Need help with sub-request handling

[Rajalakshmi Iyer]

Hello,

I am trying to write an Nginx module that tries to do the following in the
content phase handler -

   - Read the POST body
   - Call a sub-request to another location module within the same server
   - Return a 204 response after the sub-request is completed (for test
   purposes only)

Here is the pseudo code for the handler (Apologies for the longish
description, I have tried to keep the code to a minimum required to
describe the issue I am facing) -

ngx_int_t ngx_http_test_handler(ngx_http_request_t* r)
{
   ngx_http_test_ctx_t* ctx = ngx_http_get_module_ctx(r,
ngx_http_test_module);

   // Initialize request context
   if (ctx == NULL)
   {
      ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_test_ctx_t));
      ctx->waiting_more_body = false;
      ctx->read_body_done = false;
      ctx->sub_request = NULL;
      ngx_http_set_ctx(r, ctx, ngx_http_test_module);
   }

   // If sub-request is in progress
   if (ctx->sub_request && !ctx->sub_request->done)
   {
      return NGX_DONE;
   }

   // If awaiting more POST body
   if (ctx->waiting_more_body)
   {
      return NGX_DONE;
   }

   // If POST body not yet read
   if (!ctx->read_body_done)
   {
      rc = ngx_http_read_client_request_body(r,
ngx_http_test_content_phase_post_read);

      if (rc == NGX_AGAIN)
      {
         ctx->waiting_more_body = true;
         return NGX_DONE;
      }
   }

   // If body read
   if (ctx->read_body_done)
   {
      // Initiate sub-request if not yet done
      if (!ctx->sub_request)
      {
         ngx_http_test_subrequest(r);
         return NGX_DONE;
      }

      // If sub-request completed
      if (ctx->sub_request->done)
      {
         // Return test response
         r->headers_out.status = NGX_HTTP_NO_CONTENT;
         ngx_http_send_header(r);
         ngx_http_finalize_request(r, NGX_HTTP_NO_CONTENT);
      }

      // Sub-request is in progress
      return NGX_DONE;
   }

   return NGX_OK;
}


This is the post read callback hander -

static void ngx_http_ssp_content_phase_post_read(ngx_http_request_t *r)
{
   ngx_http_test_ctx_t* ctx = ngx_http_get_module_ctx(r,
ngx_http_test_module);
   ctx->read_body_done = true;
   if (ctx->waiting_more_body)
   {
      ctx->waiting_more_body = false;
      ngx_http_finalize_request(r, ngx_http_test_request_handler(r));
   }
   else
   {
      r->main->count--;
   }
}


And here is the pseudo code for the function that initiates the sub-request
-

ngx_int_t ngx_http_ssp_auction_subrequest(ngx_http_request_t* r)
{
   ngx_http_test_ctx_t* ctx = ngx_http_get_module_ctx(r,
ngx_http_test_module);

   // Setup post sub-request handler
   ngx_http_post_subrequest_t* psr = ngx_pcalloc(r->pool,
sizeof(ngx_http_post_subrequest_t));
   psr->handler = ngx_http_test_post_subrequest;
   return ngx_http_subrequest(r, &location, url_args, &ctx->sub_request,
psr, 0);
}

And finally the post sub-request handler -

ngx_int_t ngx_http_test_auction_post_subrequest(ngx_http_request_t *r, void*
data, ngx_int_t rc)
{
   // Mark the sub-request as done
   r->done = true;
   return NGX_DONE;
}


When I run this, here are the observations -

   - The ngx_http_test_auction_post_subrequest is being called twice -
      - First via the sub-request location module handler's
      ngx_http_finalize_request
      - Second via the core content phase's call to
      ngx_http_finalize_request

           Is this expected?

   - When I issue a request at the main module's entry point, I can see
   everything working, until the post subrequest handler is called twice.
   Thereafter, I don't see the test response (204) and the request just hangs.
   If I terminate nginx, I can see the 204 response.


Any pointers on what is going wrong and how to correct it is greatly
appreciated.

Thanks in advance,
Raj

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