PHP determines whether the link is an image

Method 1

Directly matches the URL link with .png, .gif, .jpg, .jpeg.

preg_match('/.*(\.png|\.jpg|\.jpeg|\.gif)$/', $url);

This is the simplest way, but it is not accurate enough because not all image links end with the image name extension.

Method 2

Use CURL to get the response header of the image URL

First create a curl and output the header file information as a data stream

$url = "http://*************";  //图片的链接地址
$ch = curl_init();
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1); //是否跟着爬取重定向的页面
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); //将curl_exec()获取的值以文本流的形式返回，而不是直接输出。
curl_setopt($ch, CURLOPT_HEADER,  1); // 启用时会将头文件的信息作为数据流输出
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5); //设置超时时间
curl_setopt($ch, CURLOPT_URL, $url);  //设置URL
$content = curl_exec($ch);
$httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);  //curl的httpcode
$headerSize = curl_getinfo($ch, CURLINFO_HEADER_SIZE); //获取头大小
curl_close($ch);

At this time, the content contains the header information and the binary content of the image, and then intercepts the header information according to the size of the header ($headerSize), and the rest is the binary content of the image.

$headers = substr($content, 0, $headerSize); //根据头大小截取头信息

The header information output structure is as follows

HTTP/1.1 200 OK
Server: JSP3/2.0.14
Date: Sun, 30 Jul 2017 06:54:47 GMT
Content-Type: image/jpeg
Content-Length: 152094
Connection: keep-alive
ETag: "7751852900776331536"
Last-Modified: Tue, 02 May 2017 10:33:16 GMT
Expires: Wed, 18 Jul 2018 06:25:38 GMT
Age: 879492
Cache-Control: max-age=31536000
Accept-Ranges: bytes
Error-Message: OK
Ohc-Response-Time: 1 0 0 0 0 0

You can see that there is Content-Type: image/jpeg, and then process the header information and take out the desired content

$head_data=preg_split('/\n/',$headers);  //逐行放入数组中
$head_data = array_filter($head_data);  //过滤空数组
$headers_arr = [];
foreach($head_data as $val){  //按:分割开
    list($k,$v) = explode(":",$val); //:前面的作为key，后面的作为value，放入数组中
    $headers_arr[$k] = $v;
}
$img_type = explode("/",trim($headers_arr['Content-Type']));  //然后将获取到的Content-Type中的值用/分隔开
if ($httpcode == 200 && strcasecmp($img_type[0],'image') == 0) {//如果httpcode为200，并且Content-type前面的部分为image，则说明该链接可以访问成功，并且是一个图片类型的
    $type = $img_type[1];
    .............
} else {//否则........
 ............
}

Method 3

Using PHP's get_headers() function, you can directly obtain the response header information, but compared to curl, you cannot set a timeout.

<?php
$url = &#39;http://www.example.com&#39;;

print_r(get_headers($url));

print_r(get_headers($url, 1));
?>

Array
(
    [0] => HTTP/1.1 200 OK
    [1] => Date: Sat, 29 May 2004 12:28:13 GMT
    [2] => Server: Apache/1.3.27 (Unix)  (Red-Hat/Linux)
    [3] => Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
    [4] => ETag: "3f80f-1b6-3e1cb03b"
    [5] => Accept-Ranges: bytes
    [6] => Content-Length: 438
    [7] => Connection: close
    [8] => Content-Type: text/html
)

Array
(
    [0] => HTTP/1.1 200 OK
    [Date] => Sat, 29 May 2004 12:28:14 GMT
    [Server] => Apache/1.3.27 (Unix)  (Red-Hat/Linux)
    [Last-Modified] => Wed, 08 Jan 2003 23:11:55 GMT
    [ETag] => "3f80f-1b6-3e1cb03b"
    [Accept-Ranges] => bytes
    [Content-Length] => 438
    [Connection] => close
    [Content-Type] => text/html
)

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