Using a string's hash as a mapping key

Question

I am trying to create mapping of type mapping(string => string) where you store some text by keyed by its the string representation of its hash, but I've been stymied by the inability to take the calculated hash value and convert it to its string representation.

I tried the below, but it doesn't work. The hashing function appears to work, but the conversion to string doesn't. (Running function hash() returns an error which I don't really understand.

pragma solidity 0.8.4;
contract HashTextMap {
    
    mapping(string=>string) textMap;
    
    
    function set(string memory text) public  {
        bytes32 val;
        val = sha256(abi.encodePacked(text));
        string memory key = string(abi.encodePacked(val));
        textMap[key] = text; 
        
    }
    function get(string memory key) public view returns(string memory) {
        return textMap[key];
    }
    
    function hash(string memory text) public pure returns(string memory) {
        bytes32 val;
        val = sha256(abi.encodePacked(text));
        string memory key = string(abi.encodePacked(val));
        return key;
        
    }
}

Running this in the remix ide, the contract compiles and sets returns normally, but attempting I can't text get because I can't get the hash using hash() which produces this error.

{ "error": "Failed to decode output: null: invalid codepoint at offset 0; unexpected continuation byte (argument=\"bytes\", value={\"0\":153,\"1\":168,\"2\":124,\"3\":145,\"4\":53,\"5\":23,\"6\":70,\"7\":37,\"8\":43,\"9\":238,\"10\":126,\"11\":38,\"12\":250,\"13\":191,\"14\":48,\"15\":2,\"16\":61,\"17\":234,\"18\":227,\"19\":36,\"20\":138,\"21\":6,\"22\":125,\"23\":166,\"24\":226,\"25\":63,\"26\":146,\"27\":129,\"28\":199,\"29\":135,\"30\":194,\"31\":139}, code=INVALID_ARGUMENT, version=strings/5.4.0)" } 

Answer 1

In case of interest, I was able to build something like this by converting the hash to a uint and then converting a uint to string. (I'm a little mystified why its so hard to convert a byte32 directly into a string, but there you go.)

contract HashTextMap {
    
    mapping(string=>string) textMap;
    
    
    function set(string memory text) public   {
        bytes32 val;
        val = sha256(abi.encodePacked(text));
        uint256 i = uint(val);
        string memory key = uint2str(i);
        textMap[key] = text;            
    }

    function get(string memory key) public view returns(string memory) {
        return textMap[key];
    }
    
    function hash(string memory text) public pure returns(string memory) {
        bytes32 val;
        val = sha256(abi.encodePacked(text));
        uint ival = uint(val);
        string memory key = uint2str(ival);
        return key;            
    }
    
    function uint2str( uint256 i ) internal pure returns (string memory str) {
        if (i == 0) { return "0";}
        uint256 j = i;
        uint256 length;
        while (j != 0) {
            length++;
            j /= 10;
        }
        bytes memory bstr = new bytes(length);
        uint256 k = length;
        j = i;
        while (j != 0) {
            bstr[--k] = bytes1(uint8(48 + j % 10));
            j /= 10;
        }
        str = string(bstr);
        return str;
    }