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);
?>
PHP - Manual: base64_decode
2024-12-21
base64_decode
(PHP 4, PHP 5, PHP 7, PHP 8)
base64_decode — 对使用 MIME base64 编码的数据进行解码
说明
base64_decode(string
$data, bool $strict = false): string
对 base64 编码的 data 进行解码。
参数
-
data -
编码过的数据。
-
strict -
当设置
strict为true时，一旦输入的数据超出了 base64 字母表，将返回false。 否则会静默丢弃无效的字符。
返回值
返回原始数据， 或者在失败时返回 false。返回的数据可能是二进制的。
更新日志
| 版本 | 说明 |
|---|---|
| 5.2.0 | 增加了 strict 。 |
范例
示例 #1 base64_decode() 示例
<?php
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str);
?>
以上例程会输出：
This is an encoded string
add a note
User Contributed Notes 17 notes
winkelnkemper at googlemail dot com ¶
11 years ago
walf ¶
6 years ago
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));
}
martinstaemmler at gmx dot net ¶
12 years ago
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,$i*256,256));
?>
where 256 can be replaced by a sufficiently small modulo 4 natural.
Tom ¶
15 years ago
This function supports "base64url" as described in Section 5 of RFC 4648, "Base 64 Encoding with URL and Filename Safe Alphabet"
<?php
function base64url_decode($base64url)
{
$base64 = strtr($base64url, '-_', '+/');
$plainText = base64_decode($base64);
return ($plainText);
}
?>
Starson ¶
15 years ago
To expand on Jes' post:
The change took place between 5.0.5 and 5.1.0. Exactly where I don't know or care.
In short php <= 5.0.5's base64_decode( $string ) will assume that a space is meant to be a + sign where php >= 5.1.0's base64_decode( $string ) will no longer make that assumption. I did not see this noted in the change log.
Please note that, as of this writing, mb_convert_encoding( $string, "UTF-8", "BASE64" ) still behaves as base64_decode( $string ) did in php <= 5.0.5 regardless of the version of php you are running.
tobias at silverxnet dot de ¶
18 years ago
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( $outputfile );
}
?>
This function decodes the given inputfile (a filename!) and saves it to the given outputfile (a filename as well) and then returns the output filename for further usage (e.g. redirect, imagejpeg() and so on).
I thought that might be helpful.
debug ¶
14 years ago
@morgangalpin att gmail dotty com
A better implementation would be the following regular expression:
^[a-zA-Z0-9/+]*={0,2}$
Which will also detect the usage of = or == at the end of the string (and only end).
If this regex isn't following proper RFC guidelines, please comment on it.
A function geared specifically toward this:
<?php
function is_base64_encoded()
{
if (preg_match('%^[a-zA-Z0-9/+]*={0,2}$%', $data)) {
return TRUE;
} else {
return FALSE;
}
};
is_base64_encoded("iash21iawhdj98UH3"); // true
is_base64_encoded("#iu3498r"); // false
is_base64_encoded("asiudfh9w=8uihf"); // false
is_base64_encoded("a398UIhnj43f/1!+sadfh3w84hduihhjw=="); // true
?>
twm at twmacinta dot com ¶
13 years ago
To follow up on Starson's post, PHP was changed to no longer treat a space as if it were a plus sign in CVS revision 1.43.2.1, which corresponds to PHP 5.1.0. You can see what happened with a diff to branch point 1.43 at:
http://cvs.php.net/viewvc.cgi/php-src/ext/standard/base64.c
The CVS log indicates that this change was made to fix bug #34214 (base64_decode() does not properly ignore whitespace).
It would seem from the comment preceding the code which was removed that the treatment of the space as if it were the plus sign was actually intentional at one time:
When Base64 gets POSTed, all pluses are interpreted as spaces.
