From 64258a2c2aa8a178afed12e886658698251eb81a Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Sun, 22 Aug 2021 17:58:21 +0200
Subject: [PATCH 1/3] rebuild-index: Ignore broken index files

Previously, an e.g. truncated index could prevent rebuild-index from
working.
---
 cmd/restic/cmd_rebuild_index.go | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/cmd/restic/cmd_rebuild_index.go b/cmd/restic/cmd_rebuild_index.go
index 707309e64..718d2c767 100644
--- a/cmd/restic/cmd_rebuild_index.go
+++ b/cmd/restic/cmd_rebuild_index.go
@@ -73,7 +73,27 @@ func rebuildIndex(opts RebuildIndexOptions, gopts GlobalOptions, repo *repositor
 		}
 	} else {
 		Verbosef("loading indexes...\n")
-		err := repo.LoadIndex(gopts.ctx)
+		mi := repository.NewMasterIndex()
+		err := repository.ForAllIndexes(ctx, repo, func(id restic.ID, idx *repository.Index, oldFormat bool, err error) error {
+			if err != nil {
+				Warnf("removing invalid index %v: %v\n", id, err)
+				obsoleteIndexes = append(obsoleteIndexes, id)
+				return nil
+			}
+
+			mi.Insert(idx)
+			return nil
+		})
+		if err != nil {
+			return err
+		}
+
+		err = mi.MergeFinalIndexes()
+		if err != nil {
+			return err
+		}
+
+		err = repo.SetIndex(mi)
 		if err != nil {
 			return err
 		}

From 877fc9f3526e94e4bf8b9537fc4d9e5ee2beef79 Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Sun, 22 Aug 2021 18:24:19 +0200
Subject: [PATCH 2/3] rebuild-index: test that invalid indexes are skipped and
 removed

---
 cmd/restic/integration_test.go | 55 ++++++++++++++++++++++++++++++++--
 1 file changed, 53 insertions(+), 2 deletions(-)

diff --git a/cmd/restic/integration_test.go b/cmd/restic/integration_test.go
index 463ea0d39..545d3f6e8 100644
--- a/cmd/restic/integration_test.go
+++ b/cmd/restic/integration_test.go
@@ -15,6 +15,7 @@ import (
 	"regexp"
 	"runtime"
 	"strings"
+	"sync"
 	"syscall"
 	"testing"
 	"time"
@@ -1416,7 +1417,7 @@ func TestFindJSON(t *testing.T) {
 	rtest.Assert(t, matches[0].Hits == 3, "expected hits to show 3 matches (%v)", datafile)
 }
 
-func TestRebuildIndex(t *testing.T) {
+func testRebuildIndex(t *testing.T, backendTestHook backendWrapper) {
 	env, cleanup := withTestEnvironment(t)
 	defer cleanup()
 
@@ -1436,8 +1437,10 @@ func TestRebuildIndex(t *testing.T) {
 		t.Fatalf("did not find hint for rebuild-index command")
 	}
 
+	env.gopts.backendTestHook = backendTestHook
 	testRunRebuildIndex(t, env.gopts)
 
+	env.gopts.backendTestHook = nil
 	out, err = testRunCheckOutput(env.gopts)
 	if len(out) != 0 {
 		t.Fatalf("expected no output from the checker, got: %v", out)
@@ -1448,9 +1451,57 @@ func TestRebuildIndex(t *testing.T) {
 	}
 }
 
+func TestRebuildIndex(t *testing.T) {
+	testRebuildIndex(t, nil)
+}
+
 func TestRebuildIndexAlwaysFull(t *testing.T) {
+	indexFull := repository.IndexFull
+	defer func() {
+		repository.IndexFull = indexFull
+	}()
 	repository.IndexFull = func(*repository.Index) bool { return true }
-	TestRebuildIndex(t)
+	testRebuildIndex(t, nil)
+}
+
+// indexErrorBackend modifies the first index after reading.
+type indexErrorBackend struct {
+	restic.Backend
+	lock     sync.Mutex
+	hasErred bool
+}
+
+func (b *indexErrorBackend) Load(ctx context.Context, h restic.Handle, length int, offset int64, consumer func(rd io.Reader) error) error {
+	return b.Backend.Load(ctx, h, length, offset, func(rd io.Reader) error {
+		// protect hasErred
+		b.lock.Lock()
+		defer b.lock.Unlock()
+		if !b.hasErred && h.Type == restic.IndexFile {
+			b.hasErred = true
+			return consumer(errorReadCloser{rd})
+		}
+		return consumer(rd)
+	})
+}
+
+type errorReadCloser struct {
+	io.Reader
+}
+
+func (erd errorReadCloser) Read(p []byte) (int, error) {
+	n, err := erd.Reader.Read(p)
+	if n > 0 {
+		p[0] ^= 1
+	}
+	return n, err
+}
+
+func TestRebuildIndexDamage(t *testing.T) {
+	testRebuildIndex(t, func(r restic.Backend) (restic.Backend, error) {
+		return &indexErrorBackend{
+			Backend: r,
+		}, nil
+	})
 }
 
 type appendOnlyBackend struct {

From 194ed195579894776028d55ca6365707d1704d6d Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Sun, 22 Aug 2021 18:29:58 +0200
Subject: [PATCH 3/3] Add changelog

---
 changelog/unreleased/pull-3488 | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 changelog/unreleased/pull-3488

diff --git a/changelog/unreleased/pull-3488 b/changelog/unreleased/pull-3488
new file mode 100644
index 000000000..5157448f5
--- /dev/null
+++ b/changelog/unreleased/pull-3488
@@ -0,0 +1,7 @@
+Bugfix: rebuild-index failed if an index file was damaged
+
+The `rebuild-index` command failed with an error if an index file was damaged
+or truncated. This has been fixed. A (slow) workaround is to use
+`rebuild-index --read-all-packs` or to manually delete the damaged index.
+
+https://github.com/restic/restic/pull/3488