => {
  if (m === 'SIGRES') {
    await stop(port)
    process.exit() // must exit eventually.
  }
})

await start(port)

process.send({
  resumeForking: true // Tell rebuild-aio to resume forking after mysql has started.
})

By default, for each child, the monitor will wait 500 ms or for a resumeForking message, whichever comes first, before continuing. A child can send resumeForking at the beginning of its script, without ever sending pauseForking, in order to speed up restart times.

Useful Globs

• projects/*/!(node_modules)/**/*.{js,mjs} - If you have a monorepo where all subprojects are siblings in a folder, you can select all files which are not in any subproject's node_modules using this glob.
• projects/*/{!(node_modules),node_modules/common}/**/*.{js,mjs} - If you have a common project in your monorepo which is included in your other projects using "common": "file:../common", then common will be placed in the node_modules folder of your other projects, so to include it in transforms, use this glob.