Build bower_components with buck

Add support for downloading npm binaries including dependencies and running them in buck genrules. In npm land, transitive dependencies are generally included in the package distribution, and there are a *lot* of them. Since we aren't redistributing these binaries and they're only part of the build process, we don't have to worry too much about licensing, only that they don't have anything totally crazy. We assume packages have a certain format and we can detect the binary to run from the genrule output filename. Actually running the binary is tricky as well, since we have to extract it first. But it might be large, so we don't want to extract it on every invocation; and naive extraction to a common location (in buck-out) is racy. So we need a custom extractor scheme using atomic rename to make this work. Download bower as an npm package and use it to download bower packages. Bower packages can come from a variety of sources, usually git repositories, so we can't simply use download_file. There is additional logic in bower to read bower.json and strip out unneeded files, so I didn't want to get into reimplementing that. The tricky thing about bower is convincing it to avoid transitive dependencies so we can let Buck handle parallelism and caching. To do this, we need to read the package information from the upstream bower repository, and explicitly ignore all listed dependencies when downloading. We combine the flattened list of bower packages in a single bower_components rule. It would be nice to have deps of each bower_component so we didn't need to flatten these, but Buck genrules don't have deps so this is a nonstarter. Considering we only expect to have a single bower_components for the whole project, hopefully this is not too onerous. This change just gets us the bower_components directory. We still have some work to do to use this from Gerrit. Plus even more work to replace the gulpfile and actually package this stuff together into a compiled JS app for the war distribution. Change-Id: Id277d2d812ffcc3bce87ff00b5894bacdffc038e
2015-11-12 15:44:08 -05:00
parent 51b05629a1
commit ffe301570c
13 changed files with 545 additions and 14 deletions
--- a/Documentation/BUCK
+++ b/Documentation/BUCK
@@ -5,8 +5,9 @@ include_defs('//tools/git.defs')

 DOC_DIR = 'Documentation'

-JSUI = '//gerrit-gwtui:ui_module'
-MAIN = '//gerrit-pgm:pgm'
+JSUI_JAVA_DEPS = ['//gerrit-gwtui:ui_module']
+JSUI_NON_JAVA_DEPS = ['//polygerrit-ui:polygerrit_components']
+MAIN_JAVA_DEPS = ['//gerrit-pgm:pgm']
 SRCS = glob(['*.txt'], excludes = ['licenses.txt'])


@@ -34,7 +35,8 @@ genasciidoc(
 genlicenses(
  name = 'licenses.txt',
  opts = ['--asciidoc'],
-  java_deps = [MAIN, JSUI],
+  java_deps = JSUI_JAVA_DEPS + MAIN_JAVA_DEPS,
+  non_java_deps = JSUI_NON_JAVA_DEPS,
  out = 'licenses.txt',
 )

@@ -42,7 +44,8 @@ genlicenses(
 genlicenses(
  name = 'js_licenses.txt',
  opts = ['--partial'],
-  java_deps = [JSUI],
+  java_deps = JSUI_JAVA_DEPS,
+  non_java_deps = JSUI_NON_JAVA_DEPS,
  out = 'js_licenses.txt',
 )

--- a/Documentation/gen_licenses.py
+++ b/Documentation/gen_licenses.py
@@ -52,6 +52,13 @@ def parse_graph():
  obj = json.load(p.stdout)
  for target, attrs in obj.iteritems():
    for dep in attrs['buck.direct_dependencies']:
+
+      # bower is only used by the build process; skip it in those cases, even if
+      # --partial is not passed.
+      if ((target == '//tools/js:download_bower'
+           or target.startswith('//lib/js:')
+          and dep == '//lib/js:bower')):
+        continue
      if target in KNOWN_PROVIDED_DEPS:
        continue

--- a/lib/BUCK
+++ b/lib/BUCK
@@ -1,14 +1,12 @@
 include_defs('//lib/maven.defs')

