GODT-1916: Use XDG_DATA_HOME to store persistent data on linux

This change ensures persistent data is stored in XDG_DATA_HOME
instead of XDG_CACHE_HOME on linux.

It adds the UserData() method on locations.Provider to return a path
suitable for storing persistent data. On linux, this returns
$XDG_DATA_HOME/protonmail (likely ~/.local/share/protonmail), and on
non-linux this returns os.UserConfigDir() because that is assumed
to be a more persistent location than os.UserCacheDir().

locations.Locations has been modified to use this new data directory;
gluon and logs are now stored here.

internal/bridge/mocks.go

@@ -63,7 +63,7 @@ func (j *TestCookieJar) Cookies(u *url.URL) []*http.Cookie {
 }
 
 type TestLocationsProvider struct {
-	config, cache string
+	config, data, cache string
 }
 
 func NewTestLocationsProvider(dir string) *TestLocationsProvider {
@@ -72,6 +72,11 @@ func NewTestLocationsProvider(dir string) *TestLocationsProvider {
 		panic(err)
 	}
 
+	data, err := os.MkdirTemp(dir, "data")
+	if err != nil {
+		panic(err)
+	}
+
 	cache, err := os.MkdirTemp(dir, "cache")
 	if err != nil {
 		panic(err)
@@ -79,6 +84,7 @@ func NewTestLocationsProvider(dir string) *TestLocationsProvider {
 
 	return &TestLocationsProvider{
 		config: config,
+		data:   data,
 		cache:  cache,
 	}
 }
@@ -87,6 +93,10 @@ func (provider *TestLocationsProvider) UserConfig() string {
 	return provider.config
 }
 
+func (provider *TestLocationsProvider) UserData() string {
+	return provider.data
+}
+
 func (provider *TestLocationsProvider) UserCache() string {
 	return provider.cache
 }

internal/locations/locations.go

@@ -36,16 +36,26 @@ import (
 // - updates: ~/.config/protonmail/<app>/updates
 // - lockfile: ~/.cache/protonmail/<app>/<app>.lock .
 type Locations struct {
-	userConfig, userCache string
-	configName            string
-	configGuiName         string
+	// userConfig is the path to the user config directory, for storing persistent config data.
+	userConfig string
+
+	// userData is the path to the user data directory, for storing persistent data.
+	userData string
+
+	// userCache is the path to the user cache directory, for storing non-essential data.
+	userCache string
+
+	configName    string
+	configGuiName string
 }
 
 // New returns a new locations object.
 func New(provider Provider, configName string) *Locations {
 	return &Locations{
-		userConfig:    provider.UserConfig(),
-		userCache:     provider.UserCache(),
+		userConfig: provider.UserConfig(),
+		userData:   provider.UserData(),
+		userCache:  provider.UserCache(),
+
 		configName:    configName,
 		configGuiName: configName + "-gui",
 	}
@@ -178,7 +188,7 @@ func (l *Locations) GetOldUpdatesPath() string {
 }
 
 func (l *Locations) getGluonPath() string {
-	return filepath.Join(l.userCache, "gluon")
+	return filepath.Join(l.userData, "gluon")
 }
 
 func (l *Locations) getGUICertPath() string {
@@ -190,7 +200,7 @@ func (l *Locations) getSettingsPath() string {
 }
 
 func (l *Locations) getLogsPath() string {
-	return filepath.Join(l.userCache, "logs")
+	return filepath.Join(l.userData, "logs")
 }
 
 func (l *Locations) getGoIMAPCachePath() string {
@@ -215,6 +225,7 @@ func (l *Locations) getUpdatesPath() string {
 func (l *Locations) Clear() error {
 	return files.Remove(
 		l.userConfig,
+		l.userData,
 		l.userCache,
 	).Except(
 		l.GetGuiLockFile(),
@@ -232,7 +243,10 @@ func (l *Locations) ClearUpdates() error {
 // Clean removes any unexpected files from the app cache folder
 // while leaving files in the standard locations untouched.
 func (l *Locations) Clean() error {
-	return files.Remove(l.userCache).Except(
+	return files.Remove(
+		l.userCache,
+		l.userData,
+	).Except(
 		l.GetGuiLockFile(),
 		l.getLogsPath(),
 		l.getUpdatesPath(),

internal/locations/locations_test.go

@@ -27,13 +27,17 @@ import (
 )
 
 type fakeAppDirs struct {
-	configDir, cacheDir string
+	configDir, dataDir, cacheDir string
 }
 
 func (dirs *fakeAppDirs) UserConfig() string {
 	return dirs.configDir
 }
 
+func (dirs *fakeAppDirs) UserData() string {
+	return dirs.dataDir
+}
+
 func (dirs *fakeAppDirs) UserCache() string {
 	return dirs.cacheDir
 }
@@ -134,6 +138,7 @@ func TestRemoveOldGoIMAPCacheFolders(t *testing.T) {
 func newFakeAppDirs(t *testing.T) *fakeAppDirs {
 	return &fakeAppDirs{
 		configDir: t.TempDir(),
+		dataDir:   t.TempDir(),
 		cacheDir:  t.TempDir(),
 	}
 }

internal/locations/provider.go

@@ -18,19 +18,22 @@
 package locations
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
+	"runtime"
 )
 
 // Provider provides standard locations.
 type Provider interface {
 	UserConfig() string
+	UserData() string
 	UserCache() string
 }
 
 // DefaultProvider is a locations provider using the system-default storage locations.
 type DefaultProvider struct {
-	config, cache string
+	config, data, cache string
 }
 
 func NewDefaultProvider(name string) (*DefaultProvider, error) {
@@ -39,6 +42,11 @@ func NewDefaultProvider(name string) (*DefaultProvider, error) {
 		return nil, err
 	}
 
+	data, err := userDataDir()
+	if err != nil {
+		return nil, err
+	}
+
 	cache, err := os.UserCacheDir()
 	if err != nil {
 		return nil, err
@@ -46,14 +54,44 @@ func NewDefaultProvider(name string) (*DefaultProvider, error) {
 
 	return &DefaultProvider{
 		config: filepath.Join(config, name),
+		data:   filepath.Join(data, name),
 		cache:  filepath.Join(cache, name),
 	}, nil
 }
 
+// UserConfig returns a directory that can be used to store user-specific configuration.
+// $XDG_CONFIG_HOME/protonmail is used on Unix systems; similar on others.
 func (p *DefaultProvider) UserConfig() string {
 	return p.config
 }
 
+// UserData returns a directory that can be used to store user-specific data.
+// $XDG_DATA_HOME/protonmail is used on Unix systems; similar on others.
+func (p *DefaultProvider) UserData() string {
+	return p.data
+}
+
+// UserCache returns a directory that can be used to store user-specific non-essential data.
+// $XDG_CACHE_HOME/protonmail is used on Unix systems; similar on others.
 func (p *DefaultProvider) UserCache() string {
 	return p.cache
 }
+
+// userDataDir returns a directory that can be used to store user-specific data.
+// This is necessary because os.UserDataDir() is not implemented by the Go standard library, sadly.
+// On non-linux systems, it is the same as os.UserConfigDir().
+func userDataDir() (string, error) {
+	if runtime.GOOS != "linux" {
+		return os.UserConfigDir()
+	}
+
+	if dir := os.Getenv("XDG_DATA_HOME"); dir != "" {
+		return dir, nil
+	}
+
+	if dir := os.Getenv("HOME"); dir != "" {
+		return filepath.Join(dir, ".local", "share"), nil
+	}
+
+	return "", errors.New("neither $XDG_DATA_HOME nor $HOME are defined")
+}