Building Entry Logic with Rust Libraries — Forge College

Want your Solana program entrypoints to be small, testable, and easy to maintain? Implementing entry logic as Rust libraries turns fragile wiring into modular, unit-testable code that integrates cleanly with local ProgramTest simulations. What you'll learn In this lesson you'll organize entrypoint code into Rust crates and modules (thin entrypoint.rs, instruction parser, processor module) so logic is reusable and testable. You will implement parsing-and-validation layers that convert raw instruction bytes into typed parameters with clear Result-based error paths. You'll practice account validation patterns including AccountInfo checks and basic PDA assertions, and you'll write processor functions that encapsulate state transitions and return precise errors rather than performing wide-ranging side effects. Finally, you'll wire the entry function to call into libraries and run local unit and ProgramTest-based integration tests to verify both happy paths and failure cases. Who this is for Intermediate Solana developers who already know the entrypoint signature and basic Rust module structure. Prior experience with Rust crates and unit tests is expected. Key topics covered - Rust crate and module layout for Solana programs: entrypoint.rs, processor, instruction parser - Parsing raw instruction bytes into typed parameters and writing clear validation error paths - Account validation and basic Program-Derived-Address (PDA) checks using AccountInfo - Thin entrypoint patterns that delegate to small, pure processor functions - Writing unit tests and using ProgramTest to simulate instruction handling locally - Designing processors that return precise Result errors for easy, deterministic testing Practice these patterns in your next local test run and learn more at: https://www.forge.college/