Create Transactions on the Solana Network

Summary #

All modifications to onchain data happen through transactions. Transactions are mostly a set of instructions that invoke Solana programs. Transactions are atomic, meaning they either succeed - if all the instructions have been executed properly - or fail as if the transaction hasn't been run at all.

Lesson #

Transactions are atomic #

Any modification to onchain data happens through transactions sent to programs.

A transaction on Solana is similar to a transaction elsewhere: it is atomic. Atomic means the entire transaction runs or fails.

Think of paying for something online:

• The balance of your account is debited
• The bank transfers the funds to the merchant

Both of these things need to happen for the transaction to be successful. If either of them fails, none of them should happen, rather than pay the merchant and not debit your account, or debit the account but not pay the merchant.

Atomic means either the transaction happens - meaning all the individual steps succeed - or the entire transaction fails.

Transactions contain instructions #

The steps within a transaction on Solana are called instructions.

Each instruction contains:

• an array of accounts that will be read from and/or written to. This is what makes Solana fast - transactions that affect different accounts are processed simultaneously
• the public key of the program to invoke
• data passed to the program being invoked, structured as a byte array

When a transaction is run, one or more Solana programs are invoked with the instructions included in the transaction.

As you might expect, @solana/web3.js provides helper functions for creating transactions and instructions. You can create a new transaction with the constructor, new Transaction(). Once created, you can add instructions to the transaction using the add() method.

One of those helper functions is SystemProgram.transfer(), which makes an instruction for the SystemProgram to transfer some SOL:

const transaction = new Transaction();
 
const sendSolInstruction = SystemProgram.transfer({
  fromPubkey: sender,
  toPubkey: recipient,
  lamports: LAMPORTS_PER_SOL * amount,
});
 
transaction.add(sendSolInstruction);

The SystemProgram.transfer() function requires:

• a public key corresponding to the sender's account
• a public key corresponding to the recipient's account
• the amount of SOL to send in lamports.

SystemProgram.transfer() returns the instruction for sending SOL from the sender to the recipient.

The program used in this instruction will be the system program (at the address 11111111111111111111111111111111), the data will be the amount of SOL to transfer (in Lamports) and the accounts will be based on the sender and recipient.

The instruction can then be added to the transaction.

Once all the instructions have been added, a transaction needs to be sent to the cluster and confirmed:

const signature = sendAndConfirmTransaction(connection, transaction, [
  senderKeypair,
]);

The sendAndConfirmTransaction() function takes the following parameters:

• a cluster connection
• a transaction
• an array of keypairs that will act as signers on the transaction - in this example, we only have one signer: the sender.

Transactions have fees #

Transaction fees are built into the Solana economy as compensation to the validator network for the CPU and GPU resources required in processing transactions. Solana transaction fees are deterministic.

The first signer included in the array of signers on a transaction is responsible for paying the transaction fee. If this signer does not have enough SOL in their account to cover the transaction fee, the transaction will be dropped with an error like:

> Transaction simulation failed: Attempt to debit an account but found no record of a prior credit.

If you get this error, it’s because your keypair is brand new and doesn’t have any SOL to cover the transaction fees. Let’s fix this by adding the following lines just after we've set up the connection:

await airdropIfRequired(
  connection,
  keypair.publicKey,
  1 * LAMPORTS_PER_SOL,
  0.5 * LAMPORTS_PER_SOL,
);

This will deposit 1 SOL into your account which you can use for testing. This won’t work on Mainnet where it would have value. But it's incredibly convenient for testing locally and on Devnet.

You can also use the Solana CLI command solana airdrop 1 to get free test SOL in your account when testing, whether locally or on devnet.

Solana Explorer #

Solana Explorer set to Devnet

All transactions on the blockchain are publicly viewable on the Solana Explorer. For example, you could take the signature returned by sendAndConfirmTransaction() in the example above, search for that signature in the Solana Explorer, then see:

• when it occurred
• which block it was included in
• the transaction fee
• and more!

Solana Explorer with details about a transaction

Lab #

We’re going to create a script to send SOL to other students.

Basic scaffolding #

We'll start by using the same packages and .env file we made earlier in Intro to Cryptography.

Create a file called transfer.ts:

import {
  Connection,
  Transaction,
  SystemProgram,
  sendAndConfirmTransaction,
  PublicKey,
} from "@solana/web3.js";
import "dotenv/config";
import { getKeypairFromEnvironment } from "@solana-developers/helpers";
 
const suppliedToPubkey = process.argv[2] || null;
 
if (!suppliedToPubkey) {
  console.log(`Please provide a public key to send to`);
  process.exit(1);
}
 
const senderKeypair = getKeypairFromEnvironment("SECRET_KEY");
 
console.log(`suppliedToPubkey: ${suppliedToPubkey}`);
 
const toPubkey = new PublicKey(suppliedToPubkey);
 
const connection = new Connection("https://api.devnet.solana.com", "confirmed");
 
console.log(
  `✅ Loaded our own keypair, the destination public key, and connected to Solana`,
);

Run the script to ensure it connects, loads your keypair, and loads:

npx esrun transfer.ts (destination wallet address)

Create the transaction and run it #

Add the following to complete the transaction and send it:

console.log(
  `✅ Loaded our own keypair, the destination public key, and connected to Solana`,
);
 
const transaction = new Transaction();
 
const LAMPORTS_TO_SEND = 5000;
 
const sendSolInstruction = SystemProgram.transfer({
  fromPubkey: senderKeypair.publicKey,
  toPubkey,
  lamports: LAMPORTS_TO_SEND,
});
 
transaction.add(sendSolInstruction);
 
const signature = await sendAndConfirmTransaction(connection, transaction, [
  senderKeypair,
]);
 
console.log(
  `💸 Finished! Sent ${LAMPORTS_TO_SEND} to the address ${toPubkey}. `,
);
console.log(`Transaction signature is ${signature}!`);

Experiment! #

Send SOL to other students in the class.

npx esrun transfer.ts (destination wallet address)

Challenge #

Answer the following questions:

• How much SOL did the transfer take? What is this in USD?

• Can you find your transaction on https://explorer.solana.com? Remember we are using the devnet network.

• How long does the transfer take?

• What do you think "confirmed" means?