This package provides a simplified in memory filesystem intended to make it easy to test packages that use the os filesystem.
If your filesystem package uses these interfaces to interact with the OS
filesystem, then they can be swapped out in test with
the in memory filesystem. For example, instead of using os.Open:
file, err := fs.Open(filename) |
var fs FS = osFS{}
type File interface {
io.Closer
io.Reader
io.ReaderAt
io.Seeker
io.Writer
io.WriterAt
Stat() (os.FileInfo, error)
Name() string
ReadDir(n int) ([]os.DirEntry, error)
Readdir(count int) ([]os.FileInfo, error)
Readdirnames(n int) ([]string, error)
}
type FS interface {
Open(name string) (File, error)
Create(name string) (File, error)
Stat(name string) (os.FileInfo, error)
Remove(name string) error
CreateTemp(dir, pattern string) (File, error)
MkdirAll(path string, perm os.FileMode) error
RemoveAll(path string) error
ReadDir(name string) ([]os.DirEntry, error)
MkdirTemp(dir, pattern string) (name string, err error)
TempDir() string
}
// osFS implements FS using the local disk.
type osFS struct{}
func (osFS) Open(name string) (File, error) { return os.Open(name) }
func (osFS) Create(name string) (File, error) { return os.Create(name) }
func (osFS) Stat(name string) (os.FileInfo, error) { return os.Stat(name) }
func (osFS) Remove(name string) error { return os.Remove(name) }
func (osFS) CreateTemp(dir, pattern string) (File, error) { return os.CreateTemp(dir, pattern) }
func (osFS) MkdirAll(path string, perms os.FileMode) error { return os.MkdirAll(path, perms) }
func (osFS) RemoveAll(path string) error { return os.RemoveAll(path) }
func (osFS) ReadDir(name string) ([]os.DirEntry, error) { return os.ReadDir(name) }
func (osFS) MkdirTemp(dir, pattern string) (name string, err error) { return os.MkdirTemp(dir, pattern) }
func (osFS) TempDir() string { return os.TempDir() } |
Using the interfaces then allows for the fs global variable to be swapped out
with an in memory instance.
// memFS implements FS using an in memory filesystem
type memFS struct{ fs *memfs.FS }
func (mfs *memFS) Open(name string) (File, error) { return mfs.fs.Open(name) }
func (mfs *memFS) Create(name string) (File, error) { return mfs.fs.Create(name) }
func (mfs *memFS) Stat(name string) (os.FileInfo, error) { return mfs.fs.Stat(name) }
func (mfs *memFS) Remove(name string) error { return mfs.fs.Remove(name) }
func (mfs *memFS) CreateTemp(dir, pattern string) (File, error) { return mfs.fs.CreateTemp(dir, pattern) }
func (mfs *memFS) MkdirAll(path string, perms os.FileMode) error { return mfs.fs.MkdirAll(path, perms) }
func (mfs *memFS) RemoveAll(path string) error { return mfs.fs.RemoveAll(path) }
func (mfs *memFS) ReadDir(name string) ([]os.DirEntry, error) { return mfs.fs.ReadDir(name) }
func (mfs *memFS) MkdirTemp(dir, pattern string) (name string, err error) { return mfs.fs.MkdirTemp(dir, pattern) }
func (mfs *memFS) TempDir() string { return mfs.fs.TempDir() }
fs = &memFS{fs: memfs.New()}
package main
import (
"bufio"
"errors"
"fmt"
"github.com/mbordner/memfs"
"io"
"os"
"path/filepath"
)
var fs FS = osFS{}
type File interface {
io.Closer
io.Reader
io.ReaderAt
io.Seeker
io.Writer
io.WriterAt
Stat() (os.FileInfo, error)
Name() string
ReadDir(n int) ([]os.DirEntry, error)
Readdir(count int) ([]os.FileInfo, error)
Readdirnames(n int) ([]string, error)
}
type FS interface {
Open(name string) (File, error)
Create(name string) (File, error)
Stat(name string) (os.FileInfo, error)
Remove(name string) error
CreateTemp(dir, pattern string) (File, error)
MkdirAll(path string, perm os.FileMode) error
RemoveAll(path string) error
ReadDir(name string) ([]os.DirEntry, error)
MkdirTemp(dir, pattern string) (name string, err error)
TempDir() string
}
// osFS implements FS using the local disk.
