Bug fix for issue CocoaLumberjack#38 - DDTTYLogger can cause a crash …

…if the log message is too big for the stack

Lumberjack/DDTTYLogger.m

@@ -1088,10 +1088,15 @@ - (void)logMessage:(DDLogMessage *)logMessage
 		}
 
 		// Convert log message to C string.
-		// The technique below is faster than using the UTF8String method.
+		// 
+		// We use the stack instead of the heap for speed if possible.
+		// But we're extra cautious to avoid a stack overflow.
 
 		NSUInteger msgLen = [logMsg lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
-		char msg[msgLen + 1];
+		const BOOL useStack = msgLen < (1024 * 4);
+
+		char msgStack[useStack ? (msgLen + 1) : 0];
+		char *msg = useStack ? msgStack : (char *)malloc(msgLen + 1);
 
 		[logMsg getCString:msg maxLength:(msgLen + 1) encoding:NSUTF8StringEncoding];
 
@@ -1219,6 +1224,10 @@ - (void)logMessage:(DDLogMessage *)logMessage
 
 			writev(STDERR_FILENO, v, 12);
 		}
+
+		if (!useStack) {
+			free(msg);
+		}
 	}
 }