bug#22855: 24.5; `url-mime-accept-string' not set in asynchronous call

[Bjarte Johansen]

Hi,

Sending a http request asynchronously through url-retrieve I am not
(always) able to dynamically bind url-mime-accept-string so I can set
the Accept header. Setting url-request-extra-headers does not help as
url-http-create-request sets "Accept: */*" and overrides any headers I
would set in url-request-extra-headers.

Example code:

    (let ((url-debug t)
          (url-request-method "POST")
          (url-request-extra-headers
            `(("Content-Type" . "application/x-www-form-urlencoded")))
          (url-request-data
            
"query=SELECT%20%3FC%20WHERE%20%7B%5B%5D%20a%20%3FC%7D%20LIMIT%201%0A")
          (url-mime-accept-string "text/csv"))
      (url-retrieve "http://live.dbpedia.org/sparql/";
                    #'(lambda (_)
                        (message (buffer-string)))))

This will sometimes return a csv file and sometimes an xml file (usually
the first time). In *URL-DEBUG* you can see that the Accept header is
not properly set.

I believe that it fails as url-http-create-request is called in the
asynchronous context and can therefore, sometimes, escape the let
binding.



In GNU Emacs 24.5.1 (x86_64-apple-darwin15.2.0, NS apple-appkit-1404.34)
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