const ws = require('ws')
const w = new ws('wss://api-pub.bitfinex.com/ws/2')

w.on('message', (msg) => console.log(msg))

let msg = JSON.stringify({ 
  event: 'subscribe', 
  channel: 'book', 
  symbol: 'tBTCUSD' 
})

w.on('open', () => w.send(msg))

wscat -c wss://api-pub.bitfinex.com/ws/2
{ "event": "subscribe", "channel": "book", "symbol": "tBTCUSD" }

ws = websocket.WebSocketApp('wss://api-pub.bitfinex.com/ws/2')

ws.on_open = lambda self: self.send('{ "event": "subscribe", "channel": "book", "symbol": "tBTCUSD"}')

ws.on_message = lambda self, evt:  print (evt)

// request
{
	event: 'subscribe',
	channel: 'book',
	symbol: SYMBOL,
	prec: PRECISION,
	freq: FREQUENCY,
	len: LENGTH,
	subId: SUBID
}

{"event":"subscribe","channel":"book","symbol":"tBTCUSD","prec":"P0","freq":"F0","len":"25","subId": 123}

// response
{
	event: 'subscribed',
	channel: 'book',
	chanId: CHANNEL_ID,
	symbol: SYMBOL,
	prec: PRECISION,
	freq: FREQUENCY,
	len: LENGTH,
	subId: SUBID,
	pair: PAIR 
}

{"event":"subscribed","channel":"book","chanId":10092,"symbol":"tETHUSD","prec":"P0","freq":"F0","len":"25","subId":123,"pair":"ETHUSD"}

// on trading pairs (ex. tBTCUSD)

[
  17082, //CHANNEL_ID
  [
    [
      7254.7, //PRICE
      3, //COUNT
      3.3 //AMOUNT
    ], //BOOK_ENTRY
    ...
  ] //BOOK_ENTRIES
]
  
// on funding currencies (ex. fUSD)

[
  431549, //CHANNEL_ID
  [
    [
      0.00023112, //RATE
      30, //PERIOD
      1, //COUNT
      -15190.7005375 //AMOUNT
    ], //BOOK_ENTRY
    ...
  ] //BOOK_ENTRIES
]

// on trading pairs (ex. tBTCUSD)

[
  17082, //CHANNEL_ID
  [
    7254.5, //PRICE
    0, //COUNT
    1 //AMOUNT
  ] //BOOK_ENTRY
]
  
// on funding currencies (ex. fUSD)

[
  348748, //CHANNEL_ID
  [
    0.00023157, //RATE
    2, //PERIOD
    1, //COUNT
    66.35007188 //AMOUNT
  ] //BOOK_ENTRY
]

//Bulk updates can be enabled using a conf event flag of 536870912

// on trading pairs (ex. tBTCUSD)

[
  17082, //CHANNEL_ID
  [
    [
      7254.5, //PRICE
      0, //COUNT
      1 //AMOUNT
    ], //BOOK_ENTRY
  	...
  ] //BOOK_ENTRIES
]
  
// on funding currencies (ex. fUSD)

[
  348748, //CHANNEL_ID
  [
    [
      0.00023157, //RATE
      2, //PERIOD
      1, //COUNT
      66.35007188 //AMOUNT
    ], //BOOK_ENTRY
    ...
  ]//BOOK_ENTRIES
]

Request fields

Fields	Type	Description
SYMBOL	String	Trading pair or funding currency
PRECISION	string	Level of price aggregation (P0, P1, P2, P3, P4). The default is P0
FREQUENCY	string	Frequency of updates (F0, F1). F0=realtime / F1=2sec. The default is F0.
LENGTH	string	Number of price points ("1", "25", "100", "250") [default="25"]
SUBID	string	Optional user-defined ID for the subscription

Book snapshot data

Index	Field	Type	Description
[0]	CHANNEL_ID	Int	Identification number assigned to the channel for the duration of this connection.
[1]	BOOK_ENTRIES	Array	Array with an array of currently active book entries (Indices [0...n] will be book entries)
[0...n]	BOOK_ENTRY	Array	Book entry or funding book entry

Book update data

Index	Field	Type	Description
[0]	CHANNEL_ID	Int	Identification number assigned to the channel for the duration of this connection.
[1]	BOOK_ENTRY	Trade	Book entry or funding book entry

Bulk update date

Index	Field	Type	Description
[0]	CHANNEL_ID	Int	Identification number assigned to the channel for the duration of this connection.
[1]	BOOK_ENTRIES	Array	Array with an array of currently active book entries (Indices [0...n] will be book entries)
[0...n]	BOOK_ENTRY	Array	Book entry or funding book entry

Book entry

Index	Field	Type	Description
[0]	PRICE	Float	Price level
[1]	COUNT	Int	Number of orders at that price level (delete price level if count = 0)
[2]	AMOUNT	Float	Total amount available at that price level. Trading: if AMOUNT > 0 then bid else ask; Funding: if AMOUNT < 0 then bid else ask;

Funding book entry

Index	Field	Type	Description
[0]	RATE	Float	Price level
[1]	PERIOD	Int	Period level
[2]	COUNT	Int	Number of orders at that price level (delete price level if count = 0)
[3]	AMOUNT	Float	Total amount available at that price level. Trading: if AMOUNT > 0 then bid else ask; Funding: if AMOUNT < 0 then bid else ask;

Algorithm to create and keep a trading book instance updated

subscribe to channel
receive the book snapshot and create your in-memory book structure
when count > 0 then you have to add or update the price level
3.1 if amount > 0 then add/update bids
3.2 if amount < 0 then add/update asks
when count = 0 then you have to delete the price level.
4.1 if amount = 1 then remove from bids
4.2 if amount = -1 then remove from asks

Algorithm to create and keep a funding book instance updated

subscribe to channel
receive the book snapshot and create your in-memory book structure
when count > 0 then you have to add or update the price level
3.1 if amount > 0 then add/update asks (offers)
3.2 if amount < 0 then add/update bids
when count = 0 then you have to delete the price level.
4.1 if amount = 1 then remove from asks (offers)
4.2 if amount = -1 then remove from bids

Node.JS example gists:

Aggregated Book: https://gist.github.com/prdn/b8c067c758aab7fa3bf715101086b47c
Raw Book: https://gist.github.com/prdn/b9c9c24fb1bb38604dcd1e94ee89dd9e

Precision Levels

Significant Digits Calculations: https://support.bitfinex.com/hc/en-us/articles/115000371105-How-is-precision-calculated-using-Significant-Digits

Precision Level	Number of significant figures
P0	5
P1	4
P2	3
P3	2
P4	1

Checksum
An Order Book Checksum can be requested through the Websocket configuration. You can find out more on the WebSocket Checksum page.

Bulk Updates
Bulk updates can be enabled by sending a conf event with a flag value of 536870912. With bulk updates enabled, updates will arrive as an array of arrays.

🚧
Error Codes
10011 : Unknown Book precision
10012 : Unknown Book length