t7599: create corrupt blob test

Teach helper/test-gvfs-protocol to be able to send corrupted
loose blobs.

Add unit test for gvfs-helper to detect receipt of a corrupted loose blob.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

t/helper/test-gvfs-protocol.c

@@ -510,6 +510,8 @@ static enum worker_result send_loose_object(const struct object_id *oid,
 	unsigned long size;
 	enum object_type type;
 	struct object_info oi = OBJECT_INFO_INIT;
+	int mayhem__corrupt_loose = string_list_has_string(&mayhem_list,
+							   "corrupt_loose");
 
 	/*
 	 * Since `test-gvfs-protocol` is mocking a real GVFS server (cache or
@@ -623,7 +625,22 @@ static enum worker_result send_loose_object(const struct object_id *oid,
 	do {
 		enum worker_result wr;
 		unsigned char *in0 = stream.next_in;
+
+		/*
+		 * Corrupt a byte in the buffer we compress, but undo it
+		 * before we compute the SHA on the portion of the raw
+		 * buffer included in the chunk we compressed.
+		 */
+		if (mayhem__corrupt_loose) {
+			logmayhem("corrupt_loose");
+			*in0 = *in0 ^ 0xff;
+		}
+
 		ret = git_deflate(&stream, Z_FINISH);
+
+		if (mayhem__corrupt_loose)
+			*in0 = *in0 ^ 0xff;
+
 		the_hash_algo->update_fn(&c, in0, stream.next_in - in0);
 
 		/* [5] */

t/t5799-gvfs-helper.sh

@@ -1288,4 +1288,36 @@ test_expect_success 'duplicate and busy: vfs- packfile' '
 	stop_gvfs_protocol_server
 '
 
+#################################################################
+# Ensure that the SHA of the blob we received matches the SHA of
+# the blob we requested.
+#################################################################
+
+# Request a loose blob from the server.  Verify that we received
+# content matches the requested SHA.
+#
+test_expect_success 'catch corrupted loose object' '
+#	test_when_finished "per_test_cleanup" &&
+	start_gvfs_protocol_server_with_mayhem corrupt_loose &&
+
+	test_must_fail \
+		git -C "$REPO_T1" gvfs-helper \
+			--cache-server=trust \
+			--remote=origin \
+			get \
+			<"$OID_ONE_BLOB_FILE" >OUT.output 2>OUT.stderr &&
+
+	stop_gvfs_protocol_server &&
+
+	# Verify corruption detected.
+	# Verify valid blob not included in response to client.
+
+	grep "hash failed for received loose object" OUT.stderr &&
+
+	# Verify that we did not write the corrupted blob to the ODB.
+
+	! verify_objects_in_shared_cache "$OID_ONE_BLOB_FILE" &&
+	git -C "$REPO_T1" fsck
+'
+
 test_done