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Http2Frame.md

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Http2Frame

HTTP/2 frame encoding and decoding. Handles the 9-byte frame header and payload serialisation for SETTINGS, PING, GOAWAY, WINDOW_UPDATE, RST_STREAM, DATA, and HEADERS frames.

Why Http2Frame?

The framing layer is the foundation of HTTP/2. This module converts between in-memory records and wire bytes using m2Codec for binary I/O. No heap allocation.

Procedures

Frame Header

PROCEDURE DecodeHeader(v: BytesView; VAR hdr: FrameHeader; VAR ok: BOOLEAN);
PROCEDURE EncodeHeader(VAR b: Buf; hdr: FrameHeader);

Decode/encode the 9-byte frame header. The 24-bit length field is composed from three ReadU8 calls (no ReadU24BE in m2Codec). The stream ID has its reserved bit masked off.

Connection Preface

PROCEDURE WritePreface(VAR b: Buf);
PROCEDURE CheckPreface(v: BytesView): BOOLEAN;

The 24-byte client magic string PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n.

SETTINGS

PROCEDURE DecodeSettings(payload: BytesView; VAR s: Settings; VAR ok: BOOLEAN);
PROCEDURE EncodeSettings(VAR b: Buf; s: Settings);
PROCEDURE EncodeSettingsAck(VAR b: Buf);

EncodeSettings writes a full frame (9 + 36 bytes for 6 standard settings). DecodeSettings updates only settings present in the payload; unknown IDs are ignored per RFC.

PING

PROCEDURE EncodePing(VAR b: Buf; data: BytesView; isAck: BOOLEAN);

8 bytes of opaque data, echoed back with ACK flag set.

GOAWAY

PROCEDURE EncodeGoaway(VAR b: Buf; lastStreamId: CARDINAL; errorCode: CARDINAL);
PROCEDURE DecodeGoaway(payload: BytesView; VAR lastStreamId: CARDINAL;
                       VAR errorCode: CARDINAL; VAR ok: BOOLEAN);

WINDOW_UPDATE

PROCEDURE EncodeWindowUpdate(VAR b: Buf; streamId: CARDINAL; increment: CARDINAL);
PROCEDURE DecodeWindowUpdate(payload: BytesView; VAR increment: CARDINAL; VAR ok: BOOLEAN);

RST_STREAM

PROCEDURE EncodeRstStream(VAR b: Buf; streamId: CARDINAL; errorCode: CARDINAL);
PROCEDURE DecodeRstStream(payload: BytesView; VAR errorCode: CARDINAL; VAR ok: BOOLEAN);

DATA / HEADERS Headers

PROCEDURE EncodeDataHeader(VAR b: Buf; streamId: CARDINAL;
                           payloadLen: CARDINAL; endStream: BOOLEAN);
PROCEDURE EncodeHeadersHeader(VAR b: Buf; streamId: CARDINAL;
                              payloadLen: CARDINAL;
                              endStream: BOOLEAN; endHeaders: BOOLEAN);

Write only the 9-byte frame header; caller appends payload bytes.