Solidity – Converting Bytes Memory to Bytes Calldata

bytessolidity

I am getting the following error:

Error: Type bytes memory is not implicitly convertible to expected type bytes calldata.

So I was wondering if it was possible to convert from bytes memory to bytes calldata, as an external function I'm using requires bytes calldata but I can only decode it into bytes memory.

Thanks in advance 😀

EDIT: I have made a contract which represents my issue as the actual one is quite long.
The error occurs on line 9 with the error TypeError: Type bytes memory is not implicitly convertible to expected type bytes calldata..

I tried putting bytes calldata instead of bytes as the type in the abi decode part was I ended up with the error ParserError: Expected ',' but got 'calldata'.

If I replace calldata with memory when specifying the types of the variables (uint a, bytes memory b, bytes memory c), I get TypeError: Invalid type for argument in function call. Invalid implicit conversion from bytes memory to bytes calldata requested. on line 11.

At this point, I don't know what to do and I've looked through many websites to try to find the answer. Here's an example contract which is similar to the part of my contract that contains the errors.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Foo {    
    // I can't change the parameters of this function but I can change the content
    function bar (bytes calldata data) public {
        (uint a, bytes calldata b, bytes calldata c) = abi.decode(data, (uint, bytes, bytes));
        
        qux(c);
    }
    
    // I can't change this function at all
    function qux (bytes calldata data) public {
        // Do something here
    }
    
    // I can change this function, the parameters are just an example
    function baz (uint _a, bytes calldata _b, bytes calldata _c) public {
        uint a = _a;
        bytes calldata b = _b;
        bytes calldata c = _c;
        
        bytes memory data = abi.encode(
            a,
            b,
            c
        );

        bar(data);
    }
}

Baz is the function that I call externally (aka the starting point).

Best Answer

The answer was given to me on reddit so here is the fixed contract for anyone who may need it :D :

// SPDX-License-Identifier: MIT pragma solidity 0.8.0;

contract Foo {
    // I can't change the parameters of this function but I can change the content
    function bar (bytes calldata data) public {
        (uint a, bytes memory b, bytes memory c) = abi.decode(data, (uint, bytes, bytes));
        this.qux(c);
    }
    
    // I can't change this function at all
    function qux (bytes calldata data) public {
        // Do something here
    }
    
    // I can change this function, the parameters are just an example
    function baz (uint _a, bytes calldata _b, bytes calldata _c) public {
        uint a = _a;
        bytes calldata b = _b;
        bytes calldata c = _c;
        
        bytes memory data = abi.encode(
            a,
            b,
            c
        );
    
        this.bar(data);
    }
}

Related Solutions

Solidity – Mapping Address to Multidimensional uint

The main issue with your code is that you are trying to return a uint[] which is an array, however you defined your variable as a mapping of mappings, and mapping and array are different types.

You could get your code to compile like this:

pragma solidity ^0.4.24;

contract test {

    mapping (address => uint[]) public transactions;

    constructor() public {
        transactions[msg.sender].push(123456);
        transactions[msg.sender].push(789101);
        transactions[msg.sender].push(865436);
    }

    function getTransactions() public view returns (uint[]) {

        return transactions[msg.sender];

    }
}

However in general, I would not recommend a single function which returns all the values. While this may be useable in a web front-end, it will not scale as a normal contract function, since eventually you will reach a number of objects in the array where the gas cost to return them all will be too large for the evm.

Instead, I suggest you break it into two functions:

pragma solidity ^0.4.24;

contract test {

    mapping (address => uint[]) public transactions;

    constructor() public {
        transactions[msg.sender].push(123456);
        transactions[msg.sender].push(789101);
        transactions[msg.sender].push(865436);
    }

    function getTransactionsLength() public view returns (uint) {

        return transactions[msg.sender].length;

    }

    function getTransactionsValue(uint index) public view returns (uint) {

        return transactions[msg.sender][index];

    }
}

One is getTransactionsLength(), and the other is getTransactionsValue(). Both of these functions return just a single uint, which means you will have predictable output size and gas costs, which means it can be used in other parts of your contract.

Furthermore, you will also create better user experiences by controlling the number of values you are showing. If you need to show all the values, you could first get the length, and then loop the value call from 0 to length-1.

But even better, you may only want to show the last 10 transactions in the UI, where then you can loop from length-1 to length-11. These may seem like complexities at first, but in reality will be simplifications to your dApp is it grows; things you will really come to appreciate from immutable programs :)

Fixing Invalid Implicit Conversion Errors from uint256 to bytes in Solidity

You are getting this error because you are trying to take the keccack256 hash of a uint, which you cannot do, according to the docs. What you must do instead is convert the uint to a bytes.

The code you want is as follows:

function random() private returns(uint){
    uint source = block.difficulty + now;
    bytes memory source_b = toBytes(source);
    return uint(keccak256(source_b));
}

function toBytes(uint256 x) public returns (bytes memory b) {
    b = new bytes(32);
    assembly { mstore(add(b, 32), x) }
}

Best Answer

Related Solutions

Solidity – Mapping Address to Multidimensional uint

Fixing Invalid Implicit Conversion Errors from uint256 to bytes in Solidity

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