app: verify a unix socket path length in socket.tcp_server()

[Totktonada]

Tarantool version: 2.3.0-225-g8d363c439.
OS version: Linux (but should be applicable for other OSes).

tarantooctl start app can successfully start an application and report incorrect console listening socket when a path exceeds UNIX_PATH_MAX (it is 108 on Linux, 104 on Mac OS). After that tarantoolctl status / stop / enter will not work properly, because actual file name of a socket will be truncated to UNIX_PATH_MAX bytes, while commands like status will try to connect using a non-truncated path.

The cause of this is socket.tcp_server(), which does not report truncation of a path as an error. It is easy to fix:

diff --git a/src/lua/socket.c b/src/lua/socket.c
index 130378caf..022dd56bb 100644
--- a/src/lua/socket.c
+++ b/src/lua/socket.c
@@ -403,7 +403,13 @@ lbox_socket_local_resolve(const char *host, const char *port,
 {
        if (strcmp(host, "unix/") == 0) {
                struct sockaddr_un *uaddr = (struct sockaddr_un *) addr;
-               if (*socklen < sizeof(*uaddr)) {
+               /*
+                * sun_path doesn't have to be null-terminated on
+                * Linux, but we ensure it is so for maximum
+                * portability.
+                */
+               if (*socklen < sizeof(*uaddr) ||
+                   strlen(port) >= sizeof(uaddr->sun_path)) {
                        errno = ENOBUFS;
                        return -1;
                }

(Yep, I know, we can use the last byte too on Linux (left sun_path non-null-terminated), but I'm afraid to do it on Mac OS: see here and here.)

However we can do some tricks: say, chdir into a directory and fill sun_path with just name w/o a full path. It works at least on Linux. This looks weird, however will be helpful in some cases.

I met this problem when tarantoolctl start <...> was run under a java testing harness, which was run in an unusual directory when maven performs testing of a freshly created release: maven checks out a tagged revision into a deeper directory and perform all actions there. I meant that a user not always control a run directory (where console sockets are created) when tarantoolctl is used as base for some other tool (BTW, our test-run tool uses it too, but just give a warning when a unix socket path exceeds 107 symbols). So I think hacking around this limit can safe time for many users, despite that it may look bad in the code. Personally I was hit by this limit many times.

However at least a proper error would be good.