add a wasm bazel toolchain (#603)

bazel/emscripten_toolchain/wasm_binary.py

@@ -0,0 +1,84 @@
+"""Unpackages a bazel emscripten archive for use in a bazel BUILD rule.
+
+This script will take a tar archive containing the output of the emscripten
+toolchain. This file contains any output files produced by a wasm_cc_binary or a
+cc_binary built with --config=wasm. The files are extracted into the given
+output path.
+
+The name of archive is expected to be of the format `foo` or `foo.XXX` and
+the contents are expected to be foo.js and foo.wasm.
+
+Several optional files may also be in the archive, including but not limited to
+foo.js.mem, pthread-main.js, and foo.wasm.map.
+
+If the file is not a tar archive, the passed file will simply be copied to its
+destination.
+
+This script and its accompanying Bazel rule should allow you to extract a
+WebAssembly binary into a larger web application.
+"""
+
+import os
+import subprocess
+import sys
+
+from absl import app
+from absl import flags
+
+FLAGS = flags.FLAGS
+flags.DEFINE_string('archive', None, 'The the archive to extract from.')
+flags.DEFINE_string('output_path', None, 'The path to extract into.')
+
+
+def ensure(f):
+  if not os.path.exists(f):
+    with open(f, 'w'):
+      pass
+
+
+def check(f):
+  if not os.path.exists(f):
+    raise Exception('Expected file in archive: %s' % f)
+
+
+def main(argv):
+  basename = os.path.basename(FLAGS.archive)
+  stem = basename.split('.')[0]
+
+  # Check the type of the input file
+  mimetype_bytes = subprocess.check_output(['file', '-Lib', FLAGS.archive])
+  mimetype = mimetype_bytes.decode(sys.stdout.encoding)
+
+  # If we have a tar, extract all files. If we have just a single file, copy it.
+  if 'tar' in mimetype:
+    subprocess.check_call(
+        ['tar', 'xf', FLAGS.archive, '-C', FLAGS.output_path])
+  elif 'binary' in mimetype:
+    subprocess.check_call([
+        'cp',
+        FLAGS.archive,
+        os.path.join(FLAGS.output_path, stem + '.wasm')])
+  elif 'text' in mimetype:
+    subprocess.check_call([
+        'cp',
+        FLAGS.archive,
+        os.path.join(FLAGS.output_path, stem + '.js')])
+  else:
+    subprocess.check_call(['cp', FLAGS.archive, FLAGS.output_path])
+
+  # At least one of these two files should exist at this point.
+  ensure(os.path.join(FLAGS.output_path, stem + '.js'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.wasm'))
+
+  # And can optionally contain these extra files.
+  ensure(os.path.join(FLAGS.output_path, stem + '.wasm.map'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.worker.js'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.js.mem'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.data'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.fetch.js'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.js.symbols'))
+  ensure(os.path.join(FLAGS.output_path, stem + '.wasm.debug.wasm'))
+
+
+if __name__ == '__main__':
+  app.run(main)