Read error: #<TypeError: can't modify frozen string> raised from HttpParser

Augusto Becciu augusto at
Wed Jun 2 16:47:44 EDT 2010

Hi Eric,

There's no way our application could be freezing that constant, at
least not intentionally.

We're using New Replic's RPM plugin, but checked it out and couldn't
find anything that could do that.

Let me know if I can help in any way.


On Wed, Jun 2, 2010 at 5:25 PM, Eric Wong <normalperson at> wrote:
> Augusto Becciu <augusto at> wrote:
>> Hey guys,
>> Started running unicorn in a production server like two weeks ago.
>> It's been running smoothly, but looking at the logs found 44
>> exceptions like this:
>> E, [2010-06-02T16:17:15.117071 #22680] ERROR -- : Read error:
>> #<TypeError: can't modify frozen string>
>> E, [2010-06-02T16:17:15.117270 #22680] ERROR -- :
>> /usr/lib/ruby/gems/1.8/gems/unicorn-0.99.0/lib/unicorn/http_request.rb:59:in
>> `headers'
> <snip>
>> Ruby version: ruby 1.8.7 (2009-12-24 patchlevel 248) [i686-linux],
>> MBARI 0x8770, Ruby Enterprise Edition 2010.01
>> Any ideas? Maybe a bug in the http parser?
> Hi Augusto,
> Somehow the reusable Unicorn::HttpRequest::BUF string constant is
> getting frozen when it shouldn't be.   Do you have any code that could
> be freezing that string?  That string object should never be returned to
> the application via any code paths in Unicorn (env or tee_input).
> --
> Eric Wong

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