Smart contract library functions for recreating the hash of an ipfs object given its content.
Add the data file to IPFS:
ipfs add testfile -q
Will return:
QmRsjnNkEpnDdmYB7wMR7FSy1eGZ12pDuhST3iNLJTzAXF
Now try the same thing with the generateHash-function:
(truffle console)
truffle(default)> fs = require('fs')
truffle(default)> var verify; verifyIPFS.new().then(a => {verify = a})
truffle(default)> var testfile = fs.readFileSync('./testfile').toString()
truffle(default)> verify.generateHash(testfile).then(a => {console.log(web3.toAscii(a))})
returns
QmRsjnNkEpnDdmYB7wMR7FSy1eGZ12pDuhST3iNLJTzAXF
generateHash returns the IPFS-hash in byte format of a given string:
function generateHash(string contentString) constant returns (bytes)
verifyHash takes a string and an IPFS-hash, and returns true if they match:
function verifyHash(string contentString, string hash) constant returns (bool) {
toBase58 converts bytes from hex format to base58:
function toBase58(bytes source) constant returns (bytes) {
Does not work for IPFS objects that are in several chunks. Contact me if you find an IPFS object in one chunk that does not work.
This allows you to store large data files on the blockchain by their IPFS hash instead of directly in contract storage. If you at a later point need any part of the data on the blockchain, you can submit it with a transaction, validate it cryptographically using this contract and then do your computations only referring to the contents of the IPFS object in memory!
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