Folder Structure

Synopsis

This document outlines the structure of Cosmos SDK modules. These ideas are meant to be applied as suggestions. Application developers are encouraged to improve upon and contribute to module structure and development design.

The required interface for a module is located in the module.go. Everything beyond this is suggestive.

Structure

A typical Cosmos SDK module can be structured as follows:

proto
└── {project_name}
    └── {module_name}
        └── {proto_version}
            ├── {module_name}.proto
            ├── genesis.proto
            ├── query.proto
            └── tx.proto

• {module_name}.proto: The module's common message type definitions.
• genesis.proto: The module's message type definitions related to genesis state.
• query.proto: The module's Query service and related message type definitions.
• tx.proto: The module's Msg service and related message type definitions.

x/{module_name}
├── client
│   ├── cli
│   │   ├── query.go
│   │   └── tx.go
│   └── testutil
│       ├── cli_test.go
│       └── suite.go
├── exported
│   └── exported.go
├── keeper
│   ├── genesis.go
│   ├── grpc_query.go
│   ├── hooks.go
│   ├── keeper.go
│   ├── keys.go
│   ├── msg_server.go
│   └── querier.go
├── simulation
│   ├── decoder.go
│   ├── genesis.go
│   ├── operations.go
│   └── params.go
├── types
│   ├── {module_name}.pb.go
│   ├── codec.go
│   ├── errors.go
│   ├── events.go
│   ├── events.pb.go
│   ├── expected_keepers.go
│   ├── genesis.go
│   ├── genesis.pb.go
│   ├── keys.go
│   ├── msgs.go
│   ├── params.go
│   ├── query.pb.go
│   └── tx.pb.go
├── module.go
├── abci.go
├── autocli.go
├── depinject.go
└── README.md

• client/: The module's CLI client functionality implementation and the module's CLI testing suite.
• exported/: The module's exported types - typically interface types. If a module relies on keepers from another module, it is expected to receive the keepers as interface contracts through the expected_keepers.go file (see below) in order to avoid a direct dependency on the module implementing the keepers. However, these interface contracts can define methods that operate on and/or return types that are specific to the module that is implementing the keepers and this is where exported/ comes into play. The interface types that are defined in exported/ use canonical types, allowing for the module to receive the keepers as interface contracts through the expected_keepers.go file. This pattern allows for code to remain DRY and also alleviates import cycle chaos.
• keeper/: The module's Keeper and MsgServer implementation.
  • abci.go: The module's BeginBlocker and EndBlocker implementations (this file is only required if BeginBlocker and/or EndBlocker need to be defined).
• simulation/: The module's simulation package defines functions used by the blockchain simulator application (simapp).
• README.md: The module's specification documents outlining important concepts, state storage structure, and message and event type definitions. Learn more how to write module specs in the spec guidelines.
• types/: includes type definitions for messages, events, and genesis state, including the type definitions generated by Protocol Buffers.
  • codec.go: The module's registry methods for interface types.
  • errors.go: The module's sentinel errors.
  • events.go: The module's event types and constructors.
  • expected_keepers.go: The module's expected keeper interfaces.
  • genesis.go: The module's genesis state methods and helper functions.
  • keys.go: The module's store keys and associated helper functions.
  • msgs.go: The module's message type definitions and associated methods.
  • params.go: The module's parameter type definitions and associated methods.
  • *.pb.go: The module's type definitions generated by Protocol Buffers (as defined in the respective *.proto files above).
• The root directory includes the module's AppModule implementation.
  • autocli.go: The module autocli options.
  • depinject.go: The module depinject options.

Note: although the above pattern is followed by most of the Cosmos SDK modules, there are some modules that don't follow this pattern. E.g x/group and x/nft dont have a types folder, instead all of the type definitions for messages, events, and genesis state are live in the root directory and the module's AppModule implementation lives in the module folder.