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4. HTTP Frames

4.1 Frame Format​

All frames begin with a fixed 9-octet header followed by a variable-length payload.

+-----------------------------------------------+
|                 Length (24)                   |
+---------------+---------------+---------------+
|   Type (8)    |   Flags (8)   |
+-+-------------+---------------+-------------------------------+
|R|                 Stream Identifier (31)                      |
+=+=============================================================+
|                   Frame Payload (0...)                      ...
+---------------------------------------------------------------+

Fields:

  • Length: 24-bit unsigned integer (payload length)
  • Type: 8-bit frame type identifier
  • Flags: 8-bit flags specific to frame type
  • R: Reserved 1-bit field
  • Stream Identifier: 31-bit stream identifier

4.2 Frame Size​

The size of a frame payload is limited by the maximum size negotiated via SETTINGS_MAX_FRAME_SIZE. Default is 2^14 (16,384) octets.

4.3 Header Compression and Decompression​

Header fields are compressed using HPACK [RFC7541]. Header field blocks are fragmented into HEADERS, PUSH_PROMISE, or CONTINUATION frames.

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