Code Review vs. Dynamic Testing explained with Minecraft

Key Takeaways

hello welcome back in this episode i want to build a few more things i want this spawn area to look very nice and i really like this hole behind me and so i wanted to make something with it so let's start off this video with a quick build sequence [Music] [Music] [Music] all right there we go a nice bridge walkway around the edge a small pond and a fountain as well as a road up to the market area also i'm alone noob is here again and while i was decorating a bit i suddenly started to hear music hopefully this doesn't get the video claimed but damn i'm jamming let's go uh-huh okay enough stop it while i decorate the base a bit and collect some materials i wanted to talk about code review versus dynamic testing so when you as a hacker try to find vulnerabilities you can try to do it blindly just test the application or maybe you have access to the source code and you read code instead and so the question might be which one is better i love code reviews and generally i think it's a waste of money and other resources when you don't have access to them it's one major reason why i don't like to do bugbounty because most of the targets are closed source but code review is not always the silver bullet i admit sometimes dynamic testing is a lot easier because maybe the code is just awful or there is just too much of it using the application and looking for functionality to then specifically test might be a lot more useful so for me in my day-to-day job doing this professionally i constantly flow between dynamic testing and code review and do whatever i feel like is the right choice at the moment that's why i think it's so important for hackers to learn coding or at least learn to read code because if you lack this tool you might be left with very inefficient dynamic testing now i wanted to briefly come back to something i did in a previous episode remember i did dynamic testing to figure out how far away creepers get scared by cats well let's see if we can find this in the code as well in net minecraft entity mob creeper entity we can find the creeper class it's very interesting to read the code here but we are mostly interested in the ai of the mob i'm looking at this code for the first time but it seems the code is very self-explanatory these goals seem to describe the goal of the mob the behavior the ai so for example with priority one the player is the active target so the creeper attacks us but there's also a visibility check for the player only if the creeper sees us it will target us and see this with a slight lower priority of 3 the creeper will flee it will flee from cats and ocelots and the distance this happens at 6 blocks this is a really cool example for code review versus dynamic testing testing for the distance a creeper will flee from a cat is easy in minecraft you have to create a small test setup but then it's easy to test and that takes maybe around the same time it takes me to open up intellij pulling up the code and finding the right class and read the value here however we never talked about finding out what a creeper is scared about in the first place is a creeper even scared of anything well maybe you would stumble over this behavior while playing maybe you observed this in the wild but if you didn't it would be quite a lot of effort to figure out what kind of other entity mob or item makes a creeper scared looking at the code here this is super simple scared of cats and ocelots but let me show you an example where i think dynamic testing is a lot more useful we know mobs can die when falling down a large distance but what's the limit how far can they fall before they die maybe we want to know that so we can build a farm where we damage them just enough for a single punch well this is of course answered in the code somewhere but it's probably calculated over time the falling speed is building up so that influences how much damage they take and then the next question how much health does a creeper have anyway here's a handle fall damage function it takes a fall distance damage multiplier and damage source it cause compute fall damage in the superclass which is fall distance minus 3 minus the status effect times the damage multiplier this means we have to figure out where handle fall damage is even called what is the damage multiplier and how much health does a creeper have you see it gets a bit convoluted why not just go in a creative world and test it build a small test platform and let creepers fall down it's a bit of a process too but you will definitely find the answer after some trial and error the height is 24 blocks now they got max damage and die with a single punch as you can see to figure this out the best strategy seems to be dynamic testing just because i know i will easily get the answer this way no need to struggle through the code cool now we saw an example for both cases i hope this shows you how important it is to choose the right strategy for whatever you want to figure out and now let's use our code review skills a bit more in hermitcraft season 9 episode 2 by doc m77 he revealed a prank let me show you a clip from his video so i actually pranked the whole server so yeah what happens if you put a turtle egg in any minecraft world exactly at 0 0 0 any zombie in the world not only you know around the player here standing globally so any zombie that is loaded by any other hermit will start trekking towards this egg globally oh here we go look at the zombies look at the congo line back there zombie tracking ain't not working anymore country roads take me home to the place i belong zero zero that is so weird turtle egg in zero zero zero and zombies from everywhere