MIME encoded-word (RFC2047) decoder

encoded-word.php

<?php

/**
 * @param string $value Raw MIME header field
 * @return string UTF-8 subject
 **/
function decode_header_field( $value )
{
	if ( preg_match( "/^\\=\\?([a-z0-9-]+)\\?([QB])\\?(.*)\\?\\=\$/i", $value, $sub ) )
	{
		$charset = strtoupper($sub[1]);
		$encoding = strtoupper($sub[2]);
		$raw = $sub[3];

		if ( $encoding == "B" )
		{
			$raw = base64_decode($raw);
		}
		elseif ( $encoding == "Q" )
		{
			$hexx = function( $h )
			{
				return hex2bin(substr($h[0],1));
			};
			$raw = preg_replace_callback( "/\\=[0-9a-f]{2}/i", $hexx, $raw );
		}
		else
		{
			return $value;
		}

		if ( $charset != "UTF-8" )
		{
			$raw = iconv( $charset, "UTF-8//IGNORE", $raw );
		}

		return $raw;
	}


	return $value;
}

$test_cases = [
	'=?utf-8?B?UmU6IENoYWluJndpcmUgcm9wZSBhY2...?=',
	'=?GB2312?B?UmU6TWFudWZhY3R1cmVyIGxvb2sgZ...?=',
	'=?utf-8?B?UmU6QW5pbWFsIGVhciB0YWcgYW5kIG...?=',
	'PCB supplier in China- RF-4, rogers, arl...',
	'=?utf-8?B?UmU6IEFtbW9uaXVtIFBvbHlwaG9zcG...?=',
	'the best price of glyphosate 41% SL From...',
	'=?utf-8?B?UmU6U2V2ZXIgaGlnaCBxdWFsaXR5IE...?=',
	'=?iso-8859-1?Q?=A1Hola,_se=F1or!?=',
];

foreach ( $test_cases as $tc )
{
	print( "{$tc}\n   " . decode_header_field( $tc ) . "\n" );
}