code.m

///////////////////////////////////////////////////////////////////////////
// Application Delegate
///////////////////////////////////////////////////////////////////////////
// The Application delegate launches a server written in C
// This server is listening for XML-RPC Calls
///////////////////////////////////////////////////////////////////////////
- (void)applicationDidFinishLaunching:(NSNotification*)aNotification
{
    Server *server = [[Server alloc] init];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [server start];
    });
}

///////////////////////////////////////////////////////////////////////////
// Server Start
///////////////////////////////////////////////////////////////////////////
// The Application delegate above calls the below code
///////////////////////////////////////////////////////////////////////////
- (void) start {
...
    xmlrpc_server_abyss(&env, &serverparm, XMLRPC_APSIZE(log_file_name));
    if (env.fault_occurred) {
        printf("xmlrpc_server_abyss() failed.  %s\n", env.fault_string);
        exit(1);
    }
}

///////////////////////////////////////////////////////////////////////////
// The C Server
// The Abyss Server (XML-RPC server) invokes some functions like the one below
// The function below works when called from an external XML RPC Program
// HOWEVER if NSApplication SendEvent is invoked it will freeze the application
///////////////////////////////////////////////////////////////////////////
static xmlrpc_value *
window_make(xmlrpc_env *   const envP,
            xmlrpc_value * const paramArrayP,
            void *         const serverInfo,
            void *         const channelInfo) {
    __block NSString* operationResult = @"";
    
    dispatch_sync(dispatch_get_main_queue(), ^{
    NextApplicationDelegate *delegate = [NSApp delegate];
    operationResult = [delegate windowMake];
    });
    
    return xmlrpc_build_value(envP, "s", [operationResult UTF8String]);
}

///////////////////////////////////////////////////////////////////////////
// NSApplication
///////////////////////////////////////////////////////////////////////////
- (void)sendEvent:(NSEvent *)event
{
    if ([event type] == NSEventTypeKeyDown) {
        NSEventModifierFlags modifierFlags = [event modifierFlags];
        char characterCodePressed = [[event charactersIgnoringModifiers] characterAtIndex: 0];
        bool controlPressed = (modifierFlags & NSEventModifierFlagControl);
        bool alternatePressed = (modifierFlags & NSEventModifierFlagOption);
        bool commandPressed = (modifierFlags & NSEventModifierFlagCommand);
        
        xmlrpc_env env;
        xmlrpc_value * resultP;
        xmlrpc_bool consumed;
        const char * const serverUrl = "http://localhost:8081/RPC2";
        const char * const methodName = "PUSH-KEY-CHORD";
        
        // Initialize our error-handling environment.
        xmlrpc_env_init(&env);
        
        // Start up our XML-RPC client library.
        xmlrpc_client_init2(&env, XMLRPC_CLIENT_NO_FLAGS, NAME, VERSION, NULL, 0);
        reportIfFaultOccurred(&env);
        
        // Make the remote procedure call
        resultP = xmlrpc_client_call(&env, serverUrl, methodName,
                                     "(bbbi)",
                                     (xmlrpc_bool) controlPressed,
                                     (xmlrpc_bool) alternatePressed,
                                     (xmlrpc_bool) commandPressed,
                                     (xmlrpc_int) characterCodePressed);
        reportIfFaultOccurred(&env);
        
        xmlrpc_read_bool(&env, resultP, &consumed);
        reportIfFaultOccurred(&env);
        printf("The sequence was consumed: %d\n", consumed);
        
        xmlrpc_client_cleanup();
        
        // If the key sequence was not consumed, pass it along
        if (!consumed) {
            [super sendEvent:event];
        }
        
    } else {
        [super sendEvent:event];
    }
}