Solana

Solana Overview

As the underlying Solana environment is different than that of Ethereum, Solidity inner workings have been modified to function properly. For example, A Solidity contract on Solana utilizes two accounts: a data account and a program account. The program account stores the contract’s executable binary and owns the data account, which holds all the storage variables. On Ethereum a single account can store executable code and data.

Contract upgrades

Provided that the data layout from a new contract is compatible with that of an old one, it is possible to update the binary in the program account and retain the same data, rendering contract upgrades implemented in Solidity unnecessary. Solana’s CLI tool provides a command to both do an initial deploy of a program, and redeploy it later.:

solana program deploy --program-id <KEYPAIR_FILEPATH> <PROGRAM_FILEPATH>

where <KEYPAIR_FILEPATH> is the program’s keypair json file and <PROGRAM_FILEPATH> is the program binary .so file. For more information about redeploying a program, check Solana’s documentation.

Data types

An account address consists of a 32-bytes key, which is represented by the address type. This data model differs from Ethereum 20-bytes addresses.
Solana’s virtual machine registers are 64-bit wide, so 64-bit integers uint64 and int64 are preferable over uint256 and int256. An operation with types wider than 64-bits is split into multiple operations, making it slower and consuming more compute units. This is the case, for instance, with multiplication, division and modulo using uint256.
Likewise, all balances and values on Solana are 64-bit wide, so the builtin functions for address .balance, .transfer() and .send() use 64-bit integers.
An address literal has to be specified using the address"36VtvSbE6jVGGQytYWSaDPG7uZphaxEjpJHUUpuUbq4D" syntax.
Ethereum syntax for addresses 0xE0f5206BBD039e7b0592d8918820024e2a7437b9 is not supported.

Runtime

The Solana target requires Solana v1.8.1.
Function selectors are eight bytes wide and known as discriminators.
Solana provides different builtins, e.g. tx.program_id and tx.accounts.
When creating a contract in Solidity using new, one needs to provide the data account address that is going to be initialized for the new contract.

Compute budget

On Ethereum, when calling a smart contract function, one needs to specify the amount of gas the operation is allowed to use. Gas serves to pay for a contract execution on chain and can be a way for giving a contract priority execution when extra gas is offered in a transaction. Each EVM instruction has an associated gas value, which translates to real ETH cost. Provided that one can afford all the gas expenses, there is no upper boundary for the amount of gas limit one can provide in a transaction, so Solidity for Ethereum has gas builtins, like gasleft, block.gaslimit, tx.gasprice or the Yul gas() builtin, which returns the amount of gas left for execution.

On the other hand, Solana is optimized for low latency and high transaction throughput and has an equivalent concept to gas: compute unit. Every smart contract function is allowed the same quantity of compute units (currently that value is 200k), and every instruction of a contract consumes exactly one compute unit. There is no need to provide an amount of compute units for a transaction and they are not charged, except when one wants priority execution on chain, in which case one would pay per compute unit consumed. Therefore, functions for gas are not available on Solidity for Solana.

Solidity for Solana incompatibilities with Solidity for Ethereum

msg.sender is not available on Solana.
There is no ecrecover() builtin function because Solana does not use the ECDSA algorithm, but there is a signatureVerify() function, which can check ed25519 signatures. As a consequence, it is not possible to recover a signer from a signature.
Try-catch statements do not work on Solana. If any external call or contract creation fails, the runtime will halt execution and revert the entire transaction.
Error definitions and reverts with error messages are not yet working for Solana.
Value transfer with function call does not work.
Many Yul builtins are not available, as specified in the availability table.
External calls on Solana require that accounts be specified, as in this example.
The ERC-20 interface is not compatible with Solana at the moment.

Build your Solidity for Solana

solang compile --target solana flipper.sol -v

This will produce two files called flipper.json and flipper.so. The former is an Anchor style IDL file and the latter is the Solana ELF shared object containing the program. For each contract in the source code, Solang will create both an IDL file and a binary file.

