jaekwon commented 6 years ago

Cosmos SDK Code Run #1

Code don't lie, check out why the Cosmos SDK is the ideal platform for scalable blockchain development.

KVStore

The KVStore provides the basic persistence layer for your SDK application.

https://github.com/cosmos/cosmos-sdk/blob/3fc7200f1d1045a19efc30395e5916f9ef1b42b7/types/store.go#L91-L121

You can mount multiple KVStores onto your application, e.g. one for staking, one for accounts, one for IBC, and so on.

https://github.com/cosmos/cosmos-sdk/blob/3fc7200f1d1045a19efc30395e5916f9ef1b42b7/examples/basecoin/app/app.go#L90

The implementation of a KVStore is responsible for providing any Merkle proofs for each query, if requested.

https://github.com/cosmos/cosmos-sdk/blob/3fc7200f1d1045a19efc30395e5916f9ef1b42b7/store/iavlstore.go#L135

Stores can be cache-wrapped to provide transactions at the persistence level (and this is well supported for iterators as well). This feature is used to provide a layer of transactional isolation for transaction processing after the "AnteHandler" deducts any associated fees for the transaction. Cache-wrapping can also be useful when implementing a virtual-machine or scripting environment for the blockchain.

go-amino

The Cosmos-SDK uses go-amino extensively to serialize and deserialize Go types into Protobuf3 compatible bytes.

Go-amino (e.g. over https://github.com/golang/protobuf) uses reflection to encode/decode any Go object. This lets the SDK developer focus on defining data structures in Go without the need to maintain a separate schema for Proto3. In addition, Amino extends Proto3 with native support for interfaces and concrete types.

For example, the Cosmos SDK's x/auth package imports the PubKey interface from tendermint/go-crypto , where PubKey implementations include those for Ed25519 and Secp256k1. Each auth.BaseAccount has a PubKey.

https://github.com/cosmos/cosmos-sdk/blob/d309abb4b9bdb01272e54e048063502110c801fa/x/auth/account.go#L35-L43

Amino knows what concrete type to decode for each interface value based on what concretes are registered for the interface.

For example, the "Basecoin" example app knows about Ed25519 and Secp256k1 keys because they are registered by the app's codec below:

https://github.com/cosmos/cosmos-sdk/blob/d309abb4b9bdb01272e54e048063502110c801fa/examples/basecoin/app/app.go#L101

For more information on Go-Amino, see https://github.com/tendermint/go-amino.

Keys, Keepers, and Mappers

The Cosmos SDK is designed to enable an ecosystem of libraries that can be imported together to form a whole application. To make this ecosystem more secure, we've developed a design pattern that follows the principle of least-authority.

Mappers and Keepers provide access to KV stores via the context. The only difference between the two is that a Mapper provides a lower-level API, so generally a Keeper might hold references to other Keepers and Mappers but not vice versa.

Mappers and Keepers don't hold any references to any stores directly. They only hold a "key" (the sdk.StoreKey below):

https://github.com/cosmos/cosmos-sdk/blob/fc0e4013278d41fab4f3ac73f28a42bc45889106/x/auth/mapper.go#L14-L24

This way, you can hook everything up in your main app.go file and see what components have access to what stores and other components.

https://github.com/cosmos/cosmos-sdk/blob/d309abb4b9bdb01272e54e048063502110c801fa/examples/basecoin/app/app.go#L65-L70

Later during the execution of a transaction (e.g. via ABCI DeliverTx after a block commit) the context is passed in as the first argument. The context includes references to any relevant KV stores, but you can only access them if you hold the associated key.

https://github.com/cosmos/cosmos-sdk/blob/fc0e4013278d41fab4f3ac73f28a42bc45889106/x/auth/mapper.go#L44-L53

Mappers and Keepers cannot hold direct references to stores because the store is not known at app initialization time. The store is dynamically created (and wrapped via CacheKVStore as needed to provide a transactional context) for every committed transaction (via ABCI DeliverTx) and mempool check transaction (via ABCI CheckTx).

Tx, Msg, Handler, and AnteHandler

A transaction (Tx interface) is a signed/authenticated message (Msg interface).

Transactions that are discovered by the Tendermint mempool are processed by the AnteHandler ("ante" just means "before") where the validity of the transaction is checked and any fees are collected.

Transactions that get committed in a block first get processed through the AnteHandler, and if the transaction is valid after fees are deducted, they are processed through the appropriate Handler.

In either case, the transaction bytes must first be parsed. The default transaction parser uses Amino. Most SDK developers will want to use the standard transaction structure defined in the x/auth package (and the corresponding AnteHandler implementation also provided in x/auth):

https://github.com/cosmos/cosmos-sdk/blob/fc0e4013278d41fab4f3ac73f28a42bc45889106/x/auth/stdtx.go#L12-L18

Various packages generally define their own message types. The Basecoin example app includes multiple message types that are registered in app.go:

https://github.com/cosmos/cosmos-sdk/blob/d309abb4b9bdb01272e54e048063502110c801fa/examples/basecoin/app/app.go#L102-L106

Finally, handlers are added to the router in your app.go file to map messages to their corresponding handlers. (In the future we will provide more routing features to enable pattern matching for more flexibility).

https://github.com/cosmos/cosmos-sdk/blob/d309abb4b9bdb01272e54e048063502110c801fa/examples/basecoin/app/app.go#L78-L83

EndBlocker

The EndBlocker hook allows us to register callback logic to be performed at the end of each block. This lets us process background events, such as processing validator inflationary atom provisions:

https://github.com/cosmos/cosmos-sdk/blob/3fc7200f1d1045a19efc30395e5916f9ef1b42b7/x/stake/handler.go#L32-L37

By the way, the SDK provides a staking module, which provides all the bonding/unbonding funcionality for the Cosmos Hub: https://github.com/cosmos/cosmos-sdk/tree/develop/x/stake (staking module)

cosmos / cosmos-sdk

(test) Coderun #1202