Capturing ASL on Mac/iOS

GFASLProxy.m

// See also https://github.com/CocoaLumberjack/CocoaLumberjack/blob/master/Classes/DDASLLogCapture.m


#import "GFASLProxy.h"
#include <asl.h>
#include <notify.h>
#include <notify_keys.h>
#include <sys/time.h>

@implementation GFASLProxy
{
	unsigned long long _lastSeenID;
	int _notifyToken;
	unsigned long long _startTime;
}
- (id)init
{
	if(!(self = [super init]))
		return nil;
	
	struct timeval timeval = {
		.tv_sec = 0
	};
	gettimeofday(&timeval, NULL);
	_startTime = timeval.tv_sec;
	
	__weak typeof(self) weakSelf = self;
	notify_register_dispatch(kNotifyASLDBUpdate, &_notifyToken, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^(int token)
	{
		[weakSelf _lookForNewMessages];
	});

	
	return self;
}
- (void)dealloc
{
	notify_cancel(_notifyToken);
}

- (void)_lookForNewMessages
{
	aslmsg query = asl_new(ASL_TYPE_QUERY);
	char stringValue[64];

	if (_lastSeenID > 0) {
		snprintf(stringValue, sizeof stringValue, "%llu", _lastSeenID);
		asl_set_query(query, ASL_KEY_MSG_ID, stringValue, ASL_QUERY_OP_GREATER | ASL_QUERY_OP_NUMERIC);
	} else {
		snprintf(stringValue, sizeof stringValue, "%llu", _startTime);
		asl_set_query(query, ASL_KEY_TIME, stringValue, ASL_QUERY_OP_GREATER_EQUAL | ASL_QUERY_OP_NUMERIC);
	}

    const char param[] = "7";  // ASL_LEVEL_DEBUG
    asl_set_query(query, ASL_KEY_LEVEL, param, ASL_QUERY_OP_LESS_EQUAL | ASL_QUERY_OP_NUMERIC);

	// Iterate over new messages.
	aslmsg msg;
	aslresponse response = asl_search(NULL, query);

	while ((msg = asl_next(response)))
	{
		[self _messageReceived:msg];

		// Keep track of which messages we've seen.
		_lastSeenID = atoll(asl_get(msg, ASL_KEY_MSG_ID));
	}
	asl_release(response);


	free(query);
}

- (void)_messageReceived:(aslmsg)msg
{
    const char* messageCString = asl_get( msg, ASL_KEY_MSG );
    const char* secondsCString = asl_get( msg, ASL_KEY_TIME );
    const char* nanoCString = asl_get( msg, ASL_KEY_TIME_NSEC );
    if ( messageCString == NULL || secondsCString == NULL || nanoCString == NULL )
        return;

    int level = [@(asl_get(msg, ASL_KEY_LEVEL)) intValue];
	NSString *levelS =
		level == ASL_LEVEL_EMERG ? @"Emergency" :
		level == ASL_LEVEL_CRIT ? @"Critical" :
		level == ASL_LEVEL_ERR ? @"Error" :
		level == ASL_LEVEL_WARNING ? @"Warning" :
		level == ASL_LEVEL_NOTICE ? @"Notice" :
		level == ASL_LEVEL_INFO ? @"Info" :
		level == ASL_LEVEL_DEBUG ? @"Debug" :
		@"Unknown";

    NSString *sender = [NSString stringWithCString:asl_get(msg, ASL_KEY_SENDER) encoding:NSUTF8StringEncoding];
    NSString *message = @(messageCString);
    NSString *secondsStr = @(secondsCString);
    NSString *nanoStr = @(nanoCString);

    NSTimeInterval seconds = [secondsStr doubleValue];
    NSTimeInterval nanoSeconds = [nanoStr doubleValue];
    NSTimeInterval totalSeconds = seconds + (nanoSeconds / 1e9);

    NSDate *timeStamp = [NSDate dateWithTimeIntervalSince1970:totalSeconds];
	
	dispatch_async(dispatch_get_main_queue(), ^{
		[self.receiver streamNamed:@"ASL" interceptedLine:message logLevel:levelS at:timeStamp source:sender];
	});
}
@end