Add script to download fuchsia sdk from GCS

Adds a script to download the Fuchsia SDK from a given GCS bucket.
This script can run as an optional gclient hook to allow for the
Fuchsia architecture to run LSC checks on commits to fuchsia.git.

Author: chaselatta

DEPS

@@ -74,6 +74,11 @@ vars = {
   # Checkout Linux dependencies only when building on Linux.
   'download_linux_deps': 'host_os == "linux"',
 
+  # Downloads the fuchsia SDK as listed in .fuchsia_sdk_version. This variable
+  # is currently only used for the Fuchsia LSC process and is not intended for
+  # local development.
+  'download_fuchsia_sdk': False,
+
   # An LLVM backend needs LLVM binaries and headers. To avoid build time
   # increases we can use prebuilts. We don't want to download this on every
   # CQ/CI bot nor do we want the average Dart developer to incur that cost.
@@ -598,7 +603,7 @@ deps = {
         'version': 'wosv2IujusWWdT2zQo42oYNwdVQqjqDzC5KqcQz9PBoC'
        }
      ],
-     'condition': 'host_os == "mac"',
+     'condition': 'host_os == "mac" and not download_fuchsia_sdk',
      'dep_type': 'cipd',
    },
    'src/fuchsia/sdk/linux': {
@@ -608,7 +613,7 @@ deps = {
         'version': 'TRF0KtYTln0E8jesSKVFIvYS565aDIi_3r5SFUkxK0MC'
        }
      ],
-     'condition': 'host_os == "linux"',
+     'condition': 'host_os == "linux" and not download_fuchsia_sdk',
      'dep_type': 'cipd',
    },
 
@@ -712,6 +717,19 @@ hooks = [
       '--fail-loudly',
     ]
   },
+  {
+    'name': 'Download Fuchsia SDK',
+    'pattern': '.',
+    'condition': 'download_fuchsia_sdk',
+    'action': [
+      'python3',
+      'src/flutter/tools/download_fuchsia_sdk.py',
+      '--fail-loudly',
+      '--verbose',
+      '--host-os',
+      Var('host_os'),
+    ]
+  },
   {
     'name': 'Setup githooks',
     'pattern': '.',

