ICS20-1 cleanup

spec/app/ics-020-fungible-token-transfer/README.md

@@ -34,7 +34,7 @@ The IBC handler interface & IBC routing module interface are as defined in [ICS
 
 ### Data Structures
 
-Only one packet data type, `FungibleTokenPacketData`, which specifies the denomination, amount, sending account, receiving account, and whether the sending chain is the source of the asset, is required.
+Only one packet data type is required: `FungibleTokenPacketData`, which specifies the denomination, amount, sending account, and receiving account.
 
 ```typescript
 interface FungibleTokenPacketData {
@@ -45,15 +45,29 @@ interface FungibleTokenPacketData {
 }
 ```
 
+As tokens are sent across chains using the ICS 20 protocol, they begin to accrue a record of channels for which they have been transferred across. This information is encoded into the `denomination` field. 
+
+The ics20 token denominations are represented the form `{ics20Port}/{ics20Channel}/{denom}`, where `ics20Port` and `ics20Channel` are an ics20 port and channel on the current chain for which the funds exist. The prefixed port and channel pair indicate which channel the funds were previously sent through. If `{denom}` contains `/`, then it must also be in the ics20 form which indicates that this token has a multi-hop record. Note that this requires that the `/` (slash character) is prohibited in non-IBC token denomination names.
+
+A sending chain may be acting as a source or sink zone. When a chain is sending tokens across a port and channel which are not equal to the last prefixed port and channel pair, it is acting as a source zone. When tokens are sent from a source zone, the destination port and channel will be prefixed onto the denomination (once the tokens are received) adding another hop to a tokens record. When a chain is sending tokens across a port and channel which are equal to the last prefixed port and channel pair, it is acting as a sink zone. When tokens are sent from a sink zone, the last prefixed port and channel pair on the denomination is removed (once the tokens are received), undoing the last hop in the tokens record. A more complete explanation is [present in the ibc-go implementation](https://github.com/cosmos/ibc-go/blob/457095517b7832c42ecf13571fee1e550fec02d0/modules/apps/transfer/keeper/relay.go#L18-L49).
+
 The acknowledgement data type describes whether the transfer succeeded or failed, and the reason for failure (if any).
 
 ```typescript
-interface FungibleTokenPacketAcknowledgement {
-  success: boolean
-  error: Maybe<string>
+type FungibleTokenPacketAcknowledgement = FungibleTokenPacketSuccess | FungibleTokenPacketError;
+
+interface FungibleTokenPacketSuccess {
+  // This is binary 0x01 base64 encoded
+  success: "AQ=="
+}
+
+interface FungibleTokenPacketError {
+  error: string
 }
 ```
 
+Note that both the `FungibleTokenPacketData` as well as `FungibleTokenPacketAcknowledgement` must be JSON-encoded (not Protobuf encoded) when they serialized into packet data. Also note that `uint256` is string encoded when converted to JSON, but must be a valid decimal number of the form `[0-9]+`.
+
 The fungible token transfer bridge module tracks escrow addresses associated with particular channels in state. Fields of the `ModuleState` are assumed to be in scope.
 
 ```typescript
@@ -202,7 +216,7 @@ function createOutgoingPacket(
   sourceChannel: string,
   timeoutHeight: Height,
   timeoutTimestamp: uint64) {
-  prefix = "{sourcePort}/{sourceChannel}"
+  prefix = "{sourcePort}/{sourceChannel}/"
   // we are the source if the denomination is not prefixed
   source = denomination.slice(0, len(prefix)) !== prefix
   if source {
@@ -226,7 +240,7 @@ function onRecvPacket(packet: Packet) {
   FungibleTokenPacketData data = packet.data
   // construct default acknowledgement of success
   FungibleTokenPacketAcknowledgement ack = FungibleTokenPacketAcknowledgement{true, null}
-  prefix = "{packet.sourcePort}/{packet.sourceChannel}"
+  prefix = "{packet.sourcePort}/{packet.sourceChannel}/"
   // we are the source if the packets were prefixed by the sending chain
   source = data.denomination.slice(0, len(prefix)) === prefix
   if source {
@@ -238,7 +252,7 @@ function onRecvPacket(packet: Packet) {
     if (err !== nil)
       ack = FungibleTokenPacketAcknowledgement{false, "transfer coins failed"}
   } else {
-    prefix = "{packet.destPort}/{packet.destChannel}"
+    prefix = "{packet.destPort}/{packet.destChannel}/"
     prefixedDenomination = prefix + data.denomination
     // sender was source, mint vouchers to receiver (assumed to fail if balance insufficient)
     err = bank.MintCoins(data.receiver, prefixedDenomination, data.amount)
@@ -275,7 +289,7 @@ function onTimeoutPacket(packet: Packet) {
 ```typescript
 function refundTokens(packet: Packet) {
   FungibleTokenPacketData data = packet.data
-  prefix = "{packet.sourcePort}/{packet.sourceChannel}"
+  prefix = "{packet.sourcePort}/{packet.sourceChannel}/"
   // we are the source if the denomination is not prefixed
   source = denomination.slice(0, len(prefix)) !== prefix
   if source {