[sample] Added samples/bootload

samples/bootload/.gitignore

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+script/
+script.bak/

samples/bootload/README.md

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+## Bootloader and Auto-updater
+
+This sample demonstrates a simple script bootloader that is able to check remote codebase updates, download updates and restart script automatically. Downloaded script is kept locally so that the program can still start up successfully after a download failure.
+
+## Usage
+
+To start the bootloader, type:
+
+```sh
+pipy bootload/main.js --args http://pipy-repo-address:6060/repo/my-codebase/
+```
+
+Or, if `pipy` can be found in the current `$PATH`, you can execute it just by:
+
+```sh
+bootload/main.js http://pipy-repo-address:6060/repo/my-codebase/
+```
+
+Downloaded script will be saved in the current directory. If a different directory is preferred, add a second argument to the command:
+
+```sh
+bootload/main.js http://pipy-repo-address:6060/repo/my-codebase/ /path/to/local/backup/folder
+```

samples/bootload/main.js

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+#!/usr/bin/env -S pipy --args
+
+var UPDATE_CHECK_INTERVAL = 5
+var CHECK_POINT_INTERVAL = 30
+var PIPY_OPTIONS = ['--no-graph']
+
+var url = pipy.argv[1]
+var rootDir = os.path.resolve(pipy.argv[2] || '')
+
+if (!url) {
+  println('missing a codebase URL')
+  return pipy.exit(-1)
+}
+
+if (!url.startsWith('http://')) {
+  println('invalid codebase URL', url)
+  return pipy.exit(-1)
+}
+
+if (!dirExists(rootDir)) {
+  println('local directory not found:', rootDir)
+  return pipy.exit(-1)
+}
+
+url = new URL(url)
+
+var client = new http.Agent(url.host)
+var currentEtag = undefined
+var currentDate = undefined
+var currentPID = 0
+
+function backup() {
+  if (!dirExists(os.path.join(rootDir, 'script.bak'))) {
+    if (dirExists(os.path.join(rootDir, 'script'))) {
+      os.rename(
+        os.path.join(rootDir, 'script'),
+        os.path.join(rootDir, 'script.bak')
+      )
+    }
+  }
+}
+
+function restore() {
+  if (dirExists(os.path.join(rootDir, 'script.bak'))) {
+    os.rmdir(os.path.join(rootDir, 'script'), { recursive: true, force: true })
+    os.rename(
+      os.path.join(rootDir, 'script.bak'),
+      os.path.join(rootDir, 'script')
+    )
+  }
+}
+
+function checkPoint() {
+  os.rmdir(os.path.join(rootDir, 'script.bak'), { recursive: true, force: true })
+}
+
+function fileExists(pathname) {
+  var s = os.stat(pathname)
+  return s && s.isFile()
+}
+
+function dirExists(pathname) {
+  var s = os.stat(pathname)
+  return s && s.isDirectory()
+}
+
+function update() {
+  new Timeout(UPDATE_CHECK_INTERVAL).wait().then(() => {
+    client.request('GET', url.path).then(res => {
+      var status = res?.head?.status
+      if (status !== 200) {
+        console.error(`Download ${url.href} -> ${status}`)
+        return update()
+      }
+      var headers = res.head.headers
+      var etag = headers['etag'] || ''
+      var date = headers['date'] || ''
+      if (etag === currentEtag && date === currentDate) return update()
+      console.info(`Codebase changed: etag = '${etag}', date = '${date}'`)
+      backup()
+      return Promise.all(
+        res.body.toString().split('\n').map(
+          path => client.request('GET', os.path.join(url.path, path)).then(
+            res => {
+              var status = res?.head?.status
+              console.info(`Download ${path} -> ${res.head.status}`)
+              return (status === 200 ? [path, res.body] : [path, null])
+            }
+          )
+        )
+      ).then(files => {
+        var base = os.path.join(rootDir, 'script')
+        var failures = false
+        files.forEach(([path, data]) => {
+          if (!data) return (failures = true)
+          var fullpath = os.path.join(base, path)
+          var dirname = os.path.dirname(fullpath)
+          os.mkdir(dirname, { recursive: true })
+          os.write(fullpath, data)
+        })
+        if (failures) {
+          console.error(`Update failed due to download failure`)
+          restore()
+          update()
+        } else {
+          console.info(`Update downloaded`)
+          currentEtag = etag
+          currentDate = date
+          start()
+          new Timeout(CHECK_POINT_INTERVAL).wait().then(() => {
+            checkPoint()
+            update()
+          })
+        }
+      })
+    })
+  })
+}
+
+function start() {
+  if (currentPID === 0) {
+    var pathPipy = pipy.argv[0]
+    var pathMain = os.path.join(rootDir, 'script/main.js')
+    if (fileExists(pathMain)) {
+      var command = [pathPipy, ...PIPY_OPTIONS, pathMain]
+      console.info('Starting', command)
+      pipeline($=>$
+        .onStart(new Data)
+        .exec(command, {
+          stderr: true,
+          onStart: pid => {
+            currentPID = pid
+            console.info('Started PID =', pid)
+          },
+          onExit: () => {
+            console.info('Process exited PID =', currentPID)
+            currentPID = 0
+          },
+        })
+        .tee('-')
+      ).spawn()
+    }
+  } else {
+    os.kill(currentPID, 1)
+  }
+}
+
+restore()
+start()
+update()