gitweb: retrieve snapshot format from PATH_INFO

We parse requests for $project/snapshot/$head.$sfx as equivalent to
$project/snapshot/$head?sf=$sfx, where $sfx is any of the known
(although not necessarily supported) snapshot formats (or its default
suffix).

The filename for the resulting package preserves the requested
extensions (so asking for a .tgz gives a .tgz, and asking for a .tar.gz
gives a .tar.gz), although for obvious reasons it doesn't preserve the
basename (git/snapshot/next.tgz returns a file names git-next.tgz).

This introduces a potential case for ambiguity if a project has a head
that ends with a snapshot-like suffix (.zip, .tgz, .tar.gz, etc) and the
sf CGI parameter is not present; however, gitweb only produces URLs with
the sf parameter currently, so this is only a potential issue for
hand-coded URLs for extremely unusual project.

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -616,6 +616,45 @@ sub evaluate_path_info {
 			$input_params{'hash_parent'} ||= $parentrefname;
 		}
 	}
+
+	# for the snapshot action, we allow URLs in the form
+	# $project/snapshot/$hash.ext
+	# where .ext determines the snapshot and gets removed from the
+	# passed $refname to provide the $hash.
+	#
+	# To be able to tell that $refname includes the format extension, we
+	# require the following two conditions to be satisfied:
+	# - the hash input parameter MUST have been set from the $refname part
+	#   of the URL (i.e. they must be equal)
+	# - the snapshot format MUST NOT have been defined already (e.g. from
+	#   CGI parameter sf)
+	# It's also useless to try any matching unless $refname has a dot,
+	# so we check for that too
+	if (defined $input_params{'action'} &&
+		$input_params{'action'} eq 'snapshot' &&
+		defined $refname && index($refname, '.') != -1 &&
+		$refname eq $input_params{'hash'} &&
+		!defined $input_params{'snapshot_format'}) {
+		# We loop over the known snapshot formats, checking for
+		# extensions. Allowed extensions are both the defined suffix
+		# (which includes the initial dot already) and the snapshot
+		# format key itself, with a prepended dot
+		while (my ($fmt, %opt) = each %known_snapshot_formats) {
+			my $hash = $refname;
+			my $sfx;
+			$hash =~ s/(\Q$opt{'suffix'}\E|\Q.$fmt\E)$//;
+			next unless $sfx = $1;
+			# a valid suffix was found, so set the snapshot format
+			# and reset the hash parameter
+			$input_params{'snapshot_format'} = $fmt;
+			$input_params{'hash'} = $hash;
+			# we also set the format suffix to the one requested
+			# in the URL: this way a request for e.g. .tgz returns
+			# a .tgz instead of a .tar.gz
+			$known_snapshot_formats{$fmt}{'suffix'} = $sfx;
+			last;
+		}
+	}
 }
 evaluate_path_info();