[removed] Disable caching of response from server

2019-01-15 08:40发布

站内文章 / 前沿技术
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问题:

I want to turn off the cache used when a URL call to a server is made from VBScript running within an application on a Windows machine. What function/method/object do I use to do this?

When the call is made for the first time, my Linux based Apache server returns a response back from the CGI Perl script that it is running. However, subsequent runs of the script seem to be using the same response as for the first time, so the data is being cached somewhere. My server logs confirm that the server is not being called in those subsequent times, only in the first time.

This is what I am doing. I am using the following code from within a commercial application (don't wish to mention this application, probably not relevant to my problem):


With CreateObject("MSXML2.XMLHTTP")
  .open "GET", "http://myserver/cgi-bin/nsr/nsr.cgi?aparam=1", False
  .send
  nsrresponse =.responseText
End With

Is there a function/method on the above object to turn off caching, or should I be calling a method/function to turn off the caching on a response object before making the URL?

I looked here for a solution: http://msdn.microsoft.com/en-us/library/ms535874(VS.85).aspx - not quite helpful enough. And here: http://www.w3.org/TR/XMLHttpRequest/ - very unfriendly and hard to read.

I am also trying to force not using the cache using http header settings and html document header meta data:

Snippet of server-side Perl CGI script that returns the response back to the calling client, set expiry to 0. 


    print $httpGetCGIRequest->header(
        -type    => 'text/html',
        -expires => '+0s',
        );

Http header settings in response sent back to client:


<html><head><meta http-equiv="CACHE-CONTROL" content="NO-CACHE"></head>
<body>
response message generated from server
</body>
</html>

The above http header and html document head settings haven't worked, hence my question.

回答1:

I don't think that the XMLHTTP object itself does even implement caching.

You send a fresh request as soon as you call .send() on it. The whole point of caching is to avoid sending requests, but that does not happen here (as far as your code sample goes).

But if the object is used in a browser of some sort, then the browser may implement caching. In this case the common approach is to include a cache-breaker into the statement: a random URL parameter you change every time you make a new request (like, appending the current time to the URL).

Alternatively, you can make your server send a Cache-Control: no-cache, no-store HTTP-header and see if that helps.

The <meta http-equiv="CACHE-CONTROL" content="NO-CACHE> is probably useless and you can drop it entirely.



回答2:

You could use WinHTTP, which does not cache HTTP responses. You should still add the cache control directive (Cache-control: no-cache) using the SetRequestHeader method, because it instructs intermediate proxies and servers not to return a previously cached response.



回答3:

If you have control over the application targeted by the XMLHTTP Request (which is true in your case), you could let it send no-cache headers in the Response. This solved the issue in my case.

Response.AppendHeader("pragma", "no-cache");
Response.AppendHeader("Cache-Control", "no-cache, no-store");

As alternative, you could also append a querystring containing a random number to each requested url.



标签： caching vbscript xmlhttprequest response
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