Cross Program Invocation (CPI)

Cross Program Invocation (CPI) on Solana

Cross Program Invocation (CPI) is a mechanism in Solana that allows one smart contract (referred to as a "program" in Solana) to call another smart contract during execution. This feature enhances modularity and reusability by enabling different programs to interact with one another, allowing developers to build complex, layered applications.

In Solana’s architecture, programs are stateless and interact with accounts that hold data. When a smart contract (program) needs to access functionality from another program (such as interacting with the Solana Token Program or other custom programs), it can invoke that program through CPI. The invoked program runs its logic as part of the original transaction.

Key Aspects of CPI:

1. Modularity: By using CPI, developers can build reusable smart contracts that other programs can call. For example, a DeFi protocol may invoke the Solana Token Program to perform token transfers during its operations, instead of implementing transfer logic itself.

2. Layered Applications: CPI allows for building layered applications, where higher-level logic (e.g., a decentralized exchange) can use foundational programs (e.g., token transfer, lending) via CPI to perform various actions within a single transaction.

3. Atomicity: CPI invocations are part of the same transaction, meaning if any part of the transaction fails (such as the invoked program), the entire transaction is rolled back. This ensures atomicity across all interactions.

4. Accounts Management: Since Solana requires accounts to be passed explicitly in transactions, when invoking another program, the caller must provide the necessary accounts for the invoked program to interact with. This ensures the invoked program has the required permissions and data access to execute successfully.

Example Use Case:

• A decentralized finance (DeFi) protocol could use CPI to call the Solana Token Program to transfer tokens between user accounts as part of a lending or trading operation. This way, the DeFi protocol doesn’t need to handle the low-level token logic and can rely on the token program’s functionality.

Challenges:

• Account Constraints: Since Solana’s programs are stateless and operate on explicit accounts, developers must ensure all necessary accounts are passed correctly when invoking other programs.

• Complexity: While CPI allows modular design, managing multiple program invocations and ensuring proper coordination between them can introduce complexity, especially in terms of account permissions and execution flow.

In summary, Cross Program Invocation (CPI) is a powerful feature in Solana that promotes composability by allowing smart contracts to interact with each other within a single transaction. This opens up possibilities for building more dynamic, modular, and reusable decentralized applications.