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Re: nginx_http_write_filter_module.c

Maxim Dounin
June 21, 2023 12:02PM
Hello!

On Wed, Jun 21, 2023 at 11:36:54AM +0000, Yuval Abadi via nginx wrote:

> Nginx 1.23.2
>
> The cpi ngx_http_write_filter(ngx_http_request_t *r, ngx_chain_t *in)
>
> Loop over the request out buffers and in chain
>
> If calculate size of combined buffer to write.
>
> I add body replacement on chain.
> It have value, but ngx_buf_size(cl->buf);
> Return it have 0. Size.
>
> (l->buf->last - cl->buf->pos) give the correct size
>
> So the buffer not written.
>
> Only the header part send back to client
>
> Any idea?
>
> 2023/06/21 10:45:31 [debug] 22962#22962: *3 write old buf t:1 f:0 00005600970D81E0, pos 00005600970D81E0, size: 179 file: 0, size: 0
> 2023/06/21 10:45:31 [debug] 22962#22962: *3 write new buf t:0 f:0 00005600970D8098, pos 00005600970D8098, size: 247 file: 0, size: 0
> 2023/06/21 10:45:31 [debug] 22962#22962: *3 http write filter: l:1 f:0 s:179
> 2023/06/21 10:45:31 [debug] 22962#22962: *3 http write filter limit 2097152
> 2023/06/21 10:45:31 [debug] 22962#22962: *3 writev: 179 of 179

Note the "t:0" part in the relevant debug log line: it suggests
that the cl->buf->temporary flag is not set.

If the cl->buf->memory flag isn't set as well, this basically
means that buffer does not reference any memory at all (even if
cl->buf->post / cl->buf->last pointers are set). For such a
buffer ngx_buf_size() will return the file size. And, since the
buffer does not reference file data as well (note "f:0"), it is
expected to be 0 (and it is, as per "file: 0, size: 0").

So it looks like the behaviour you observe is the result of
forgotten cl->buf->memory (or cl->buf->temporary) flag. Check
your code to see if the buffer flags are set correctly, it looks
like they aren't.

See

http://nginx.org/en/docs/dev/development_guide.html#buffer

for basic information about memory buffers and some basic
examples. For additional information, check nginx code.

--
Maxim Dounin
http://mdounin.ru/
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Subject Author Posted

nginx_http_write_filter_module.c

Yuval Abadi via nginx June 21, 2023 07:38AM

Re: nginx_http_write_filter_module.c

Maxim Dounin June 21, 2023 12:02PM

Re: nginx_http_write_filter_module.c

Yuval Abadi via nginx June 27, 2023 06:54AM



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