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

[Savely Krasovsky]

In my case I provision VMs using Terraform and Ignition and the only way to do it it to set
-fw_cfg with giant inline JSON. At first it was fine, but now my config exceeded
~40Kb and I faced with this issue. This patch helped, hope this will be fixed.

12.03.2025 14:27, Dominik Csapak пишет:

> 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.
>
> 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?
>
>   src/PVE/APIServer/AnyEvent.pm | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/PVE/APIServer/AnyEvent.pm b/src/PVE/APIServer/AnyEvent.pm
> index 8a52836..43ced75 100644
> --- a/src/PVE/APIServer/AnyEvent.pm
> +++ b/src/PVE/APIServer/AnyEvent.pm
> @@ -52,7 +52,7 @@ use PVE::APIServer::Utils;
>   
>   my $limit_max_headers = 64;
>   my $limit_max_header_size = 8*1024;
> -my $limit_max_post = 64*1024;
> +my $limit_max_post = 512*1024;
>   
>   my $known_methods = {
>       GET => 1,
> @@ -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),
>   		timeout => $self->{timeout},
>   		linger => 0, # avoid problems with ssh - really needed ?
>   		on_eof   => sub {