README.md

Day 4: Require, Revert, and Custom Errors in Solana

Day 4 of RareSkills Solana Course.

Setup

1. Configure Solana to run on localhost: solana config set --url localhost
2. Run the test validator node on another terminal: solana-test-validator
3. Run Solana logs on another terminal: solana logs
4. Build Anchor program: anchor build
5. Sync program_id with Anchor key: anchor keys sync
6. Run tests: anchor test --skip-local-validator

Notes

• When stopping transactions with invalid parameters:
  • Ethereum triggers a revert
  • while Solana returns an error.
• require! macro can be used as an alternative to if statements.
• Solana programs should always return an Ok(()) or an Error.
  • All functions in Solana have a return type of Result<()>.
• In Anchor, errors are an enum with the #[error_code] attribute.

Exercises

1. What pattern do you notice with the Error number? What happens to the error codes if you change the order of the errors in the Enum MyError?

   • The Anchor error codes start at 6000, and increments by 1 from the first record in the MyError enum. (6000, 6001, ...)

2. Use this code block which adds the new func and error to the existing code: Before you run this, what do you think the new error code will be?

   • The new error code will be 6002, since there are three records in the MyError enum.

3. What happens if you put a msg! macro before the return error statements in a Solana program function? What happens if you replace return err! with Ok(())?

   • The msg! will not print when there's an error.
   • Replacing return err! with Ok(()) will result in the transaction succeeding, printing the message Will this print?".

References

• Errors
• ErrorCode