Improve path handling in proxy_logging

In the access log, proxy_logging places the URL path,
double-URL-encoded (e.g. " " -> %20 -> %2520).

In the WSGI environment, env['PATH_INFO'] is the unquoted path sent by
the client, e.g. "/v1/a/c/o" or "/v1/a/c/obj with spaces" or
"/v1/a/c/u-\xf0\x9f\xa4\x94". On the request, we have the "path"
attribute, which returns the quoted form of env["PATH_INFO"].

Note that, under Python 2, these are always str objects, not unicode.

Swift used to log this:

    quote(quote(unquote(
        req.path.decode('utf-8', 'replace').encode('utf-8')), "/:"))

There's a lot going on here. Let's look at the innermost expression:

    req.path.decode('utf-8', 'replace').encode('utf-8')

This appears to be trying to replace invalid UTF-8 sequences with the
Unicode replacement character. However, since we start from
"req.path", which quotes its input, we don't have any non-ASCII bytes,
so the decode/encode is a no-op. That is, if env["PATH_INFO"] had
"\xff\xff" in it, req.path would have "%FF%FF", so there's no invalid
byte sequences to escape.

So, without changing the output, we can simplify the above code to:

    quote(quote(unquote(req.path), "/:"))

The second call to quote() has a second argument of "/:", so neither
slashes or colons are quoted. This was introduced in commit cd8af3f8f1
as part of a change to log client IPv6 addresses (from
env["REMOTE_ADDR") without escaping the colons. However, cd8af3f8f1
also applied that to the logging of env["PATH_INFO"]. This seems
unhelpful since IPv6 addresses in URL paths are not particularly
common, so I've removed it. The change is backwards-compatible since a
double-unquote of the logged value will still return the original
PATH_INFO.

With that in mind, let's simplify further. req.path quotes
env["PATH_INFO"], so that cancels out one unquote() call, leaving us
with this:

    quote(req.path_info)

which produces basically the same result as before, but faster.

Change-Id: I7e665eb55a9524aa49e2578f2084d8354f6c1e31

swift/common/middleware/proxy_logging.py

@@ -75,10 +75,10 @@ import sys
 import time
 
 import six
-from six.moves.urllib.parse import quote, unquote
+from six.moves.urllib.parse import quote
 from swift.common.swob import Request
 from swift.common.utils import (get_logger, get_remote_client,
-                                get_valid_utf8_str, config_true_value,
+                                config_true_value,
                                 InputProxy, list_from_csv, get_policy_index)
 
 from swift.common.storage_policy import POLICIES
@@ -152,8 +152,7 @@ class ProxyLoggingMiddleware(object):
         :param resp_headers: dict of the response headers
         """
         resp_headers = resp_headers or {}
-        req_path = get_valid_utf8_str(req.path)
-        the_request = quote(unquote(req_path), QUOTE_SAFE)
+        the_request = req.path
         if req.query_string:
             the_request = the_request + '?' + req.query_string
         logged_headers = None