Encode a big file using base64 - php

Question

I'm trying to encode/decode a file that is several MBs or sometimes GBs in base64 encoding however some pieces of data gets encoded/decoded in a wrong way which results in strange characters like: � �̴.
I'm reading the file chunk by chunk encoding and saving each individually (Probably that's the problem however i cannot figure it out).
Here is what i have tried so far:
<?php
function encode_file($Ifilename, $Efilename){
$handle = fopen($Ifilename, 'rb');
$outHandle = fopen($Efilename, 'wb');
$bufferSize = 8151;
while(!feof($handle)){
$buffer = fread($handle, $bufferSize);
$ebuffer = base64_encode($buffer);
fwrite($outHandle, $ebuffer);
}
fclose($handle);
fclose($outHandle);
}
function decode_file($Ifilename, $Efilename){
$handle = fopen($Ifilename, 'rb');
$outHandle = fopen($Efilename, 'wb');
$bufferSize = 8151;
while(!feof($handle)){
$buffer = fread($handle, $bufferSize);
$dbuffer = base64_decode($buffer);
fwrite($outHandle, $dbuffer);
}
fclose($handle);
fclose($outHandle);
}
encode_file('input.txt', 'out.bin');//Big text file ~4MBs
decode_file('out.bin', 'out.txt');

Answer 1

After reading the whole Wikipedia article on base64, I found that every 3 characters encodes to 4 base64 characters, this is what was causing the file corruption.
The fix is to simply set the buffer to n when encoding, where n is a multiple of 3.
When decoding set the buffer to N, where N is a multiple of 4.
The working code:
<?php
function encode_file($Ifilename, $Efilename){
$handle = fopen($Ifilename, 'rb');
$outHandle = fopen($Efilename, 'wb');
$bufferSize = 3 * 256;// 3 bytes of ASCII encodes to 4 bytes of base64
while(!feof($handle)){
$buffer = fread($handle, $bufferSize);
$ebuffer = base64_encode($buffer);
fwrite($outHandle, $ebuffer);
}
fclose($handle);
fclose($outHandle);
}
function decode_file($Ifilename, $Efilename){
$handle = fopen($Ifilename, 'rb');
$outHandle = fopen($Efilename, 'wb');
$bufferSize = 4 * 256; // 4 bytes of base64 decodes to 3 bytes of ASCII
while(!feof($handle)){
$buffer = fread($handle, $bufferSize);
$dbuffer = base64_decode($buffer);
fwrite($outHandle, $dbuffer);
}
fclose($handle);
fclose($outHandle);
}
encode_file('input.txt', 'out.bin');
decode_file('out.bin', 'output.txt');