Intro to Anchor development

Summary #

• Programs on Solana have instruction handlers, which are functions that take arguments from incoming instructions. They are the entry point for any operation in a program.
• Rust is the most common language for building Solana programs. The Anchor framework takes care of common grunt work - like reading data from incoming instructions, and checking the right accounts are provided - so you can focus on building your Solana program.

Lesson #

Before we begin, make sure you have Anchor installed. You can follow this lesson on local-setup.

Solana's capacity to execute arbitrary code is a key part of its power. Solana programs, (sometimes called "smart contracts"), are the very foundation of the Solana ecosystem. And as developers and creators continuously conceive and deploy new programs, the collection of Solana programs continues to expand daily.

Every popular Solana exchange, borrow-lend app, digital art auction house, perps platform, and prediction market is a program.

This lesson will give you a basic introduction to writing and deploying a Solana program using the Rust programming language and the Anchor framework.

What is Anchor? #

Anchor makes writing Solana programs easier, faster, and more secure, making it the "go-to" framework for Solana development. It makes it easier to organize and reason about your code, implements common security checks automatically, and removes a significant amount of boilerplate code that is otherwise associated with writing a Solana program.

Anchor program structure #

Anchor uses macros and traits to simplify Rust code for you. These provide a clear structure to your program so you can focus more on its functionality.

Some important macros provided by Anchor are:

• declare_id! - a macro for declaring the program’s onchain address
• #[program] - an attribute macro used to denote the module containing the program’s instruction handlers.
• Accounts - a trait applied to structs representing the list of accounts required for an instruction.
• #[account] - an attribute macro used to define custom account types for the program.

Let's talk about each of them before putting all the pieces together.

Declare your program ID #

The declare_id macro sets the onchain address of the Anchor program (i.e. the programId). When you create a new Anchor program, the framework generates a default keypair. This keypair is used to deploy the program unless specified otherwise. The public key of this keypair is used as the programId in the declare_id! macro.

declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");

Define instruction logic #

The #[program] attribute macro defines the module containing all of your program's instruction handlers. This is where you implement the business logic for each operation in your program.

Each public function in the module with the #[program] attribute will be treated as a separate instruction handler.

Each instruction handler (function) requires a parameter of type Context and can include more parameters as needed. Anchor will automatically handle instruction data deserialization so that you can work with instruction data as Rust types.

#[program]
mod program_module_name {
    use super::*;
 
    pub fn instruction_one(ctx: Context<InstructionAccounts>, instruction_data: u64) -> Result<()> {
		ctx.accounts.account_name.data = instruction_data;
        Ok(())
    }
}

• The #[program] attribute macro is used to denote the module containing the program’s instruction logic.
• use super::*; is used to bring all the items from the parent module into scope, which are needed to define the instruction logic.
• Next, there is the instruction handler function. This function just writes some data (instruction_data in this case) to an account.

Instruction Context #

The Context type exposes instruction metadata and accounts to your instruction logic.

pub struct Context<'a, 'b, 'c, 'info, T: Bumps> {
    /// Currently executing program id.
    pub program_id: &'a Pubkey,
    /// Deserialized accounts.
    pub accounts: &'b mut T,
    /// Remaining accounts given but not deserialized or validated.
    /// Be very careful when using this directly.
    pub remaining_accounts: &'c [UncheckedAccount<'info>],
    /// Bump seeds found during constraint validation. This is provided as a
    /// convenience so that handlers don't have to recalculate bump seeds or
    /// pass them in as arguments.
    /// Type is the bumps struct generated by #[derive(Accounts)]
    pub bumps: T::Bumps,
}

Context is a generic type where T defines the list of accounts an instruction handler requires. When you use Context, you specify the concrete type of T as a struct that adopts the Accounts trait.

The first argument of every instruction handler must be Context. Context takes a generic of your Accounts struct, eg, if AddMovieReview was the struct holding the accounts, the context for the add_movie_review() function would be Context<AddMovieReview>.

