gitweb: check given hash before trying to create snapshot

Makes things nicer in cases when you hand craft the snapshot URL but
make a typo in defining the hash variable (e.g. netx instead of next);
you will now get an error message instead of a broken tarball.

Tests for t9501 are included to demonstrate added functionality.

Signed-off-by: Mark Rada <marada@uwaterloo.ca>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

gitweb/gitweb.perl

@@ -5196,8 +5196,11 @@ sub git_snapshot {
 		die_error(403, "Unsupported snapshot format");
 	}
 
-	if (!defined $hash) {
-		$hash = git_get_head_hash($project);
+	my $type = git_get_type("$hash^{}");
+	if (!$type) {
+		die_error(404, 'Object does not exist');
+	}  elsif ($type eq 'blob') {
+		die_error(400, 'Object is not a tree-ish');
 	}
 
 	my $name = $project;

t/t9501-gitweb-standalone-http-status.sh

@@ -75,4 +75,43 @@ test_expect_success \
 test_debug 'cat gitweb.output'
 
 
+# ----------------------------------------------------------------------
+# snapshot hash ids
+
+test_expect_success 'snapshots: good tree-ish id' '
+	gitweb_run "p=.git;a=snapshot;h=master;sf=tgz" &&
+	grep "Status: 200 OK" gitweb.output
+'
+test_debug 'cat gitweb.output'
+
+test_expect_success 'snapshots: bad tree-ish id' '
+	gitweb_run "p=.git;a=snapshot;h=frizzumFrazzum;sf=tgz" &&
+	grep "404 - Object does not exist" gitweb.output
+'
+test_debug 'cat gitweb.output'
+
+test_expect_success 'snapshots: bad tree-ish id (tagged object)' '
+	echo object > tag-object &&
+	git add tag-object &&
+	git commit -m "Object to be tagged" &&
+	git tag tagged-object `git hash-object tag-object` &&
+	gitweb_run "p=.git;a=snapshot;h=tagged-object;sf=tgz" &&
+	grep "400 - Object is not a tree-ish" gitweb.output
+'
+test_debug 'cat gitweb.output'
+
+test_expect_success 'snapshots: good object id' '
+	ID=`git rev-parse --verify HEAD` &&
+	gitweb_run "p=.git;a=snapshot;h=$ID;sf=tgz" &&
+	grep "Status: 200 OK" gitweb.output
+'
+test_debug 'cat gitweb.output'
+
+test_expect_success 'snapshots: bad object id' '
+	gitweb_run "p=.git;a=snapshot;h=abcdef01234;sf=tgz" &&
+	grep "404 - Object does not exist" gitweb.output
+'
+test_debug 'cat gitweb.output'
+
+
 test_done