+define_license(name = 'antlr')
 define_license(name = 'Apache1.1')
 define_license(name = 'Apache2.0')
-define_license(name = 'CC-BY3.0')
-define_license(name = 'MPL1.1')
-define_license(name = 'PublicDomain')
-define_license(name = 'antlr')
 define_license(name = 'args4j')
 define_license(name = 'automaton')
 define_license(name = 'bouncycastle')
+define_license(name = 'CC-BY3.0')
 define_license(name = 'clippy')
 define_license(name = 'codemirror')
 define_license(name = 'diffy')
@@ -17,12 +15,18 @@ define_license(name = 'freebie_application_icon_set')
 define_license(name = 'h2')
 define_license(name = 'jgit')
 define_license(name = 'jsch')
+define_license(name = 'MPL1.1')
 define_license(name = 'ow2')
+define_license(name = 'page.js')
+define_license(name = 'polymer')
 define_license(name = 'postgresql')
 define_license(name = 'prologcafe')
+define_license(name = 'promise-polyfill')
 define_license(name = 'protobuf')
+define_license(name = 'PublicDomain')
 define_license(name = 'slf4j')
 define_license(name = 'xz')
+
 define_license(name = 'DO_NOT_DISTRIBUTE')

 maven_jar(
--- a/lib/LICENSE-page.js
+++ b/lib/LICENSE-page.js
@@ -0,0 +1,20 @@
+(The MIT License)
+
+Copyright (c) 2012 TJ Holowaychuk <tj@vision-media.ca>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the 'Software'), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
--- a/lib/LICENSE-polymer
+++ b/lib/LICENSE-polymer
@@ -0,0 +1,27 @@
+Copyright (c) 2014 The Polymer Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
--- a/lib/LICENSE-promise-polyfill
+++ b/lib/LICENSE-promise-polyfill
@@ -0,0 +1,20 @@
+Copyright (c) 2014 Taylor Hakes
+Copyright (c) 2014 Forbes Lindesay
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
--- a/lib/js.defs
+++ b/lib/js.defs
@@ -0,0 +1,79 @@
+# Copyright (C) 2015 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+def npm_binary(
+    name,
+    version,
+    sha1 = '',
+    visibility = ['PUBLIC']):
+
+  dir = '%s-%s' % (name, version)
+  filename = '%s.tgz' % dir
+  dest = '%s@%s.npm_binary.tgz' % (name, version)
+  url = 'http://registry.npmjs.org/%s/-/%s' % (name, filename)
+  cmd = ['$(exe //tools:download_file)', '-o', '$OUT', '-u', url]
+  if sha1:
+    cmd.extend(['-v', sha1])
+  genrule(
+    name = name,
+    cmd = ' '.join(cmd),
+    out = dest,
+    license = 'DO_NOT_DISTRIBUTE',
+    visibility = visibility,
+  )
+
+
+def run_npm_binary(target):
+  return '$(location //tools/js:run_npm_binary) $(location %s)' % target
+
+
+def bower_component(
+    name,
+    package,
+    version,
+    license,
+    sha1 = '',
+    visibility = ['PUBLIC']):
+  genrule(
+    name = name,
+    cmd = ' '.join([
+      '$(exe //tools/js:download_bower)',
+      '-b', '"%s"' % run_npm_binary('//lib/js:bower'),
+      '-n', name,
+      '-p', package,
+      '-v', version,
+      '-s', sha1,
+      '-o', '$OUT',
+    ]),
+    out = '%s-%s.zip' % (name, version),
+    license = license,
+    visibility = visibility,
+  )
+
+
+def bower_components(
+    name,
+    deps,
+    visibility = ['PUBLIC']):
+  bc = '$TMP/bower_components'
+  cmds = ['mkdir %s' % bc, 'cd %s' % bc]
+  for dep in deps:
+    cmds.append('unzip $(location %s)' % dep)
+  cmds.extend(['cd $TMP', 'zip -r $OUT bower_components'])
+  genrule(
+    name = name,
+    cmd = ' && '.join(cmds),
+    out = '%s.bower_components.zip' % name,
+    visibility = visibility,
+  )
--- a/lib/js/BUCK
+++ b/lib/js/BUCK
