fastcgi_read_timeout with PHP backend

[B.R.]

Hello,

I am trying to understand how fastcgi_read_timout works in Nginx.

Here is what I wanna do:
I list files (few MB each) on a distant place which I copy one by one
(loop) on the local disk through PHP.
I do not know the amount of files I need to copy, thus I do not know the
total amount of time I need for the script to finish its execution. What I
know is that I can ensure is a processing time limit per file.
I would like my script not to be forcefully interrupted by either sides
(PHP or Nginx) before completion.


What I did so far:
- PHP has a 'max_execution_time' of 30s (default?). In the loop copying
files, I use the set_time_limit() procedure to reinitialize the limit
before each file copy, hence each file processing has 30s to go: way enough!

- The problem seems to lie on the Nginx side, with the
'fastcgi_read_timeout' configuration entry.
I can't ensure what maximum time I need, and I would like not to use
way-off values such as 2 weeks or 1 year there. ;o)
What I understood from the
documentation<http://nginx.org/en/docs/http/ngx_http_fastcgi_module.html#fastcgi_read_timeout>is
that the timeout is reinitialized after a successful read: am I right?

The challenge is now to cut any buffering occurring on the PHP side and let
Nginx manage it (since the buffering will occur after content is being read
from the backend). Here is what I did:
* PHP's zlib.output_compression is deactivated by default in PHP
* I deactivated PHP's output_buffering (default is 4096 bytes)
* I am using the PHP flush() procedure at the end of each iteration of the
copying loop, after a message is written to the output


Current state:
* The script seems to still be cut after the expiration of the
'fastcgi_read_timout' limit (confirmed by the error log entry 'upstream
timed out (110: Connection timed out) while reading upstream')
* The PHP loop is entered several times since multiple files have been
copied
* The output sent to the browser is cut before any output from the loop
appears

It seems that there is still some unwanted buffering on the PHP side.
I also note that the PHP's flush() procedure doesn't seem to work since the
output in the browser doesn't contain any message written after eahc file
copy.

Am I misunderstanding something about Nginx here (especially about the
'fastcgi_read_timeout' directive)?
Have you any intel/piece of advice on hte matter?

Thanks,
---
*B. R.*
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