feat(usrsctp): add component (sctplab/usrsctp + ESP-IDF lwIP integration)

[vikramdattu]

Draft — sits behind #1060 (libsrtp) + #1061 (libwebsockets) on the same migration track from idf-extra-components. Will flip to ready-for-review after either lands and we apply the consistent review feedback here.

Summary

Adds usrsctp — userspace SCTP stack (RFC 4960) wrapping sctplab/usrsctp pinned at commit 2e1ab10. Used by WebRTC data channels (SCTP-over-DTLS-over-UDP) and by other consumers that need a portable SCTP implementation on platforms without a kernel SCTP.

Pairs naturally with libwebsockets and libsrtp in the WebRTC transport neighbourhood — that's the reason for landing here rather than in idf-extra-components.

Patches

Five ESP-IDF-specific patches applied at configure time. See patches/README.md for the full ledger.

#	Patch	Status
0001	Added LWIP support — userspace conn transport routes packets through lwIP for the espnetif path	Upstream PR in flight: sctplab/usrsctp#743. Drops + re-pin once it lands.
0002	Allocate larger sin6 structure — fixes an on-stack overflow when the wrapper passes the v6 socket address	Local bug fix; happy to upstream as a small standalone PR.
0003	ESP_PLATFORM: thread-safe netif APIs	ESP-IDF-specific; stays downstream.
0004	feat(esp): allocate usrsctp thread stacks from SPIRAM	ESP-IDF-specific (helps on memory-constrained C5 / C6); stays downstream.
0005	Fix non-LWIP / Linux-target buildability in 0001	Folds into 0001 when it lands upstream.

Layout

components/usrsctp/
├── CMakeLists.txt        # ESP-IDF component registration + idempotent patch-apply loop
├── Kconfig               # debug + thread-stack location toggles
├── idf_component.yml     # registry manifest (tags, sbom)
├── sbom_usrsctp.yml      # SBOM for the wrapped upstream
├── patches/              # 5 patches + README ledger
├── examples/get_started/ # minimal init/shutdown sanity app
├── test_apps/            # embedded Unity smoke (esp32 + esp32c3)
├── host_test/            # Linux-target socket-lifecycle test
├── usrsctp_register.c    # empty TU so idf_component_register has a source
└── usrsctp/              # sctplab/usrsctp submodule @ 2e1ab10

Local verification

• pre-commit clean (yaml/copyright/astyle/codespell/eradicate/yapf/isort/flake8).
• examples/get_started/ builds clean on esp32 with IDF v5.5.
• .github/workflows/usrsctp__build.yml mirrors the lws_build.yml / libsrtp__build.yml pattern — label-gated on usrsctp. Maintainer drops the label and CI builds the get_started + test_apps matrix on release-v5.4 / release-v5.5 plus the host_test runs on the Linux target.
• Downstream verification: this same wrapper (under the previous local name esp_usrsctp) drives the WebRTC data-channel transport for our ESP32-P4 KVS WebRTC port in production.

Previously

Initially prepared as espressif/idf-extra-components#754 (Draft). Moved here per discussion with @euripedesrocha — esp-protocols is the right neighbourhood for transport-stack components.

Related

• feat(libsrtp): add component (libsrtp v2.8.0 + ESP-IDF mbedTLS port) #1060 — libsrtp (SRTP/SRTCP packet protection, sibling on the WebRTC transport path)
• feat(lws): add Kconfig toggles + bump submodule #1061 — libwebsockets Kconfig toggles + submodule bump
• sctplab/usrsctp#743 — upstream PR for the LWIP layer (patch 0001 disappears when it lands)

cc @euripedesrocha @david-cermak

[david-cermak]

Question (before review): Wouldn't it be easier to support linux/BSD like socket API with usrsctp upstream?

[vikramdattu]

@david-cermak Yes, that's exactly the direction — the actual LWIP socket integration is already up at sctplab/usrsctp#743 (open, awaiting review). Until it lands, this component pins our fork; once merged upstream, the esp-protocols wrapper shrinks to build glue only.