Spot Websockets (v2) Level3 Checksum
This page describes how to maintain the book and generate the checksum for the websockets (v2) level3 channel. The feed describes the individual orders at each price level.
The checksum verification is optional. It provides an additional check that the client copy has been constructed correctly and is synchronised to the exchange. The checksum can be verified on every update or periodically depending on the throughput / processing requirements of the client.
The mechanisms for generating the checksum are very similar between book and level3 feeds. The level3 feed has an extra level of granularity (i.e. the orders at each price level), the checksum takes this into account and also verifies the sequence of orders in the book (i.e. queue priority).
The checksum is only calculated for the top 10 price levels of the book regardless of the subscription depth.
Maintaining the level3 Channel
All orders in a level3 message should be processed before the checksum is calculated. An update message may contain many updates to either the bids and/or asks.
A price level with no orders or no order quantity should be removed from your book. Note, if a price level is removed from the subscribed levels (i.e. result of trades/cancels) then all the orders at the next available price level will be published to keep the subscription depth at the specified number of levels.
Additionally, after each update, the book should be truncated to your subscribed depth. In other words, if you are subscribed with "depth": 10 and an insert into the middle of the book results in you having 11 bids, you must remove the 11th worst bid.
Checksum Calculation
The level3 checksum logic is similar to level2 book logic. The primary difference, level3 checksum will iterate through the orders in the price levels.
The limit_price and order_qty fields are pushed onto the wire containing full precision. To keep the full precision through deserialization and decoding, parse the level3 message using a decimal or string decoder.
Example code for decoding message with full precision:
async for bytes in websocket:
message = json.loads(bytes, parse_float=Decimal)
self.on_message(message)
Checksum Steps with Example
This example data below can be used as input to your l3 book checksum calculator to confirm correct behaviour.
Example level3 snapshot:
{
"channel": "level3",
"type": "snapshot",
"data": [
{
"symbol": "BTC/USD",
"checksum": 1063832831,
"bids": [
{
"order_id": "OTCFZG-YOE2Q-LQKNM3",
"limit_price": "44939.4",
"order_qty": "0.88968699",
"timestamp": "2024-01-08T12:26:39.526146327Z"
},
{
"order_id": "OFGP5R-B3E7G-54EZD6",
"limit_price": "44939.4",
"order_qty": "0.45210000",
"timestamp": "2024-01-08T12:26:39.530287934Z"
},
{
"order_id": "OMPHVY-IZPJ4-KOKA3P",
"limit_price": "44939.4",
"order_qty": "0.10000000",
"timestamp": "2024-01-08T12:26:39.576380340Z"
},
{
"order_id": "OAI5QZ-AMPLW-NBNO72",
"limit_price": "44939.4",
"order_qty": "0.14296323",
"timestamp": "2024-01-08T12:26:39.602118534Z"
},
{
"order_id": "O7VFZI-CTFWH-FF6EIR",
"limit_price": "44939.4",
"order_qty": "0.25000000",
"timestamp": "2024-01-08T12:26:41.780601700Z"
},
{
"order_id": "O472V3-ZG4EZ-OLD66C",
"limit_price": "44939.4",
"order_qty": "0.10292988",
"timestamp": "2024-01-08T12:26:43.087136366Z"
},
{
"order_id": "OEK26P-BGPUK-LDHMD2",
"limit_price": "44939.4",
"order_qty": "0.33880000",
