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Messages

MsgTransfer​

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

type MsgTransfer struct {
  SourcePort        string
  // with IBC v2 SourceChannel will be a client ID
  SourceChannel     string 
  Token             sdk.Coin
  Sender            string
  Receiver          string
  // If you are sending with IBC v1 protocol, either timeout_height or timeout_timestamp must be set.
  // If you are sending with IBC v2 protocol, timeout_timestamp must be set, and timeout_height must be omitted. 
  TimeoutHeight     ibcexported.Height
  // Timeout timestamp in absolute nanoseconds since unix epoch.
  TimeoutTimestamp  uint64
  // optional Memo field
  Memo              string
  // optional Encoding field 
  Encoding          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:
  • Sender is empty.
  • Receiver is empty or contains more than 2048 bytes.
  • Memo contains more than 32768 bytes.
  • TimeoutHeight and TimeoutTimestamp are both zero for IBC Classic.
    • Note that TimeoutHeight as a concept is removed in IBC v2, hence this must always be emitted and only TimeoutTimestamp used.

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. Note that in IBC v2 a pair of clients are connected and the SourceChannel is referring to the source ClientID.

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.

Encoding​

In IBC v2, the encoding method used by an application has more flexibility as it is specified within a Payload, rather than negotiated and fixed during an IBC classic channel handshake. Certain encoding types may be more suited to specific blockchains, e.g. ABI encoding is more gas efficient to decode in an EVM than JSON or Protobuf.

Within ibc-go, JSON, protobuf and ABI encoding are supported and can be used, see the transfer packet types.