Each program will need to be deployed to a program_id. Usually, the program_id is a well-known account which is specified in the Solidity source code using the @program_id("F1ipperKF9EfD821ZbbYjS319LXYiBmjhzkkf5a26rC") annotation on the contract. A private key for the account is needed to deploy. You can generate your own private key using the command line tool solana-keygen.

echo "[4,10,246,143,43,1,234,17,159,249,41,16,230,9,198,162,107,221,233,124,34,15,16,57,205,53,237,217,149,17,229,195,3,150,242,90,91,222,117,26,196,224,214,105,82,62,237,137,92,67,213,23,14,206,230,155,43,36,85,254,247,11,226,145]" > flipper-keypair.json
solana program deploy flipper.so

After deploying the program, you can start on the client side, which needs the anchor npm library:

npm install @project-serum/anchor

Write the following javascript to a file called flipper.js.

const { readFileSync } = require('fs');
const anchor = require('@project-serum/anchor');

const IDL = JSON.parse(readFileSync('./flipper.json', 'utf8'));
const PROGRAM_SO = readFileSync('./flipper.so');

(async function () {
    const provider = anchor.AnchorProvider.env();

    const dataAccount = anchor.web3.Keypair.generate();

    const programId = new anchor.web3.PublicKey(IDL.metadata.address);

    const wallet = provider.wallet.publicKey;

    const program = new anchor.Program(IDL, programId, provider);

    await program.methods.new(wallet, true)
        .accounts({ dataAccount: dataAccount.publicKey })
        .signers([dataAccount]).rpc();

    const val1 = await program.methods.get()
        .accounts({ dataAccount: dataAccount.publicKey })
        .view();

    console.log(`state: ${val1}`);

    await program.methods.flip()
        .accounts({ dataAccount: dataAccount.publicKey })
        .rpc();

    const val2 = await program.methods.get()
        .accounts({ dataAccount: dataAccount.publicKey })
        .view();

    console.log(`state: ${val2}`);
})();

Now you’ll have to set the ANCHOR_WALLET and ANCHOR_PROVIDER_URL environment variables to the correct values in order to run the example.

export ANCHOR_WALLET=$HOME/.config/solana/id.json
export ANCHOR_PROVIDER_URL=http://127.0.0.1:8899
node flipper.js

For more examples, see the solang’s integration tests.

Using the Anchor client library

Some notes on using the anchor javascript npm library.

Solidity function names are converted to camelCase. This means that if in Solidity a function is called foo_bar(), you must write fooBar() in your javascript.
Anchor only allows you to call .view() on Solidity functions which are declared view or pure.
Named return values in Solidity are also converted to camelCase. Unnamed returned are given the name return0, return1, etc, depending on the position in the returns values.
Only return values from view and pure functions can be decoded. Return values from other functions and are not accessible. This is a limitation in the Anchor library. Possibly this can be fixed.
In the case of an error, no return data is decoded. This means that the reason provided in revert('reason'); is not available as a return value.
Number arguments for functions are expressed as BN values and not plain javascript Number or BigInt.

Calling Anchor Programs from Solidity

It is possible to call Anchor Programs from Solidity. You first have to generate a Solidity interface file from the IDL file using the Generate Solidity interface from IDL. Then, import the Solidity file in your Solidity using the import "..."; syntax. Say you have an anchor program called bobcat with a function pounce, you can call it like so:

import "bobcat.sol";
import "solana";

contract example {
    function test(address a, address b) public {
        // The list of accounts to pass into the Anchor program must be passed
        // as an array of AccountMeta with the correct writable/signer flags set
        AccountMeta[2] am = [
            AccountMeta({pubkey: a, is_writable: true, is_signer: false}),
            AccountMeta({pubkey: b, is_writable: false, is_signer: false})
        ];

        // Any return values are decoded automatically
        int64 res = bobcat.pounce{accounts: am}();
    }
}

Setting the program_id for a contract

When developing contracts for Solana, programs are usually deployed to a well known account. The account can be specified in the source code using an annotation @program_id. If you want to instantiate a contract using the new ContractName() syntax, then the contract must have a program_id annotation.

