blockchain

#!/usr/bin/php
<?php
/**
 * A very simple BlockChain implementation intended to illustrate the concept.
 *
 * The block index simply maps a block to a disk offset for convenience.
 * It's not necessary, but it makes it much easier to quickly locate any
 * block within the chain.
 *
 * ISAM index:
 * [4] count
 * -----------
 * [4] offset
 * [4] length
 * ...
 *
 * Block format:
 * [4] magic
 * [1] format (0x01)
 * [4] timestamp
 * [n] hash of previous block
 * [4] data length
 * [?] data
 *
 *
 */
define('_magic', 0xD5E8A97F);
define('_hashalg', 'sha256');
define('_hashlen', 32);
define('_blksize', (13 + _hashlen));

/*
$res = addblock('blockchain.dat','Some data');
if ($res!==TRUE) exit("ERROR: ".$res."\n");
*/

function addblock($fn, $data, $genesis = false)
{
    $indexfn = $fn . '.idx';
    if (!$genesis) {
        if (!file_exists($fn)) {
            return ('Missing blockchain data file!');
        }
        if (!file_exists($indexfn)) {
            return ('Missing blockchain index file!');
        }
        // get disk location of last block from index
        if (!$ix = fopen($indexfn, 'r+b')) {
            return ("Can't open " . $indexfn);
        }
        $maxblock = unpack('V', fread($ix, 4))[1];
        $zpos = (($maxblock * 8) - 4);
        fseek($ix, $zpos, SEEK_SET);
        $ofs = unpack('V', fread($ix, 4))[1];
        $len = unpack('V', fread($ix, 4))[1];
        // read last block and calculate hash
        if (!$bc = fopen($fn, 'r+b')) {
            return ("Can't open " . $fn);
        }
        fseek($bc, $ofs, SEEK_SET);
        $block = fread($bc, $len);
        $hash = hash(_hashalg, $block);
        // add new block to the end of the chain
        fseek($bc, 0, SEEK_END);
        $pos = ftell($bc);
        write_block($bc, $data, $hash);
        fclose($bc);
        // update index
        update_index($ix, $pos, strlen($data), ($maxblock + 1));
        fclose($ix);
        return true;
    } else {
        if (file_exists($fn)) {
            return ('Blockchain data file already exists!');
        }
        if (file_exists($indexfn)) {
            return ('Blockchain index file already exists!');
        }
        $bc = fopen($fn, 'wb');
        $ix = fopen($indexfn, 'wb');
        write_block($bc, $data, str_repeat('00', _hashlen));
        update_index($ix, 0, strlen($data), 1);
        fclose($bc);
        fclose($ix);
        return true;
    }
}

function write_block(&$fp, $data, $prevhash)
{
    fwrite($fp, pack('V', _magic), 4);                // Magic
    fwrite($fp, chr(1), 1);                           // Version
    fwrite($fp, pack('V', time()), 4);                // Timestamp
    fwrite($fp, hex2bin($prevhash), _hashlen);        // Previous Hash
    fwrite($fp, pack('V', strlen($data)), 4);         // Data Length
    fwrite($fp, $data, strlen($data));                // Data
}

function update_index(&$fp, $pos, $datalen, $count)
{
    fseek($fp, 0, SEEK_SET);
    fwrite($fp, pack('V', $count), 4);                // Record count
    fseek($fp, 0, SEEK_END);
    fwrite($fp, pack('V', $pos), 4);                  // Offset
    fwrite($fp, pack('V', ($datalen + _blksize)), 4);        // Length
}