What

Phase 2 of #1060. Extend tests/support/ (the network::test_support static helper library shipped in #1060) so that the loopback peers actually speak each protocol's framing on top of the byte-level transport already in place. Today the fixture provides:

• hermetic_transport_fixture — shared io_context + worker thread, make_loopback_tcp_pair(), make_loopback_udp_pair()
• mock_tls_socket — RSA-2048 self-signed cert, server/client ssl::context, tls_loopback_listener (accepts one connection, no application framing)
• mock_udp_peer — UDP wrapper + stub QUIC long-header Initial-packet builder
• mock_ws_handshake — RFC 6455 client upgrade and frame builders

What is missing — and is the blocker for the six in-flight coverage sub-issues — is the server-side application framing that lets the client's post-connect code paths actually run. Examples:

• http2_client::get/post/put/del/start_stream/write_stream all early-return through is_connected(). With the current tls_loopback_listener, the TLS handshake completes so is_connected() is true, but the next operation needs the peer to send the HTTP/2 SETTINGS preface and acknowledge stream HEADERS / DATA frames, which the listener never does. The methods therefore exit on the next state guard before reaching the code we want to cover.
• grpc::client.cpp needs the same h2 framing plus gRPC length-prefix replies (HEADERS → DATA(grpc-frame) → HEADERS(trailers)).
• quic_socket.cpp needs a peer that completes the Initial → Handshake → 1-RTT cryptographic state transitions, not just sends an Initial stub.
• quic_server::handle_packet() and websocket_server::handle_new_connection() are private; tests/support/README.md (lines 92-96) acknowledges that these need a friend-test injection point to drive directly.

This issue ships those missing pieces.

Scope

Out of scope

• New protocol implementations or behavioral changes to src/
• Test cases themselves — those land in test(http2): expand http2_client.cpp coverage to 80% line / 70% branch #1062-test(websocket): expand websocket_server.cpp coverage to 80% line / 70% branch #1067 follow-ups once this fixture is available
• Public-facing API additions

Why

The six coverage sub-issues #1062, #1063, #1064, #1065, #1066, #1067 (children of #953 epic) all share one root cause: most uncovered code in their target files sits behind a connected protocol peer. The DISABLED_ConnectToHttpbin style integration tests reach external internet hosts and are unsuitable for CI. Each PR landed under those six issues honestly reported Part of #N rather than Closes #N because the >=80% line / >=70% branch acceptance criteria are unreachable without this infrastructure.

Without Phase 2:

• test(http2): expand http2_client.cpp coverage to 80% line / 70% branch #1062-test(websocket): expand websocket_server.cpp coverage to 80% line / 70% branch #1067 cannot be closed
• Expand unit test coverage from 40% to 80% #953 epic cannot reach 80% coverage target
• Future protocol regression bugs continue to require external-network integration tests that flake or get skipped in CI

With Phase 2:

• Each follow-up PR per sub-issue can drive private/post-connect methods directly, lift line coverage above 80% and branch coverage above 70%
• All six sub-issues become closeable
• A reusable substrate exists for any future protocol-level test in this repo

Where

• tests/support/ — new files listed above; extend tests/support/CMakeLists.txt to compile and link them into network_test_support
• tests/support/README.md — document new peers and friend-test injection points
• src/internal/protocols/quic/quic_server.h — add friend declaration gated on BUILD_TESTING
• src/internal/protocols/websocket/websocket_server.h — same
• tests/CMakeLists.txt — already links network::test_support; no change expected

How

Phased delivery

Each phase is independently shippable as one PR. Total estimated 4-5 PRs.

Per skill rules each phase PR stays in S/M size band. Coverage expansion to >=80% / >=70% remains the responsibility of the existing follow-up sub-issues, which become unblocked phase by phase.

Acceptance criteria for closing this issue

• All five phases (2A-2E) merged to develop
• Each peer documented in tests/support/README.md with a copy-paste composition example
• CI green on every phase PR
• At least one previously-impossible test pattern demonstrated per protocol family
• No public-API or src/ behavioral changes (verified by reviewer)

Non-goals (explicitly)

• This issue does NOT close test(http2): expand http2_client.cpp coverage to 80% line / 70% branch #1062-test(websocket): expand websocket_server.cpp coverage to 80% line / 70% branch #1067. Each of those six is closed by its own follow-up PR after the relevant phase merges.
• This issue does NOT introduce flake. All peers bind 127.0.0.1:0 (kernel-assigned ephemeral port) per the hermetic discipline already established in infra: hermetic transport fixture for HTTP/2 / QUIC / WebSocket / gRPC unit tests #1060.

Related

• Part of Expand unit test coverage from 40% to 80% #953 (epic: 40% → 80% coverage)
• Phase 2 of infra: hermetic transport fixture for HTTP/2 / QUIC / WebSocket / gRPC unit tests #1060 (infra: hermetic transport fixture) — closed 2026-04-27
• Unblocks test(http2): expand http2_client.cpp coverage to 80% line / 70% branch #1062, test(grpc): expand client.cpp coverage to 80% line / 70% branch #1063, test(http2): expand http2_server.cpp coverage to 80% line / 70% branch #1064, test(quic): expand internal/quic_socket.cpp coverage to 80% line / 70% branch #1065, test(quic): expand experimental/quic_server.cpp coverage to 80% line / 70% branch #1066, test(websocket): expand websocket_server.cpp coverage to 80% line / 70% branch #1067