filemapping: add support for io/fs (including e.g. go:embed filesyste…

…ms) (#16)

* filemapping: add support for io/fs (including e.g. go:embed filesystems)

* fix: *os.File build error on Windows

* tests: document & unit test io/fs

* tests: use go:embed for testing & push minimum Go version to 1.18

* fix: missing imports in windows filemapping

* fix: another missing import

README.md

@@ -18,9 +18,13 @@ requiring a context string respectively.
 ```go
 import "github.com/snapcore/go-gettext"
 
+//go:embed translations
+var assets embed.FS
+
 domain := &gettext.TextDomain{
 	Name:      "messages",
-	LocaleDir: "path/to/translations",
+	LocaleDir: "./translations",
+	LocaleFS:  assets,  // leave away to use the filesystem directly
 }
 // or use domain.Locale(lang...) to open a different locale's catalog
 locale := domain.UserLocale()

filemapping.go

@@ -2,8 +2,8 @@ package gettext
 
 import (
 	"fmt"
+	"io/fs"
 	"io/ioutil"
-	"os"
 	"runtime"
 )
 
@@ -21,7 +21,7 @@ func (m *fileMapping) Close() error {
 	return m.closeMapping()
 }
 
-func openMapping(f *os.File) (*fileMapping, error) {
+func openMapping(f fs.File) (*fileMapping, error) {
 	fi, err := f.Stat()
 	if err != nil {
 		return nil, err

filemapping_unix.go

@@ -1,15 +1,22 @@
+//go:build !windows
 // +build !windows
 
 package gettext
 
 import (
+	"errors"
+	"io/fs"
 	"os"
 	"syscall"
 )
 
-func (m *fileMapping) tryMap(f *os.File, size int64) error {
+func (m *fileMapping) tryMap(f fs.File, size int64) error {
 	var err error
-	m.data, err = syscall.Mmap(int(f.Fd()), 0, int(size), syscall.PROT_READ, syscall.MAP_PRIVATE)
+	of, ok := f.(*os.File)
+	if !ok {
+		return errors.New("virtual filesystem doesn't support mmap")
+	}
+	m.data, err = syscall.Mmap(int(of.Fd()), 0, int(size), syscall.PROT_READ, syscall.MAP_PRIVATE)
 	if err != nil {
 		return err
 	}

filemapping_windows.go

@@ -1,16 +1,22 @@
 package gettext
 
 import (
+	"errors"
+	"io/fs"
 	"os"
 	"syscall"
 	"unsafe"
 )
 
 // Adapted from https://github.com/golang/exp/blob/master/mmap/mmap_windows.go
 
-func (m *fileMapping) tryMap(f *os.File, size int64) error {
+func (m *fileMapping) tryMap(f fs.File, size int64) error {
+	of, ok := f.(*os.File)
+	if !ok {
+		return errors.New("virtual filesystem doesn't support mmap")
+	}
 	low, high := uint32(size), uint32(size>>32)
-	fmap, err := syscall.CreateFileMapping(syscall.Handle(f.Fd()), nil, syscall.PAGE_READONLY, high, low, nil)
+	fmap, err := syscall.CreateFileMapping(syscall.Handle(of.Fd()), nil, syscall.PAGE_READONLY, high, low, nil)
 	if err != nil {
 		return err
 	}

gettext.go

@@ -4,6 +4,7 @@ package gettext
 
 import (
 	"fmt"
+	"io/fs"
 	"os"
 	"path"
 	"sync"
@@ -17,8 +18,11 @@ type TextDomain struct {
 	// Name is the name of the text domain
 	Name string
 	// LocaleDir is the base directory holding translations of the
-	// domain.  If it is empty, DefaultLocaleDir will be used.
+	// domain.  If it is empty, DefaultLocaleDir will be used if LocaleFS is nil; otherwise the root of LocaleFS will be used.
 	LocaleDir string
+	// LocaleFS is the filesystem used to access LocaleDir.
+	// When nil, the normal OS filesystem will be used.
+	LocaleFS fs.FS
 	// PathResolver is called to determine the path of a
 	// particular locale's translations.  If it is nil then
 	// DefaultResolver will be used, which implements the standard
@@ -62,7 +66,7 @@ func (t *TextDomain) load(locale string) *mocatalog {
 	}
 
 	localeDir := t.LocaleDir
-	if localeDir == "" {
+	if localeDir == "" && t.LocaleFS == nil {
 		localeDir = DefaultLocaleDir
 	}
 	resolver := t.PathResolver
@@ -71,7 +75,13 @@ func (t *TextDomain) load(locale string) *mocatalog {
 	}
 	t.cache[locale] = nil
 	path := resolver(localeDir, locale, t.Name)
-	f, err := os.Open(path)
+	var f fs.File
+	var err error
+	if t.LocaleFS != nil {
+		f, err = t.LocaleFS.Open(path)
+	} else {
+		f, err = os.Open(path)
+	}
 	if err != nil {
 		return nil
 	}

gettext_test.go

@@ -1,6 +1,7 @@
 package gettext
 
 import (
+	"embed"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -271,3 +272,12 @@ func TestNotMoFile(t *testing.T) {
 	)
 
 }
+
+//go:embed testdata
+var assets embed.FS
+
+func TestFS(t *testing.T) {
+	translations := &TextDomain{Name: "messages", LocaleDir: "testdata", LocaleFS: assets, PathResolver: my_resolver}
+	en := translations.Locale("en")
+	assert_equal(t, en.Gettext("greeting"), "Hello")
+}

go.mod

@@ -1,3 +1,3 @@
 module github.com/snapcore/go-gettext
 
-go 1.13
+go 1.18

mofile.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
+	"io/fs"
 	"os"
 	"sort"
 	"strings"
@@ -223,7 +224,7 @@ func ParseMO(file *os.File) (Catalog, error) {
 	return Catalog{[]*mocatalog{mo}}, nil
 }
 
-func parseMO(file *os.File) (*mocatalog, error) {
+func parseMO(file fs.File) (*mocatalog, error) {
 	m, err := openMapping(file)
 	if err != nil {
 		return nil, err