Gateway: EstimateAmt

REST API

Get estimation for the user’s transfer request

GET https://cbridge-prod2.celer.app/v2/estimateAmt

Here is a sample request for estimateAmt:

https://cbridge-prod2.celer.app/v2/estimateAmt?src_chain_id=1&dst_chain_id=56&token_symbol=USDT&amt=1000000&usr_addr=0xaa47c83316edc05cf9ff7136296b026c5de7eccd&slippage_tolerance=3000

Path Parameters

{
  "err": null,
  "eq_value_token_amt": "1000000999999999872",
  "bridge_rate": 1.000001,
  "perc_fee": "0",
  "base_fee": "605437528092011966",
  "slippage_tolerance": 3000,
  "max_slippage": 608436,
  "estimated_receive_amt": "394563471907987906",
  "drop_gas_amt": "0"
}

GRPC-Web API

// import estimateAmt request message 
import { 
    EstimateAmtRequest, 
    EstimateAmtResponse 
} from "../ts-proto/sgn/gateway/v1/gateway_pb";

// import grpc-web WebClient
import { 
    WebClient 
} from "../ts-proto/sgn/gateway/v1/GatewayServiceClientPb";

const estimateRequest = new EstimateAmtRequest();
estimateRequest.setSrcChainId(1);
estimateRequest.setDstChainId(56);
estimateRequest.setTokenSymbol("USDT");
estimateRequest.setUsrAddr(0xaa47c83316edc05cf9ff7136296b026c5de7eccd);
estimateRequest.setSlippageTolerance(3000);
estimateRequest.setAmt("100000");

const client = new WebClient(`https://cbridge-prod2.celer.app`, null, null);
const res = await client.estimateAmt(estimateRequest, null);

Request Parameters

Note: Which value is suitable for slippage_tolerance?

cBridge gateway uses slippage_tolerance_rate to represent user’s slippage for on-chain transaction. The range of slippage_tolerance_rate is from [0, 1)

The calculation formula between slippage_tolerance and slippage_tolerance_rate is

slippage_tolerance_rate = slippage_tolerance / 1M

Hence, if the user sets slippage_tolerance with 0.05%, slippage_tolerance in the request will be 0.05% * 1M = 500

Moreover, if the user sets slippage_tolerance with 0.050123%, the calculation will lead to 0.050123% * 1M = 501.23. However, gateway will only accept integer as slippage_tolerance. The final value should be 501

Note: You need to find out whether this transfer is used for pegged token according to PeggedPairConfigs. Moreover, slippage will not be effective if is_pagged is true

Response Parameters

Note: How to calculate max_slippage?

There are several factors influencing the final value for max_slippage, all of them are inside the response. Since we cannot guarantee user receiving more tokens on destination chain, there is slippage adjustment in the end.

1. estimate_dst_amt = user_transfer_amount_on_src_chain * bridge_rate
2. estimate_min_dst_amt = estimate_dst_amt * (1 - slippage_tolerance_rate) - base_fee - perc_fee
3. max_slippage_rate = 1 - estimate_min_dst_amt / user_transfer_amount_on_src_chain
4. max_slippage = max(max_slippage_rate * 1M, minimalMaxSlippage)

Note: Minimum receiving amount calculation

amount = eq_value_token_amt * (1 - max_slippage/1M)

Note: The on-chain send transaction failed mostly when slippage is too small to be processed by cBridge system.

To avoid the potential on-chain failure and waste of gas, we recommend you compare max_slippage with minimalMaxSlippage on cBridge contract before sending on-chain transaction. If max_slippage is less than minimalMaxSlippage, guide user increasing input value slippage_tolerance.

Moreover, since max_slippage, bridge_rate, perc_fee and base_fee may change when user interacting with your application, we should get the lastest estimation before final submit to avoid on-chain send failure.

Note: The cross-chain transfer is accepted only. if src_chain_id is the same as dst_chain_id, it may lead to an error

Error handling

Error Code Description

Error with high frequency

ERROR_CODE_INBOUND_LIQUIDITY_LIMIT & ERROR_CODE_LIQ_OVER_CAP

The sending amount is beyond liquidity pool limit. It will happen only for liquidity pool-based transfer. The calculation for inbound liquidity limit of source chain token liquidity pool is TOTAL_LIQUIDITY_ADDED - TOTAL__LIQUIDITY_RELAYED - TOTAL__LIQUIDITY_WITHDRAWN. Once this error code is given, you have to let the users decrease their input sending amount.

ERROR_CODE_NO_ENOUGH_TOKEN_ON_DST_CHAIN

Destination chain doesn’t have enough token for this transfer. It may happen for pool based transfer which bridge rate is fixed to 1.

Estimated Time of Arrival for Transfer

To provide a better user experience, cBridge has a request to indicate user how long it will take to finish a transfer. You may also use this to provide a better time estimation for the users.

Request Sample

GET https://cbridge-prod2.celer.app/v2/getLatest7DayTransferLatencyForQuery

https://cbridge-prod2.celer.app/v2/getLatest7DayTransferLatencyForQuery?src_chain_id=1&dst_chain_id=56

Path Parameters

{
  "err": null,
  "median_transfer_latency_in_second": 325.818221
}