Where in the project structure is the layer responsible for data transfer between components usually located?

In a Go project structure, the layer responsible for data transfer between components is usually placed in a separate package, often called service, usecase, or interactor.

This layer acts as an intermediary between, for example, controllers (HTTP handlers) and data access layers (repositories). It encapsulates business logic and facilitates data transfer between components without tightly coupling them.

An example structure:

/project
  /cmd
  /internal
    /handler    // HTTP handlers
    /service    // business logic, data transfer between layers
    /repository // database access

Such separation helps maintain a clean architecture and makes testing and code maintenance easier.