Transactions
are objects created by end-users to trigger state changes in the application. {synopsis}
- Anatomy of a Cosmos SDK Application {prereq}
Transactions are comprised of metadata held in contexts and sdk.Msg
s that trigger state changes within a module through the module's Protobuf Msg
service.
When users want to interact with an application and make state changes (e.g. sending coins), they create transactions. Each of a transaction's sdk.Msg
must be signed using the private key associated with the appropriate account(s), before the transaction is broadcasted to the network. A transaction must then be included in a block, validated, and approved by the network through the consensus process. To read more about the lifecycle of a transaction, click here.
Transaction objects are Cosmos SDK types that implement the Tx
interface
+++ https://github.com/cosmos/cosmos-sdk/blob/v0.40.0-rc3/types/tx_msg.go#L49-L57
It contains the following methods:
- GetMsgs: unwraps the transaction and returns a list of contained
sdk.Msg
s - one transaction may have one or multiple messages, which are defined by module developers. - ValidateBasic: lightweight, stateless checks used by ABCI messages
CheckTx
andDeliverTx
to make sure transactions are not invalid. For example, theauth
module'sStdTx
ValidateBasic
function checks that its transactions are signed by the correct number of signers and that the fees do not exceed what the user's maximum. Note that this function is to be distinct fromsdk.Msg
ValidateBasic
methods, which perform basic validity checks on messages only. WhenrunTx
is checking a transaction created from theauth
module, it first runsValidateBasic
on each message, then runs theauth
module AnteHandler which callsValidateBasic
for the transaction itself.
As a developer, you should rarely manipulate Tx
directly, as Tx
is really an intermediate type used for transaction generation. Instead, developers should prefer the TxBuilder
interface, which you can learn more about below.
Every message in a transaction must be signed by the addresses specified by its GetSigners
. The Cosmos SDK currently allows signing transactions in two different ways.
The most used implementation of the Tx
interface is the Protobuf Tx
message, which is used in SIGN_MODE_DIRECT
:
Because Protobuf serialization is not deterministic, the Cosmos SDK uses an additional TxRaw
type to denote the pinned bytes over which a transaction is signed. Any user can generate a valid body
and auth_info
for a transaction, and serialize these two messages using Protobuf. TxRaw
then pins the user's exact binary representation of body
and auth_info
, called respectively body_bytes
and auth_info_bytes
. The document that is signed by all signers of the transaction is SignDoc
(deterministically serialized using ADR-027):
Once signed by all signers, the body_bytes
, auth_info_bytes
and signatures
are gathered into TxRaw
, whose serialized bytes are broadcasted over the network.
The legacy implemention of the Tx
interface is the StdTx
struct from x/auth
:
The document signed by all signers is StdSignDoc
:
which is encoded into bytes using Amino JSON. Once all signatures are gathered into StdTx
, StdTx
is serialized using Amino JSON, and these bytes are broadcasted over the network.
Other sign modes, most notably SIGN_MODE_TEXTUAL
, are being discussed. If you wish to learn more about them, please refer to ADR-020.
The process of an end-user sending a transaction is:
- decide on the messages to put into the transaction,
- generate the transaction using the Cosmos SDK's
TxBuilder
, - broadcast the transaction using one of the available interfaces.
The next paragraphs will describe each of these components, in this order.
::: tip
Module sdk.Msg
s are not to be confused with ABCI Messages which define interactions between the Tendermint and application layers.
:::
Messages (or sdk.Msg
s) are module-specific objects that trigger state transitions within the scope of the module they belong to. Module developers define the messages for their module by adding methods to the Protobuf Msg
service, and also implement the corresponding MsgServer
.
Each sdk.Msg
s is related to exactly one Protobuf Msg
service RPC, defined inside each module's tx.proto
file. An SKD app router automatically maps every sdk.Msg
to a corresponding RPC. Protobuf generates a MsgServer
interface for each module Msg
service, and the module developer needs to implement this interface.
