[PATCH] hgweb: emit a valid, weak ETag

[Anton Shestakov]

# HG changeset patch
# User Anton Shestakov <av6 at dwimlabs.net>
# Date 1468005984 -28800
#      Sat Jul 09 03:26:24 2016 +0800
# Node ID 47eb9964a1d6e545342011f4bf2574695dd87169
# Parent  b4d117cee636be8a566f56e84d4b351a736a1299
hgweb: emit a valid, weak ETag

Previously, ETag headers from hgweb weren't correctly formed, because rfc2616
(section 14, header definitions) requires double quotes around the content of
the header. str(web.mtime) didn't do that.

Additionally, strong ETags signify that the resource representations are
byte-for-byte identical. That is, they can be reconstructed from byte ranges if
client so wishes. Considering ETags for all hgweb pages is just mtime of
00changelog.i and doesn't consider of e.g. .hg/hgrc with description, contact
and other fields, it's clearly shouldn't be strong. The W/ prefix marks it as
weak, which still allows caching the whole served file/page, but doesn't allow
byte-range requests.

diff --git a/mercurial/hgweb/common.py b/mercurial/hgweb/common.py
--- a/mercurial/hgweb/common.py
+++ b/mercurial/hgweb/common.py
@@ -187,7 +187,7 @@ def get_contact(config):
             os.environ.get("EMAIL") or "")
 
 def caching(web, req):
-    tag = str(web.mtime)
+    tag = 'W/"%s"' % web.mtime
     if req.env.get('HTTP_IF_NONE_MATCH') == tag:
         raise ErrorResponse(HTTP_NOT_MODIFIED)
     req.headers.append(('ETag', tag))