php: get client location city based on ip address

iplocation.php

<?php
/**
 * 根据用户IP获取用户所在城市
 * @param  string $userip IP
 * @return string         Location
 * @todo Implement this service in an OOP way, and Silington Pattern
 */
function get_client_location($userip) {

	//IP数据库路径
	$dat_path = 'qqwry.dat';
	$useripAddr1 = "";

	//打开IP数据库
	if (!$fd = @fopen($dat_path, 'rb')){
		return 'IP data file not exists or access denied';
	}

	//explode函数分解IP地址，运算得出整数形结果
	$userip = explode('.', $userip);
	$useripNum = $userip[0] * 16777216 + $userip[1] * 65536 + $userip[2] * 256 + $userip[3];

	//获取IP地址索引开始和结束位置
	$DataBegin = fread($fd, 4);
	$DataEnd = fread($fd, 4);
	$useripbegin = implode('', unpack('L', $DataBegin));
	if ($useripbegin < 0) $useripbegin += pow(2, 32);
	$useripend = implode('', unpack('L', $DataEnd));
	if ($useripend < 0) $useripend += pow(2, 32);
	$useripAllNum = ($useripend - $useripbegin) / 7 + 1;

	$BeginNum = 0;
	$EndNum = $useripAllNum;

	$userip1num = $BeginNum;
	$userip2num = $EndNum;

	//使用二分查找法从索引记录中搜索匹配的IP地址记录
	while($userip1num>$useripNum || $userip2num<$useripNum) {
		$Middle= intval(($EndNum + $BeginNum) / 2);

		//偏移指针到索引位置读取4个字节
		fseek($fd, $useripbegin + 7 * $Middle);
		$useripData1 = fread($fd, 4);
		if (strlen($useripData1) < 4) {
			fclose($fd);
			return 'File Error';
		}

		//提取出来的数据转换成长整形，如果数据是负数则加上2的32次幂
		$userip1num = implode('', unpack('L', $useripData1));
		if ($userip1num < 0) {
			$userip1num += pow(2, 32);
		}

		//提取的长整型数大于我们IP地址则修改结束位置进行下一次循环
		if ($userip1num > $useripNum) {
			$EndNum = $Middle;
			continue;
		}

		//取完上一个索引后取下一个索引
		$DataSeek = fread($fd, 3);
		if (strlen($DataSeek) < 3) {
			fclose($fd);
			return 'File Error';
		}

		$DataSeek = implode('', unpack('L', $DataSeek.chr(0)));
		fseek($fd, $DataSeek);
		$useripData2 = fread($fd, 4);
		if (strlen($useripData2) < 4) {
			fclose($fd);
			return 'File Error';
		}

		$userip2num = implode('', unpack('L', $useripData2));
		if ($userip2num < 0) $userip2num += pow(2, 32);

		//找不到IP地址对应城市
		if ($userip2num < $useripNum) {
			if ($Middle == $BeginNum) {
				fclose($fd);
				return 'No Data';
			}
			$BeginNum = $Middle;
		}
	}

	$useripFlag = fread($fd, 1);
	if ($useripFlag == chr(1)) {
		$useripSeek = fread($fd, 3);
		if (strlen($useripSeek) < 3) {
			fclose($fd);
			return 'System Error';
		}
		$useripSeek = implode('', unpack('L', $useripSeek.chr(0)));
		fseek($fd, $useripSeek);
		$useripFlag = fread($fd, 1);
	}

	if ($useripFlag == chr(2)) {
		$AddrSeek = fread($fd, 3);
		if (strlen($AddrSeek) < 3) {
			fclose($fd);
			return 'System Error';
		}
		$useripFlag = fread($fd, 1);
		if ($useripFlag == chr(2)) {
			$AddrSeek2 = fread($fd, 3);
			if (strlen($AddrSeek2) < 3) {
				fclose($fd);
				return 'System Error';
			}
			$AddrSeek2 = implode('', unpack('L', $AddrSeek2.chr(0)));
			fseek($fd, $AddrSeek2);
		} else {
			fseek($fd, -1, SEEK_CUR);
		}

		$AddrSeek = implode('', unpack('L', $AddrSeek.chr(0)));
		fseek($fd, $AddrSeek);

		while(($char = fread($fd, 1)) != chr(0)) {
			$useripAddr1 .= $char;
		}
	} else {
		fseek($fd, -1, SEEK_CUR);
		while(($char = fread($fd, 1)) != chr(0))
			$useripAddr1 .= $char;

		$useripFlag = fread($fd, 1);
		if ($useripFlag == chr(2)) {
			$AddrSeek2 = fread($fd, 3);
			if (strlen($AddrSeek2) < 3) {
				fclose($fd);
				return 'System Error';
			}
			$AddrSeek2 = implode('', unpack('L', $AddrSeek2.chr(0)));
			fseek($fd, $AddrSeek2);
		} else {
			fseek($fd, -1, SEEK_CUR);
		}

	}
	fclose($fd);
	return $useripAddr1;
}

/**
 * PHP获取当前用户IP地址
 * @return string IP
 */
function get_client_ip() {
	$client_ip = null;
	if (isset($_SERVER["HTTP_VIA"])) {
		$client_ip = $_SERVER["HTTP_X_FORWARDED_FOR"];
	} else {
		$client_ip = $_SERVER["REMOTE_ADDR"];
	}
	return $client_ip;
}