步骤：

1，匹配URL中的主机名和文件部分

2，创建socket并连接到目标服务器

3，构造HTTP请求并发送

4，读取HTTP响应并解析

5，保存内容到文件并关闭socket连接

代码实现如下：

/*

* 使用socket获取远程资源(网页，图片等)

* url 资源URL

* savepath 资源的保存路径

* return true/false

*/

function get_remote_picture($url,$savepath="./"){

set_time_limit(0);

$pattern = '/(http:\/\/)?([^\/]+)(.+)/';

$res = preg_match($pattern, $url, $matches);

if($res == 0){

return false;

}

$host = "";//主机名

$file = "";//请求的文件

if(count($matches) == 3){

$host = $matches[1];

$file = $matches[2];

}else if(count($matches) == 4){

$host = $matches[2];

$file = $matches[3];

}else{

return false;

}

$socket = socket_create(AF_INET,SOCK_STREAM,SOL_TCP);

$res = socket_connect($socket,gethostbyname($host),80);

if(!$res){

//echo socket_strerror(socket_last_error($socket));

socket_close($socket);

return false;

}

$request = "";

$request .= "GET $file HTTP/1.1\r\n";

$request .= "Host: $host\r\n";

$request .= "Connection: close\r\n\r\n";

$len = socket_write($socket,$request);

$response = "";

while($buf=socket_read($socket,512)){

if(strlen($buf) == 0){

break;

}

$response .= $buf;

}

if(strpos($response,"\r\n\r\n")){

$arr = explode("\r\n\r\n",$response);

if(!file_exists($savepath)){

@mkdir($savepath);

}

$savepath = rtrim($savepath,'/').'/';

file_put_contents($savepath.basename($file),$arr[1]);

}else{

socket_close($socket);

return false;

}

socket_close($socket);

return true;

}

/* 获取百度logo */

$url = "http://su.bdimg.com/static/superplus/img/logo_white.png";

$result = get_remote_picture($url);

if($result){

echo 'get remote picture success';

}else{

echo 'get remote picture failed';

}