Add support for Unix sockets #1552

fpagliughi · 2025-01-02T04:20:29Z

Adds support for UNIX-domain sockets on *nix platforms.
It implements issue #864.

This allows clients to communicate with an MQTT server over UNIX-domain sockets on *nix systems. (Not on Windows). This is opt-in with a CMake build option, PAHO_WITH_UNIX_SOCKETS.

This can increase performance and reduce latency since UNIX sockets have a much simpler network stack than TCP. But perhaps more importantly, it provides increased security with more fine-grained control when clients reside on the same host as the broker. Access to the broker can be done using file permissions (with groups, owners, etc).

The clients can request a socket of this type using a URI of unix:///path/to/socket/file. The socket file is created by the server when it binds and listens on the UNIX socket.

The implementation here is fairly trivial. The library must now recognize the unix:// scheme in the URI, then create and connect to a socket using a sockaddr_un socket address containing the path to the socket file.

After that all communications and closing the socket are handled by the same code that manages TCP connections. A socket is a socket.

This was tested on Linux and macOS with the mosquitto server. By definition it requires a broker running on the same host whereby it communicates with the clients using the local file system.

The mosquitto configuration file can be as simple as:

allow_anonymous true    
listener 0 /tmp/mosquitto.sock

This PR also updates several of the simple sample apps to take a URI at the command line, allowing them to be used to try this out, like:

MQTTAsync_publish unix:///tmp/mosquitto.sock

vjardin

Thansk @fpagliughi ; it'll be a nice security and performance improvement. I took the liberty to review your commits.

src/MQTTAsyncUtils.h

src/MQTTClient.c

src/MQTTProtocolOut.c

vjardin · 2025-01-02T11:03:08Z

src/MQTTAsync.c

@@ -329,6 +329,9 @@ int MQTTAsync_createWithOptions(MQTTAsync* handle, const char* serverURI, const
 	{
 		if (strncmp(URI_TCP, serverURI, strlen(URI_TCP)) != 0
 		 && strncmp(URI_MQTT, serverURI, strlen(URI_MQTT)) != 0
+#if defined(UNIXSOCK)


you should avoid such if defined() in order to avoid code complexity. The error cases can be handled for WIN32 or non UNIXSOCK into the function Socket_unix_new() that can be available for all the cases, but that should return a runtime ERROR when Unixsock is not available.

So the code will be easier to read.

I disagree here. The conditional compilation ensures that unix:// is reported as an unsupported protocol if support is not compiled into the library - just the same way it's done with ssl://, mqtts://, and wss://.

vjardin · 2025-01-02T11:05:54Z

src/samples/MQTTClient_publish.c

@@ -34,7 +34,10 @@ int main(int argc, char* argv[])
    MQTTClient_deliveryToken token;
    int rc;

-    if ((rc = MQTTClient_create(&client, ADDRESS, CLIENTID,
+	const char* uri = (argc > 1) ? argv[1] : ADDRESS;


ident issue.

src/samples/MQTTClient_publish_async.c

vjardin · 2025-01-02T11:06:32Z

src/samples/MQTTAsync_subscribe.c

@@ -137,7 +137,10 @@ int main(int argc, char* argv[])
 	int rc;
 	int ch;

-	if ((rc = MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL))
+	const char* uri = (argc > 1) ? argv[1] : ADDRESS;


ident issue

src/samples/MQTTAsync_publish.c

vjardin · 2025-01-02T11:07:28Z

src/Socket.c

+			if (1)
+			{
+				int optsend = 100; //2 * 1440;
+				printf("Setting optsend to %d\n", optsend);
+				if (setsockopt(*sock, SOL_SOCKET, SO_SNDBUF, (void*)&optsend, sizeof(optsend)) != 0)
+					Log(LOG_ERROR, -1, "Could not set SO_SNDBUF for socket %d", *sock);
+			}
+#endif


you are not changing any code -> ident issue. The diff should be empty.

