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, 8 insertions, 0 deletions

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index 5e86987f221..15a01a8324b 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -308,6 +308,14 @@ StreamServerPort(int family, char *hostName, unsigned short portNumber,
 		 * that file path
 		 */
 		UNIXSOCK_PATH(unixSocketPath, portNumber, unixSocketDir);
+		if (strlen(unixSocketPath) >= UNIXSOCK_PATH_BUFLEN)
+		{
+			ereport(LOG,
+					(errmsg("Unix-domain socket path \"%s\" is too long (maximum %d bytes)",
+							unixSocketPath,
+							(int) (UNIXSOCK_PATH_BUFLEN - 1))));
+			return STATUS_ERROR;
+		}
 		if (Lock_AF_UNIX(unixSocketDir, unixSocketPath) != STATUS_OK)
 			return STATUS_ERROR;
 		service = unixSocketPath;