@program_id("Foo5mMfYo5RhRcWa4NZ2bwFn4Kdhe8rNK5jchxsKrivA")
contract Foo {
    function say_hello() public pure {
        print("Hello from foo");
    }
}

contract Bar {
    Foo public foo;

    function create_foo(address new_address) public {
        foo = new Foo{address: new_address}();
    }

    function call_foo() public pure {
        foo.say_hello();
    }
}

Note

The program_id Foo5mMfYo5RhRcWa4NZ2bwFn4Kdhe8rNK5jchxsKrivA was generated using the command line:

solana-keygen grind --starts-with Foo:1

Setting the payer, seeds, bump, and space for a contract

When a contract is instantiated, there are two accounts required: the program account to hold the executable code and the data account to save the state variables of the contract. The program account is deployed once and can be reused for updating the contract. When each Solidity contract is instantiated (also known as deployed), the data account has to be created. This can be done by the client-side code, and then the created blank account is passed to the transaction that runs the constructor code.

Alternatively, the data account can be created by the constructor, on chain. When this method is used, some parameters must be specified for the account using annotations. Those are placed before the constructor. If there is no constructor present, then an empty constructor can be added. The constructor arguments can be used in the annotations.

@program_id("Foo5mMfYo5RhRcWa4NZ2bwFn4Kdhe8rNK5jchxsKrivA")
contract Foo {

    @space(500 + 12)
    @seed("Foo")
    @seed(seed_val)
    @bump(bump_val)
    @payer(payer)
    constructor(address payer, bytes seed_val, bytes1 bump_val) {
        // ...
    }
}

Creating an account needs a payer, so at a minimum the @payer annotation must be specified. If it is missing, then the data account must be created client-side. The @payer requires an address. This can be a constructor argument or an address literal.

The size of the data account can be specified with @space. This is a uint64 expression which can either be a constant or use one of the constructor arguments. The @space should at least be the size given when you run solang -v:

$ solang compile --target solana -v examples/solana/flipper.sol
...
info: contract flipper uses at least 17 bytes account data
...

If the data account is going to be a program derived address, then the seeds and bump have to be provided. There can be multiple seeds, and an optional single bump. If the bump is not provided, then the seeds must not create an account that falls on the curve. The @seed can be a string literal, or a hex string with the format hex"4142", or a constructor argument of type bytes. The @bump must a single byte of type bytes1.

Transferring native value with a function call

The Solidity language on Ethereum allows value transfers with an external call or constructor, using the auction.bid{value: 501}() syntax. Solana Cross Program Invocation (CPI) does not support this, which means that:

Specifying value: on an external call or constructor is not permitted

The payable keyword has no effect

msg.value is not supported

Note

A naive way to implement this is to let the caller transfer native balance and then inform the callee about the amount transferred by specifying this in the instruction data. However, it would be trivial to forge such an operation.

Receive function

In Solidity the receive() function, when defined, is called whenever the native balance for an account gets credited, for example through a contract calling account.transfer(value);. On Solana, there is no method that implements this. The balance of an account can be credited without any code being executed.

receive() functions are not permitted on the Solana target.

`msg.sender` not available on Solana

On Ethereum, msg.sender is used to identify either the account that submitted the transaction, or the caller when one contract calls another. On Ethereum, each contract execution can only use a single account, which provides the code and data. On Solana, each contract execution uses many accounts. Consider a rust contract which calls a Solidity contract: the rust contract can access a few data accounts, and which of those would be considered the caller? So in many cases there is not a single account which can be identified as a caller. In addition to that, the Solana VM has no mechanism for fetching the caller accounts. This means there is no way to implement msg.sender.

The way to implement this on Solana is to have an authority account for the contract that must be a signer for the transaction (note that on Solana there can be many signers too). This is a common construct on Solana contracts.

import 'solana';

contract AuthorityExample {
    address authority;
    uint64 counter;

    modifier needs_authority() {
        for (uint64 i = 0; i < tx.accounts.length; i++) {
            AccountInfo ai = tx.accounts[i];

            if (ai.key == authority && ai.is_signer) {
                _;
                return;
            }
        }

        print("not signed by authority");
        revert();
    }

    constructor(address initial_authority) {
        authority = initial_authority;
    }

    function set_new_authority(address new_authority) needs_authority public {
        authority = new_authority;
    }

    function inc() needs_authority public {
        counter += 1;
    }

    function get() public view returns (uint64) {
        return counter;
    }
}

Builtin Imports

Some builtin functionality is only available after importing. The following structs can be imported via the special builtin import file solana.

import {AccountMeta, AccountInfo} from 'solana';

Note that {AccountMeta, AccountInfo} can be omitted, renamed or imported via import object.

