[RFC idea] DTLS support in ext/openssl (Openssl\Dtls)

Hi all, I'd like to gauge interest in adding DTLS support to ext/openssl before writing a formal RFC. Problem ------- PHP can speak TLS, but only as a stream wrapper where OpenSSL owns the socket end to end. There are two gaps: * No DTLS (RFC 6347, the UDP counterpart of TLS) at all. * No way to run (D)TLS over a transport the application controls. Several modern protocols are built on DTLS where the application must own the packet flow: WebRTC data channels and DTLS-SRTP (RFC 5764), CoAP over DTLS, SIP media keying, and any case where DTLS records are multiplexed with other traffic on one UDP port. Today these are only reachable from PHP through FFI to libssl or an external process. DTLS has been an open request since 2018 (bug #76629) with no implementation so far. Proposal (sketch) ----------------- A small, transport-agnostic DTLS endpoint class whose packet I/O goes through memory BIOs, so the application moves datagrams in/out itself: namespace Openssl; final class Dtls { public const int HANDSHAKE_ERROR = -1; public const int HANDSHAKE_CONTINUE = 0; public const int HANDSHAKE_FINISHED = 1; public function __construct(bool $isServer = false, ?string $certificate = null, ?string $privateKey = null) {} public function getFingerprint(?string $digestAlgo = null): string {} public function getPeerFingerprint(?string $digestAlgo = null): ?string {} public function isHandshakeFinished(): bool {} public function handshake(): int {} // HANDSHAKE_* constants public function feed(string $datagram): int {} public function pull(): ?string {} public function write(string $data): int {} public function read(): string|false {} public function exportKeys(string $label, int $length): string|false {} } The application drives the handshake by pumping datagrams between peers (feed/pull), verifies the peer out of band via getPeerFingerprint(), then exchanges data with write()/read(). exportKeys() exposes SSL_export_keying_material (RFC 5705), which is what DTLS-SRTP needs. Status ------ I've already written a working proof-of-concept against master, with .phpt tests; the full ext/openssl suite is green. I'm sharing it only to make the discussion concrete -- I'm very open to changing the shape (this is the point of asking first), and I'll only open a PR/RFC properly if there's interest. I can post the branch/PR link on request. Questions --------- * Is DTLS something we want in core ext/openssl, or is this better left to userland/FFI? * Is the object + memory-BIO design the right direction? Should the constructor also accept OpenSSLCertificate/OpenSSLAsymmetricKey objects in addition to PEM? * How should we treat the server-side HelloVerifyRequest cookie exchange (DoS amplification mitigation) -- required for v1, or acceptable as future scope with a documented caveat? * (Cc ext/openssl maintainers -- your view would be especially valuable.) Thanks for any feedback. Gianfrancesco Aurecchia