A typical Cosmos SDK directory structure is as follows
x/{module}
├── client
│ ├── cli
│ │ ├── query.go
│ │ └── tx.go
│ └── rest
│ ├── query.go
│ └── tx.go
├── exported
│ └── exported.go
├── keeper
│ ├── invariants.go
│ ├── genesis.go
│ ├── keeper.go
│ ├── ...
│ └── querier.go
│ └── grpc_query.go
├── types
│ ├── codec.go
│ ├── errors.go
│ ├── events.go
│ ├── expected_keepers.go
│ ├── genesis.go
│ ├── keys.go
│ ├── msgs.go
│ ├── params.go
│ ├── types.proto
│ ├── ...
│ └── querier.go
│ └── {module_name}.pb.go
│ └── query.pb.go
│ └── genesis.pb.go
├── simulation
│ ├── decoder.go
│ ├── genesis.go
│ ├── operations.go
│ ├── params.go
│ └── proposals.go
├── abci.go
├── handler.go
├── ...
└── module.go
abci.go: The module's BeginBlocker and EndBlocker implementations (if any).
client/: The module's CLI and REST client functionality implementation and testing.
exported/: The module's exported types -- typically type interfaces. If a module relies on other module keepers, it is expected to receive them as interface contracts through the expected_keepers.go (which are detailed below) design to avoid having a direct dependency on the implementing module. However, these contracts can define methods that operate on and/or return types that are specific to the contract's implementing module and this is where exported/ comes into play. Types defined here allow for expected_keepers.go in other modules to define contracts that use single canonical types. This pattern allows for code to remain DRY and also alleviates import cycle chaos.
handler.go: The module's message handlers.
keeper/: The module's keeper implementation along with any auxiliary implementations such as the querier and invariants.
types/: The module's type definitions such as messages, KVStore keys, parameter types, Protocol Buffer definitions, and expected_keepers.go contracts.
module.go: The module's implementation of the AppModule and AppModuleBasic interfaces.