扩展 HttpSocket 以用于 Amazon 等其他用途，适用于 1.3.x 和 2.x
在尝试使用 Amazon API 时，我阅读了很多关于 Amazon 规则的信息，该规则只允许每秒进行 1 次请求，否则如果网站经常忽略此规则，将被拒绝访问 Amazon。因此，我开始着手解决这个问题，使用 CakePHP，最终得到了几个对其他人可能也有一定用处的类。本文的源代码可从 Github 下载。主分支适用于 CakePHP1.3.x，现在还有一个 2.x 分支。
对于 Amazon 请求频率问题，显而易见的解决方案是确保您的网站每秒不超过 1 次请求。我决定使用锁定文件方法来实现这一点，该方法会整理正在进行的请求。
这里介绍的系统由 3 个类和一个接口组成。
ISocket 接口简单地概述了 CakePHP 中 HttpSocket 所实现的方法。
interface ISocket {
public function put($uri = null, $data = array(), $request = array());
public function delete($uri = null, $data = array(), $request = array());
public function get($uri=NULL, $query = array(), $request = array());
public function post($uri = null, $data = array(), $request = array());
}
抽象类 BaseSocket 封装任何实现 ISocket 的类，并负责将调用传递给该类。
abstract class BaseSocket implements ISocket {
private $_socket;
public function __construct( ISocket $socket ) {
$this->_socket = $socket;
}
public function delete($uri = null, $data = array(), $request = array()) {
return $this->_socket->delete($uri,$data,$request);
}
public function post($uri = null, $data = array(), $request = array()) {
return $this->_socket->post($uri,$data,$request);
}
public function get($uri = NULL, $query = array(), $request = array()) {
return $this->_socket->get($uri,$query,$request);
}
public function put($uri = null, $data = array(), $request = array()) {
return $this->_socket->put($uri,$data,$request);
}
}
NormalSocket 类只是扩展了 HttpSocket 并实现了 ISocket，这使得它可以被 BaseSocket 使用。除此之外，它与 CakePHP 提供的 HttpSocket 相同。
class NormalSocket extends HttpSocket implements ISocket {
public function __construct($config = array() ) {
parent::__construct($config);
}
}
您可以像使用 HttpSocket 一样使用 NormalSocket。
/* Create a NormalSocket which has the same usage as HttpSocket */
$ns = new NormalSocket();
/* Get content from a URI */
$response = $ns->get($uri);
ThrottledSocket 会限制另一个实现 ISocket 的对象，该对象在构造函数中传递。
class ThrottledSocket extends BaseSocket implements ISocket {
/**
* Filename used for synchronisation
*/
private $_filename;
/**
* Create a Throttled Socket.
*/
public function __construct(ISocket $socket) {
parent::__construct($socket);
$this->_filename = ROOT . DIRECTORY_SEPARATOR . APP_DIR . DIRECTORY_SEPARATOR . 'tmp' . DIRECTORY_SEPARATOR . 'throttle.dat';
if (!file_exists($this->_filename)) {
file_put_contents($this->_filename, time());
}
}
/**
* Issues a GET request to the specified URI, query, and request.
*/
public function get($uri=NULL, $query = array(), $request = array()) {
$delay = $this->throttle();
if ($delay > 0) {
sleep($delay);
}
return parent::get($uri, $query, $request);
}
/**
* Issues a POST request to the specified URI, query, and request.
*/
public function post($uri = null, $data = array(), $request = array()) {
$delay = $this->throttle();
if ($delay > 0) {
sleep($delay);
}
return parent::post($uri, $query, $request);
}
/**
* Introduce a delay. Requests are only allowed to be sent
* once a second.
