php实现短链接系统

短链接的好处：
节省网址长度，便于社交化传播。(短信或者微博，字数长度受限制时。这样的短链接制作二维码也是易于识别)
方便后台跟踪点击量、地域分布等用户统计。（统计流量访问，延伸可以做网址举报屏蔽。只屏蔽短链接即可，控制输出）
规避关键词、域名屏蔽手段。
隐藏真实地址，适合做付费推广链接。

实现思路：

将传入的长链接存入数据库中，并记录创建时间，返回自增ID。

将返回的id进行10进制转64进制编码：如自增id为10时，64进制转换为A；即使当我们记录到1亿条时，1亿的64进制为：F9eEA，才5个字符长度，非常适合作为短链接的参数。
然后组合成 http://域名/编码参数/。我们既得到了短链接。当我们访问短链接时，解析参数转为10进制。到数据库中查找获得相应的链接，进行301跳转。此功能既为完成。

步骤如下：

1、修改host文件->配置网站虚拟目录->进行URL重写
1.1 修改hosts文件，将测试域名指向本机ip

C:WindowsSystem32driversetchosts
127.0.0.1      		 d.cn 

1.2 配置apache，添加虚拟域名映射，参考：http://blog.csdn.net/nuli888/article/details/51830659

<VirtualHost *:80>
    DocumentRoot "D:/webroot/test/link"
    ServerName d.cn
    <Directory "D:/webroot/test/link">
		DirectoryIndex index.html index.php 
		AllowOverride All
		Order deny,allow
		Allow from all
	</Directory>
</VirtualHost>


<VirtualHost *:80>
    DocumentRoot "D:/webroot"
    ServerName localhost
    <Directory "D:/webroot">
		DirectoryIndex index.html index.PHP 
		AllowOverride All
		Order deny,allow
		Allow from all
	</Directory>
</VirtualHost>

1.3 配置.htaccess文件，将短连接重定向，设置如下：

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^(S{1,7})$ index.php?code=$1 [L]
</IfModule>

URL短链接的实现原理和方法

2、增加64进制编码与解码方法：

func.php

<?php
function b64dec($b64) { //64进制转换成10进制
    $map = array(
        "0"=>0,"1"=>1,"2"=>2,"3"=>3,"4"=>4,"5"=>5,"6"=>6,"7"=>7,"8"=>8,"9"=>9,
        "A"=>10,"B"=>11,"C"=>12,"D"=>13,"E"=>14,"F"=>15,"G"=>16,"H"=>17,"I"=>18,"J"=>19,
        "K"=>20,"L"=>21,"M"=>22,"N"=>23,"O"=>24,"P"=>25,"Q"=>26,"R"=>27,"S"=>28,"T"=>29,
        "U"=>30,"V"=>31,"W"=>32,"X"=>33,"Y"=>34,"Z"=>35,"a"=>36,"b"=>37,"c"=>38,"d"=>39,
        "e"=>40,"f"=>41,"g"=>42,"h"=>43,"i"=>44,"j"=>45,"k"=>46,"l"=>47,"m"=>48,"n"=>49,
        "o"=>50,"p"=>51,"q"=>52,"r"=>53,"s"=>54,"t"=>55,"u"=>56,"v"=>57,"w"=>58,"x"=>59,
        "y"=>60,"z"=>61,"_"=>62,"="=>63
    );
    $dec = 0;
    $len = strlen($b64);
    for ($i = 0; $i < $len; $i++) {
        $b = $map[$b64{$i}];
        if ($b === NULL) {
            return FALSE;
        }
        $j = $len - $i - 1;
        $dec += ($j == 0 ? $b : (2 << (6 * $j - 1)) * $b);
    }
    return $dec;
}
function decb64($dec) { //10进制转换成64进制
    if ($dec < 0) {
        return FALSE;
    }
    $map = array(
        0=>"0",1=>"1",2=>"2",3=>"3",4=>"4",5=>"5",6=>"6",7=>"7",8=>"8",9=>"9",
		10=>"A",11=>"B",12=>"C",13=>"D",14=>"E",15=>"F",16=>"G",17=>"H",18=>"I",19=>"J",
		20=>"K",21=>"L",22=>"M",23=>"N",24=>"O",25=>"P",26=>"Q",27=>"R",28=>"S",29=>"T",
		30=>"U",31=>"V",32=>"W",33=>"X",34=>"Y",35=>"Z",36=>"a",37=>"b",38=>"c",39=>"d",
		40=>"e",41=>"f",42=>"g",43=>"h",44=>"i",45=>"j",46=>"k",47=>"l",48=>"m",49=>"n",
		50=>"o",51=>"p",52=>"q",53=>"r",54=>"s",55=>"t",56=>"u",57=>"v",58=>"w",59=>"x",
		60=>"y",61=>"z",62=>"_",63=>"=",
    );
	$b64 = "";
    do {
        $b64 = $map[($dec % 64)] . $b64;
        $dec /= 64;
    } while ($dec >= 1);
	return $b64;
	
}

3、创建数据表links

CREATE TABLE `links` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `url` varchar(255) DEFAULT NULL,
  `ctime` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=26262628 DEFAULT CHARSET=latin1;


-- ----------------------------
-- Records of links
-- ----------------------------
INSERT INTO `links` VALUES ("10900", "http://www.cnblogs.com", "1489568387");
INSERT INTO `links` VALUES ("10901", "http://www.baidu.com", "1489569782");

4、创建短链接生成与长链接获取功能

index.php

<?php
include "func.php";
define("HOST","localhost");
define("DB_NAME","test");
define("USER","root");
define("PASS","123456");

function make_short_url($url){
	$url=str_ireplace("http://","",$url);
	$pdo = new PDO("mysql:host=".HOST.";dbname=".DB_NAME,USER,PASS); 
	$rs = $pdo ->query("select id from links where url="".$url.""");
	$row = $rs -> fetch(); 
	if($row==false){
		$pdo -> exec("insert into links(url,ctime) values("".$url."","".mktime()."")"); 
		$id=$pdo -> lastinsertid(); 
		return "http://d.cn/".decb64($id);
	}else{
		return "http://d.cn/".decb64($row["id"]);
	}
}

function get_long_url($code){
	$pdo = new PDO("mysql:host=".HOST.";dbname=".DB_NAME,USER,PASS); 
	$rs = $pdo ->query("select url from links where id="".b64dec($code).""");
	$row = $rs -> fetch(); 
	if($row==false){
		print "链接错误";
		exit;
	}else{
		return "http://".$row["url"];
	}
}
//参数的接收与短链接返回部分
if($_GET["code"]){
	$code=trim($_GET["code"],"/");
	$url=get_long_url($code);
	if($url){
		header("location:$url");
	}
}elseif($_GET["url"]){
	$url=trim($_GET["url"]);
	print make_short_url($url);
}

5、测试

返回内容为：http://d.cn/2gL。在浏览器中访问http://d.cn/2gL,即会跳转到http://www.baidu.com

一个短链接已经基本实现，仍然有一些可待优化的地方。如跳转方式改为301跳转；数据库数据量大时，可以采取分库操作。或者用memcache或者redis缓存服务器来代替mysql，提升效率等等