This design puts more responsibility on module developers, allowing application developers to reuse common functionalities without having to implement state transition logic repetitively.
To learn more about Protobuf Msg
services and how to implement MsgServer
, click here.
While messages contain the information for state transition logic, a transaction's other metadata and relevant information are stored in the TxBuilder
and Context
.
The TxBuilder
interface contains data closely related with the generation of transactions, which an end-user can freely set to generate the desired transaction:
+++ https://github.com/cosmos/cosmos-sdk/blob/v0.40.0-rc3/client/tx_config.go#L32-L45
Msg
s, the array of messages included in the transaction.GasLimit
, option chosen by the users for how to calculate how much gas they will need to pay.Memo
, a note or comment to send with the transaction.FeeAmount
, the maximum amount the user is willing to pay in fees.TimeoutHeight
, block height until which the transaction is valid.Signatures
, the array of signatures from all signers of the transaction.
As there are currently two sign modes for signing transactions, there are also two implementations of TxBuilder
:
- wrapper for creating transactions for
SIGN_MODE_DIRECT
, - StdTxBuilder for
SIGN_MODE_LEGACY_AMINO_JSON
.
However, the two implementation of TxBuilder
should be hidden away from end-users, as they should prefer using the overarching TxConfig
interface:
+++ https://github.com/cosmos/cosmos-sdk/blob/v0.40.0-rc3/client/tx_config.go#L21-L30
TxConfig
is an app-wide configuration for managing transactions. Most importantly, it holds the information about whether to sign each transaction with SIGN_MODE_DIRECT
or SIGN_MODE_LEGACY_AMINO_JSON
. By calling txBuilder := txConfig.NewTxBuilder()
, a new TxBuilder
will be created with the appropriate sign mode.
Once TxBuilder
is correctly populated with the setters exposed above, TxConfig
will also take care of correctly encoding the bytes (again, either using SIGN_MODE_DIRECT
or SIGN_MODE_LEGACY_AMINO_JSON
). Here's a pseudo-code snippet of how to generate and encode a transaction, using the TxEncoder()
method:
txBuilder := txConfig.NewTxBuilder()
txBuilder.SetMsgs(...) // and other setters on txBuilder
bz, err := txConfig.TxEncoder()(txBuilder.GetTx())
// bz are bytes to be broadcasted over the network
Once the transaction bytes are generated, there are currently three ways of broadcasting it.
Application developers create entrypoints to the application by creating a command-line interface, gRPC and/or REST interface, typically found in the application's ./cmd
folder. These interfaces allow users to interact with the application through command-line.
For the command-line interface, module developers create subcommands to add as children to the application top-level transaction command TxCmd
. CLI commands actually bundle all the steps of transaction processing into one simple command: creating messages, generating transactions and broadcasting. For concrete examples, see the Interacting with a Node section. An example transaction made using CLI looks like:
simd tx send $MY_VALIDATOR_ADDRESS $RECIPIENT 1000stake
gRPC is introduced in Cosmos SDK 0.40 as the main component for the Cosmos SDK's RPC layer. The principal usage of gRPC is in the context of modules' Query
services. However, the Cosmos SDK also exposes a few other module-agnostic gRPC services, one of them being the Tx
service:
+++ https://github.com/cosmos/cosmos-sdk/blob/v0.40.0-rc3/proto/cosmos/tx/v1beta1/service.proto
The Tx
service exposes a handful of utility functions, such as simulating a transaction or querying a transaction, and also one method to broadcast transactions.
Examples of broadcasting and simulating a transaction are shown here.
Each gRPC method has its corresponding REST endpoint, generated using gRPC-gateway. Therefore, instead of using gRPC, you can also use HTTP to broadcast the same transaction, on the POST /cosmos/tx/v1beta1/txs
endpoint.
An example can be seen here
The three methods presented above are actually higher abstractions over the Tendermint RPC /broadcast_tx_{async,sync,commit}
endpoints, documented here. This means that you can use the Tendermint RPC endpoints directly to broadcast the transaction, if you wish so.
Learn about the context {hide}