Through this context argument the instruction can then access:

• The accounts passed into the instruction (ctx.accounts)
• The program ID (ctx.program_id) of the executing program
• The remaining accounts (ctx.remaining_accounts). The remaining_accounts is a vector that contains all accounts that were passed into the instruction handler but are not declared in the Accounts struct.
• The bumps for any PDA accounts in the Accounts struct (ctx.bumps)
• The seeds for any PDA accounts in tha Accounts struct (ctx.seeds)

Define instruction accounts #

The Accounts trait:

• Defines a structure of validated accounts for an instruction handler
• Makes accounts accessible through an instruction handler's Context
• Is typically applied using #[derive(Accounts)]
• Implements an Accounts deserializer on the struct
• Performs constraint checks for secure program execution

Example:

• instruction_one requires a Context<InstructionAccounts>
• InstructionAccounts struct is implemented with #[derive(Accounts)]
• It includes accounts like account_name, user, and system_program
• Constraints are specified using the #account(..) attribute

#[program]
mod program_module_name {
    use super::*;
    pub fn instruction_one(ctx: Context<InstructionAccounts>, instruction_data: u64) -> Result<()> {
		...
        Ok(())
    }
}
 
#[derive(Accounts)]
pub struct InstructionAccounts<'info> {
    #[account(
        init,
        payer = user,
        space = DISCRIMINATOR + AccountStruct::INIT_SPACE
    )]
    pub account_name: Account<'info, AccountStruct>,
 
    #[account(mut)]
    pub user: Signer<'info>,
 
    pub system_program: Program<'info, System>,
}

When instruction_one is invoked, the program:

• Checks that the accounts passed into the instruction handler match the account types specified in the InstructionAccounts struct
• Checks the accounts against any additional constraints specified

Account validation #

You may have noticed in the previous example that one of the accounts in InstructionAccounts was of type Account, one was of type Signer, and one was of type Program.

Anchor provides a number of account types that can be used to represent accounts. Each type implements different account validation. We'll go over a few of the common types you may encounter, but be sure to look through the full list of account types.

Account #

Account is a wrapper around UncheckedAccount that verifies program ownership and deserializes the underlying data into a Rust type.

// Deserializes this info
pub struct UncheckedAccount<'a> {
    pub key: &'a Pubkey,
    pub is_signer: bool,
    pub is_writable: bool,
    pub lamports: Rc<RefCell<&'a mut u64>>,
    pub data: Rc<RefCell<&'a mut [u8]>>,    // <---- deserializes account data
    pub owner: &'a Pubkey,    // <---- checks owner program
    pub executable: bool,
    pub rent_epoch: u64,
}

Recall the previous example where InstructionAccounts had a field account_name:

pub account_name: Account<'info, AccountStruct>

The Account wrapper here does the following:

• Deserializes the account data in the format of type AccountStruct
• Checks that the program owner of the account matches the program owner specified for the AccountStruct type.

When the account type specified in the Account wrapper is defined within the same crate using the #[account] attribute macro, the program ownership check is against the programId defined in the declare_id! macro.

The following are the checks performed:

// Checks
Account.info.owner == T::owner()
!(Account.info.owner == SystemProgram && Account.info.lamports() == 0)

Signer #

The Signer type validates that the given account signed the transaction. No other ownership or type checks are done. You should only use the Signer when the underlying account data is not required in the instruction.

For the user account in the previous example, the Signer type specifies that the user account must be a signer of the instruction.

The following check is performed for you:

// Checks
Signer.info.is_signer == true

Program #

The Program type validates that the account is a certain program.

For the system_program account in the previous example, the Program type is used to specify the program should be the system program. Anchor provides a System type which includes the programId of the system program to check against.

The following checks are performed for you:

//Checks
account_info.key == expected_program
account_info.executable == true

Add constraints with #[account(..)] #

The #[account(..)] attribute macro is used to apply constraints to accounts. We'll go over a few constraint examples in this and future lessons, but at some point be sure to look at the full list of possible constraints.

Recall again the account_name field from the InstructionAccounts example.

