<?php
/*
 * Reading a BZIP2 file can be tricky, and I never seen a complete example of
 * code that account for any possible failure that may happen accessing a file
 * in general, and decoding compressed data in this specific case.
 * The example that follows is my attempt to address this gap.
 * Some things that worth noting are:
 * - Encoding/decoding errors must be detected with bzerrno().
 * - bzopen() may fail returning FALSE if the file cannot be created or read,
 *   but succeeds also if the file is not properly encoded.
 * - bzread() may fail returning FALSE if it fails reading from the source, but
 *   it returns the empty string on end of file and on encoding error.
 * - bzread() may still return corrupted data with no error whatsoever until the
 *   BZIP2 algo encounters the first hash code, so data retrieved cannot be
 *   trusted until the very end of the file has been reached.
 */

// Safety first:
error_reporting(-1);
// On error, set $php_errormsg:
ini_set("track_errors", "1");

/**
 * Reads and displays on stdout the content of a BZIP2 compressed file with
 * full error detection.
 * @param string $fn Filename.
 * @return void
 */
function displaysBZIP2File($fn)
{
    echo "Reading $fn:\n";
    $bz = @bzopen($fn, "r");
    if( $bz === FALSE ){
        echo "ERROR: bzopen() failed: $php_errormsg\n";
        return;
    }
    $errno = bzerrno($bz);
    if( $errno != 0 ){
        // May detect "DATA_ERROR_MAGIC" (not a BZIP2 file), or "DATA_ERROR"
        // (BZIP2 decoding error) and maybe others BZIP2 errors too.
        echo "ERROR: bzopen(): BZIP2 decoding failed: ", bzerrstr($bz), "\n";
        @bzclose($bz);
        return;
    }
    while(! feof($bz) ) {
        $s = bzread($bz, 100);
        if( $s === FALSE ){
            echo "ERROR: bzread() failed: $php_errormsg\n";
            @bzclose($bz);
            return;
        }
        $errno = bzerrno($bz);
        if( $errno != 0 ){
            // May detect "DATA_ERROR" (BZIP2 decoding error) and maybe others
            // BZIP2 errors too.
            echo "ERROR: bzread(): BZIP2 decoding failed: ", bzerrstr($bz), "\n";
            @bzclose($bz);
            return;
        }
        echo "read: ", var_export($s, true), "\n";
    }
    if( ! bzclose($bz) ){
        echo "ERROR: bzclose() failed: $php_errormsg\n";
    }
}

// Target file:
$fn = "test.bz2";

// Test 1: writes and read a good BZIP2 file:
file_put_contents($fn, bzcompress("Content of the file."));
displaysBZIP2File($fn); // works ok.

// Test 2: invalid content, not a BZIP2 file:
file_put_contents($fn, "This ia plain text file, no compression at all!");
displaysBZIP2File($fn); // ERROR: bzread(): BZIP2 decoding failed: DATA_ERROR_MAGIC

// Test 3: creates a corrupted BZIP2 file:
$plain = str_repeat("Quite random string. ", 1000);
$compressed = bzcompress($plain);
$compressed_corrupted = $compressed;
$compressed_corrupted[(int)(strlen($compressed)/2)] = 'X'; // put random char in middle
file_put_contents($fn, $compressed_corrupted);
displaysBZIP2File($fn);
// Only after some Kbytes of garbage, it tells:
// ERROR: bzread(): BZIP2 decoding failed: DATA_ERROR

// Safe coding against headache, ever.
?>

<?php
/**
 * @return bool
 * @param string $in
 * @param string $out
 * @desc compressing the file with the bzip2-extension
*/
function bzip2 ($in, $out)
{
    if (!file_exists ($in) || !is_readable ($in))
        return false;
    if ((!file_exists ($out) && !is_writeable (dirname ($out)) || (file_exists($out) && !is_writable($out)) ))
        return false;
    
    $in_file = fopen ($in, "rb");
    $out_file = bzopen ($out, "wb");
    
    while (!feof ($in_file)) {
        $buffer = fgets ($in_file, 4096);
         bzwrite ($out_file, $buffer, 4096);
    }

    fclose ($in_file);
    bzclose ($out_file);
    
    return true;
}

/**
 * @return bool
 * @param string $in
 * @param string $out
 * @desc uncompressing the file with the bzip2-extension
*/
function bunzip2 ($in, $out)
{
    if (!file_exists ($in) || !is_readable ($in))
        return false;
    if ((!file_exists ($out) && !is_writeable (dirname ($out)) || (file_exists($out) && !is_writable($out)) ))
        return false;

    $in_file = bzopen ($in, "rb");
    $out_file = fopen ($out, "wb");

    while ($buffer = bzread ($in_file, 4096)) {
        fwrite ($out_file, $buffer, 4096);
    }
 
    bzclose ($in_file);
    fclose ($out_file);
    
    return true;
}
?>