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Programming on Solana

Intro & Motivation

This guide is meant to serve as an intro to coding on the Solana Blockchain, using an escrow program as an example. We'll go through the code together, building the escrow program step by step. I've also created a UI you will be able to use to try out your program. Additionally, you'll get to play with the (shameless plug) spl-token-ui.

Most of the info in this blog post can be found somewhere in the docs or in example programs. Having said this, I have not found a guide that both walks through most of the coding theory step by step and applies it in practice. I hope this post achieves this, interweaving the theory and practice of solana programs. It requires no previous knowledge of Solana. While this is not a Rust tutorial, I will link to the Rust docs (opens new window)whenever I introduce a new concept. I will also link to the relevant Solana docs although you don't have to read them to follow along.

Important theory will be sprinkled into the post like this:

On Solana, smart contracts are called programs

and at the end of each section summarized like this:

theory recap πŸ“š

- On Solana, smart contracts are called programs
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I do not claim to explain all topics but hope this will be a solid starting point from which the reader can explore Solana further. If you're new to Solana and Rust and want to finish this post without breaks and leave with a solid understanding of all concepts discussed and links mentioned I recommend allocating an entire day to the post.

If something is not working and you just cannot figure out why, have a look at the final code here.

The Final Product

Before we start coding, let's look at the final product to understand what we are building: an escrow program.

What is an escrow?
An escrow smart contract is a good example to look at and build because it highlights well what a blockchain makes possible while still being easy to understand, allowing us to focus on the code itself. For those unfamiliar with the concept, here is a brief explainer.

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Imagine Alice has an asset A and Bob has an asset B. They would like to trade their assets but neither wants to send their asset first. After all, what if the other party does not hold up their end of the trade and runs away with both assets? A deadlock will be reached where no party wants to send their asset first.

The traditional way to solve this problem is to introduce a third party C which both A and B trust. A or B can now go first and send their asset to C. C then waits for the other party to send their asset and only then does C release both assets.

The blockchain way is to replace the trusted third party C with code on a blockchain, specifically a smart contract that verifiably acts the same way a trusted third party would. A smart contract is superior to a trusted third party because of a number of reasons e.g. can you be sure that the trusted third party isn't colluding with the person on the other side of the trade? You can be sure with a smart contract because you can look at the code before running it.

I'll end this background section here. The internet already has a lot of material on escrows on blockchains. Let's now look at how to build such an escrow on Solana.

Building the escrow program - Alice's Transaction

Setting up the project

Head over to the template repo, click Use this template, and set up a repo. The Solana ecosystem is still young so this is what we've got for now. Vscode with the Rust extension is what I use. You'll also need Rust. Additionally, go here (opens new window)to install the Solana dev tools. (If you're on mac and there are no binaries for the version you want, follow the "build from source" section and add installed the bins to path. If it doesn't build because a command cannot be found, try installing coreutils and binutils with homebrew).

If you don't know how to test solana programs yet, remove all the testing code. Testing programs is a topic for another blog post. Remove the testing code in as well as the tests folder next to src. Lastly, remove the testing dependencies from Cargo.toml. It should now look like this:

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