warning

This document is relevant only for fungible token transfers over channels on v1 of the ICS-20 protocol.

Messages

MsgTransfer

A fungible token cross chain transfer is achieved by using the MsgTransfer:

type MsgTransfer struct {
  SourcePort        string
  SourceChannel     string
  Token             sdk.Coin
  Sender            string
  Receiver          string
  TimeoutHeight     ibcexported.Height
  TimeoutTimestamp  uint64
  Memo              string
}

This message is expected to fail if:

• SourcePort is invalid (see 24-host naming requirements.
• SourceChannel is invalid (see 24-host naming requirements).
• Token is invalid:
  • Amount is not positive.
  • Denom is not a valid IBC denomination as per ADR 001 - Coin Source Tracing.
• Sender is empty.
• Receiver is empty or contains more than 2048 bytes.
• Memo contains more than 32768 bytes.
• TimeoutHeight and TimeoutTimestamp are both zero.

This message will send a fungible token to the counterparty chain represented by the counterparty Channel End connected to the Channel End with the identifiers SourcePort and SourceChannel.

The denomination provided for transfer should correspond to the same denomination represented on this chain. The prefixes will be added as necessary upon by the receiving chain.

If the Amount is set to the maximum value for a 256-bit unsigned integer (i.e. 2^256 - 1), then the whole balance of the corresponding denomination will be transferred. The helper function UnboundedSpendLimit in the types package of the transfer module provides the sentinel value that can be used.

Memo

The memo field was added to allow applications and users to attach metadata to transfer packets. The field is optional and may be left empty. When it is used to attach metadata for a particular middleware, the memo field should be represented as a json object where different middlewares use different json keys.

For example, the following memo field is used by the callbacks middleware to attach a source callback to a transfer packet:

{
  "src_callback": {
    "address": "callbackAddressString",
    // optional
    "gas_limit": "userDefinedGasLimitString",
  }
}

You can find more information about other applications that use the memo field in the chain registry.