Can Go Applications Mock or Monitor Filesystem I/O Operations?

Mocking and Abstracting the Filesystem in Go

Question:
Is it possible to monitor I/O operations performed by a Go application on the underlying filesystem? Additionally, can the physical filesystem be replaced with an in-memory counterpart?

Answer:
Yes, it is possible to abstract and mock the filesystem in Go. Here is an approach inspired by Andrew Gerrand's insights:

Define a fileSystem interface representing essential filesystem operations:

type fileSystem interface {
    Open(name string) (file, error)
    Stat(name string) (os.FileInfo, error)
}

Create a file interface for file-related operations:

type file interface {
    io.Closer
    io.Reader
    io.ReaderAt
    io.Seeker
    Stat() (os.FileInfo, error)
}

Implement a default osFS type that utilizes the local disk:

type osFS struct{}

func (osFS) Open(name string) (file, error)        { return os.Open(name) }
func (osFS) Stat(name string) (os.FileInfo, error) { return os.Stat(name) }

In your application code, pass the fileSystem interface as an argument or embed it within a wrapper type:

func myFunc(fs fileSystem) {
    f, err := fs.Open("my_file.txt")
    ...
}

To use an in-memory filesystem, create a memoryFS type that implements the fileSystem interface and stores files in an internal data structure. This can allow you to intercept and log all I/O events while using a mock filesystem:

type memoryFS struct {
    files map[string][]byte
}

func (mfs memoryFS) Open(name string) (file, error) {
    ...
}

func (mfs memoryFS) Stat(name string) (os.FileInfo, error) {
    ...
}

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