sync: Support authentication to manifest server with .netrc

When using the --smart-sync or --smart-tag option, and the specified
manifest server is hosted on a server that requires authentication,
repo sync fails with the error: HTTP 401 Unauthorized.

Add support for getting the credentials from the .netrc file.

If a .netrc file exists in the user's home directory, and it contains
credentials for the hostname of the manifest server specified in the
manifest, use the credentials to authenticate with the manifest server
using the URL syntax extension for Basic Authentication:

  http://user:password@host:port/path

Credentials from the .netrc file are only used if the manifest server
URL specified in the manifest does not already include credentials.

Change-Id: I06e6586e8849d0cd12fa9746789e8d45d5b1f848

subcmds/sync.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import netrc
 from optparse import SUPPRESS_HELP
 import os
 import re
@@ -21,6 +22,7 @@ import socket
 import subprocess
 import sys
 import time
+import urlparse
 import xmlrpclib
 
 try:
@@ -365,8 +367,34 @@ uncommitted changes are present' % project.relpath
         print >>sys.stderr, \
             'error: cannot smart sync: no manifest server defined in manifest'
         sys.exit(1)
+
+      manifest_server = self.manifest.manifest_server
+      if not '@' in manifest_server:
+        try:
+          info = netrc.netrc()
+        except IOError:
+          print >>sys.stderr, '.netrc file does not exist or could not be opened'
+        else:
+          try:
+            parse_result = urlparse.urlparse(manifest_server)
+            if parse_result.hostname:
+              username, _account, password = \
+                info.authenticators(parse_result.hostname)
+          except TypeError:
+            # TypeError is raised when the given hostname is not present
+            # in the .netrc file.
+            print >>sys.stderr, 'No credentials found for %s in .netrc' % \
+                                parse_result.hostname
+          except netrc.NetrcParseError as e:
+            print >>sys.stderr, 'Error parsing .netrc file: %s' % e
+          else:
+            if (username and password):
+              manifest_server = manifest_server.replace('://', '://%s:%s@' %
+                                                        (username, password),
+                                                        1)
+
       try:
-        server = xmlrpclib.Server(self.manifest.manifest_server)
+        server = xmlrpclib.Server(manifest_server)
         if opt.smart_sync:
           p = self.manifest.manifestProject
           b = p.GetBranch(p.CurrentBranch)