"timestamp": "2024-01-08T12:26:43.822433365Z"
},
{
"order_id": "OSMYPE-S5VOC-YSS3WM",
"limit_price": "44939.4",
"order_qty": "1.28140860",
"timestamp": "2024-01-08T12:26:45.066096694Z"
},
{
"order_id": "OJPMIN-NXZL5-SOWP6V",
"limit_price": "44937.1",
"order_qty": "0.03346877",
"timestamp": "2024-01-08T12:26:39.691304329Z"
},
{
"order_id": "O6PUGE-SQWYQ-TRJEEE",
"limit_price": "44934.7",
"order_qty": "0.35630000",
"timestamp": "2024-01-08T12:26:44.129718463Z"
},
{
"order_id": "OPUOGC-Q532V-3OKLPM",
"limit_price": "44930.2",
"order_qty": "0.22734299",
"timestamp": "2024-01-08T12:26:30.769031831Z"
},
{
"order_id": "OCIU7J-VB3CI-HPULSF",
"limit_price": "44930.2",
"order_qty": "0.01000000",
"timestamp": "2024-01-08T12:26:36.054352106Z"
},
{
"order_id": "ORWVAF-LJFLY-ZWEHDQ",
"limit_price": "44930.2",
"order_qty": "0.05550000",
"timestamp": "2024-01-08T12:26:36.635882793Z"
},
{
"order_id": "OYRAHE-PI5AN-7KOQ4E",
"limit_price": "44930.2",
"order_qty": "0.70000000",
"timestamp": "2024-01-08T12:26:37.296554518Z"
},
{
"order_id": "OGBHYU-UILDD-6DLLYJ",
"limit_price": "44930.2",
"order_qty": "0.15000000",
"timestamp": "2024-01-08T12:26:41.222733191Z"
},
{
"order_id": "O74ZBU-K2TKC-R76XSW",
"limit_price": "44928.0",
"order_qty": "0.00105240",
"timestamp": "2024-01-08T12:26:23.542563322Z"
},
{
"order_id": "OQVTQF-Y56MR-BM6LWL",
"limit_price": "44919.6",
"order_qty": "0.33870000",
"timestamp": "2024-01-08T12:26:42.808132842Z"
},
{
"order_id": "OYEH6U-ZCHA2-3HFR3W",
"limit_price": "44919.5",
"order_qty": "0.07610000",
"timestamp": "2024-01-08T12:26:34.269600037Z"
},
{
"order_id": "OLGPG7-HVKXU-J6SANK",
"limit_price": "44912.0",
"order_qty": "0.35630000",
"timestamp": "2024-01-08T12:26:34.961292766Z"
},
{
"order_id": "OHGC3L-FRZQ3-UIVZRU",
"limit_price": "44909.7",
"order_qty": "0.06690000",
"timestamp": "2024-01-08T12:26:31.912880024Z"
},
{
"order_id": "O73C6Y-VZXYA-H4LDFY",
"limit_price": "44901.9",
"order_qty": "0.00088982",
"timestamp": "2024-01-08T12:26:42.883315043Z"
}
],
"asks": [
{
"order_id": "OFVLAA-HRSSP-BK75KB",
"limit_price": "44939.5",
"order_qty": "4.52308393",
"timestamp": "2024-01-08T12:18:05.770906486Z"
},
{
"order_id": "OYBAMK-O5DKX-WMPUTM",
"limit_price": "44939.5",
"order_qty": "0.00111261",
"timestamp": "2024-01-08T12:18:12.847426441Z"
},
{
"order_id": "O3DRCT-J5M2S-KYV526",
"limit_price": "44939.5",
"order_qty": "0.00100000",
"timestamp": "2024-01-08T12:26:42.108176464Z"
},
{
"order_id": "OF3X3A-72WZY-6EKA5F",
"limit_price": "44939.5",
"order_qty": "0.01000000",
"timestamp": "2024-01-08T12:26:43.955098263Z"
},
{
"order_id": "OF5UA6-6IIZ2-YGQTSJ",
"limit_price": "44950.0",
"order_qty": "0.10334926",
"timestamp": "2024-01-08T12:25:52.800473795Z"
},
{
"order_id": "OSDOZX-7UZ6Y-QDNPVI",
"limit_price": "44953.0",
"order_qty": "0.00064537",
"timestamp": "2024-01-08T12:24:58.086806970Z"
},
{
"order_id": "OV7KTS-A2TWV-3XKRIA",
"limit_price": "44955.0",
"order_qty": "0.00250000",
"timestamp": "2024-01-08T12:21:52.257936228Z"
},
{
"order_id": "OOF2V5-RYOHC-GLRNPM",
"limit_price": "44959.6",
"order_qty": "0.35630000",
"timestamp": "2024-01-08T12:26:44.202823127Z"
},
{
"order_id": "OTVOVS-QLST3-3JG7JI",
"limit_price": "44959.6",
"order_qty": "0.35630000",
"timestamp": "2024-01-08T12:26:44.203383999Z"
},
{
"order_id": "OGZCIU-RDQ77-DAAL3P",
"limit_price": "44960.1",
"order_qty": "0.00338072",
"timestamp": "2024-01-08T12:26:42.724829715Z"