start walking there but why and how could you figure something out like this well i'm 99.9 confident that this was not found accidentally in game who would come up with testing that but if you read the code around mob ai it could be obvious check this out here's the zombie entity class and it has an ai goal to destroy any egg specifically the turtle egg block this inherits from the step and destroy block goal so this seems to be generally ai code to take a step so walk towards and destroy a target block and here's that class in the tick method it always takes the mob position but only does something if the mob reaches the target block which means the ai to walk the egg is somewhere else probably in the other class it inherits from move to target goal in that tick function if we found a target and this tick goal is executed we would start moving towards that so how do we even get a target block to work towards where is target position set well look here at the find target position function here takes the current mob position and searches all blocks in an area around with some nested loops and if a particular position is in walking range and at this position we have the target block an egg then we remember this position as the target position but clearly an egg at 0 0 0 would not be in range for a mob very far away so this loop is probably not interesting for us so where else is the target position set and look at that in the constructor the target position is set to the origin block the block position which x y and z values are all zero sounds suspicious right i think we're on the right track obviously this is just meant as a temporary value but this means the ai goal is always initialized to 0 0 0 by default let's go back down to the step and destroy block goal class here's a function that determines if this ai goal can start to be executed and here we can see if the zombie has an available target this ai goal can be started when do we have an available target if we have a target position set which we have it's never null it's initialized with the origin and then it checks this position with is target pos this function takes the corresponding chunk of the world to check the target block and if the block is the target block so if it's a turtle egg this will return true so if a turtle egg happens to be at 0 0 0 then this check will always be true the zombie has an available target in the goal selector class this is the class deciding which goals to execute so basically decide the ai behavior of the zombie here it will now be able to start on the egg destroy goal which makes the zombie move towards the egg on every tick so yeah if you read minecraft code for fun because maybe you want to optimize a zombie form and you want to understand the zombie ai you could stumble over this bug maybe you notice the target pause can never be no so that makes the behavior weird and now understanding this code we can also check if this applies to other mobs is there any other mob with a step and destroy block goal turns out no the zombie is the only one that uses it but there's also the more general class move to target post goal that one is used by a few other ai goal classes while this class is kinda the root of the bug it's initializing the target position to the origin this can start method is safe it only returns true if find target pause is true and that searches blocks nearby so this ai generally doesn't trigger if the target block is not in range the zombie bug only happens because step and destroy block goal overwrites the can start method and changes that behavior so let's see if other ai classes overwrite the can start method as well and maybe they have a similar bug cat sit on block goal looks safe it does call into the superclass can start method and same for go to bed and sleep goal fox eating berries goal also calls the super class all of them call the parent class can start which will check with find target pause if the target block is within range looks like the bug only affects zombies by the way the server starts to see a bit more activity i try to afk sometimes to be able to record in case people join and yeah i was able to capture a few players spawning in my trap they only can get out if they have a fly hack though and turns out of course they do to record the spawn area i was also laying a bit further away behind the tree and of course players also found me there but where is everybody i was really hoping people would start expanding my base building their own houses or whatever up there but nothing i'm still alone maybe they don't play on here and just join or they go on their own adventure which is of course also cool maybe in the future i could try to find their bases i have access to the server so we could try to find where they are at some point anyway i want to build another farm as well maybe a small bee farm candles and honey blocks would be cool and i built it below the market but it kind of looked like so i decided to try to make like a flowery greenhouse kind of thing with lots of glass so i had to gather some more sand and smelt it and then just try to build one by the way this was not planned in creative before this is me actually trying to make something in survival but i don't know it looked kind of bad i also expanded the bee farm with a few more hives that i collected by the way the barrels on top are used to feed the farm with shears and bottles i thought it could be nice once we expand the market up here it looks very organic anyway after the first iteration i decided to change a few things remove the fence posts and replace it with strip wood logs and added a bit more supporting ceiling and cool be farm done so see you next episode [Music] you