LightMessaging

LightMessaging is an inter-process communication header-only library by Ryan Petrich. According to its GitHub page, it is a "simple low-level replacement for CFMessagePort".

How to use this library

Headers are available from LightMessaging's GitHub project. If using Theos, place the headers in $THEOS/include/LightMessaging.

Include directive

#import <LightMessaging/LightMessaging.h>

RocketBootstrap

LightMessaging uses RocketBootstrap by default, so be sure to have it set up (instructions here). To have LightMessaging **not** use RBS, add the following directive before including the LM header:

#define LIGHTMESSAGING_USE_ROCKETBOOTSTRAP 0

Server

It is recommended that this is done in somewhere better designed to act as a server, such as SpringBoard or a daemon.

The Callback

void some_callback(CFMachPortRef port,
                   LMMessage *request,
                   CFIndex size,
                   void *info)
{
	// get the reply port
	mach_port_t replyPort = request->head.msgh_remote_port;

	// sanity check
	if (size < sizeof(LMMessage)) {
		LMSendReply(replyPort, NULL, 0);
		LMResponseBufferFree((LMResponseBuffer *)request);
		return;
	}
    
	// get the data you recieved
	void *data = LMMessageGetData(request);

	// send some data back
	const char *msg = "lol";
	LMSendReply(replyPort, msg, strlen(msg) + 1);

	// free the response buffer??
	LMResponseBufferFree((LMResponseBuffer *)request);
}

Starting the Server

LMStartService("net.iphonedevwiki.some.server", CFRunLoopGetCurrent(), (CFMachPortCallBack)some_callback);

Client

This can be run anywhere that has the appropriate permissions to send/receive data on a message port.

// setup connection
LMConnection connection = {
	MACH_PORT_NULL,
	"net.iphonedevwiki.some.server"
};

//send message
LMResponseBuffer buffer;
const char *msg = "lol wtf";
SInt32 messageId = 0x1111; // this is arbitrary i think
LMConnectionSendTwoWay(&connection, messageId, msg, strlen(msg) + 1, &buffer);
LMMessage *response = &(buffer.message);

// do whatever you want !!!!
const char *data = LMMessageGetData(response);

Type helpers

There are some cool helper functions for if you want to send Images / PropertyLists / etc instead of just strings. Look at the header file or other examples to see how to use them.

Examples

• libcanopenurl
• AppList

External links

• rpetrich's JailbreakCon 2016 keynote on IPC
• LightMessaging.h