如何测试“If-Modified-Since” HTTP头支持

问题描述

使用PHP如何准确测试远程网站是否支持If-Modified-SinceHTTP标头。

我已经阅读，如果远程文件您GET自从头请求中指定的日期以来已被修改 - 它应该返回200 OK状态。如果没有被修改，它应该返回304未修改。

因此，我的问题是，如果服务器不支持If-Modified-Since但仍返回200 OK？ / p>

有几个工具，检查您的网站是否支持If-Modified-Since，所以我想我问他们是如何工作的。

编辑：

我使用Curl执行了一些测试，发送以下内容：

  curl_setopt（$ ch，CURLOPT_HTTPHEADER，array（If-Modified-Since：.gmdate（'D，d MYH：i：s \G\M\ T'，time（）+ 60 * 60 * 60 * 60）））; 
 curl_setopt（$ ch，CURLOPT_URL，$ url）; 
 curl_setopt（$ ch，CURLOPT_RETURNTRANSFER，true）; 
 curl_setopt（$ ch，CURLOPT_FOLLOWLOCATION，true）; 
 curl_setopt（$ ch，CURLOPT_MAXREDIRS，5）; 
 curl_setopt（$ ch，CURLOPT_HEADER，true）; 
 curl_setopt（$ ch，CURLOPT_NOBODY，true）; 
 curl_setopt（$ ch，CURLOPT_AUTOREFERER，true）; 
 curl_setopt（$ ch，CURLOPT_FORBID_REUSE，true）; 
 curl_setopt（$ ch，CURLOPT_CONNECTTIMEOUT，4）; 
 curl_setopt（$ ch，CURLOPT_TIMEOUT，4）; 
  

未来日期google.com返回;

  HTTP / 1.0 304未修改
日期：Fri，05 Feb 2010 16:11:54 GMT 
服务器：gws 
 X-XSS保护：0 
 X-Cache：MISS。 
 Via：1.0。：80（squid）
连接：close 
  

如果我发送;

  curl_setopt（$ ch，CURLOPT_HTTPHEADER，array（If-Modified-Since：.gmdate ，d MYH：i：s \G\M\T'，time（） -  60 * 60 * 60 * 60）））; 
 curl_setopt（$ ch，CURLOPT_URL，$ url）; 
 curl_setopt（$ ch，CURLOPT_RETURNTRANSFER，true）; 
 curl_setopt（$ ch，CURLOPT_FOLLOWLOCATION，true）; 
 curl_setopt（$ ch，CURLOPT_MAXREDIRS，5）; 
 curl_setopt（$ ch，CURLOPT_HEADER，true）; 
 curl_setopt（$ ch，CURLOPT_NOBODY，true）; 
 curl_setopt（$ ch，CURLOPT_AUTOREFERER，true）; 
 curl_setopt（$ ch，CURLOPT_FORBID_REUSE，true）; 
 curl_setopt（$ ch，CURLOPT_CONNECTTIMEOUT，4）; 
 curl_setopt（$ ch，CURLOPT_TIMEOUT，4）; 
  

过去的日期，google.com返回;

  HTTP / 1.0 200 OK 
日期：Fri，05 Feb 2010 16:09:12 GMT 
 Expires：-1 
 Cache-Control：private，max-age = 0 
 Content-Type：text / html; charset = ISO-8859-1 
服务器：gws 
 X-XSS保护：0 
 X-Cache：MISS。 
 Via：1.0。：80（squid）
连接：close 
  

然后我将两者发送到bbc.co.uk（不支持它）;

未来的一个返回;

  HTTP / 1.1 200 OK 
日期：Fri，05 Feb 2010 16:12:51 GMT 
服务器：Apache 
 Set-Cookie： BBC-UID = 84bb66bc648318e367bdca3ad1d48cf627005b54f090f211a2182074b4ed92c40ForbSoft％20Web％20Diagnostics％20％28URL％20Validator％29; expires = Tue，04-Feb-14 16:12:51 GMT; path = /; domain = bbc.co.uk; 
 Accept-Ranges：bytes 
 Cache-Control：max-age = 0 
 Expires：Fri，05 Feb 2010 16:12:51 GMT 
 Pragma：no-cache 
 Content-Length：111677 
 Content-Type：text / html 
  

过去的回报;

  HTTP / 1.1 200 OK 
 Date：Fri，05 Feb 2010 16:14:01 GMT 
服务器：Apache 
 Set-Cookie：BBC-UID = 841b66ec4424cd91e81e88a014a3c5e50ed4e20c0e07174c4ff59675cd2fa210ForbSoft％20Web％20Diagnostics％20％28URL％20Validator％29; expires = Tue，04-Feb-14 16:14:01 GMT; path = /; domain = bbc.co.uk; 
 Accept-Ranges：bytes 
 Cache-Control：max-age = 0 
 Expires：Fri，05 Feb 2010 16:14:01 GMT 
 Pragma：no-cache 
 Content-Length：111672 
 Content-Type：text / html 
  

解决方案

我已经进行了一些测试，它似乎工作如下：

如果您发送的If-Modified-Since标题的日期是过去的日期（当前时间之前的5分钟），那么网站.com，w3.org，mattcutts.com将返回HTTP / 1.1 304 Not Modified标题。网站如yahoo.com，bbc.co.uk和stackoverflow.com总是返回HTTP / 1.1 200 OK。

Last-Modified标题无需做任何事情与If-Modified-Since，因为发送回HTTP / 1.1 304 Not Modified头的整个点是，你不必发送正文因此，我的问题的答案是，如果一个网站没有返回一个HTTP / 1.1 304不支持当您发送If-Modified-Since 5分钟前标题时，网站不能正确支持If-Modified-Since请求。

编辑：我忘了添加一个好的测试是让对域的正常HEAD请求（例如w3.org），获取上次修改日期，然后用If-Modified-Since：进行另一请求。这将测试支持上次修改值和If-Modified-Since请求。请注意：只是因为服务器发送回上次修改日期并不意味着它支持If-Modified-Since

Using PHP how can I accurately test that a remote website supports the "If-Modified-Since" HTTP header.

