o/snapstate: move auxinfo functions to snapstate backend with metadata helpers

overlord/snapstate/aux_store_info.go → overlord/snapstate/backend/aux_store_info.go

@@ -1,7 +1,7 @@
 // -*- Mode: Go; indent-tabs-mode: t -*-
 
 /*
- * Copyright (C) 2018-2022 Canonical Ltd
+ * Copyright (C) 2018-2025 Canonical Ltd
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
@@ -17,7 +17,7 @@
  *
  */
 
-package snapstate
+package backend
 
 import (
 	"encoding/json"
@@ -30,27 +30,27 @@ import (
 	"github.com/snapcore/snapd/snap"
 )
 
-// auxStoreInfo is information about a snap (*not* a snap revision), not
+// AuxStoreInfo is information about a snap (*not* a snap revision), not
 // needed in the state, that may be stored to augment the information
 // returned for locally-installed snaps
-type auxStoreInfo struct {
+type AuxStoreInfo struct {
 	Media    snap.MediaInfos `json:"media,omitempty"`
 	StoreURL string          `json:"store-url,omitempty"`
 	// XXX this is now included in snap.SideInfo.EditedLinks but
 	// continue having this to support old snapd
 	Website string `json:"website,omitempty"`
 }
 
-func auxStoreInfoFilename(snapID string) string {
+func AuxStoreInfoFilename(snapID string) string {
 	return filepath.Join(dirs.SnapAuxStoreInfoDir, snapID) + ".json"
 }
 
-// retrieveAuxStoreInfo loads the stored per-snap auxiliary store info into the given *snap.Info
-func retrieveAuxStoreInfo(info *snap.Info) error {
+// RetrieveAuxStoreInfo loads the stored per-snap auxiliary store info into the given *snap.Info
+func RetrieveAuxStoreInfo(info *snap.Info) error {
 	if info.SnapID == "" {
 		return nil
 	}
-	f, err := os.Open(auxStoreInfoFilename(info.SnapID))
+	f, err := os.Open(AuxStoreInfoFilename(info.SnapID))
 	if err != nil {
 		if os.IsNotExist(err) {
 			return nil
@@ -59,7 +59,7 @@ func retrieveAuxStoreInfo(info *snap.Info) error {
 	}
 	defer f.Close()
 
-	var aux auxStoreInfo
+	var aux AuxStoreInfo
 	dec := json.NewDecoder(f)
 	if err := dec.Decode(&aux); err != nil {
 		return fmt.Errorf("cannot decode auxiliary store info for snap %q: %v", info.InstanceName(), err)
@@ -79,15 +79,15 @@ func retrieveAuxStoreInfo(info *snap.Info) error {
 }
 
 // keepAuxStoreInfo saves the given auxiliary store info to disk.
-func keepAuxStoreInfo(snapID string, aux *auxStoreInfo) error {
+func keepAuxStoreInfo(snapID string, aux AuxStoreInfo) error {
 	if snapID == "" {
 		return nil
 	}
 	if err := os.MkdirAll(dirs.SnapAuxStoreInfoDir, 0755); err != nil {
 		return fmt.Errorf("cannot create directory for auxiliary store info: %v", err)
 	}
 
-	af, err := osutil.NewAtomicFile(auxStoreInfoFilename(snapID), 0644, 0, osutil.NoChown, osutil.NoChown)
+	af, err := osutil.NewAtomicFile(AuxStoreInfoFilename(snapID), 0644, 0, osutil.NoChown, osutil.NoChown)
 	if err != nil {
 		return fmt.Errorf("cannot create file for auxiliary store info for snap %s: %v", snapID, err)
 	}
@@ -109,7 +109,7 @@ func discardAuxStoreInfo(snapID string) error {
 	if snapID == "" {
 		return nil
 	}
-	if err := os.Remove(auxStoreInfoFilename(snapID)); err != nil && !os.IsNotExist(err) {
+	if err := os.Remove(AuxStoreInfoFilename(snapID)); err != nil && !os.IsNotExist(err) {
 		return fmt.Errorf("cannot remove auxiliary store info file for snap %s: %v", snapID, err)
 	}
 	return nil

overlord/snapstate/aux_store_info_test.go → overlord/snapstate/backend/aux_store_info_test.go

