Dealing with buffered data with upstream generated response

Umesh Sirsiwal usirsiwal at
Tue Nov 29 19:19:10 UTC 2011

Thanks Maxim,

>> I am developing a body filter which transforms outgoing stream. As
>> part of the function, the incoming stream is copied in new buffer
>> and sent. This in some cases results in a condition where my filter
>> has busy buffers but the upper layers don't have any busy buffer. In
>> our case the data is generated by upstream module. Since upstream
>> module does not pay attention to connection->buffered, the
>> output_filter is never called again to flush my busy buffers and the
>> transfer just hangs.
>> Adding r->connection->buffered to the or condition solves the hang.
>>             if (u->out_bufs || u->busy_bufs) {
>>                  rc = ngx_http_output_filter(r, u->out_bufs);
>>                  if (rc == NGX_ERROR) {
>>                      ngx_http_upstream_finalize_request(r, u, 0);
>>                      return;
>>                  }
>>                  ngx_chain_update_chains(&u->free_bufs,&u->busy_bufs,
>> &u->out_bufs, u->output.tag);
>>              }
>> Is this nginx bug or am I missing something?
> I tend to think this is a bug, and it should probably manifest
> itself with e.g. gzip filter as well.
> (Well, as far as I see transfer shouldn't hang completely, but it
> will be only resumed as soon as upstream sends some more data or
> closes connection.)
In our application we use Upstream KeepAlive module to keep the upstream 
connection open. So if this happens towards the end of the last 
subrequest response, the connection hangs.
> It would be superb if you'll be able to provide test case which
> catches this for our test suite (
I will try to see if I can reproduce it with gzip filter. I should be 
able to reproduce it with 
limit-rate+gzip-filter+proxy+upstream-keepalive module combination. But, 
I am not sure if the nginx-test test-suite includes upstream-keepalive.

> I'll look into this more closely as time permits.
> Maxim Dounin
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