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Http2Types.md

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Http2Types

Constants, frame types, error codes, settings, and shared types for HTTP/2 (RFC 7540 / RFC 9113).

Why Http2Types?

Centralises all wire protocol constants so other modules import numeric values by name rather than scattering magic numbers.

Constants

Frame Types

Constant Value Description
FrameData 0 DATA frame
FrameHeaders 1 HEADERS frame
FramePriority 2 PRIORITY frame
FrameRstStream 3 RST_STREAM frame
FrameSettings 4 SETTINGS frame
FramePushPromise 5 PUSH_PROMISE frame
FramePing 6 PING frame
FrameGoaway 7 GOAWAY frame
FrameWindowUpdate 8 WINDOW_UPDATE frame
FrameContinuation 9 CONTINUATION frame

Frame Flags

Constant Value Used By
FlagEndStream 1 DATA, HEADERS
FlagAck 1 SETTINGS, PING
FlagEndHeaders 4 HEADERS, CONTINUATION
FlagPadded 8 DATA, HEADERS
FlagPriority 32 HEADERS

Error Codes

ErrNoError (0) through ErrHttp11Required (13) per RFC 7540 Section 7.

Settings

SetHeaderTableSize (1) through SetMaxHeaderListSize (6) with default values matching RFC 7540 Section 6.5.2.

Stream FSM

7 states (StIdle..StClosed) and 9 events (EvSendH..EvRecvPP) for the per-stream state machine.

Connection FSM

6 states (ConnIdle..ConnClosed) and 9 events (CEvSendPreface..CEvConnError).

Types

FrameHeader

TYPE FrameHeader = RECORD
  length:   CARDINAL;   (* 24-bit payload length *)
  ftype:    CARDINAL;   (* frame type 0..255 *)
  flags:    CARDINAL;   (* frame flags 0..255 *)
  streamId: CARDINAL;   (* 31-bit stream identifier *)
END;

Settings

TYPE Settings = RECORD
  headerTableSize:     CARDINAL;
  enablePush:          CARDINAL;
  maxConcurrentStreams: CARDINAL;
  initialWindowSize:   CARDINAL;
  maxFrameSize:        CARDINAL;
  maxHeaderListSize:   CARDINAL;
END;

HeaderEntry

TYPE HeaderEntry = RECORD
  name:    ARRAY [0..127] OF CHAR;
  nameLen: CARDINAL;
  value:   ARRAY [0..4095] OF CHAR;
  valLen:  CARDINAL;
END;

Procedures

InitDefaultSettings

PROCEDURE InitDefaultSettings(VAR s: Settings);

Fill a Settings record with RFC 7540 default values.