websocket_frame.nx

websocket_frame.nx -- RFC 6455 WebSocket frame parser + builder. Parses and emits individual frames. The handshake (HTTP Upgrade + Sec-WebSocket-Key + Sec-WebSocket-Accept) goes in a separate websocket_handshake.nx that will build on sha1.nx + base64.nx + this module. Frame layout (RFC 6455 §5.2): 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-------+-+-------------+-------------------------------+ |F|R|R|R| opcode|M| Payload len | Extended payload length | |I|S|S|S| (4) |A| (7) | (16/64) | |N|V|V|V| |S| | (if payload len==126/127) | | |1|2|3| |K| | | +-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - + | Extended payload length continued, if payload len == 127 | + - - - - - - - - - - - - - - - +-------------------------------+ | |Masking-key, if MASK set to 1 | +-------------------------------+-------------------------------+ | Masking-key (continued) | Payload Data | +-------------------------------- - - - - - - - - - - - - - - - + Opcodes: 0x0 continuation frame 0x1 text frame (UTF-8) 0x2 binary frame 0x8 close 0x9 ping 0xA pong Invariants: WS1 Client -> server frames MUST be masked (RFC). We set this flag on encode per the `masked` arg; callers MUST supply a random 4-byte mask when sending from a client. WS2 Server -> client frames MUST NOT be masked. WS3 Payload length encoding: 7-bit inline (0..125), or 126 + 16-bit extended, or 127 + 64-bit extended. WS4 Masking is reversible -- apply mask twice = identity.