96 lines
6.8 KiB
Markdown
96 lines
6.8 KiB
Markdown
<!--
|
|
order: 4
|
|
-->
|
|
|
|
# Main Components of the Cosmos SDK
|
|
|
|
The Cosmos SDK is a framework that facilitates the development of secure state-machines on top of Tendermint. At its core, the SDK is a boilerplate implementation of the [ABCI](./sdk-app-architecture.md#abci) in Golang. It comes with a [`multistore`](../core/store.md#multistore) to persist data and a [`router`](../core/baseapp.md#routing) to handle transactions.
|
|
|
|
Here is a simplified view of how transactions are handled by an application built on top of the Cosmos SDK when transferred from Tendermint via `DeliverTx`:
|
|
|
|
1. Decode `transactions` received from the Tendermint consensus engine (remember that Tendermint only deals with `[]bytes`).
|
|
2. Extract `messages` from `transactions` and do basic sanity checks.
|
|
3. Route each message to the appropriate module so that it can be processed.
|
|
4. Commit state changes.
|
|
|
|
## `baseapp`
|
|
|
|
`baseapp` is the boilerplate implementation of a Cosmos SDK application. It comes with an implementation of the ABCI to handle the connection with the underlying consensus engine. Typically, a Cosmos SDK application extends `baseapp` by embedding it in [`app.go`](../basics/app-anatomy.md#core-application-file). See an example of this from the SDK application tutorial:
|
|
|
|
+++ https://github.com/cosmos/sdk-tutorials/blob/c6754a1e313eb1ed973c5c91dcc606f2fd288811/app.go#L72-L92
|
|
|
|
The goal of `baseapp` is to provide a secure interface between the store and the extensible state machine while defining as little about the state machine as possible (staying true to the ABCI).
|
|
|
|
For more on `baseapp`, please click [here](../core/baseapp.md).
|
|
|
|
## Multistore
|
|
|
|
The Cosmos SDK provides a [`multistore`](../core/store.md#multistore) for persisting state. The multistore allows developers to declare any number of [`KVStores`](../core/store.md#base-layer-kvstores). These `KVStores` only accept the `[]byte` type as value and therefore any custom structure needs to be marshalled using [a codec](../core/encoding.md) before being stored.
|
|
|
|
The multistore abstraction is used to divide the state in distinct compartments, each managed by its own module. For more on the multistore, click [here](../core/store.md#multistore)
|
|
|
|
## Modules
|
|
|
|
The power of the Cosmos SDK lies in its modularity. SDK applications are built by aggregating a collection of interoperable modules. Each module defines a subset of the state and contains its own message/transaction processor, while the SDK is responsible for routing each message to its respective module.
|
|
|
|
Here is a simplified view of how a transaction is processed by the application of each full-node when it is received in a valid block:
|
|
|
|
```
|
|
+
|
|
|
|
|
| Transaction relayed from the full-node's
|
|
| Tendermint engine to the node's application
|
|
| via DeliverTx
|
|
|
|
|
|
|
|
+---------------------v--------------------------+
|
|
| APPLICATION |
|
|
| |
|
|
| Using baseapp's methods: Decode the Tx, |
|
|
| extract and route the message(s) |
|
|
| |
|
|
+---------------------+--------------------------+
|
|
|
|
|
|
|
|
|
|
|
+---------------------------+
|
|
|
|
|
|
|
|
| Message routed to
|
|
| the correct module
|
|
| to be processed
|
|
|
|
|
|
|
|
+----------------+ +---------------+ +----------------+ +------v----------+
|
|
| | | | | | | |
|
|
| AUTH MODULE | | BANK MODULE | | STAKING MODULE | | GOV MODULE |
|
|
| | | | | | | |
|
|
| | | | | | | Handles message,|
|
|
| | | | | | | Updates state |
|
|
| | | | | | | |
|
|
+----------------+ +---------------+ +----------------+ +------+----------+
|
|
|
|
|
|
|
|
|
|
|
|
|
|
+--------------------------+
|
|
|
|
|
| Return result to Tendermint
|
|
| (0=Ok, 1=Err)
|
|
v
|
|
```
|
|
|
|
Each module can be seen as a little state-machine. Developers need to define the subset of the state handled by the module, as well as custom message types that modify the state (*Note:* `messages` are extracted from `transactions` by `baseapp`). In general, each module declares its own `KVStore` in the `multistore` to persist the subset of the state it defines. Most developers will need to access other 3rd party modules when building their own modules. Given that the Cosmos-SDK is an open framework, some of the modules may be malicious, which means there is a need for security principles to reason about inter-module interactions. These principles are based on [object-capabilities](../core/ocap.md). In practice, this means that instead of having each module keep an access control list for other modules, each module implements special objects called `keepers` that can be passed to other modules to grant a pre-defined set of capabilities.
|
|
|
|
SDK modules are defined in the `x/` folder of the SDK. Some core modules include:
|
|
|
|
- `x/auth`: Used to manage accounts and signatures.
|
|
- `x/bank`: Used to enable tokens and token transfers.
|
|
- `x/staking` + `x/slashing`: Used to build Proof-Of-Stake blockchains.
|
|
|
|
In addition to the already existing modules in `x/`, that anyone can use in their app, the SDK lets you build your own custom modules. You can check an [example of that in the tutorial](https://cosmos.network/docs/tutorial/keeper.html).
|
|
|
|
## Next {hide}
|
|
|
|
Learn more about the [anatomy of an SDK application](../basics/app-anatomy.md) {hide}
|