contract string parameter

Question

I'm trying to call Smart Contract with next method signature

calculateHash(string)

and Code like:

function calculateHash( string testStr ) constant returns ( bytes32 ){
    return sha3( testStr );
  }

I have next Sha3: 0xa8cbcecd37e0c4ac16c3135987b900352c43486006715fbca927444ab937b3af so first 4 bytes looks like 0xa8cbcecd Parameter for example is "Hello, Words!" According to ABI documentation I should encocde it like

bytes, of length k (which is assumed to be of type uint256):

enc(X) = enc(k) pad_right(X), i.e. the number of bytes is encoded as a uint256 followed by the actual value of X as a byte sequence, followed by the minimum number of zero-bytes such that len(enc(X)) is a multiple of 32.

string:

enc(X) = enc(enc_utf8(X)), i.e. X is utf-8 encoded and this value is interpreted as of bytes type and encoded further. Note that the length used in this subsequent encoding is the number of bytes of the utf-8 encoded string, not its number of characters.

so in my case it is

enc(enc_utf8("Hello, World!)) = end(Ox48656c6c6f2c20576f726c6421) = 
000000000000000000000000000000000000000000000000000000000000000d
48656c6c6f2c20576f726c642100000000000000000000000000000000000000

so full POST looks like

{"method":"eth_call","params":[{"from":"0x0027440CB2A41a3CF38Da9f89B0380311D146330","to":"0x3aDbCF5E934B0D78F0012C173032E2e2f3586F63","data":"0xa8cbcecd000000000000000000000000000000000000000000000000000000000000000d48656c6c6f2c20576f726c642100000000000000000000000000000000000000"}],"id":2,"jsonrpc":"2.0"}

But I have next return {
    "jsonrpc": "2.0",
    "result": "0x",
    "id": 2
}

Where is my mistake? Thank you Alex

Answer 1

the problem was fixed, I forgot about offset for dynamic parameters So encoding was correct 000000000000000000000000000000000000000000000000000000000000000d 48656c6c6f2c20576f726c642100000000000000000000000000000000000000 but I have to add next to start after method signature 0000000000000000000000000000000000000000000000000000000000000020 so full part looks like

0000000000000000000000000000000000000000000000000000000000000020 000000000000000000000000000000000000000000000000000000000000000d 48656c6c6f2c20576f726c642100000000000000000000000000000000000000 a little strange, but working