type osFS struct{}
func (osFS) Open(name string) (File, error) { return os.Open(name) }
func (osFS) Create(name string) (File, error) { return os.Create(name) }
func (osFS) Stat(name string) (os.FileInfo, error) { return os.Stat(name) }
func (osFS) Remove(name string) error { return os.Remove(name) }
func (osFS) CreateTemp(dir, pattern string) (File, error) { return os.CreateTemp(dir, pattern) }
func (osFS) MkdirAll(path string, perms os.FileMode) error { return os.MkdirAll(path, perms) }
func (osFS) RemoveAll(path string) error { return os.RemoveAll(path) }
func (osFS) ReadDir(name string) ([]os.DirEntry, error) { return os.ReadDir(name) }
func (osFS) MkdirTemp(dir, pattern string) (name string, err error) {
return os.MkdirTemp(dir, pattern)
}
func (osFS) TempDir() string { return os.TempDir() }
// memFS implements FS using an in memory filesystem
type memFS struct{ fs *memfs.FS }
func (mfs *memFS) Open(name string) (File, error) { return mfs.fs.Open(name) }
func (mfs *memFS) Create(name string) (File, error) { return mfs.fs.Create(name) }
func (mfs *memFS) Stat(name string) (os.FileInfo, error) { return mfs.fs.Stat(name) }
func (mfs *memFS) Remove(name string) error { return mfs.fs.Remove(name) }
func (mfs *memFS) CreateTemp(dir, pattern string) (File, error) {
return mfs.fs.CreateTemp(dir, pattern)
}
func (mfs *memFS) MkdirAll(path string, perms os.FileMode) error { return mfs.fs.MkdirAll(path, perms) }
func (mfs *memFS) RemoveAll(path string) error { return mfs.fs.RemoveAll(path) }
func (mfs *memFS) ReadDir(name string) ([]os.DirEntry, error) { return mfs.fs.ReadDir(name) }
func (mfs *memFS) MkdirTemp(dir, pattern string) (name string, err error) {
return mfs.fs.MkdirTemp(dir, pattern)
}
func (mfs *memFS) TempDir() string { return mfs.fs.TempDir() }
func main() {
fs = &memFS{fs: memfs.New()}
fmt.Println(fs.TempDir())
err := WriteContent("/test/test", []byte(`test data`))
if err != nil {
panic(err)
}
data, err := GetContent("/test/test")
if err != nil {
panic(err)
}
fmt.Println(string(data))
}
// GetContent returns the contents for a File
func GetContent(filename string) ([]byte, error) {
file, err := fs.Open(filename)
if err != nil {
return nil, err
}
defer func() {
_ = file.Close()
}()
fileInfo, err := file.Stat()
if err != nil {
return nil, err
}
filesize := fileInfo.Size()
buffer := make([]byte, filesize)
bytesRead, err := file.Read(buffer)
if err != nil {
return nil, err
}
if bytesRead != int(filesize) {
return nil, errors.New("didn't read all of the File")
}
return buffer, nil
}
// WriteContent writes bytes to a File replacing the existing File or creating new
func WriteContent(filename string, data []byte) error {
dir := filepath.Dir(filename)
if _, err := fs.Stat(dir); errors.Is(err, os.ErrNotExist) {
_ = fs.MkdirAll(dir, 0700) // Create your File
}
f, err := fs.Create(filename)
if err != nil {
return err
}
w := bufio.NewWriter(f)
defer func() {
_ = f.Close()
}()
_, err = w.Write(data)
if err != nil {
return err
}
err = w.Flush()
if err != nil {
return err
}
return nil
}