# Get The Basic Idea About Solana Program

###### tags: `solana`

## Index
- Concepts
- Accounts
- Executable & Writable
- Program & Client
- Counter Example

## Concepts

### Accounts

Accounts are just **buffers** that store serialized binary data on chain.

| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |

### Executable & Writable
- Programs are stored in **executable** accounts
- Programs are stateless on Solana.
- States are stored in non-executable accounts which can be **writable** or **read-only**
- Think state accounts as rows in database. They can be modified and queried

### Program & Client
You may think programs (smart contract) as AWS Lambda functions.

Just like client-server model that we are familiar in web2, we develop and deploy prgrams then use clients to interact with them.

## Counter Example

[offical repo](https://github.com/solana-labs/example-helloworld)

Program

pub fn process_instruction(
    program_id: &Pubkey, // Public key of the account the hello world program was loaded into
    accounts: &[AccountInfo], // The account to say hello to
    _instruction_data: &[u8], // Ignored, all helloworld instructions are hellos
) -> ProgramResult {
    msg!("Hello World Rust program entrypoint");

    // Iterating accounts is safer than indexing
    let accounts_iter = &mut accounts.iter();

    // Get the account to say hello to
    let account = next_account_info(accounts_iter)?;

    // The account must be owned by the program in order to modify its data
    if account.owner != program_id {
        msg!("Greeted account does not have the correct program id");
        return Err(ProgramError::IncorrectProgramId);
    }

    // Increment and store the number of times the account has been greeted
    let mut greeting_account = GreetingAccount::try_from_slice(&account.data.borrow())?;
    greeting_account.counter += 1;
    greeting_account.serialize(&mut &mut account.data.borrow_mut()[..])?;

    msg!("Greeted {} time(s)!", greeting_account.counter);

    Ok(())
}

Client (partial)

...
// Establish connection to the cluster
const connection = new Connection(RPCURL, 'confirmed');
const version = await connection.getVersion();
console.log('Connection to cluster established:', RPCURL, version);

// Get the payer to pay this transaction
var secretKeyString = await fs.readFile(payer_keypair_path, {encoding: 'utf8'});
var secretKey = Uint8Array.from(JSON.parse(secretKeyString));
const payerKeypair =  Keypair.fromSecretKey(secretKey);
console.log("Payer: ", payerKeypair.publicKey.toBase58());

// Get the program's pubkey (ID)
secretKeyString = await fs.readFile(program_keypair_path, {encoding: 'utf8'});
secretKey = Uint8Array.from(JSON.parse(secretKeyString));
const programKeypair = Keypair.fromSecretKey(secretKey);
const programId = programKeypair.publicKey
console.log("Program ID: ", programId.toBase58());

// Invoke our Hello Solana Program
const instruction = new TransactionInstruction({
    keys: [],
    programId,
    data: Buffer.alloc(0),
});

await sendAndConfirmTransaction(
    connection,
    new Transaction().add(instruction),
    [payerKeypair],
);

## Resources
- Learn Solana by examples: [Solana By Example](https://n795113.github.io/solana-by-example/)
- Concept Overview: [ok so what the fuck is the deal with solana anyway](https://2501babe.github.io/posts/solana101.html)
- All dev knowledge about Solana: https://solanacookbook.com
- Taiwan Solana dev community: https://solmeet.dev/
- Learn Rust From scratch: https://rust-lang.tw/book-tw/
- Learn Ethereum: [https://cryptozombies.io/](https://cryptozombies.io/)