@@ -0,0 +1,115 @@
+include_defs('//lib/js.defs')
+
+# WHEN REVIEWING NEW NPM_BINARY RULES:
+#
+# You must check licenses in the transitive closure of dependencies to ensure
+# they can be used by Gerrit. (npm binaries are not distributed with Gerrit
+# releases, so we are less restrictive in our selection of licenses, but we
+# still need to do a sanity check.)
+#
+# To do this:
+#   npm install -g license-checker
+#   mkdir /tmp/npmtmp
+#   cd /tmp/npmtmp
+#   npm install <package>@<version>
+#   license-checker
+# (Piping to grep -o 'licenses:.*' and/or sort -u may make the output saner.)
+
+npm_binary(
+  name = 'bower',
+  version = '1.6.5',
+  sha1 = '59d457122a161e42cc1625bbab8179c214b7ac11',
+)
+
+# bower_components are listed without transitive dependencies; the whole
+# flattened dependency tree needs to be included in
+# //polygerrit-ui:polygerrit_components.
+#
+# To print a full dependency tree with specific versions (i.e. not semantic
+# versions containing ~ or ^), use bower-dependency-tree:
+#   npm install -g bower-dependency-tree
+#   cd polygerrit-ui
+#   bower-dependency-tree --production
+#
+# Pull the name and package strings from the initial "Fetching" lines, and the
+# actual versions from the dependency tree output.
+
+bower_component(
+  name = 'iron-a11y-keys',
+  package = 'PolymerElements/iron-a11y-keys',
+  version = '1.0.3',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'iron-a11y-keys-behavior',
+  package = 'PolymerElements/iron-a11y-keys-behavior',
+  version = '1.0.8',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'iron-ajax',
+  package = 'PolymerElements/iron-ajax',
+  version = '1.0.8',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'iron-input',
+  package = 'PolymerElements/iron-input',
+  version = '1.0.6',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'iron-meta',
+  package = 'PolymerElements/iron-meta',
+  version = '1.1.1',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'iron-validatable-behavior',
+  package = 'PolymerElements/iron-validatable-behavior',
+  version = '1.0.5',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'page',
+  package = 'visionmedia/page.js',
+  version = '1.6.4',
+  license = 'page.js',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'polymer',
+  package = 'Polymer/polymer',
+  version = '1.2.1',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'promise-polyfill',
+  package = 'polymerlabs/promise-polyfill',
+  version = '1.0.0',
+  license = 'promise-polyfill',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
+
+bower_component(
+  name = 'webcomponentsjs',
+  package = 'webcomponentsjs',
+  version = '0.7.16',
+  license = 'polymer',
+  sha1 = 'da39a3ee5e6b4b0d3255bfef95601890afd80709',
+)
--- a/polygerrit-ui/BUCK
+++ b/polygerrit-ui/BUCK
@@ -0,0 +1,17 @@
+include_defs('//lib/js.defs')
+
+bower_components(
+  name = 'polygerrit_components',
+  deps = [
+      '//lib/js:iron-a11y-keys',
+      '//lib/js:iron-a11y-keys-behavior',
+      '//lib/js:iron-ajax',
+      '//lib/js:iron-input',
+      '//lib/js:iron-meta',
+      '//lib/js:iron-validatable-behavior',
+      '//lib/js:page',
+      '//lib/js:polymer',
+      '//lib/js:promise-polyfill',
+      '//lib/js:webcomponentsjs',
+  ],
+)
--- a/polygerrit-ui/bower.json
+++ b/polygerrit-ui/bower.json
@@ -1,21 +1,18 @@
 {
  "name": "polygerrit",
  "version": "0.0.0",
-  "authors": [
