Hold persistent proxy connection open while fetching clone.bundle

The persistent proxy may choose to present a per-process cookie file
that gets cleaned up after the process exits, to help with the fact
that libcurl cannot save cookies atomically when a cookie file is
shared across processes. We were letting this cleanup happen
immediately by closing stdin as soon as we read the configuration
option, resulting in a nonexistent cookie file by the time we use the
config option.

Work around this by converting the cookie logic to a context manager
method, which closes the process only when we're done with the cookie
file.

Change-Id: I12a88b25cc19621ef8161337144c1b264264211a

project.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 from __future__ import print_function
-import traceback
+import contextlib
 import errno
 import filecmp
 import os
@@ -26,6 +26,7 @@ import sys
 import tarfile
 import tempfile
 import time
+import traceback
 
 from color import Coloring
 from git_command import GitCommand, git_require
@@ -1946,7 +1947,7 @@ class Project(object):
         os.remove(tmpPath)
     if 'http_proxy' in os.environ and 'darwin' == sys.platform:
       cmd += ['--proxy', os.environ['http_proxy']]
-    cookiefile = self._GetBundleCookieFile(srcUrl)
+    with self._GetBundleCookieFile(srcUrl) as cookiefile:
       if cookiefile:
         cmd += ['--cookie', cookiefile]
       if srcUrl.startswith('persistent-'):
@@ -1994,6 +1995,7 @@ class Project(object):
     except OSError:
       return False
 
+  @contextlib.contextmanager
   def _GetBundleCookieFile(self, url):
     if url.startswith('persistent-'):
       try:
@@ -2001,7 +2003,7 @@ class Project(object):
             ['git-remote-persistent-https', '-print_config', url],
             stdin=subprocess.PIPE, stdout=subprocess.PIPE,
             stderr=subprocess.PIPE)
-        p.stdin.close()  # Tell subprocess it's ok to close.
+        try:
           prefix = 'http.cookiefile='
           cookiefile = None
           for line in p.stdout:
@@ -2009,19 +2011,23 @@ class Project(object):
             if line.startswith(prefix):
               cookiefile = line[len(prefix):]
               break
+          # Leave subprocess open, as cookie file may be transient.
+          if cookiefile:
+            yield cookiefile
+            return
+        finally:
+          p.stdin.close()
           if p.wait():
             err_msg = p.stderr.read()
             if ' -print_config' in err_msg:
               pass  # Persistent proxy doesn't support -print_config.
             else:
               print(err_msg, file=sys.stderr)
-        if cookiefile:
-          return cookiefile
       except OSError as e:
         if e.errno == errno.ENOENT:
           pass  # No persistent proxy.
         raise
-    return GitConfig.ForUser().GetString('http.cookiefile')
+    yield GitConfig.ForUser().GetString('http.cookiefile')
 
   def _Checkout(self, rev, quiet=False):
     cmd = ['checkout']