#[account(
    init,
    payer = user,
    space = DISCRIMINATOR + AccountStruct::INIT_SPACE
)]
pub account_name: Account<'info, AccountStruct>,
#[account(mut)]
pub user: Signer<'info>,

Notice that the #[account(..)] attribute contains three comma-separated values:

• init - creates the account via a CPI to the system program and initializes it (sets its account discriminator)
• payer - specifies the payer for the account initialization to be the user account defined in the struct
• space- the space allocated on the blockchain to store the account.
  • DISCRIMINATOR is the first 8 bytes of an account, which Anchor uses to save the type of the account.
  • AccountStruct::INIT_SPACE is the total size of space required for all the items in the AccountStruct.
  • The very need of using this space constraint can be eliminated by using #[derive(InitSpace)] macro. We'll see how to use that further in this lesson.

For user we use the #[account(..)] attribute to specify that the given account is mutable. The user account must be marked as mutable because lamports will be deducted from the account to pay for the initialization of account_name.

#[account(mut)]
pub user: Signer<'info>,

Note that the init constraint placed on account_name automatically includes a mut constraint so that both account_name and user are mutable accounts.

#[account] #

The #[account] attribute is applied to structs representing the data structure of a Solana account. It implements the following traits:

• AccountSerialize
• AccountDeserialize
• AnchorSerialize
• AnchorDeserialize
• Clone
• Discriminator
• Owner

You can read more about the details of each trait. However, mostly what you need to know is that the #[account] attribute enables serialization and deserialization, and implements the discriminator and owner traits for an account.

The discriminator is an 8-byte unique identifier for an account type derived from the first 8 bytes of the SHA256 hash of the account type's name. The first 8 bytes are reserved for the account discriminator when implementing account serialization traits (which is almost always in an Anchor program).

As a result, any calls to AccountDeserialize's try_deserialize will check this discriminator. If it doesn't match, an invalid account was given, and the account deserialization will exit with an error.

The #[account] attribute also implements the Owner trait for a struct using the programId declared by declareId of the crate #[account] is used in. In other words, all accounts initialized using an account type defined using the #[account] attribute within the program are also owned by the program.

As an example, let's look at AccountStruct used by the account_name of InstructionAccounts

#[derive(Accounts)]
pub struct InstructionAccounts {
    #[account(init,
        payer = user,
        space = DISCRIMINATOR + AnchorStruct::INIT_SPACE
    )]
    pub account_name: Account<'info, AccountStruct>,
    ...
}
 
#[account]
#[derive(InitSpace)]
pub struct AccountStruct {
    data: u64
}
 
const DISCRIMINATOR: usize = 8;

The #[account] attribute ensures that it can be used as an account in InstructionAccounts.

When the account_name account is initialized:

• The first 8 bytes is set as the AccountStruct discriminator using the DISCRIMINATOR constant.
• The data field of the account will match AccountStruct
• The account owner is set as the programId from declare_id

Bring it all together #

When you combine all of these Anchor types you end up with a complete program. Below is an example of a basic Anchor program with a single instruction that:

• Initializes a new account
• Updates the data field on the account with the instruction data passed into the instruction

// Use this import to gain access to common anchor features
use anchor_lang::prelude::*;
 
// Program onchain address
declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");
 
// Instruction logic
#[program]
mod program_module_name {
    use super::*;
    pub fn instruction_one(ctx: Context<InstructionAccounts>, instruction_data: u64) -> Result<()> {
        ctx.accounts.account_name.data = instruction_data;
        Ok(())
    }
}
 
// Validate incoming accounts for instructions
#[derive(Accounts)]
pub struct InstructionAccounts<'info> {
    #[account(init,
        payer = user,
        space = DISCRIMINATOR + AccountStruct::INIT_SPACE
    )]
    pub account_name: Account<'info, AccountStruct>,
    #[account(mut)]
    pub user: Signer<'info>,
    pub system_program: Program<'info, System>,
}
 
// Define custom program account type
#[account]
#[derive(InitSpace)]
pub struct AccountStruct {
    data: u64
}
 
const DISCRIMINATOR: usize = 8;

Key takeaways: #

• The whole program structure can be broadly divided into three parts:
  1. Account constraints: define the accounts required for the instructions, as well as rules to apply to them - e.g., whether they need to sign the transaction, if they should be created on demand, how addresses for PDAs, etc.
  2. Instruction handlers: implement program logic, as functions inside the#[program] module.
  3. Accounts: define the format used for data accounts.

You are now ready to build your own Solana program using the Anchor framework!

Lab #

Before we begin, install Anchor by following the steps from the Anchor docs.