// Now AccountMeta will be known as AM
import {AccountMeta as AM} from 'solana';

// Now AccountMeta will be available as solana.AccountMeta
import 'solana' as solana;

Note

The import file solana is only available when compiling for the Solana target.

Builtin AccountInfo

The account info of all the accounts passed into the transaction. AccountInfo is a builtin structure with the following fields:

address key: The address (or public key) of the account
uint64 lamports: The lamports of the accounts. This field can be modified, however the lamports need to be balanced for all accounts by the end of the transaction.
bytes data`: The account data. This field can be modified, but use with caution.
address owner: The program that owns this account
uint64 rent_epoch: The next epoch when rent is due.
bool is_signer: Did this account sign the transaction
bool is_writable: Is this account writable in this transaction
bool executable: Is this account a program

Builtin AccountMeta

When doing an external call (aka CPI), AccountMeta specifies which accounts should be passed to the callee.

address pubkey: The address (or public key) of the account
bool is_writable: Can the callee write to this account
bool is_signer: Can the callee assume this account signed the transaction

Builtin create_program_address

This function returns the program derived address for a program address and the provided seeds. See the Solana documentation on program derived addresses.

import {create_program_address} from 'solana';

contract pda {
    address token = address"TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA";

    function create_pda(bytes seed2) public returns (address) {
        return create_program_address(["kabang", seed2], token);
    }
}

Builtin try_find_program_address

This function returns the program derived address for a program address and the provided seeds, along with a seed bump. See the Solana documentation on program derived addresses.

import {try_find_program_address} from 'solana';

contract pda {
    address token = address"TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA";

    function create_pda(bytes seed2) public returns (address, bytes1) {
        return try_find_program_address(["kabang", seed2], token);
    }
}

Solana Library

In Solang’s Github repository, there is a directory called solana-library. It contains libraries for Solidity contracts to interact with Solana specific instructions. We provide two libraries: one for SPL tokens and another for Solana’s system instructions. In order to use those functionalities, copy the correspondent library file to your project and import it.

SPL-token

spl-token is the Solana native way of creating tokens, minting, burning and transferring token. This is the Solana equivalent of ERC-20 and ERC-721. Solang’s repository contains a library SplToken to use spl-token from Solidity. The file spl_token.sol should be copied into your source tree, and then imported in your solidity files where it is required. The SplToken library has doc comments explaining how it should be used.

There is an example in our integration tests of how this should be used. See token.sol and token.spec.ts.

System Instructions

Solana’s system instructions enable developers to interact with Solana’s System Program. There are functions to create new accounts, allocate account data, assign accounts to owning programs, transfer lamports from System Program owned accounts and pay transaction fees. More information about the functions offered can be found both on Solana documentation and on Solang’s system_instruction.sol file.

The usage of system instructions needs the correct setting of writable and signer accounts when interacting with Solidity contracts on chain. Examples are available on Solang’s integration tests. See system_instruction_example.sol and system_instruction.spec.ts

Solana

Solana Overview

Contract upgrades

Data types

Runtime

Compute budget

Solidity for Solana incompatibilities with Solidity for Ethereum

Build your Solidity for Solana

Using the Anchor client library

Calling Anchor Programs from Solidity

Setting the program_id for a contract

Setting the payer, seeds, bump, and space for a contract

Transferring native value with a function call

Receive function

msg.sender not available on Solana

Builtin Imports

Builtin AccountInfo

Builtin AccountMeta

Builtin create_program_address

Builtin try_find_program_address

Solana Library

SPL-token

System Instructions

`msg.sender` not available on Solana