MEDIUM: unix: implement support for Linux abstract namespace sockets
These sockets are the same as Unix sockets except that there's no need
for any filesystem access. The address may be whatever string both sides
agree upon. This can be really convenient for inter-process communications
as well as for chaining backends to frontends.
These addresses are forced by prepending their address with "abns@" for
"abstract namespace".
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index 3fa383d..f2621fa 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -188,45 +188,46 @@
if (ext)
goto fd_ready;
- /* 1. create socket names */
- if (!path[0]) {
- msg = "Invalid empty name for a UNIX socket";
- goto err_return;
- }
+ if (path[0]) {
+ ret = snprintf(tempname, MAXPATHLEN, "%s.%d.tmp", path, pid);
+ if (ret < 0 || ret >= MAXPATHLEN) {
+ msg = "name too long for UNIX socket";
+ goto err_return;
+ }
- ret = snprintf(tempname, MAXPATHLEN, "%s.%d.tmp", path, pid);
- if (ret < 0 || ret >= MAXPATHLEN) {
- msg = "name too long for UNIX socket";
- goto err_return;
- }
+ ret = snprintf(backname, MAXPATHLEN, "%s.%d.bak", path, pid);
+ if (ret < 0 || ret >= MAXPATHLEN) {
+ msg = "name too long for UNIX socket";
+ goto err_return;
+ }
- ret = snprintf(backname, MAXPATHLEN, "%s.%d.bak", path, pid);
- if (ret < 0 || ret >= MAXPATHLEN) {
- msg = "name too long for UNIX socket";
- goto err_return;
- }
+ /* 2. clean existing orphaned entries */
+ if (unlink(tempname) < 0 && errno != ENOENT) {
+ msg = "error when trying to unlink previous UNIX socket";
+ goto err_return;
+ }
- /* 2. clean existing orphaned entries */
- if (unlink(tempname) < 0 && errno != ENOENT) {
- msg = "error when trying to unlink previous UNIX socket";
- goto err_return;
- }
+ if (unlink(backname) < 0 && errno != ENOENT) {
+ msg = "error when trying to unlink previous UNIX socket";
+ goto err_return;
+ }
- if (unlink(backname) < 0 && errno != ENOENT) {
- msg = "error when trying to unlink previous UNIX socket";
- goto err_return;
- }
+ /* 3. backup existing socket */
+ if (link(path, backname) < 0 && errno != ENOENT) {
+ msg = "error when trying to preserve previous UNIX socket";
+ goto err_return;
+ }
- /* 3. backup existing socket */
- if (link(path, backname) < 0 && errno != ENOENT) {
- msg = "error when trying to preserve previous UNIX socket";
- goto err_return;
+ strncpy(addr.sun_path, tempname, sizeof(addr.sun_path));
+ addr.sun_path[sizeof(addr.sun_path) - 1] = 0;
}
-
- /* 4. prepare new socket */
+ else {
+ /* first char is zero, it's an abstract socket whose address
+ * is defined by all the bytes past this zero.
+ */
+ memcpy(addr.sun_path, path, sizeof(addr.sun_path));
+ }
addr.sun_family = AF_UNIX;
- strncpy(addr.sun_path, tempname, sizeof(addr.sun_path));
- addr.sun_path[sizeof(addr.sun_path) - 1] = 0;
fd = socket(PF_UNIX, SOCK_STREAM, 0);
if (fd < 0) {
@@ -254,9 +255,9 @@
/* <uid> and <gid> different of -1 will be used to change the socket owner.
* If <mode> is not 0, it will be used to restrict access to the socket.
* While it is known not to be portable on every OS, it's still useful
- * where it works.
+ * where it works. We also don't change permissions on abstract sockets.
*/
- if (!ext &&
+ if (!ext && path[0] &&
(((listener->bind_conf->ux.uid != -1 || listener->bind_conf->ux.gid != -1) &&
(chown(tempname, listener->bind_conf->ux.uid, listener->bind_conf->ux.gid) == -1)) ||
(listener->bind_conf->ux.mode != 0 && chmod(tempname, listener->bind_conf->ux.mode) == -1))) {
@@ -275,21 +276,21 @@
goto err_unlink_temp;
}
- /* 5. install.
- * Point of no return: we are ready, we'll switch the sockets. We don't
+ /* Point of no return: we are ready, we'll switch the sockets. We don't
* fear loosing the socket <path> because we have a copy of it in
- * backname.
+ * backname. Abstract sockets are not renamed.
*/
- if (!ext && rename(tempname, path) < 0) {
+ if (!ext && path[0] && rename(tempname, path) < 0) {
msg = "cannot switch final and temporary UNIX sockets";
goto err_rename;
}
- /* 6. cleanup. If we're bound to an fd inherited from the parent, we
+ /* Cleanup: If we're bound to an fd inherited from the parent, we
* want to ensure that destroy_uxst_socket() will never remove the
- * path, and for this we simply clear the path to the socket.
+ * path, and for this we simply clear the path to the socket, which
+ * under Linux corresponds to an abstract socket.
*/
- if (!ext)
+ if (!ext && path[0])
unlink(backname);
else
((struct sockaddr_un *)&listener->addr)->sun_path[0] = 0;