[pve-devel] [RFC PATCH http-server] fix #6230: increase allowed post size

[Thomas Lamprecht]

Am 12.03.25 um 14:27 schrieb Dominik Csapak:
> In some situations, e.g. having a large resource mapping, the UI can
> generate a request that is bigger than the current limit of 64KiB.
> 
> Our files in pmxcfs can grow up to 1 MiB, so theoretically, a single
> mapping can grow to that size. In practice, a single entry will have
> much less. In #6230, a user has a mapping with about ~130KiB.
> 
> Increase the limit to 512KiB so we have a bit of buffer left.

s/buffer/headroom/ ?

> 
> We have to also increase the 'rbuf_max' size here, otherwise the request
> will fail (since the buffer is too small for the request).
> Since the post limit and the rbuf_max are tightly coupled, let it
> reflect that in the code. To do that sum the post size + max header
> size there.
> 
> Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
> ---
> sending as RFC because:
> * not sure about the rbuf_max calculation, but we have to increase it
>   when we increase $limit_max_post. (not sure how much is needed exactly)
> * ther are alternative ways to deal with that, but some of those are vastly
>   more work:
>   - optimize the pci mapping to reduce the number of bytes we have to
>     send (e.g. by reducing the property names, or somehow magically
>     detect devices that belong together)
>   - add a new api for the mappings that can update the entries without
>     sending the whole mapping again (not sure if we can make this
>     backwards compatible)
>   - ignore the problem and simply tell the users to edit the file
>     manually (I don't like this one...)
> 
> also, I tried to benchmark this, but did not find a tool that does this
> in a good way (e.g. apachebench complained about ssl, and i couldn't get
> it to work right). @Thomas you did such benchmarks laft according to git
> log, do you remember what you used then?

argh, my commit message back then looks like I tried to write what I used
but then fubmled (or got knocked on the head) and sent it out unfinished.
To my defence, Wolfgang applied it ;P

I'm not totally sure what I used back then, might have been something
custom-made too. FWIW, recently I used oha [0] and found it quite OK, albeit
I did not try it with POST data, but one can define the method and pass a
request body from CLI argument directly or a file, and it has a flag to
allow "insecure" TLS certs.

[0]: https://github.com/hatoo/oha

> @@ -1891,7 +1891,7 @@ sub accept_connections {
>  	    $self->{conn_count}++;
>  	    $reqstate->{hdl} = AnyEvent::Handle->new(
>  		fh => $clientfh,
> -		rbuf_max => 64*1024,
> +		rbuf_max => $limit_max_post + ($limit_max_headers * $limit_max_header_size),

The header part is wrong as the header limits are independent, i.e., the
request must have less than $limit_max_headers separate headers and all
those together must be smaller than $limit_max_header_size.

So just adding $limit_max_header_size is enough, no multiplication required.

>  		timeout => $self->{timeout},
>  		linger => 0, # avoid problems with ssh - really needed ?
>  		on_eof   => sub {