stackedfs

stackedfs allows for overlaying different sources to read a file. Think of OverlayFS for Go. It works great with the embed directive and requires at least Go 1.16 because of the fs.FS interface it makes heavy use of.

Install

go get -u github.com/jojomi/stackedfs

Example usage

package main

import (
	"embed"
	"io/fs"
	"os"
	"path/filepath"

	"github.com/kardianos/osext"
	"github.com/rs/zerolog/log"
	"gitlab.com/jojomi/zeiterfassung/stackedfs"
)

//go:embed templates/*
var embeddedTemplates embed.FS

func getTemplateReader() (*stackedfs.StackedFS, error) {
	result := stackedfs.NewStackedFS()

	// add the paths for overwriting the embedded resource files
	paths := getLocalOverwritePaths()
	for _, p := range paths {
		result.AddFS(os.DirFS(filepath.Join(p, "templates")))
	}

	// use the embedded variant as default if nothing else has matched
	subFS, err := fs.Sub(embeddedTemplates, "templates")
	if err != nil {
		return nil, err
	}
	result.AddFS(subFS)

	return result, nil
}

func getLocalOverwritePaths() []string {
	// override paths
	// 1. WORKING_DIR
	// 2. ~/BINARY_NAME/
	// 3. BINARY_DIR

	var (
		binaryName = "stackfs-test"
		folders []string
	)

	workingPath, err := os.Getwd()
	if err != nil {
		log.Fatal().Err(err).Msg("working dir not found")
	}

	home, err := os.UserHomeDir()
	if err != nil {
		log.Fatal().Err(err).Msg("home dir not found")
	}
	homePath := filepath.Join(home, "."+binaryName)

	binaryPath, err := osext.ExecutableFolder()
	if err != nil {
		log.Fatal().Err(err).Msg("binary path not found")
	}

	return append(folders, workingPath, homePath, binaryPath)
}