appendfs

appendfs

The appendfs package provides an extended file system interface that goes beyond the standard functionality of io/fs. The primary goal of this interface is to ensure that the provided file system is capable of creating new files and directories.

Interface: FS

The FS interface combines several interfaces from the standard io/fs package and the external github.com/je4/filesystem/v3/pkg/writefs package. It serves as a central abstraction for file systems that can be both read from and written to.

type FS interface {
    fs.FS
    writefs.MkDirFS
    writefs.CreateFS
}

It includes the following functionalities:

• fs.FS: Standard read access (Open(name string) (File, error)).
• writefs.MkDirFS: Creation of directories.
• writefs.CreateFS: Creation of files for write access.

Functions

Sub(fsys FS, path string) (FS, error)

The Sub function creates a sub-file system (Sub-FS) based on a given path. It ensures that the resulting file system also satisfies the FS interface.

This is particularly useful for restricting operations to a specific subdirectory of an OCFL storage or an object, while still maintaining write permissions.

Example:

subFS, err := appendfs.Sub(rootFS, "v1/content")
if err != nil {
    // Error handling
}

// Now you can work in subFS as if "v1/content" were the root.
f, err := subFS.Create("data.txt")

EnsureFS(fsys fs.FS) (FS, error)

The helper function EnsureFS checks if a given fs.FS implements the appendfs.FS interface (i.e., supports write access). If it does, it returns the casted interface; otherwise, an error is reported.

Project Usage

appendfs.FS is used in many places within gocfl to abstract the storage layer. It allows other packages (such as ocfl, extension, etc.) to create files and directories without having to worry about the underlying implementation (local file system, S3, etc.).