(PHP 4, PHP 5, PHP 7, PHP 8)
base64_decode — MIME base64 方式によりエンコードされたデータをデコードする
base64 でエンコードされた string
をデコードします。
デコードされたデータを返します。失敗した場合に false を返します。
戻り値はバイナリになることもあります。
例1 base64_decode() の例
<?php
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str);
?>上の例の出力は以下となります。
This is an encoded string
If you want to save data that is derived from a Javascript canvas.toDataURL() function, you have to convert blanks into plusses. If you do not do that, the decoded data is corrupted:
<?php
$encodedData = str_replace(' ','+',$encodedData);
$decocedData = base64_decode($encodedData);
?>I had some trouble trying to let base64_decode decode base64-strings longer than ~5k chars.
The base64-decoding function is a homomorphism between modulo 4 and modulo 3-length segmented strings. That motivates a divide and conquer approach: Split the encoded string into substrings counting modulo 4 chars, then decode each substring and concatenate all of them.
Then instead of
<?php $decoded = base64_decode($encoded); ?>
for big $encoded strings, it's saver to use
<?php
$decoded = "";
for ($i=0; $i < ceil(strlen($encoded)/256); $i++)
$decoded = $decoded . base64_decode(substr($encoded,$i*256,256));
?>
where 256 can be replaced by a sufficiently small modulo 4 natural.This function supports "base64url" as described in Section 5 of RFC 4648, "Base 64 Encoding with URL and Filename Safe Alphabet"
<?php
function base64url_decode($base64url)
{
$base64 = strtr($base64url, '-_', '+/');
$plainText = base64_decode($base64);
return ($plainText);
}
?>Note, that padding characters are not limited to "=". any character(s) at the end of the string that cannot be decoded will be interpreted as padding. if $strict is set to true, of course padding characters are limited to base64 characters.
examples:
<?php
// $strict = false;
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw';
echo base64_decode($str); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA';
echo base64_decode($str); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA=';
echo base64_decode($str); // This is an encoded string
// $strict = true;
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str, true); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw';
echo base64_decode($str, true); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA';
echo base64_decode($str, true); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA=';
echo base64_decode($str, true); // This is an encoded string
?>Base64 for URL parameters/filenames, that adhere to RFC 4648.
Defaults to dropping the padding on encode since it's not required for decoding, and keeps the URL free of % encodings.
<?php
function base64url_encode($data, $pad = null) {
$data = str_replace(array('+', '/'), array('-', '_'), base64_encode($data));
if (!$pad) {
$data = rtrim($data, '=');
}
return $data;
}
function base64url_decode($data) {
return base64_decode(str_replace(array('-', '_'), array('+', '/'), $data));
}function is_base64($str){
if($str === base64_encode(base64_decode($str))){
return true;
}
return false;
}
---------------------------------------------------------------------------
---------------------------------------------------------------------------
---------------------------------------------------------------------------
$str = 'VGhpcyBpcyBiYXNlNjQgZW5jb2RlIHN0cmluZw==';
if(is_base64($str)){
print base64_decode($str);
}I was wondering how to decode attached images within mails. Basically they are mostly JPEG files, so it was obviously to write a function that decodes JPEG images.
I guess the plainest way to do so was the following:
<?php
function base64_to_jpeg( $inputfile, $outputfile ) {
/* read data (binary) */
$ifp = fopen( $inputfile, "rb" );
$imageData = fread( $ifp, filesize( $inputfile ) );
fclose( $ifp );
/* encode & write data (binary) */
$ifp = fopen( $outputfile, "wb" );
fwrite( $ifp, base64_decode( $imageData ) );
fclose( $ifp );
/* return output filename */
return( $outputfile );
}
?>
This function decodes the given inputfile (a filename!) and saves it to the given outputfile (a filename as well) and then returns the output filename for further usage (e.g. redirect, imagejpeg() and so on).
I thought that might be helpful.