email-address-validation.php
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	<?php

	/*
	* Simple e-mail validation, nearly without regular expressions.
	* Copyright (C) 2007 Stefan Majewsky
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
	*/

	//Validates e-mail addresses as specified by:
	//* RFC 2822 ("Internet Message Format")
	//* RFC 1034/1035 ("Domain Name System") for the domain part
	function isEmailAddress($val) {
	//Annotation: You should know the following ASCII codes when reading this function: " == 34, . == 46, @ == 64, \ == 92
	$val = (string) $val; //ensure that the parameter is a string
	$length = strlen($val);
	if ($length < 3) return false; //cannot be OK, at least three chars (local part, "@", domain part) necessary
	$isLocalPart = true; //true if scanning the local part (switched by "@")
	static $localPartChars = "/[A-Za-z0-9.!#\$%&'*+\\-\/=?^_`{\|}~]/";//characters allowed in the local part (if not quoted)
	$isLocalPartQuoted = (substr($val, 0, 1) == '"'); //is the local part quoted with '"' chars?
	$isEscaping = false; //was the last character a backslash?
	$isClosingQuoteOccured = false; //only necessary if the local part is quoted
	//(escaping and quoting allows all characters from ASCII 32 to 127 in the local part)
	$localPartCount = ($isLocalPartQuoted ? 1 : 0); //counter for characters in the local part (and the "@")
	$domainPartCount = 0; //counter for characters in the domain part
	$labelLength = 0; //measures the length of labels in the domain part

	for ($pos = ($isLocalPartQuoted ? 1 : 0); $pos < $length; $pos++) { //check each character for compliance
	$current = substr($val, $pos, 1); //get current char
	$ordinal = ord($current); //get ASCII code for this char

	if ($isLocalPart) {
	//character in local part or the "@"
	$localPartCount++;
	//special treatment for escaped chars
	if ($isEscaping) {
	if (($ordinal < 32) \|\| ($ordinal > 127)) return false;
	$isEscaping = false;
	continue; //suppress further checks
	}
	//special treatment if the local part is quoted
	if ($isLocalPartQuoted) {
	if (($ordinal < 32) \|\| ($ordinal > 127)) return false;
	if ($isClosingQuoteOccured) { //the last char was the closing quote (i.e. end of local part) -> this char must be "@"
	if ($ordinal == 64) {
	$isLocalPart = false; //it is the "@" -> the next char starts the domain part
	} else {
	return false; //another quote occured after the closing quote
	}
	}
	$isClosingQuoteOccured = ($ordinal == 34); //true means: found '"' which (in this case) is the closing quote for the local part
	continue; //suppress further checks
	}
	//normal treatment for local part characters
	if (!preg_match($localPartChars, $current)) { //character not allowed in local part -> it may be the "@"
	if ($ordinal == 64) {
	$isLocalPart = false; //it is the "@" -> the next char starts the domain part
	} else {
	return false; //illegal char occured
	}
	}
	} else {
	//character in domain part
	$domainPartCount++;
	if (($ordinal < 32) \|\| ($ordinal > 127)) return false;
	if ($ordinal == 46) { //"." occured - starting next label
	$labelLength = 0;
	} else { //next character in this label
	$labelLength++;
	if ($labelLength == 64) { //a label may not be longer than 63 characters
	return false;
	}
	}
	}
	} //end of character loop -> no errors occured -> check the calculated values

	return
	($isLocalPartQuoted)
	? ($localPartCount >= 4) //must be at least the quotes, one character, and the '@', e.g. '"a"@'
	: ($localPartCount >= 2) //must be at least one character and the '@', e.g. 'a@'
	&& ($domainPartCount >= 1) //must be at least one character
	&& ($localPartCount <= 64) //recommendation of RFC 2822
	&& ($domainPartCount <= 255) //recommendation of RFC 2822
	;
	}

	?>

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	Nov 21 2014, 7:03 PM

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