Gateway: EstimateAmt

Get estimation for the user's transfer request.

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

Name	Type	Description
src_chain_id*	Number	source chain id, given by transfer configs
dst_chain_id*	Number	destination chain Id, given by transfer configs
token_symbol*	String	symbol of token to be transfered, given by transfer configs
usr_addr	String	user's wallet address
amt*	String	Token amount to be transfered. It should contain token's decimal. For example, if the user wants to transfer 1 tokenA and A's decimal is 4, then amt should be 10000
slippage_tolerance*	Number	value between 1 and 1M - 1, see details below
is_pegged	Bool	set true if transfer pegged token

200: OK

{
  "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

Name	Type	Description
src_chain_id	Number	Source Chain Id, given by transfer configs
dst_chain_id	Number	Destination Chain Id, given by transfer configs
token_symbol	String	Symbol of token to be transfered, given by transfer configs
usr_addr	String	User's wallet address(Not required for multi-chain token transfer)
slippage_tolerance	Number	Slippage for onchain transaction(User's input)
amt	String	Token amount to be transfered. Token's decimal should be used here. For example, if the user wants to transfer 1 tokenA and A's decimal is 4, then amt should be 10000
is_pegged		Used for pegged token transfer only

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

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

Name	Type	Description
eq_value_token_amt	String	Token amount in destination chain
bridge_rate	Number	Bridge rate between source chain and destination chain
perc_fee	String	Protocol fee
base_fee	String	Base fee
slippage_tolerance	Number	The same number as slippage_tolerance in request
max_slippage	Number	slippage will be used to submit on-chain transaction, see below for calculation detail. used for xLiquidity transfer only
estimated_receive_amt	String	receiving amount estimation on destination chain

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)

Minimum receiving amount calculation

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

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.

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 Code	Error Number	Description
ERROR_CODE_UNDEFINED	0	Error code placeholder
ERROR_CODE_COMMON	500	Chain is disabled
ERROR_NO_TOKEN_ON_DST_CHAIN	1001	Token not supported on destination chain
ERROR_NO_TOKEN_ON_SRC_CHAIN	1002	Token not supported on source chain
ERROR_CODE_NO_ENOUGH_TOKEN_ON_DST_CHAIN	1004	Destination chain token is not enough for transfer
ERROR_CODE_INBOUND_LIQUIDITY_LIMIT	1005	Token pool epoch volume cap reached
ERROR_CODE_TRANSFER_DISABLED	1009	Token transfer between source chain and destination(both direction) is disabled
ERROR_CODE_BAD_LIQ_SLIPPAGE	1012	Bad slippage
ERROR_CODE_ADDRESS_BLOCKED	1015	This address is blocked due to potential security risks, which is alerted by third party organization. Those risks include hacker's address, money laundering and etc.
ERROR_CODE_BLOCK_BRIDGE_DIRECT	1016	Token transfer from source chain to destination(one direction) is disabled
ERROR_CODE_LIQ_OVER_CAP	1017	Token pool total cap reached
ErrCode_ERROR_CODE_VPN_BLOCK	1018	VPN is not allowed when getting transfer estimation

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

Name	Type	Description
src_chain_id*	Number	source chain id
dst_chain_id*	Number	destination chain id

200: OK

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