@@ -1,7 +1,7 @@
 // -*- Mode: Go; indent-tabs-mode: t -*-
 
 /*
- * Copyright (C) 2018-2022 Canonical Ltd
+ * Copyright (C) 2018-2025 Canonical Ltd
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
@@ -17,7 +17,7 @@
  *
  */
 
-package snapstate_test
+package backend_test
 
 import (
 	"path/filepath"
@@ -26,7 +26,7 @@ import (
 
 	"github.com/snapcore/snapd/dirs"
 	"github.com/snapcore/snapd/osutil"
-	"github.com/snapcore/snapd/overlord/snapstate"
+	"github.com/snapcore/snapd/overlord/snapstate/backend"
 	"github.com/snapcore/snapd/snap"
 )
 
@@ -40,30 +40,30 @@ func (s *auxInfoSuite) SetUpTest(c *check.C) {
 
 func (s *auxInfoSuite) TestAuxStoreInfoFilename(c *check.C) {
 	// precondition check
-	filename := snapstate.AuxStoreInfoFilename("some-snap-id")
+	filename := backend.AuxStoreInfoFilename("some-snap-id")
 	c.Check(filename, check.Equals, filepath.Join(dirs.SnapAuxStoreInfoDir, "some-snap-id.json"))
 }
 
 func (s *auxInfoSuite) TestAuxStoreInfoRoundTrip(c *check.C) {
 	media := snap.MediaInfos{{Type: "1-2-3-testing"}}
 	info := &snap.Info{SuggestedName: "some-snap"}
 	info.SnapID = "some-id"
-	filename := snapstate.AuxStoreInfoFilename(info.SnapID)
+	filename := backend.AuxStoreInfoFilename(info.SnapID)
 	c.Assert(osutil.FileExists(filename), check.Equals, false)
-	c.Check(snapstate.RetrieveAuxStoreInfo(info), check.IsNil)
+	c.Check(backend.RetrieveAuxStoreInfo(info), check.IsNil)
 	c.Check(info.Media, check.HasLen, 0)
 	c.Check(info.Website(), check.Equals, "")
 	c.Check(info.StoreURL, check.Equals, "")
 
-	aux := &snapstate.AuxStoreInfo{
+	aux := backend.AuxStoreInfo{
 		Media:    media,
 		Website:  "http://example.com/some-snap",
 		StoreURL: "https://snapcraft.io/some-snap",
 	}
-	c.Assert(snapstate.KeepAuxStoreInfo(info.SnapID, aux), check.IsNil)
+	c.Assert(backend.KeepAuxStoreInfo(info.SnapID, aux), check.IsNil)
 	c.Check(osutil.FileExists(filename), check.Equals, true)
 
-	c.Assert(snapstate.RetrieveAuxStoreInfo(info), check.IsNil)
+	c.Assert(backend.RetrieveAuxStoreInfo(info), check.IsNil)
 	c.Check(info.Media, check.HasLen, 1)
 	c.Check(info.Media, check.DeepEquals, media)
 	c.Check(info.Website(), check.Equals, "http://example.com/some-snap")
@@ -75,7 +75,7 @@ func (s *auxInfoSuite) TestAuxStoreInfoRoundTrip(c *check.C) {
 	info.EditedLinks = map[string][]string{
 		"website": {"http://newer-website-com"},
 	}
-	c.Assert(snapstate.RetrieveAuxStoreInfo(info), check.IsNil)
+	c.Assert(backend.RetrieveAuxStoreInfo(info), check.IsNil)
 	c.Check(info.Media, check.HasLen, 1)
 	c.Check(info.Media, check.DeepEquals, media)
 	c.Check(info.Website(), check.Equals, "http://newer-website-com")
@@ -86,13 +86,13 @@ func (s *auxInfoSuite) TestAuxStoreInfoRoundTrip(c *check.C) {
 	info.LegacyWebsite = ""
 	info.StoreURL = ""
 
