# Behaviour Accept header vs. respond\_to

**URL:** <https://www.ruby-forum.com/t/behaviour-accept-header-vs-respond-to/151065>\
**Category:** Rails\
**Created:** [October 16, 2008, 1:30pm UTC](https://www.ruby-forum.com/t/behaviour-accept-header-vs-respond-to/151065 "2008-10-16T13:30:57Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![tieleman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/65b543/32.png) [@tieleman](https://www.ruby-forum.com/u/tieleman)\
**Post date:** [October 16, 2008, 1:30pm UTC](https://www.ruby-forum.com/t/behaviour-accept-header-vs-respond-to/151065/1 "2008-10-16T13:30:57Z")

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Hi list,

I noticed some strange behaviour while testing out a couple of things  
regarding building an API. Suppose I have a very basic Rails app with  
just one resource “widgets”, I’d have the following URLs:

[http://somehost/widgets](http://somehost/widgets)  
[http://somehost/widgets.xml](http://somehost/widgets.xml)

First URL shows the widgets index using HTML, the second one using  
XML. If however, instead of requesting “widgets.xml”, I’m requesting  
just the first URL but with setting the HTTP Accept header to “Accept:  
application/xml” I would expect to get results using my XML builder.  
However, it returns HTML content (and sets Content-Type to “text/  
html”).

Now, this is clearly different behaviour for what would be identical  
requests. However, if I include a respond\_to block in my controller:

respond\_to do |format|  
format.html  
format.xml  
end

It works just as expected: setting the Accept header does in fact  
influence what is returned (XML or HTML). However, this means I have  
to include a respond\_to block in every controller method, which I  
think is undesirable.

So in conclusion, format switching works without respond\_to block, but  
only if you specify an extension in the URL, not if you use the  
“Accept:” header. If you include a respond\_to block, then format  
switching works also by using the “Accept:” header.

Can someone explain if (and why) this behaviour is correct? Using  
Rails 2.1.1.

Kind regards,

Sjoerd Tieleman

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<div class="post-metadata">

**Author:** ![tieleman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/65b543/32.png) [@tieleman](https://www.ruby-forum.com/u/tieleman)\
**Post date:** [October 16, 2008, 5:12pm UTC](https://www.ruby-forum.com/t/behaviour-accept-header-vs-respond-to/151065/2 "2008-10-16T17:12:12Z")

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On Oct 16, 6:26 am, tieleman [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> just the first URL but with setting the HTTP Accept header to "Accept:  
> end
> 
> Can someone explain if (and why) this behaviour is correct? Using  
> Rails 2.1.1.
> 
> Kind regards,
> 
> Sjoerd Tieleman

I believe it’s because in the first case, /widgets.xml, your routes.rb  
is helping to determine the :format for you (assuming you’ve still got  
the default routes in your routes.rb).

Rails won’t look at the Accept header automatically - you have to use  
a respond\_to block to do that. As for why that is, I’m not sure - I  
agree it might be nice for Rails to set the :format based on the  
Accept header as well as by route pattern.

Jeff

[purpleworkshops.com](http://purpleworkshops.com)

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