Block diagram
The WebSocket protocol establishes a two-way communication channel via TCP.
Messages are made up of one or more dataframes, and are delineated by
frames with the fin bit set.
This page hosts a formal specification of WebSocket using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
meta:
id: websocket
title: WebSocket
xref:
rfc: 6455
wikidata: Q859938
license: CC0-1.0
endian: be
doc: |
The WebSocket protocol establishes a two-way communication channel via TCP.
Messages are made up of one or more dataframes, and are delineated by
frames with the `fin` bit set.
seq:
- id: initial_frame
type: initial_frame
- id: trailing_frames
type: dataframe
if: initial_frame.header.finished != true
repeat: until
repeat-until: _.header.finished
types:
frame_header:
seq:
- id: finished
-orig-id: fin
type: b1
- id: reserved
-orig-id: 'rsv1, rsv2, rsv3'
type: b3
- id: opcode
enum: opcode
type: b4
- id: is_masked
type: b1
- id: len_payload_primary
type: b7
- id: len_payload_extended_1
type: u2
if: len_payload_primary == 126
- id: len_payload_extended_2
type: u4
if: len_payload_primary == 127
- id: mask_key
type: u4
if: is_masked
instances:
len_payload:
value: |
len_payload_primary <= 125 ? len_payload_primary : (
len_payload_primary == 126 ? len_payload_extended_1 : len_payload_extended_2
)
initial_frame:
seq:
- id: header
type: frame_header
- id: payload_bytes
size: header.len_payload
if: 'header.opcode != opcode::text'
- id: payload_text
size: header.len_payload
type: str
encoding: UTF-8
if: 'header.opcode == opcode::text'
dataframe:
seq:
- id: header
type: frame_header
- id: payload_bytes
size: header.len_payload
if: '_root.initial_frame.header.opcode != opcode::text'
- id: payload_text
size: header.len_payload
type: str
encoding: UTF-8
if: '_root.initial_frame.header.opcode == opcode::text'
enums:
opcode:
0: continuation
1: text
2: binary
3: reserved_3
4: reserved_4
5: reserved_5
6: reserved_6
7: reserved_7
8: close
9: ping
0xA: pong
0xB: reserved_control_b
0xC: reserved_control_c
0xD: reserved_control_d
0xE: reserved_control_e
0xF: reserved_control_f