How can I return an array of integers from Solana rust program function to front end?

Question

I don't know how can I write a smart contract in Solana that after executing the logic, returns an array of integers, strings, ... to the client, and how can I fetch it using Web3?

Answer 1

There's a syscall available to on-chain programs called set_return_data, which puts data into a buffer that can be read by the higher-level programs using get_return_data. This all mediated through opaque byte buffers, so you'll need to know how to decode the response.

If you want to fetch the data from the client side, you can simulate the transaction and read the data back from the return_data field in the response: https://edge.docs.solana.com/developing/clients/jsonrpc-api#results-50

The RPC support in simulated transactions is very new in version 1.11, but the return data is available in earlier versions.

Source code for set_return_data at https://github.com/solana-labs/solana/blob/658752cda710cb358d7ccbbc2cee06bf8009c2d4/sdk/program/src/program.rs#L102

Source code for get_return_data at https://github.com/solana-labs/solana/blob/658752cda710cb358d7ccbbc2cee06bf8009c2d4/sdk/program/src/program.rs#L117

Answer 2

So, programs do not return data (other than success or failure).

However; most programs write data to a program owned account's data field and this could be read from client apps (Rust, Python, TS/JS, etc.).

If using the Solana web3 library, you can call getAccountInfo on the Connection object. This will return the byte array of the account. You will then need to deserialize that data. You have to know how the program serializes the data to reverse it successfully.

Check the Solana Cookbook for overview using borsh https://solanacookbook.com/guides/serialization.html#how-to-deserialize-account-data-on-the-client