},
{
"order_id": "OVLG3E-HYBQM-CWNGCY",
"limit_price": "44960.2",
"order_qty": "0.88967575",
"timestamp": "2024-01-08T12:26:12.935924248Z"
},
{
"order_id": "OWEOFO-HUCJC-T37MVO",
"limit_price": "44967.0",
"order_qty": "3.14392283",
"timestamp": "2024-01-08T12:26:39.474431925Z"
},
{
"order_id": "OVYTHY-D2N76-5QYREQ",
"limit_price": "44978.5",
"order_qty": "0.06778960",
"timestamp": "2024-01-08T12:26:41.229379178Z"
},
{
"order_id": "OFO525-PHRVS-236RMN",
"limit_price": "44979.2",
"order_qty": "0.35630000",
"timestamp": "2024-01-08T12:26:20.271584488Z"
}
]
}
]
}
Generate Checksum String
The checksum is generated by iterating through the top 10 price levels in each side of book to generate a string representation, then passing this string to a CRC32 checksum function. The final checksum is a integer value.
1, Generate formatted string for each price level in the asks (sorted by price from low to high), then iterating through each order in a price level:
- Remove the decimal character, '.', from the
limit_price, i.e. "44939.5" -> "449395". - Remove all leading zero characters from the
limit_price. i.e. "449395" -> "449395". - Remove the decimal character, '.', from the
order_qty, i.e. "4.52308393" -> "452308393". - Remove all leading zero characters from the
order_qty. i.e. "452308393" -> "452308393". - Add the
limit_price+order_qty(449395452308393) string to the asks concatenation. - Repeat for the remaining 9 price levels.
44939545230839344939511126144939510000044939510000004495001033492644953064537449550250000449596356300004495963563000044960133807244960288967575449670314392283449785677896044979235630000
2, Generate formatted string for each price level in the bids (sorted by price from high to low), then iterating through each order in a price level:
- Remove the decimal character, '.', from the
limit_price, i.e. "44939.4" -> "449394". - Remove all leading zero characters from the
limit_price. i.e. "449394" -> "449394". - Remove the decimal character, '.', from the
order_qty, i.e. "0.88968699" -> "088968699". - Remove all leading zero characters from the
order_qty. i.e. "088968699" -> "88968699". - Add the
limit_price+order_qty(44939488968699) string to the bids concatenation. - Repeat for the remaining 9 price levels.
449394889686994493944521000044939410000000449394142963234493942500000044939410292988449394338800004493941281408604493713346877449347356300004493022273429944930210000004493025550000449302700000004493021500000044928010524044919633870000449195761000044912035630000449097669000044901988982
Generate Integer Value from Checksum String
3, Concatenate the generated asks + bids strings.
44939545230839344939511126144939510000044939510000004495001033492644953064537449550250000449596356300004495963563000044960133807244960288967575449670314392283449785677896044979235630000449394889686994493944521000044939410000000449394142963234493942500000044939410292988449394338800004493941281408604493713346877449347356300004493022273429944930210000004493025550000449302700000004493021500000044928010524044919633870000449195761000044912035630000449097669000044901988982
4, Feed the concatenated string as input to a CRC32 checksum function.
1063832831
This value can now be compared to the checksum received to ensure your local book is accurate.
Optionally, depending on the CRC32 checksum function, the result may need to be cast to unsigned 32-bit integer.