How can I set the Accept Header for a link on a web page?

Question

This is mostly an ivory tower question, since I can easily just make a new URL endpoint. But basically, I'd like to be able to serve up CSV when the user has the Accept header configured to include text/csv. That's trivial on the server side, but on the client side I don't know how to set the Accept header unless I'm using XHR or some other "non-browser" client. Is there a way in HTML to set the Accept header in a link or in JS to set the Accept header when using window.location?

Answer 1

I figure I might as well put this here for the next thousand people looking at the post. You cannot do it.

Answer 2

Update:

I will leave my original answer below for posterity, but I now see that I didn't really answer the question. There isn't a way to do this "natively", the best approach I can think of would be to use a data uri (http://en.wikipedia.org/wiki/Data_URI_scheme) and have AJAX do the work for you:

// aware that you didn't mention jQuery, but you can do this with or without var download = function(){     var mime = this.getAttribute('data-mime-type');     $.ajax({         accepts: mime,         success: function(data){             var uri = 'data:'+mime+';charset=UTF-8,' + encodeURIComponent(data);             window.location = uri;         }     })     return false; } 

With the same idea used in the example below:

<a href="/some-csv-endpoint" data-mime-type="text/csv">Download CSV</a>

document.querySelectorAll('a[data-mime-type]').onclick = download;

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Original Answer

There is no built-in way to force an 'Accept' header on a link (via HTML or Javascript). I think you could pull this off fairly easily using a very small amount of server & client-side code though. Should be easy in any language, my example is PHP:

function get_accepted_headers() {     $headers = apache_request_headers();     if(array_key_exists('Accept', $headers)) {         $accepted = explode(',', $headers['Accept']);         return $accepted;     }     return array(); } 

Add a data-accept attribute to your download links:

<a href="/some-csv-file.csv" data-accept="text/csv">Download CSV</a>

Then attach a click event handler to ensure that the user accepts the specified content type:

// will end up with something like: ["text/html", "application/xhtml+xml", "application/xml;q=0.9", "image/webp", "*/*;q=0.8"] var user_headers = <?=stripslashes(json_encode(get_accepted_headers()))?>; var click_header_check = function() {     var accept = this.getAttribute('data-accept');     if(user_headers.indexOf(accept) == -1) {         console.log('User does not explicitly accept content-type: %s', accept);         return false;     }     window.location = this.href;     return; }  // attach the event listener document.querySelector('a[data-accept]').onclick = click_header_check; 

Not sure if this is what you were looking for, but hope that it helps.