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 c1775ea45bd..a89701ce1df 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -476,6 +476,14 @@ static int
 Lock_AF_UNIX(unsigned short portNumber, char *unixSocketName)
 {
 	UNIXSOCK_PATH(sock_path, portNumber, unixSocketName);
+	if (strlen(sock_path) >= UNIXSOCK_PATH_BUFLEN)
+	{
+		ereport(LOG,
+				(errmsg("Unix-domain socket path \"%s\" is too long (maximum %d bytes)",
+						sock_path,
+						(int) (UNIXSOCK_PATH_BUFLEN - 1))));
+		return STATUS_ERROR;
+	}
 
 	/*
 	 * Grab an interlock file associated with the socket file.