browser wasm

interfaces/Crafter.Network-HTTP3.cppm

@@ -43,11 +43,33 @@ namespace Crafter::HTTP3 {
     export inline constexpr std::uint64_t kFrameData     = 0x00;
     export inline constexpr std::uint64_t kFrameHeaders  = 0x01;
     export inline constexpr std::uint64_t kFrameSettings = 0x04;
+    // WebTransport bidirectional stream frame type (draft-ietf-webtrans-http3).
+    // Distinct from normal HTTP/3 frames — its body is unbounded (runs to FIN)
+    // rather than length-prefixed, and the first bytes of the body are the
+    // session id varint.
+    export inline constexpr std::uint64_t kFrameWtStream = 0x41;
 
     // ---------------- Unidirectional stream types (RFC 9114 §6.2) ----------------
     export inline constexpr std::uint64_t kStreamControl  = 0x00;
     export inline constexpr std::uint64_t kStreamQpackEnc = 0x02;
     export inline constexpr std::uint64_t kStreamQpackDec = 0x03;
+    // WebTransport unidirectional stream type (draft-ietf-webtrans-http3).
+    // After this varint comes a session id varint, then opaque payload to FIN.
+    export inline constexpr std::uint64_t kStreamWt       = 0x54;
+
+    // ---------------- SETTINGS parameter identifiers ----------------
+    // Required to negotiate WebTransport over HTTP/3 + HTTP/3 datagrams.
+    export inline constexpr std::uint64_t kSettingQpackMaxTableCapacity  = 0x01; // RFC 9204
+    export inline constexpr std::uint64_t kSettingQpackBlockedStreams    = 0x07; // RFC 9204
+    export inline constexpr std::uint64_t kSettingEnableConnectProtocol = 0x08; // RFC 9220
+    export inline constexpr std::uint64_t kSettingH3Datagram             = 0x33; // RFC 9297
+    // Legacy identifiers from older WebTransport / H3-DATAGRAM drafts. Chrome
+    // (as of M120-ish) advertises and looks for the draft-02 / draft-04 ids
+    // alongside the RFC ones; if we only send the modern ids it decides we
+    // don't support WebTransport and aborts with ERR_METHOD_NOT_SUPPORTED.
+    export inline constexpr std::uint64_t kSettingH3DatagramDraft04      = 0xffd277;   // draft-ietf-masque-h3-datagram-04
+    export inline constexpr std::uint64_t kSettingEnableWebTransport     = 0x2b603742; // draft-02 boolean
+    export inline constexpr std::uint64_t kSettingWtMaxSessions          = 0xc671706a; // draft-ietf-webtrans-http3 (-07+)
 
     // ---------------- Errors ----------------
     export class HTTP3ProtocolError : public std::runtime_error {
@@ -575,4 +597,55 @@ namespace Crafter::HTTP3 {
         EncodeVarint(0, out);                       // frame length 0
         return out;
     }
+
+    // Server-side variant that advertises WebTransport-over-HTTP/3 support
+    // to the peer. Without these three SETTINGS the browser silently rejects
+    // the extended CONNECT and the WebTransport.ready promise never resolves.
+    // `maxSessions` becomes the value of SETTINGS_WT_MAX_SESSIONS.
+    export inline std::vector<std::uint8_t> BuildWebTransportControlStreamPrelude(
+        std::uint64_t maxSessions = 1)
+    {
+        // Encode the SETTINGS body first so we can write its length. The two
+        // QPACK settings declare we run with no dynamic table — sent
+        // explicitly because some HTTP/3 stacks (Chrome among them) refuse
+        // to consider the peer ready for extended-CONNECT until they have
+        // seen a baseline QPACK configuration. The draft-02 ENABLE_WEBTRANSPORT
+        // and draft-04 H3_DATAGRAM ids are sent alongside their RFC counterparts
+        // for compatibility with current Chrome (which still negotiates the
+        // draft form even when advertising RFC support).
+        std::vector<std::uint8_t> body;
+        EncodeVarint(kSettingQpackMaxTableCapacity, body); EncodeVarint(0, body);
+        EncodeVarint(kSettingQpackBlockedStreams,   body); EncodeVarint(0, body);
+        EncodeVarint(kSettingEnableConnectProtocol, body); EncodeVarint(1, body);
+        EncodeVarint(kSettingH3Datagram,            body); EncodeVarint(1, body);
+        EncodeVarint(kSettingH3DatagramDraft04,     body); EncodeVarint(1, body);
+        EncodeVarint(kSettingEnableWebTransport,    body); EncodeVarint(1, body);
+        EncodeVarint(kSettingWtMaxSessions,         body); EncodeVarint(maxSessions, body);
+
+        std::vector<std::uint8_t> out;
+        EncodeVarint(kStreamControl, out);
+        WriteFrame(out, kFrameSettings, body.data(), body.size());
+        return out;
+    }
+
+    // Prefix bytes that go on the front of an outgoing WT bidi stream — the
+    // peer reads these to know which session the stream belongs to. After
+    // this prefix the stream contains opaque WebTransport payload until FIN
+    // (there is no length field — WT_STREAM is the only HTTP/3 frame whose
+    // body runs to end-of-stream).
+    export inline std::vector<std::uint8_t> BuildWtBidiPrefix(std::uint64_t sessionId) {
+        std::vector<std::uint8_t> out;
+        EncodeVarint(kFrameWtStream, out);
+        EncodeVarint(sessionId, out);
+        return out;
+    }
+
+    // Prefix bytes that go on the front of an outgoing WT unidi stream
+    // (server-initiated → client). Stream-type varint then session id.
+    export inline std::vector<std::uint8_t> BuildWtUnidiPrefix(std::uint64_t sessionId) {
+        std::vector<std::uint8_t> out;
+        EncodeVarint(kStreamWt, out);
+        EncodeVarint(sessionId, out);
+        return out;
+    }
 }