-	c.Assert(snapstate.DiscardAuxStoreInfo(info.SnapID), check.IsNil)
+	c.Assert(backend.DiscardAuxStoreInfo(info.SnapID), check.IsNil)
 	c.Assert(osutil.FileExists(filename), check.Equals, false)
 
-	c.Check(snapstate.RetrieveAuxStoreInfo(info), check.IsNil)
+	c.Check(backend.RetrieveAuxStoreInfo(info), check.IsNil)
 	c.Check(info.Media, check.HasLen, 0)
 	c.Check(info.Website(), check.Equals, "")
 	c.Check(info.StoreURL, check.Equals, "")
 
-	c.Check(snapstate.DiscardAuxStoreInfo(info.SnapID), check.IsNil)
+	c.Check(backend.DiscardAuxStoreInfo(info.SnapID), check.IsNil)
 }

overlord/snapstate/backend/export_test.go

@@ -36,6 +36,9 @@ var (
 	RemoveIfEmpty      = removeIfEmpty
 	SnapDataDirs       = snapDataDirs
 	SnapCommonDataDirs = snapCommonDataDirs
+
+	KeepAuxStoreInfo    = keepAuxStoreInfo
+	DiscardAuxStoreInfo = discardAuxStoreInfo
 )
 
 func MockWrappersAddSnapdSnapServices(f func(s *snap.Info, opts *wrappers.AddSnapdSnapServicesOptions, inter wrappers.Interacter) (wrappers.SnapdRestart, error)) (restore func()) {

overlord/snapstate/backend/metadata.go

@@ -0,0 +1,76 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2025 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package backend
+
+// InstallStoreMetadata saves revision-agnostic metadata to disk for the snap
+// with the given snap ID. At the moment, this metadata includes auxiliary
+// store information. Returns a closure to undo the function's actions,
+// depending on whether it's a first install or if there are other instances.
+func InstallStoreMetadata(snapID string, aux AuxStoreInfo, linkCtx LinkContext) (undo func(), err error) {
+	if snapID == "" {
+		return func() {}, nil
+	}
+	if err := keepAuxStoreInfo(snapID, aux); err != nil {
+		return nil, err
+	}
+	// TODO: install other types of revision-agnostic metadata
+	return func() {
+		UninstallStoreMetadata(snapID, linkCtx)
+	}, nil
+}
+
+// UninstallStoreMetadata removes revision-agnostic metadata from disk for the
+// snap with the given snap ID. At the moment, this metadata includes auxiliary
+// store information. The given linkCtx governs what metadata is removed and
+// what is preserved.
+func UninstallStoreMetadata(snapID string, linkCtx LinkContext) error {
+	if linkCtx.HasOtherInstances || snapID == "" {
+		return nil
+	}
+	if linkCtx.FirstInstall {
+		// only discard aux store info if there are no other revision of the
+		// snap present, in case we want to roll-back the discard, and need the
+		// auxinfo on disk to re-populate an old snap.Info. This might occur if
+		// e.g. we unlinked the snap and now need to undoUnlinkSnap.
+		if err := discardAuxStoreInfo(snapID); err != nil {
+			return err
+		}
+	}
+	// TODO: discard other types of revision-agnostic metadata
+	return nil
+}
+
+// DiscardStoreMetadata removes revision-agnostic metadata from disk for the
+// snap with the given snap ID, and is intended to be called when the final
+// revision of that snap is being discarded. At the moment, this metadata
+// includes auxiliary store information. If hasOtherInstances is false, this
+// function does nothing, as another instance of the same snap may still
+// require this metadata.
+func DiscardStoreMetadata(snapID string, hasOtherInstances bool) error {
+	if hasOtherInstances || snapID == "" {
+		return nil
+	}
+	if err := discardAuxStoreInfo(snapID); err != nil {
+		return err
+	}
+	// TODO: discard other types of revision-agnostic metadata which should be
+	// removed when the final revision of the snap is discarded
+	return nil
+}