From what I have read, if the remote file you GET has been modified since the date specified in the header request - it should return a 200 OK status. If it hasn't been modified, it should return a 304 Not Modified.

Therefore my question is, what if the server doesn't support "If-Modified-Since" but still returns a 200 OK?

There are a few tools out there that check if your website supports "If-Modified-Since" so I guess I'm asking how they work.

Edit:

I have performed some testing using Curl, sending the following;

curl_setopt($ch, CURLOPT_HTTPHEADER, array("If-Modified-Since: ".gmdate('D, d M Y H:i:s \G\M\T',time()+60*60*60*60)));
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_MAXREDIRS, 5);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_NOBODY, true);
curl_setopt($ch, CURLOPT_AUTOREFERER, true);
curl_setopt($ch, CURLOPT_FORBID_REUSE, true);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 4);
curl_setopt($ch, CURLOPT_TIMEOUT, 4);

i.e. a date in the future google.com returns;

HTTP/1.0 304 Not Modified
Date: Fri, 05 Feb 2010 16:11:54 GMT
Server: gws
X-XSS-Protection: 0
X-Cache: MISS from .
Via: 1.0 .:80 (squid)
Connection: close

and if I send;

curl_setopt($ch, CURLOPT_HTTPHEADER, array("If-Modified-Since: ".gmdate('D, d M Y H:i:s \G\M\T',time()-60*60*60*60)));
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_MAXREDIRS, 5);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_NOBODY, true);
curl_setopt($ch, CURLOPT_AUTOREFERER, true);
curl_setopt($ch, CURLOPT_FORBID_REUSE, true);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 4);
curl_setopt($ch, CURLOPT_TIMEOUT, 4);

i.e. a date in the past, google.com returns;

HTTP/1.0 200 OK
Date: Fri, 05 Feb 2010 16:09:12 GMT
Expires: -1
Cache-Control: private, max-age=0
Content-Type: text/html; charset=ISO-8859-1
Server: gws
X-XSS-Protection: 0
X-Cache: MISS from .
Via: 1.0 .:80 (squid)
Connection: close

If I then send both to bbc.co.uk (which doesn't support it);

The future one returns;

HTTP/1.1 200 OK
Date: Fri, 05 Feb 2010 16:12:51 GMT
Server: Apache
Set-Cookie: BBC-UID=84bb66bc648318e367bdca3ad1d48cf627005b54f090f211a2182074b4ed92c40ForbSoft%20Web%20Diagnostics%20%28URL%20Validator%29; expires=Tue, 04-Feb-14 16:12:51 GMT; path=/; domain=bbc.co.uk;
Accept-Ranges: bytes
Cache-Control: max-age=0
Expires: Fri, 05 Feb 2010 16:12:51 GMT
Pragma: no-cache
Content-Length: 111677
Content-Type: text/html

The date in the past returns;

HTTP/1.1 200 OK
Date: Fri, 05 Feb 2010 16:14:01 GMT
Server: Apache
Set-Cookie: BBC-UID=841b66ec44232cd91e81e88a014a3c5e50ed4e20c0e07174c4ff59675cd2fa210ForbSoft%20Web%20Diagnostics%20%28URL%20Validator%29; expires=Tue, 04-Feb-14 16:14:01 GMT; path=/; domain=bbc.co.uk;
Accept-Ranges: bytes
Cache-Control: max-age=0
Expires: Fri, 05 Feb 2010 16:14:01 GMT
Pragma: no-cache
Content-Length: 111672
Content-Type: text/html

So my question still stands.

解决方案

I have performed some testing on this and it appears to work as follows;

If you send an If-Modified-Since header with a date that is in the past (5 mins previous to the current time should do it) then sites such as google.com, w3.org, mattcutts.com will return a "HTTP/1.1 304 Not Modified" header. Sites such as yahoo.com, bbc.co.uk and stackoverflow.com always return a "HTTP/1.1 200 OK".

The "Last-Modified" header has nothing to do with "If-Modified-Since" because the whole point of sending back a "HTTP/1.1 304 Not Modified" header is that you don't have to send the body with it (thus saving bandwidth - which is the whole point behind this).

Therefore, the answer to my question is that if a site doesn't return a "HTTP/1.1 304 Not Modified" header when you send an "If-Modified-Since 5 mins ago" header, the site doesn't support the "If-Modified-Since" request properly.

If I am incorrect, please say so and provide testing to show.

Edit: I forgot to add that a good test is to make a normal HEAD request to the domain (e.g. w3.org), grab the "Last Modified" date and then make another request with "If-Modified-Since:". This will test that both the "Last Modified" value and "If-Modified-Since" request are supported. Please Note: just because the server sends back a "Last Modified" date doesn't mean it supports "If-Modified-Since"

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