*/
private function throttle() {
$curtime = time();
$filetime = $curtime;
$fp = fopen($this->_filename, "r+");
if (flock($fp, LOCK_EX)) {
$nbr = fread($fp, filesize($this->_filename));
$filetime = intval(trim($nbr));
$curtime = time();
if ($curtime > $filetime) {
$filetime = $curtime;
} else {
$filetime++;
}
rewind($fp);
ftruncate($fp, 0);
fprintf($fp, "%d", $filetime);
flock($fp, LOCK_UN);
}
fclose($fp);
return $filetime - $curtime;
}
}
您可以按如下方式使用 ThrottledSocket…
$ts = new ThrottledSocket(new NormalSocket());
/* Requests to Throttled socket now happen only once per second */
$response = $ts->get($uri);
CachedSocket 会缓存另一个实现 ISocket 的对象，该对象在构造函数中传递。该类使用标准的 CakePHP 缓存机制来缓存封装套接字返回的响应。
class CachedSocket extends BaseSocket implements ISocket {
/**
* The cache key
*/
private $_cacheKey;
/**
* The duration of the cache in seconds
*/
private $_cacheDuration;
/**
* Create the object and assign a cache key.
*/
public function __construct(ISocket $socket, $key, $duration=3600) {
parent::__construct($socket);
$this->_cacheKey = $key;
$this->_cacheDuration = $duration;
}
/**
* Set the number of seconds for which responses should be cached.
*/
public function setCacheDuration($duration) {
$this->_cacheDuration = $duration;
}
/**
* Set the cache key
*/
public function setCacheKey($key) {
$this->_cacheKey = $key;
}
/**
* GET Request a URL.
*/
public function get($uri=NULL, $query = array(), $request = array()) {
$response = Cache::read($this->_cacheKey);
if ($response === false) {
$response = parent::get($uri, $query, $request);
if ($response) {
Cache::set(array('duration' => '+' . $this->_cacheDuration . ' seconds'));
Cache::write($this->_cacheKey, $response);
}
}
return $response;
}
/**
* POST Request a URL.
*/
public function post($uri=NULL, $query = array(), $request = array()) {
$response = Cache::read($this->_cacheKey);
if ($response === false) {
$response = parent::post($uri, $query, $request);
if ($response) {
Cache::set(array('duration' => '+' . $this->_cacheDuration . ' seconds'));
Cache::write($this->_cacheKey, $response);
}
}
return $response;
}
}
您可以使用 CachedSocket 来缓存来自 HttpSocket 的响应
/* Cache the NormalSocket with the key 'CacheKey' for 1 hour */
$cs = new CachedSocket(new NormalSocket(), 'CacheKey', 3600 );
/* Requests to Cached socket now return the cached response for the next hour */
$response = $cs->get($uri);
通过这种封装其他实现 ISocket 对象的系统，我们可以缓存受限请求，这对于访问 Amazon 非常理想。一旦发出请求，响应就会被缓存，因此只有在必要时才会发出 Amazon 请求，并且每秒不会发出超过一次请求。
function GetBookByAsin( $asin ) {
/* Throttle an HttpSocket to send requests at once a second */
$ts = new ThrottledSocket( new NormalSocket() );
/* Cache the throttled socket */
$amazonSocket = new CachedSocket( $ts, 'ASIN' . $asin, 3600 );
/* Build amazon request URL in $url */
$response = $amazonSocket->get($url);
/* Process XML returned by Amazon or by the Cache */
}
示例函数第一次被调用时，它将发出对 Amazon 的受限请求并缓存响应。在接下来的一个小时内，对同一项目的任何请求都将返回缓存的响应，而不会向 Amazon 发出任何调用。
源代码可从上面显示的 GitHub URL 获取，您只需将这些类复制到您的 app/libs（或 2.x 的 app/Lib）目录中并使用它们即可。我已经记录了每个类，并提供了一些测试用例。
在测试用例中可以看到将套接字类封装到其他类中的另一个好处。创建一个实现 ISocket 的虚拟类并将其提供给 CachedSocket 或 ThrottledSocket 很容易，这样就可以测试这些类，而无需进行任何实际请求。