`max_webtransport_sessions` is advertised but not enforced

Version

h3 0.0.8

Platform

Linux desktop 7.1.7 NixOS x86_64 GNU/Linux

Summary

max_webtransport_sessions is advertised but not enforced

Code Sample

Static check:

rg -n 'max_webtransport_sessions' h3/src

For h3 0.0.8, references are limited to configuration defaults, settings parsing/serialization, and the builder setter; there is no runtime admission check.

Behavioral peer pseudocode:

let mut builder = h3::server::builder();
builder
    .enable_extended_connect(true)
    .enable_datagram(true)
    .enable_webtransport(true)
    .max_webtransport_sessions(1);

let mut h3 = builder.build(quic).await?;

// A non-compliant peer opens two valid WebTransport CONNECT requests.
let first = h3.accept().await?.unwrap().resolve_request().await?;
let second = h3.accept().await?.unwrap().resolve_request().await?;

// h3 delivers both to the application; it does not reject the second from
// the configured maximum. Application code must count/reject it itself.

Expected Behavior

The API contract should be explicit:

• If the value is only an advertised peer obligation, name and document it as such and expose enough information for the application to enforce violations.
• If it is a server limit, track active sessions and reject excess CONNECT requests with the protocol-appropriate response while allowing up to the configured count.

Actual Behavior

server::Builder::max_webtransport_sessions(value) stores value in configuration and serializes it into SETTINGS_WEBTRANSPORT_MAX_SESSIONS. No active-session counter or request rejection references the configured field after settings serialization.

The method's Rustdoc says it “Limits the maximum number of WebTransport sessions,” but h3 itself continues delivering extended CONNECT request streams without checking the limit. Moreover, h3-webtransport 0.1.2 moves the whole h3 connection into one WebTransportSession, so its public API cannot naturally operate the configured number of concurrent sessions when the value is greater than one.

Suggested upstream fix

Clarify whether the setting is declarative or enforced. Add active-session lifecycle hooks and admission enforcement, or rename the builder operation to make its settings-only behavior explicit. h3-webtransport should support multiple session drivers on one h3 connection if values greater than one are intended to be usable.

Start in h3/src by tracing server::Builder::max_webtransport_sessions from configuration and SETTINGS_WEBTRANSPORT_MAX_SESSIONS serialization into request handling. Compare that behavior with h3-webtransport 0.1.2's single-session API and determine whether the setting is declarative or enforced. Done means the contract is explicit and the API behavior, documentation, and session handling agree.