For this lab we'll create a simple counter program with two instructions:

• The first instruction will initialize an account to store our counter
• The second instruction will increment the count stored in the counter

1. Setup #

Create a new project called anchor-counter by running anchor init:

anchor init anchor-counter

Change into the new directory, then run anchor build

cd anchor-counter
anchor build

Anchor build will also generate a keypair for your new program - the keys are saved in the target/deploy directory.

Open the file lib.rs and look at declare_id!:

declare_id!("BouTUP7a3MZLtXqMAm1NrkJSKwAjmid8abqiNjUyBJSr");

and then run...

anchor keys sync

You'll see the Anchor updates both:

• The key used in declare_id!() in lib.rs
• The key in Anchor.toml

To match the key generated during anchor build:

Found incorrect program id declaration in "anchor-counter/programs/anchor-counter/src/lib.rs"
Updated to BouTUP7a3MZLtXqMAm1NrkJSKwAjmid8abqiNjUyBJSr
 
Found incorrect program id declaration in Anchor.toml for the program `anchor_counter`
Updated to BouTUP7a3MZLtXqMAm1NrkJSKwAjmid8abqiNjUyBJSr
 
All program id declarations are synced.

Finally, delete the default code in lib.rs until all that is left is the following:

use anchor_lang::prelude::*;
 
declare_id!("your-private-key");
 
#[program]
pub mod anchor_counter {
    use super::*;
}

2. Implement Counter #

First, let's use the #[account] attribute to define a new Counter account type. The Counter struct defines one count field of type u64. This means that we can expect any new accounts initialized as a Counter type to have a matching data structure. The #[account] attribute also automatically sets the discriminator for a new account and sets the owner of the account as the programId from the declare_id! macro. We also use the #[derive(InitSpace)] macro for convenient space allocation.

#[account]
#[derive(InitSpace)]
pub struct Counter {
    pub count: u64,
}
 
const DISCRIMINATOR: usize = 8;

3. Implement Context type Initialize #

Next, using the #[derive(Accounts)] macro, let's implement the Initialize type that lists and validates the accounts used by the initialize instruction. It'll need the following accounts:

• counter - the counter account initialized in the instruction
• user - payer for the initialization
• system_program - the system program is required for the initialization of any new accounts

#[derive(Accounts)]
pub struct Initialize<'info> {
    #[account(init,
        payer = user,
        space = DISCRIMINATOR + Counter::INIT_SPACE
    )]
    pub counter: Account<'info, Counter>,
    #[account(mut)]
    pub user: Signer<'info>,
    pub system_program: Program<'info, System>,
}

4. Add the initialize instruction handler #

Now that we have our Counter account and Initialize type , let's implement the initialize instruction handler within #[program]. This instruction handler requires a Context of type Initialize and takes no additional instruction data. In the instruction logic, we are simply setting the counter account's count field to 0.

pub fn initialize(ctx: Context<Initialize>) -> Result<()> {
    let counter = &mut ctx.accounts.counter;
    counter.count = 0;
    msg!("Counter Account Created");
    msg!("Current Count: { }", counter.count);
    Ok(())
}

5. Implement Context type Update #

Now, using the #[derive(Accounts)] macro again, let's create the Update type that lists the accounts that the increment instruction handler requires. It'll need the following accounts:

• counter - an existing counter account to increment
• user - payer for the transaction fee

Again, we'll need to specify any constraints using the #[account(..)] attribute:

#[derive(Accounts)]
pub struct Update<'info> {
    #[account(mut)]
    pub counter: Account<'info, Counter>,
    pub user: Signer<'info>,
}

6. Add increment instruction handler #

Lastly, within #[program], let's implement an increment instruction handler to increment the count once a counter account is initialized by the first instruction handler. This instruction handler requires a Context of type Update (implemented in the next step) and takes no additional instruction data. In the instruction logic, we are simply incrementing an existing counter account's count field by 1.

pub fn increment(ctx: Context<Update>) -> Result<()> {
    let counter = &mut ctx.accounts.counter;
    msg!("Previous counter: {}", counter.count);
    counter.count = counter.count.checked_add(1).unwrap();
    msg!("Counter incremented. Current count: {}", counter.count);
    Ok(())
}