-    "Andrew Bonventre <andybons@google.com>"
-  ],
-  "description": "Gerrit UI in Polymer",
+  "description": "Gerrit UI in Polymer; DO NOT PUBLISH, used only for dependency management",
  "private": true,
  "dependencies": {
    "polymer": "Polymer/polymer#^1.1",
    "page": "visionmedia/page.js#~1.6",
    "iron-ajax": "PolymerElements/iron-ajax#~1.0",
    "iron-a11y-keys": "PolymerElements/iron-a11y-keys#~1.0",
-    "iron-input": "PolymerElements/iron-input#~1.0",
-    "iron-test-helpers": "PolymerElements/iron-test-helpers#~1.0"
+    "iron-input": "PolymerElements/iron-input#~1.0"
  },
  "devDependencies": {
    "web-component-tester": "*",
+    "iron-test-helpers": "PolymerElements/iron-test-helpers#~1.0",
    "test-fixture": "PolymerElements/test-fixture#^1.0.0"
  }
 }
--- a/tools/js/BUCK
+++ b/tools/js/BUCK
@@ -0,0 +1,11 @@
+python_binary(
+  name = 'download_bower',
+  main = 'download_bower.py',
+  visibility = ['PUBLIC'],
+)
+
+python_binary(
+  name = 'run_npm_binary',
+  main = 'run_npm_binary.py',
+  visibility = ['PUBLIC'],
+)
--- a/tools/js/download_bower.py
+++ b/tools/js/download_bower.py
@@ -0,0 +1,140 @@
+#!/usr/bin/env python
+# Copyright (C) 2015 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import hashlib
+import json
+import optparse
+import os
+import shutil
+import subprocess
+import sys
+
+CACHE_DIR = os.path.expanduser(os.path.join(
+    '~', '.gerritcodereview', 'buck-cache', 'downloaded-artifacts'))
+
+
+def hash_file(h, p):
+  with open(p, 'rb') as f:
+    while True:
+      b = f.read(8192)
+      if not b:
+        break
+      h.update(p)
+
+
+def hash_dir(dir):
+  # It's hard to get zipfiles to hash deterministically. Instead, do a sorted
+  # walk and hash filenames and contents together.
+  h = hashlib.sha1()
+
+  for root, dirs, files in os.walk(dir):
+    dirs.sort()
+    for f in sorted(files):
+      p = os.path.join(root, f)
+      h.update(p)
+      hash_file(h, p)
+
+  return h.hexdigest()
+
+
+def bower_cmd(bower, *args):
+  cmd = bower.split(' ')
+  cmd.extend(args)
+  return cmd
+
+
+def bower_info(bower, name, package, version):
+  cmd = bower_cmd(bower, '-l=error', '-j',
+                  'info', '%s#%s' % (package, version))
+  p = subprocess.Popen(cmd , stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+  out, err = p.communicate()
+  if p.returncode:
+    sys.stderr.write(err)
+    raise OSError('Command failed: %s' % cmd)
+
+  try:
+    info = json.loads(out)
+  except ValueError:
+    raise ValueError('invalid JSON from %s:\n%s' % (cmd, out))
+  info_name = info.get('name')
+  if info_name != name:
+    raise ValueError('expected package name %s, got: %s' % (name, info_name))
+  return info
+
+
+def ignore_deps(info):
+  # Tell bower to ignore dependencies so we just download this component. This
+  # is just an optimization, since we only pick out the component we need, but
+  # it's important when downloading sizable dependency trees.
+  #
+  # As of 1.6.5 I don't think ignoredDependencies can be specified on the
+  # command line with --config, so we have to create .bowerrc.
+  deps = info.get('dependencies')
+  if deps:
+    with open(os.path.join('.bowerrc'), 'w') as f:
+      json.dump({'ignoredDependencies': deps.keys()}, f)
+
+
+def cache_entry(name, version, sha1):
+  c = os.path.join(CACHE_DIR, '%s-%s.zip' % (name, version))
+  if sha1:
+    c += '-%s' % sha1
+  return c
+
+
+def main(args):