This line changes them back. It's not exactly the Base64 spec,
but it is completely compatible with it (the spec says that spaces
are invalid). This will also save many people considerable
headache.
if (ch == ' ') ch = '+';
However, RFC 3548 states that characters not in the Base64 alphabet should either be ignored or cause the implementation to reject the encoding and RFC 2045 says they should be ignored. So the original code was unfortunately not fully compatible with the spec or other implementations. It may have also masked problems with code not properly escaping POST variables.
user at sfdsfd dot com ¶
2 years ago
function is_base64($str){
if($str === base64_encode(base64_decode($str))){
return true;
}
return false;
}
---------------------------------------------------------------------------
---------------------------------------------------------------------------
---------------------------------------------------------------------------
$str = 'VGhpcyBpcyBiYXNlNjQgZW5jb2RlIHN0cmluZw==';
if(is_base64($str)){
print base64_decode($str);
}
nicolem2005 at gmail dot com ¶
10 years ago
base64_decode seems to fail when decoding big files/strings. I had an issue decoding a 7MB image file. Here is a solution that worked for me:
$decodedstring=base64_decode(chunk_split($encodedstring));
mcalwell ¶
13 years ago
I had a problem testing whether an imap message body was base64 encoded on a pre 5.2.* server. I had been using this function on a post 5.2 server.
I found that the function imap_base64() returns FALSE on failing to decode a string, and that I could use that to check instead.
<?php
if(imap_base64($body)) $body = imap_base64($body);
?>
nsayer at kfu dot com ¶
20 years ago
I used to do uudecode as a C module, but I've discovered a really fast way to do it in PHP. Here it is:
<?php
function uudecode($encode) {
$b64chars="ABCDEFGHIJKLMNOPQRSTUVWXYZ\
abcdefghijklmnopqrstuvwxyz0123456789+/";
$encode = preg_replace("/^./m","",$encode);
$encode = preg_replace("/\n/m","",$encode);
for($i=0; $i<strlen($encode); $i++) {
if ($encode[$i] == '`')
$encode[$i] = ' ';
$encode[$i] = $b64chars[ord($encode[$i])-32];
}
while(strlen($encode) % 4)
$encode .= "=";
return base64_decode($encode);
}
?>
This is the PHP equivalent to perl's unpack("u",___). That is, you need to strip the 'begin' and 'end' lines from the typical uuencoded file.
Klaus Fehrenbacher ¶
19 years ago
this script can correct the bug
<?php
$enc = chunk_split(preg_replace('!\015\012|\015|\012!','',$enc));
$enc = base64_decode($enc);
?>
dimagolov at yahoo dot com ¶
12 years ago
Here is function to decode Base 62 (see http://en.wikipedia.org/wiki/Base_62) string to number. It is used by MTA in message id, e.g. by Exim
<?php
function base62_decode($str) {
$ret= 0;
for ($i= 0, $l= strlen($str); $i < $l; $i++) {
$val= ord($str[$i]);
if (ctype_digit($str[$i]))
$val-= ord('0');
else if (ctype_upper($str[$i]))
$val-= ord('A') - 10;
else if (ctype_lower($str[$i]))
$val-= ord('a') - 36;
else
$val= 0;
$ret= $ret * 62 + $val;
}
return $ret;
}
?>
zmorris at zsculpt dot com ¶
14 years ago
Here is a drop-in replacement for base64_decode(), based on a faster version of morgangalpin's code:
<?php
// workaround for bug in php 4.3.11 through 4.4.7, 5.1.2 through 5.2.4 and perhaps others (http://bugs.php.net/bug.php?id=37244)
function base64_decode_fix( $data, $strict = false )
{
if( $strict )
if( preg_match( '![^a-zA-Z0-9/+=]!', $data ) )
return( false );
return( base64_decode( $data ) );
}
?>
markandrewslade at gmail dot com ¶
6 years ago
The docs don't make this explicitly clear, but if you omit `$strict` or set it to `false` then invalid characters in the encoded input will be silently ignored.
<?php
echo base64_decode('VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw=='); // "This is an encoded string"
echo base64_decode('$VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw=='); // "This is an encoded string"
echo base64_decode('$VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==', true); // false
?>
alvaro at demogracia dot com ¶
13 years ago
You can do partial decoding (e.g. from buffered input streams) if you choose a chunk length that is multiple of 4:
<?php
$encoded = base64_encode('The quick brown fox jumps over the lazy dog');
for($i=0, $len=strlen($encoded); $i<$len; $i+=4){
echo base64_decode( substr($encoded, $i, 4) );
}
?>
4 encoded chars represent 3 original chars. The "=" character is used as padding.
官方地址：https://www.php.net/manual/en/function.base64-decode.php
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