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Transactions
NOTE: The specification documented below is still highly active in development and subject to change.
Routing
Ethermint needs to parse and handle transactions routed for both the EVM and for
the Cosmos hub. We attempt to achieve this by mimicking Geth's Transaction structure and utilizing
the Payload as the potential encoding of a Cosmos-routed transaction. What
designates this encoding, and ultimately routing, is the Transaction.Recipient
address -- if this address matches some global unique predefined and configured
address, we regard it as a transaction meant for Cosmos, otherwise, the transaction
is a pure Ethereum transaction and will be executed in the EVM.
For Cosmos routed transactions, the Transaction.Payload will contain an
embedded encoded type: EmbeddedTx. This structure is analogous to the Cosmos
SDK sdk.StdTx. If a client wishes to send an EmbeddedTx, it must first encode
the embedded transaction, and then encode the embedding Transaction.
Note: The Transaction and EmbeddedTx types utilize the Amino object serialization protocol and as such,
the Transaction is not an exact replica of what will be found in Ethereum. Our
goal is to utilize Geth as a library, at least as much as possible, so it should
be expected that these types and the operations you may perform on them will keep
in line with Ethereum.
Being that Ethermint implements the ABCI application interface, as transactions
are sent they are passed through a series of handlers. Once such handler, runTx,
is responsible for invoking the TxDecoder which performs the business logic of
properly deserializing raw transaction bytes into either an Ethereum transaction
or a Cosmos transaction.
Transactions & Messages
The SDK distinguishes between transactions (sdk.Tx) and messages (sdk.Msg).
A sdk.Tx is a list of sdk.Msgs wrapped with authentication and fee data. Users
can create messages containing arbitrary information by implementing the sdk.Msg
interface.
In Ethermint, the Transaction type implements the Cosmos SDK sdk.Tx interface.
It addition, it implements the Cosmos SDK sdk.Msg interface for the sole purpose
of being to perform basic validation checks in the BaseApp. It, however, has
no distinction between transactions and messages.
The EmbeddedTx, being analogous to the Cosmos SDK sdk.StdTx, implements the
Cosmos SDK sdk.Tx interface.
Signatures
Ethermint supports EIP-155
signatures. A Transaction is expected to have a single signature for Ethereum
routed transactions. However, just as in Cosmos, Ethermint will support multiple
signers for EmbeddedTx Cosmos routed transactions. Signatures over the
Transaction type are identical to Ethereum. However, the EmbeddedTx contains
a canonical signature structure that contains the signature itself and other
information such as an account's sequence number. The sequence number is expected
to increment every time a message is signed by a given account. This, in addition
to the chain ID, prevents "replay attacks", where the same message could be
executed over and over again.
An EmbeddedTx list of signatures must much the unique list of addresses returned
by each message's GetSigners call. In addition, the address of first signer of
the EmbeddedTx is responsible for paying the fees.
Gas & Fees
TODO