+  opts = optparse.OptionParser()
+  opts.add_option('-n', help='short name of component')
+  opts.add_option('-b', help='bower command')
+  opts.add_option('-p', help='full package name of component')
+  opts.add_option('-v', help='version number')
+  opts.add_option('-s', help='expected content sha1')
+  opts.add_option('-o', help='output file location')
+  opts, _ = opts.parse_args()
+
+  outzip = os.path.join(os.getcwd(), opts.o)
+  # TODO(dborowitz): match download_file behavior of pulling any old file from
+  # the cache if there is no -s
+  # Also don't double-append sha1.
+  cached = cache_entry(opts.n, opts.v, opts.s)
+  if os.path.isfile(cached):
+    shutil.copyfile(cached, outzip)
+    return 0
+
+  info = bower_info(opts.b, opts.n, opts.p, opts.v)
+  ignore_deps(info)
+  subprocess.check_call(
+      bower_cmd(opts.b, '--quiet', 'install', '%s#%s' % (opts.p, opts.v)))
+  name = info['name']
+  sha1 = hash_dir(name)
+
+  if opts.s and sha1 != opts.s:
+    print((
+      '%s#%s:\n'
+      'expected %s\n'
+      'received %s\n') % (opts.p, opts.v, opts.s, sha1), file=sys.stderr)
+    return 1
+
+  os.chdir('bower_components')
+  cmd = ['zip', '-q', '-r', outzip, opts.n]
+  subprocess.check_call(cmd)
+  shutil.copyfile(outzip, cache_entry(opts.n, opts.v, sha1))
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))
--- a/tools/js/run_npm_binary.py
+++ b/tools/js/run_npm_binary.py
@@ -0,0 +1,91 @@
+#!/usr/bin/env python
+# Copyright (C) 2015 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import atexit
+import hashlib
+import os
+import shutil
+import sys
+import tarfile
+import tempfile
+
+
+def hash_file(p):
+  d = hashlib.sha1()
+  with open(p, 'rb') as f:
+    while True:
+      b = f.read(8192)
+      if not b:
+        break
+      d.update(b)
+  return d.hexdigest()
+
+
+def extract(path, outdir, bin):
+  if os.path.exists(os.path.join(outdir, bin)):
+    return # Another process finished extracting, ignore.
+
+  # Use a temp directory adjacent to outdir so shutil.move can use the same
+  # device atomically.
+  tmpdir = tempfile.mkdtemp(dir=os.path.dirname(outdir))
+  def cleanup():
+    try:
+      shutil.rmtree(tmpdir)
+    except OSError:
+      pass # Too late now
+  atexit.register(cleanup)
+
+  def extract_one(mem):
+    dest = os.path.join(outdir, mem.name)
+    tar.extract(mem, path=tmpdir)
+    try:
+      os.makedirs(os.path.dirname(dest))
+    except OSError:
+      pass # Either exists, or will fail on the next line.
+    shutil.move(os.path.join(tmpdir, mem.name), dest)
+
+  with tarfile.open(path, 'r:gz') as tar:
+    for mem in tar.getmembers():
+      if mem.name != bin:
+        extract_one(mem)
+    # Extract bin last so other processes only short circuit when extraction is
+    # finished.
+    extract_one(tar.getmember(bin))
+
+
+def main(args):
+  path = args[0]
+  suffix = '.npm_binary.tgz'
+  tgz = os.path.basename(path)
+  parts = tgz[:-len(suffix)].split('@')
+
+  if not tgz.endswith(suffix) or len(parts) != 2:
+    print('usage: %s <path/to/npm_binary>' % sys.argv[0], file=sys.stderr)
+    return 1
+
+  name, version = parts
+  outdir = '%s-%s' % (path[:-len(suffix)], hash_file(path))
+  rel_bin = os.path.join('package', 'bin', name)
+  bin = os.path.join(outdir, rel_bin)
+  if not os.path.isfile(bin):
+    extract(path, outdir, rel_bin)
+
+  os.execv(bin, args[1:])
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))