7. Build #

All together, the complete program will look like this:

use anchor_lang::prelude::*;
 
declare_id!("BouTUP7a3MZLtXqMAm1NrkJSKwAjmid8abqiNjUyBJSr");
 
#[program]
pub mod anchor_counter {
    use super::*;
 
    pub fn initialize(ctx: Context<Initialize>) -> Result<()> {
        let counter = &mut ctx.accounts.counter;
        counter.count = 0;
        msg!("Counter account created. Current count: {}", counter.count);
        Ok(())
    }
 
    pub fn increment(ctx: Context<Update>) -> Result<()> {
        let counter = &mut ctx.accounts.counter;
        msg!("Previous counter: {}", counter.count);
        counter.count = counter.count.checked_add(1).unwrap();
        msg!("Counter incremented. Current count: {}", counter.count);
        Ok(())
    }
}
 
#[derive(Accounts)]
pub struct Initialize<'info> {
    #[account(init,
        payer = user,
        space = DISCRIMINATOR + Counter::INIT_SPACE
    )]
    pub counter: Account<'info, Counter>,
    #[account(mut)]
    pub user: Signer<'info>,
    pub system_program: Program<'info, System>,
}
 
#[derive(Accounts)]
pub struct Update<'info> {
    #[account(mut)]
    pub counter: Account<'info, Counter>,
    pub user: Signer<'info>,
}
 
#[account]
#[derive(InitSpace)]
pub struct Counter {
    pub count: u64,
}
 
const DISCRIMINATOR: usize = 8;

Run anchor build to build the program.

8. Testing #

Anchor tests are typically Typescript integration tests that use the mocha test framework. We'll learn more about testing later, but for now navigate to anchor-counter.ts and replace the default test code with the following:

import * as anchor from "@coral-xyz/anchor";
import { Program } from "@coral-xyz/anchor";
import { expect } from "chai";
import { AnchorCounter } from "../target/types/anchor_counter";
 
describe("anchor-counter", () => {
  // Configure the client to use the local cluster.
  const provider = anchor.AnchorProvider.env();
  anchor.setProvider(provider);
 
  const program = anchor.workspace.AnchorCounter as Program<AnchorCounter>;
 
  const counter = anchor.web3.Keypair.generate();
 
  it("Is initialized!", async () => {});
 
  it("Incremented the count", async () => {});
});

The above code generates a new keypair for the counter account we'll be initializing and creates placeholders for a test of each instruction.

Next, create the first test for the initialize instruction:

it("Is initialized!", async () => {
  // Add your test here.
  const tx = await program.methods
    .initialize()
    .accounts({ counter: counter.publicKey })
    .signers([counter])
    .rpc();
 
  const account = await program.account.counter.fetch(counter.publicKey);
  expect(account.count.toNumber()).to.equal(0);
});

Next, create the second test for the increment instruction:

it("Incremented the count", async () => {
  const tx = await program.methods
    .increment()
    .accounts({ counter: counter.publicKey, user: provider.wallet.publicKey })
    .rpc();
 
  const account = await program.account.counter.fetch(counter.publicKey);
  expect(account.count.toNumber()).to.equal(1);
});

Lastly, run anchor test and you should see the following output:

anchor-counter
✔ Is initialized! (290ms)
✔ Incremented the count (403ms)
 
 
2 passing (696ms)

Running anchor test automatically spins up a local test validator, deploys your program, and runs your mocha tests against it. Don't worry if you're confused by the tests for now - we'll dig in more later.

Congratulations, you just built a Solana program using the Anchor framework! Feel free to reference the solution code if you need some more time with it.

Challenge #

Now it's your turn to build something independently. Because we're starting with simple programs, yours will look almost identical to what we just created. It's useful to try and get to the point where you can write it from scratch without referencing prior code, so try not to copy and paste here.

1. Write a new program that initializes a counter account
2. Implement both an increment and decrement instruction
3. Build and deploy your program like we did in the lab
4. Test your newly deployed program and use Solana Explorer to check the program logs

As always, get creative with these challenges and take them beyond the basic instructions if you want - and have fun!

Try to do this independently if you can! But if you get stuck, feel free to reference the solution code.