After experimenting a little more, it looks it happens when I return error
codes that don't fall between NGX_OK - NGX_ABORT. After changing my code to
return NGX_DECLINED, the error log went away.

On Thu, Jul 5, 2018 at 5:44 PM Dk Jack <dnj0496@gmail.com> wrote:

> Hi,
> I have an nginx module. The purpose of my module is to inspect every
> request and make a binary decision (i.e drop or allow). When dropping, I am
> sending a custom status code and response message. I've setup my module
> handler to be called in the NGX_HTTP_REWRITE_PHASE. Things seem to be
> working fine for the most part except for a small issue.
>
> I am seeing 'header already sent' messages in the nginx error.log. In my
> handler, I create a context for my module and attach it request using
> the ngx_http_set_ctx call. I am using the context to store some info and
> also to prevent my module from processing the same request multiple times.
> My module processes the request only once.
>
> I get the 'header already sent' message only for a fraction of the
> requests. The messages seem to be generated only for requests that I
> allowed in my module. In my module handler, I return an NGX_DECLINED return
> code when I allow a request. The message is not generated for every allowed
> request but only for some of the allowed requests. When the error is
> generated it is always for POST request and not all POST requests cause
> this error message to be logged.
>
> Could someone explain what could be going on here or where I should look
> at next to debug this further? Any pointers are appreciated. Thanks.
>
> Dk.
>
>
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