I disagree in the sense that the previous indenting was incorrect and misleading. Admittedly, this has nothing to do with the rest of the PR; it's a holdover from my initial attempt to modify Socket_new() for UNIX sockets, before deciding that adding a separate Socket_unix_new() would be more clear.

I'd prefer to keep it.

fpagliughi · 2025-01-02T16:21:14Z

@vjardin Thanks so much for the review! So nice to have this quick feedback. I made some changes, and added my reasoning for not making other changes.

vjardin · 2025-01-02T17:21:03Z

OK, LGTM.

Regaarding NOSIGPIPE, if it is not defined, it means that you should handle the SIGPIPE, I did not check if it is properly done. But in 2025, it should not be a topic !

fpagliughi · 2025-01-02T17:44:09Z

For years I made the argument to implement UNIX sockets for MQTT to reduce latency in local systems, but that never seemed to sway people. The security argument gets people's attention.

But I just ran my first test, compiling this branch into the Paho Rust library and using it on an MQTT v5 RPC system that I have for one of my customers. Each service exports a ping function to check that it's alive and responsive. The full round-trip is four publishes:

client [request] -> broker -> service [response] -> broker -> client

I just tried it to compare localhost TCP to Unix sockets:

$ svcctl ping  -U tcp://localhost:1883                                   
Service responded in 43.247ms

$ svcctl ping -U unix:///tmp/mosquitto.sock
Service responded in 2.530ms

Using TCP takes 43ms... using UNIX sockets takes 2.5ms.

That's a 94% reduction in round-trip latency!!!

@icraggs : I need this mergerd and released ASAP!!! :-)

vjardin · 2025-01-02T18:02:29Z

Same, this requirement of unix socket is for both security and performances.

icraggs · 2025-01-02T18:20:34Z

Great! Does this change the external interfaces - as in could we have it in the next 1.3.n release?

I'm close to getting a 1.3.14 release out (I'm doing a proxy issue at the moment ) @fpagliughi could you take a look at this build issue to help me out? #1376

fpagliughi · 2025-01-02T19:06:51Z

Hey @icraggs, no this doesn't change the external interfaces. When built in, it just allows the library to recognize a new URI scheme ("unix://") and handle it accordingly. I would love to get it into v1.3.x

I will squash the commits in this PR to make it easy to apply to both branches, and run some tests myself to merge and build in the develop branch.

fpagliughi · 2025-01-02T19:07:35Z

Later today I can get a Windows machine running and test #1376

fpagliughi · 2025-01-02T22:40:50Z

OK, I squashed this PR and then tried to cherry-pick the resulting commit into the develop branch. It didn't merge cleanly due to the choose-an-interface code from v1.4 in Socket.c

So I cleaned up the merge and created another pull request, #1553.

So both PRs can be landed into their target branches... this one into v1.4 and the other into develop.

icraggs · 2025-01-03T15:08:51Z

I use the paho_c_pub and paho_c_sub samples a lot. Their interface is similar to mosquitto_pub and sub. You can try the unix sockets without any changes, for instance:

build.paho/src/samples/paho_c_pub x --connection unix:///tmp/mosquitto.sock --trace protocol

vjardin suggested changes Jan 2, 2025

View reviewed changes

fpagliughi force-pushed the unix-sockets-new branch from a605d50 to 62f0d6a Compare January 2, 2025 21:39

fpagliughi mentioned this pull request Jan 2, 2025

Added support for UNIX-domain sockets for v1.3.x #1553

Merged

Added support for UNIX-domain sockets

5337ac3

fpagliughi force-pushed the unix-sockets-new branch from 62f0d6a to 5337ac3 Compare January 2, 2025 22:28

icraggs added this to the 1.3.14 milestone Jan 3, 2025

icraggs merged commit e470865 into eclipse-paho:1.4 Jan 3, 2025
5 checks passed

fpagliughi deleted the unix-sockets-new branch January 6, 2025 13:17

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Add support for Unix sockets #1552

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Add support for Unix sockets #1552

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