bin/fetch-gn is 3.5x faster

Change-Id: I8098a38eb81efe0a73201c1f00dff8363b9c2075
Reviewed-on: https://skia-review.googlesource.com/7025
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>

1 files changed, 22 insertions, 10 deletions

diff --git a/bin/fetch-gn b/bin/fetch-gn
index 16e287513e..d5de7e4fd6 100755
--- a/bin/fetch-gn
+++ b/bin/fetch-gn
@@ -5,25 +5,37 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import hashlib
 import os
 import shutil
 import stat
 import sys
 import urllib2
 
-def gn_path():
-  if 'linux' in sys.platform:
-    return 'buildtools/linux64/gn'
-  if 'darwin' in sys.platform:
-    return 'buildtools/mac/gn'
-  return 'buildtools/win/gn.exe'
+os.chdir(os.path.join(os.path.dirname(__file__), os.pardir))
 
-sha1 = open(gn_path() + '.sha1').read()
+gn_path = 'buildtools/linux64/gn' if 'linux'  in sys.platform else \
+          'buildtools/mac/gn'     if 'darwin' in sys.platform else \
+          'buildtools/win/gn.exe'
 
-with open(gn_path(), 'wb') as f:
+sha1 = open(gn_path + '.sha1').read().strip()
+
+def sha1_of_file(path):
+  h = hashlib.sha1()
+  if os.path.isfile(path):
+    with open(path, 'rb') as f:
+      h.update(f.read())
+  return h.hexdigest()
+
+if sha1_of_file(gn_path) != sha1:
+  with open(gn_path, 'wb') as f:
     f.write(urllib2.urlopen('https://chromium-gn.storage-download.googleapis.com/' + sha1).read())
 
-os.chmod(gn_path(), stat.S_IRUSR | stat.S_IWUSR | stat.S_IXUSR |
+  os.chmod(gn_path, stat.S_IRUSR | stat.S_IWUSR | stat.S_IXUSR |
                     stat.S_IRGRP                | stat.S_IXGRP |
                     stat.S_IROTH                | stat.S_IXOTH )
-shutil.copy(gn_path(), 'bin');
+
+gn_copy_path = os.path.join('bin', os.path.basename(gn_path))
+if sha1_of_file(gn_copy_path) != sha1:
+  shutil.copy(gn_path, gn_copy_path)
+