nginx_http_write_filter_module.c

[Yuval Abadi]

Thanks

From: nginx <nginx-bounces at nginx.org> on behalf of Maxim Dounin <mdounin at mdounin.ru>
Date: Wednesday, 21 June 2023 at 19:01
To: Yuval Abadi via nginx <nginx at nginx.org>
Subject: Re: nginx_http_write_filter_module.c
EXTERNAL MAIL: nginx-bounces at nginx.org

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

https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fnginx.org%2Fen%2Fdocs%2Fdev%2Fdevelopment_guide.html%23buffer&data=05%7C01%7Cy.abadi%40f5.com%7C93490412a0ae47a77b2808db7270cf46%7Cdd3dfd2f6a3b40d19be0bf8327d81c50%7C0%7C0%7C638229601077880722%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=lfQi%2FWoc7nk3Zr8R6I1X9DAE%2BZ36sfkMT6%2Fnw7YFgR8%3D&reserved=0<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
https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmdounin.ru%2F&data=05%7C01%7Cy.abadi%40f5.com%7C93490412a0ae47a77b2808db7270cf46%7Cdd3dfd2f6a3b40d19be0bf8327d81c50%7C0%7C0%7C638229601077880722%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=rrIFE5kKXycRGSmQ64bP%2BwDfaqpEVKZfndVRYmgxNyE%3D&reserved=0<http://mdounin.ru/>
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