Posts

I was always wondering how Flash loans actually work, how can we get uncollateralized loan on blockchain. I got better understanding of Flash loans while solving Free Rider problem. In this post, I tried to explain how Flash loans actually work using pseudo code. If you want to have a look at actual solidity code. See Reference section. What are Flash Loans? Flash loans are uncollateralized loans in DeFi. They enable users to borrow liquidity instantly without any collateral. There is a catch, the borrowed amount needs to be paid back in the same transaction, along with some fees which can vary for different protocols. It’s a bit difficult to understand how this actually happens, so we will look at some code examples to understand how this is achieved. ...

Recently, I came across bots doing arbitrage on Solana. Was reading about wormhole hack and how it created great opportunities for bots to make free money. Note that the wormhole hack was a long tail event. In general, arbitrage is a very competitive space and needs constant improvements in strategy. Misaka wrote a detailed analysis on bots which made money in the “Golden 30 mins” just after the hacker dumped stolen ETH into Solana AMM pools. Quoting from the post ...

I recently came across a post “How to become a Smart Contract Auditor” by cmichel. The post breaks down the skills required and points to good resources to get started with Smart Contract security. Before this, I was exploring development on Ethereum using Solidity. Solving these challenges has given me better insights to look at code from a security perspective and improved overall Solidity skills. Code solutions can be found on my fork of damn-vulnerable-defi repo. Feel free to suggest/comment some other ways to exploit the challenges or any gas optimizations (I didn’t tried to optimize for gas while writing exploits) ...

In this post, we are going to look into how raydium swap works using Serum CLOB (Central limit order book). Before diving into how swap works in raydium, let’s have a brief look into Solana blockchain and Serum DEX. Solana It’s a layer 1 blockchain similar to ethereum but with improvements like supporting very high TPS, parallel smart contract runtime, etc. If you are interested in finding out what makes Solana great in comparison to other layer 1 solutions out there. Give this post a read by Anatoly Yakovenko. ...

Annotations are one of those features of Java whose working is not much clear to the developers. This post is for self reference for annotations in java. Some example of annotations below - @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE) public @interface FunctionalInterface { } @Target(ElementType.METHOD) @Retention(RetentionPolicy.SOURCE) public @interface Override { } Any annotation has a retention policy attached to it. There are 3 types of “Retention Policy” SOURCE -> These annotations are in source code only. When the “.java” file is compiled to “.class” these annotations are gone. ...

In this post, we are going to create a Generic Segment Tree. Before creating a Generic Segment Tree, we will try to solve a basic segment tree problem and try to find what part of our code is problem specific and abstract it out i.e there are some things which are common in any segment tree problem like creating the tree, querying the tree, etc. We will try to identify the piece of logic which is specific to our problem. Lets take the example of the “range sum problem”. ...

In this post, I am going to discuss a scenario where I had to use “git rebasing” for something other than squashing commits. Lets build up from the starting, I am going to use a short form “CR” for code review. When I have to work on a feature, I generally cut a branch from the mainline and start development on it. git checkout -b feature-branch-101 The above command will create a branch named “feature-branch-101” and make it the current branch. I start implementing the feature. Let’s say I made a commit (Commit A) and raised a CR corresponding to that commit. And continued development, till the CR comments came I did 2 more commits (Commit B and C). Now the repository scenario is something like below. ...

Before starting with the post, try to find the output for below code snippet: Integer a = 100; Integer b = 100; System.out.println(a == b); Integer c = 1000; Integer d = 1000; System.out.println(c == d); Note the answer somewhere, we will come back to it after looking at some concepts which will help in answering this. Auto-boxing and Auto-unboxing in Java Integer i = 2 doesn’t make sense as i is an object reference and you are assigning it a literal. But this works because of auto-boxing in Java. ...

In this post, we are going to discuss about: what streams are in context of CS their support in Java lazy evaluation in streams how to create finite and infinite streams how streams along with functions help in writing declarative code Stream by definition is a sequence of data which can be finite or infinite. Wikipedia: Stream is a sequence of data elements made available overtime. A Stream can be thought of as items on conveyer belt being processed one at a time rather than in batches. ...

In this post, I am going to share my observation after playing with Xms parameter in JVM on different Operating Systems. Initially, my understanding of Xms was that Xms is the minimum heap space the JVM should get before starting the Java process, if this much main memory (RAM) isn’t available then program should not start. So I wrote a simple program which just outputs a String. // Simple program that I ran with different Xms values public class Test { public static void main(String[] args) { System.out.println("yo man"); } } Compiled above program using ...