tools/download_fuchsia_sdk.py

@@ -0,0 +1,176 @@
+#!/usr/bin/env python3
+# Copyright 2013 The Flutter Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# The return code of this script will always be 0, even if there is an error,
+# unless the --fail-loudly flag is passed.
+
+
+import argparse
+import tarfile
+import json
+import os
+import shutil
+import subprocess
+import sys
+
+SRC_ROOT = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+FUCHSIA_SDK_DIR = os.path.join(SRC_ROOT, 'fuchsia', 'sdk')
+FLUTTER_DIR = os.path.join(SRC_ROOT, 'flutter')
+SDK_VERSION_INFO_FILE = os.path.join(FLUTTER_DIR, '.fuchsia_sdk_version')
+
+# Prints to stderr.
+def eprint(*args, **kwargs):
+  print(*args, file=sys.stderr, **kwargs)
+
+def FileNameForBucket(bucket):
+  return bucket.split('/')[-1]
+
+def DownloadFuchsiaSDKFromGCS(bucket, verbose):
+  file = FileNameForBucket(bucket)
+  url = 'https://storage.googleapis.com/{}'.format(bucket)
+  dest = os.path.join(FUCHSIA_SDK_DIR, file)
+
+  if verbose:
+    print('Fuchsia SDK url: "%s"' % url)
+    print('Fuchsia SDK destination path: "%s"' % dest)
+
+  if os.path.isfile(dest):
+    os.unlink(dest)
+
+  curl_command = [
+    'curl',
+    '--retry', '3',
+    '--continue-at', '-', '--location',
+    '--output', dest,
+    url,
+  ]
+  if verbose:
+    print('Running: "%s"' % (' '.join(curl_command)))
+  curl_result = subprocess.run(
+    curl_command,
+    stdout=subprocess.PIPE,
+    stderr=subprocess.PIPE,
+    universal_newlines=True,
+  )
+  if curl_result.returncode == 0 and verbose:
+    print('curl output:stdout:\n{}\nstderr:\n{}'.format(
+      curl_result.stdout, curl_result.stderr,
+    ))
+  elif curl_result.returncode != 0:
+    eprint('Failed to download: stdout:\n{}\nstderr:\n{}'.format(
+      curl_result.stdout, curl_result.stderr,
+    ))
+    return None
+
+  return dest
+
+def OnErrorRmTree(func, path, exc_info):
+  """
+  Error handler for ``shutil.rmtree``.
+
+  If the error is due to an access error (read only file)
+  it attempts to add write permission and then retries.
+  If the error is for another reason it re-raises the error.
+
+  Usage : ``shutil.rmtree(path, onerror=onerror)``
+  """
+  import stat
+  # Is the error an access error?
+  if not os.access(path, os.W_OK):
+    os.chmod(path, stat.S_IWUSR)
+    func(path)
+  else:
+    raise
+
+def ExtractGzipArchive(archive, host_os, verbose):
+  sdk_dest = os.path.join(FUCHSIA_SDK_DIR, host_os)
+  if os.path.isdir(sdk_dest):
+    shutil.rmtree(sdk_dest, onerror=OnErrorRmTree)
+
+  extract_dest = os.path.join(FUCHSIA_SDK_DIR, 'temp')
+  if os.path.isdir(extract_dest):
+    shutil.rmtree(extract_dest, onerror=OnErrorRmTree)
+  os.makedirs(extract_dest, exist_ok=True)
+
+  if verbose:
+    print('Extracting "%s" to "%s"' % (archive, extract_dest))
+
+  with tarfile.open(archive, 'r') as z:
+    z.extractall(extract_dest)
+
+  shutil.move(extract_dest, sdk_dest)
+
+
+# Reads the version file and returns the bucket to download
+# The file is expected to live at the flutter directory and be named .fuchsia_sdk_version.
+#
+# The file is a JSON file which contains a single object with the following schema:
+# ```
+# {
+#    "protocol": "gcs",
+#    "identifiers": [
+#      {
+#        "host_os": "linux",
+#        "bucket": "fuchsia-artifacts/development/8824687191341324145/sdk/linux-amd64/core.tar.gz"
+#      }
+#    ]
+# }
+# ```
+def ReadVersionFile(host_os):
+  with open(SDK_VERSION_INFO_FILE) as f:
+    try:
+      version_obj = json.loads(f.read())
+      if version_obj['protocol'] != 'gcs':
+        eprint('The gcs protocol is the only suppoted protocl at this time')
+        return None
+      for id_obj in version_obj['identifiers']:
+        if id_obj['host_os'] == host_os:
+          return id_obj['bucket']
+    except:
+      eprint('Could not read JSON version file')
+      return None
+
+def Main():
+  parser = argparse.ArgumentParser()
+  parser.add_argument(
+    '--fail-loudly',
+    action='store_true',
+    default=False,
+    help="Return an error code if a prebuilt couldn't be fetched and extracted")
+
+  parser.add_argument(
+    '--verbose',
+    action='store_true',
+    default='LUCI_CONTEXT' in os.environ,
+    help='Emit verbose output')
+
+  parser.add_argument(
+    '--host-os',
+    help='The host os')
+
+  args = parser.parse_args()
+  fail_loudly = 1 if args.fail_loudly else 0
+  verbose = args.verbose
+  host_os = args.host_os
+
+  bucket = ReadVersionFile(host_os)
+
+  if bucket is None:
+    eprint('Unable to find bucket in version file')
+    return fail_loudly
+
+  archive = DownloadFuchsiaSDKFromGCS(bucket, verbose)
+  if archive is None:
+    eprint('Failed to download SDK from %s' % bucket)
+    return fail_loudly
+
+  ExtractGzipArchive(archive, host_os, verbose)
+
+  success = True
+  return 0 if success else fail_loudly
+
+
+if __name__ == '__main__':
+  sys.exit(Main())