Produce a more useful error message for over-length Unix socket paths.

The length of a socket path name is constrained by the size of struct
sockaddr_un, and there's not a lot we can do about it since that is a
kernel API.  However, it would be a good thing if we produced an
intelligible error message when the user specifies a socket path that's too
long --- and getaddrinfo's standard API is too impoverished to do this in
the natural way.  So insert explicit tests at the places where we construct
a socket path name.  Now you'll get an error that makes sense and even
tells you what the limit is, rather than something generic like
"Non-recoverable failure in name resolution".

Per trouble report from Jeremy Drake and a fix idea from Andrew Dunstan.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 5070f08404d..8acd2c3917f 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -790,7 +790,7 @@ static int
 connectDBStart(PGconn *conn)
 {
 	int			portnum;
-	char		portstr[128];
+	char		portstr[MAXPGPATH];
 	struct addrinfo *addrs = NULL;
 	struct addrinfo hint;
 	const char *node;
@@ -842,6 +842,15 @@ connectDBStart(PGconn *conn)
 		node = NULL;
 		hint.ai_family = AF_UNIX;
 		UNIXSOCK_PATH(portstr, portnum, conn->pgunixsocket);
+		if (strlen(portstr) >= UNIXSOCK_PATH_BUFLEN)
+		{
+			appendPQExpBuffer(&conn->errorMessage,
+							  libpq_gettext("Unix-domain socket path \"%s\" is too long (maximum %d bytes)\n"),
+											portstr,
+											(int) (UNIXSOCK_PATH_BUFLEN - 1));
+			conn->options_valid = false;
+			goto connect_errReturn;
+		}
 #else
 		/* Without Unix sockets, default to localhost instead */
 		node = "localhost";