Expose Pingora max_h2_streams for HTTP/2/h2c upstreams

[yachnytskyi]

Thank you for developing Pingap.

Pingap already supports HTTP/2 upstream connections through the alpn upstream setting. This also allows a cleartext HTTP/2/h2c connection when the upstream does not use TLS:

[upstreams.app]
addrs = ["127.0.0.1:8080"]
alpn = "H2"

However, Pingora’s PeerOptions::max_h2_streams option does not appear to be exposed through Pingap’s upstream configuration.

Pingora defines:

/// How many concurrent h2 streams are allowed in the same connection.
pub max_h2_streams: usize,

and its current default is:

max_h2_streams: 1,

Pingap’s UpstreamConf exposes alpn, connection timeouts, idle timeout, TCP keepalive and related options. When constructing an upstream HttpPeer, Pingap assigns:

p.options.alpn = self.alpn.clone();

but does not assign p.options.max_h2_streams.

This means that an HTTP/2 or h2c upstream appears to retain Pingora’s default of one concurrent stream per connection. That prevents users from configuring practical HTTP/2 multiplexing between Pingap and an application backend.

Proposed configuration

Please consider adding an optional upstream setting:

[upstreams.app]
addrs = ["127.0.0.1:8080"]
alpn = "H2"
max_h2_streams = 100

For example, it could be represented in UpstreamConf as:

pub max_h2_streams: Option<usize>,

stored in the Pingap Upstream structure and applied when constructing the peer:

if let Some(max_h2_streams) = self.max_h2_streams {
    p.options.max_h2_streams = max_h2_streams;
}

Keeping the option optional would preserve the existing Pingora default and backward compatibility.

Requested scope

• Add max_h2_streams to UpstreamConf.
• Validate that the configured value is greater than zero.
• Store and apply it to HttpPeer.options.max_h2_streams.
• Expose it through Pingap’s web administration interface.
• Add English and Chinese field descriptions.
• Document it in the upstream configuration examples.
• Add configuration parsing and serialization tests.
• Add a test verifying that the configured value reaches the generated HttpPeer.

Motivation

This would be useful for:

• Axum and other h2c application backends.
• gRPC and Connect RPC services.
• Concurrent or long-lived streaming requests.
• Reducing the number of upstream TCP connections.
• Receiving the main multiplexing benefit of HTTP/2 instead of limiting every connection to one active stream.

Relevant code:

• Pingap upstream configuration:
  https://github.com/vicanso/pingap/blob/main/pingap-config/src/common.rs

• Pingap upstream peer construction:
  https://github.com/vicanso/pingap/blob/main/pingap-upstream/src/upstream.rs

• Pingora PeerOptions:
  https://github.com/cloudflare/pingora/blob/main/pingora-core/src/upstreams/peer.rs

Would you consider exposing this option?

[vicanso]

@yachnytskyi The latest version already supports it.

[yachnytskyi]

@vicanso many thanks