GNU bug report logs - #33002
26.1; EWW sends unspecific "Accept: */*" header

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Winston Weinert <winston <at> ml1.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.1; EWW sends unspecific "Accept: */*" header
Date: Wed, 10 Oct 2018 00:11:03 -0500

I noticed EWW sends header "Accept: */*", which appears to prevent
HTTP servers that provide multiple content types from picking a sensible
response content type.

More information about the Accept header with a list of RFCs at the
bottom of the page can be found here [1]. For comparison lynx sends a
more specific header, which indicates It'd prefer common web content
types before anything else [2]. I experienced this particular bug when
browsing [3], which uses the Accept header to determine when to show the
built-in API Explorer. In a web browser it shows a HTML form to interact
with the API, however actual API clients use "Accept: application/json"
or similar to get the desired format.


Regards,
Winston Weinert


[1]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept
[2]: "Accept: text/html, text/plain, text/sgml, text/css, 
application/xhtml+xml, */*;q=0.01"
[3]: https://restframework.herokuapp.com/


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Message #8 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Federico Tedin <federicotedin <at> gmail.com>
To: winston <at> ml1.net
Cc: 33002 <at> debbugs.gnu.org
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Sat, 13 Oct 2018 18:59:05 -0300

> I noticed EWW sends header "Accept: */*", which appears to prevent
> HTTP servers that provide multiple content types from picking a sensible
> response content type.
>
> More information about the Accept header with a list of RFCs at the
> bottom of the page can be found here [1]. For comparison lynx sends a
> more specific header, which indicates It'd prefer common web content
> types before anything else [2]. I experienced this particular bug when
> browsing [3], which uses the Accept header to determine when to show the
> built-in API Explorer. In a web browser it shows a HTML form to interact
> with the API, however actual API clients use "Accept: application/json"
> or similar to get the desired format.

I've been looking into this problem. It seems that EWW uses
url-retrieve to retrieve HTTP contents, which then calls url-http.  In
url-http, the variable url-mime-accept-string is used as the value for
the HTTP Accept header (if it is set to nil, "*/*" is used
instead). By default, url-mime-accept-string is set to nil.

We could temporarily set the variable url-mime-accept-string with
another value when url-retrieve is called by EWW. I am not sure what
the default value should be, or if it should be configurable. Maybe
the same value used by Lynx would be a good starting point.

Message #11 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Federico Tedin <federicotedin <at> gmail.com>
To: John Smith <winston <at> ml1.net>
Cc: 33002 <at> debbugs.gnu.org
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Sun, 4 Nov 2018 00:15:38 -0300

[Message part 1 (text/plain, inline)]

I've created a small patch which introduces a new variable, its value is
used as the value for the 'Accept' HTTP header in requests created by EWW.
As the default value I chose to use the same Lynx uses.

[eww.patch (text/x-patch, attachment)]

Message #14 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Federico Tedin <federicotedin <at> gmail.com>
Cc: 33002 <at> debbugs.gnu.org, winston <at> ml1.net
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Sun, 04 Nov 2018 19:27:11 +0200

> From: Federico Tedin <federicotedin <at> gmail.com>
> Date: Sun, 4 Nov 2018 00:15:38 -0300
> Cc: 33002 <at> debbugs.gnu.org
> 
> I've created a small patch which introduces a new variable, its value is
> used as the value for the 'Accept' HTTP header in requests created by EWW.
> As the default value I chose to use the same Lynx uses.

Does it really make sense to make this a customizable option?  How
would an average user choose a value for this option?

I think EWW should decide by itself what header to send.

Thanks.

Message #17 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Federico Tedin <federicotedin <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 33002 <at> debbugs.gnu.org, John Smith <winston <at> ml1.net>
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Sun, 4 Nov 2018 15:29:49 -0300

[Message part 1 (text/plain, inline)]

> Does it really make sense to make this a customizable option?  How
> would an average user choose a value for this option?
>
> I think EWW should decide by itself what header to send.

I agree, it is not something most people will want to change. If they
really want to change it though, they can just do (setq
eww-accept-content-types ...). I've changed the patch to use defvar
instead of defcustom.

[eww.patch (text/x-patch, attachment)]

Message #20 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Federico Tedin <federicotedin <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 33002 <at> debbugs.gnu.org, John Smith <winston <at> ml1.net>
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Tue, 13 Nov 2018 18:26:53 -0300

Eli, sorry to bother you. Just wanted to know if the last patch I sent
is OK or if it needs any further changes.

Thanks.

Message #23 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Federico Tedin <federicotedin <at> gmail.com>,
 Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: 33002 <at> debbugs.gnu.org, winston <at> ml1.net
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Wed, 14 Nov 2018 05:31:25 +0200

> From: Federico Tedin <federicotedin <at> gmail.com>
> Date: Tue, 13 Nov 2018 18:26:53 -0300
> Cc: John Smith <winston <at> ml1.net>, 33002 <at> debbugs.gnu.org
> 
> Eli, sorry to bother you. Just wanted to know if the last patch I sent
> is OK or if it needs any further changes.

I still don't think that a variable is the right solution for this.
Perhaps Lars (CC'ed) or someone else has an opinion or a better
proposal?

Message #26 received at 33002 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 33002 <at> debbugs.gnu.org, winston <at> ml1.net,
 Federico Tedin <federicotedin <at> gmail.com>
Subject: Re: bug#33002: 26.1; EWW sends unspecific "Accept: */*" header
Date: Mon, 13 May 2019 14:08:09 -0400

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Federico Tedin <federicotedin <at> gmail.com>
>> Date: Tue, 13 Nov 2018 18:26:53 -0300
>> Cc: John Smith <winston <at> ml1.net>, 33002 <at> debbugs.gnu.org
>> 
>> Eli, sorry to bother you. Just wanted to know if the last patch I sent
>> is OK or if it needs any further changes.
>
> I still don't think that a variable is the right solution for this.
> Perhaps Lars (CC'ed) or someone else has an opinion or a better
> proposal?

I think it makes sense to use a variable here -- if for no other reason
that the string is used two different places in the eww source code, and
avoiding repeating that long string is nice.  But leaving it
undocumented (in the manual) is fine, I think, as I don't see anybody
ever wanting to change it.

So I've applied Federico's patch to Emacs 27.1.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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