[PATCH] git-remote-testpy: fix patch hashing on Python 3

From: John Keeping <john@keeping.me.uk>
Date: Jan 27, 2013, 14:50 UTC
Message-ID: <20130127145056.GP7498@serenity.lan>
In-Reply-To: <20130127141329.GN7498@serenity.lan>

When this change was originally made (0846b0c - git-remote-testpy: hash bytes explicitly , I didn't realised that the "hex" encoding we chose is a "bytes to bytes" encoding so it just fails with an error on Python 3 in the same way as the original code.

It is not possible to provide a single code path that works on Python 2 and Python 3 since Python 2.x will attempt to decode the string before encoding it, which fails for strings that are not valid in the default encoding. Python 3.1 introduced the "surrogateescape" error handler which handles this correctly and permits a bytes -> unicode -> bytes round-trip to be lossless.

At this point Python 3.0 is unsupported so we don't go out of our way to try to support it.

Helped-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: John Keeping <john@keeping.me.uk>
---
On Sun, Jan 27, 2013 at 02:13:29PM +0000, John Keeping wrote:

Show 18 quoted lines

> On Sun, Jan 27, 2013 at 05:44:37AM +0100, Michael Haggerty wrote:
> > So to handle all of the cases across Python versions as closely as
> > possible to the old 2.x code, it might be necessary to make the code
> > explicitly depend on the Python version number, like:
> > 
> >     hasher = _digest()
> >     if sys.hexversion < 0x03000000:
> >         pathbytes = repo.path
> >     elif sys.hexversion < 0x03010000:
> >         # If support for Python 3.0.x is desired (note: result can
> >         # be different in this case than under 2.x or 3.1+):
> >         pathbytes = repo.path.encode(sys.getfilesystemencoding(),
> > 'backslashreplace')
> >     else
> >         pathbytes = repo.path.encode(sys.getfilesystemencoding(),
> > 'surrogateescape')
> >     hasher.update(pathbytes)
> >     repo.hash = hasher.hexdigest()

How about this?

 git-remote-testpy.py | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/git-remote-testpy.py b/git-remote-testpy.py
index c7a04ec..16b0c52 100644
--- a/git-remote-testpy.py
+++ b/git-remote-testpy.py
@@ -36,6 +36,22 @@ if sys.hexversion < 0x02000000:
     sys.stderr.write("git-remote-testgit: requires Python 2.0 or later.\n")
     sys.exit(1)
 
+
+def _encode_filepath(path):
+    """Encodes a Unicode file path to a byte string.
+
+    On Python 2 this is a no-op; on Python 3 we encode the string as
+    suggested by [1] which allows an exact round-trip from the command line
+    to the filesystem.
+
+    [1] http://docs.python.org/3/c-api/unicode.html#file-system-encoding
+
+    """
+    if sys.hexversion < 0x03000000:
+        return path
+    return path.encode('utf-8', 'surrogateescape')
+
+
 def get_repo(alias, url):
     """Returns a git repository object initialized for usage.
     """
@@ -45,7 +61,7 @@ def get_repo(alias, url):
     repo.get_head()
 
     hasher = _digest()
-    hasher.update(repo.path.encode('hex'))
+    hasher.update(_encode_filepath(repo.path))
     repo.hash = hasher.hexdigest()
 
     repo.get_base_path = lambda base: os.path.join(

-- 
1.8.1.1