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Merge pull request #3164 from MichaelEischer/improve-context-cancel

Improve context cancel handling in archiver and backends
This commit is contained in:
Alexander Neumann 2020-12-29 17:03:42 +01:00 committed by GitHub
commit b2efa0af39
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5 changed files with 125 additions and 1 deletions

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@ -0,0 +1,9 @@
Bugfix: Never create invalid snapshots on backup interruption
When canceling a backup run in the wrong moment it was possible that
restic created a snapshot with an invalid "null" tree. This caused
check and other operations to fail. The backup command now properly
handles interruptions and never saves a snapshot in that case.
https://github.com/restic/restic/issues/3151
https://github.com/restic/restic/pull/3164

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@ -178,6 +178,10 @@ func (arch *Archiver) saveTree(ctx context.Context, t *restic.Tree) (restic.ID,
s.TreeBlobs++
s.TreeSize += uint64(len(buf))
}
// The context was canceled in the meantime, res.ID() might be invalid
if ctx.Err() != nil {
return restic.ID{}, s, ctx.Err()
}
return res.ID(), s, nil
}
@ -803,7 +807,8 @@ func (arch *Archiver) Snapshot(ctx context.Context, targets []string, opts Snaps
t.Kill(nil)
werr := t.Wait()
debug.Log("err is %v, werr is %v", err, werr)
if err == nil || errors.Cause(err) == context.Canceled {
// Use werr when it might contain a more specific error than "context canceled"
if err == nil || (errors.Cause(err) == context.Canceled && werr != nil) {
err = werr
}

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@ -3,6 +3,7 @@ package archiver
import (
"bytes"
"context"
"io"
"io/ioutil"
"os"
"path/filepath"
@ -15,6 +16,7 @@ import (
"time"
"github.com/google/go-cmp/cmp"
"github.com/restic/restic/internal/backend/mem"
"github.com/restic/restic/internal/checker"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/fs"
@ -1814,6 +1816,69 @@ func TestArchiverErrorReporting(t *testing.T) {
}
}
type noCancelBackend struct {
restic.Backend
}
func (c *noCancelBackend) Test(ctx context.Context, h restic.Handle) (bool, error) {
return c.Backend.Test(context.Background(), h)
}
func (c *noCancelBackend) Remove(ctx context.Context, h restic.Handle) error {
return c.Backend.Remove(context.Background(), h)
}
func (c *noCancelBackend) Save(ctx context.Context, h restic.Handle, rd restic.RewindReader) error {
return c.Backend.Save(context.Background(), h, rd)
}
func (c *noCancelBackend) Load(ctx context.Context, h restic.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
return c.Backend.Load(context.Background(), h, length, offset, fn)
}
func (c *noCancelBackend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, error) {
return c.Backend.Stat(context.Background(), h)
}
func (c *noCancelBackend) List(ctx context.Context, t restic.FileType, fn func(restic.FileInfo) error) error {
return c.Backend.List(context.Background(), t, fn)
}
func (c *noCancelBackend) Delete(ctx context.Context) error {
return c.Backend.Delete(context.Background())
}
func TestArchiverContextCanceled(t *testing.T) {
ctx, cancel := context.WithCancel(context.Background())
cancel()
tempdir, removeTempdir := restictest.TempDir(t)
TestCreateFiles(t, tempdir, TestDir{
"targetfile": TestFile{Content: "foobar"},
})
defer removeTempdir()
// Ensure that the archiver itself reports the canceled context and not just the backend
repo, _ := repository.TestRepositoryWithBackend(t, &noCancelBackend{mem.New()})
back := restictest.Chdir(t, tempdir)
defer back()
arch := New(repo, fs.Track{FS: fs.Local{}}, Options{})
_, snapshotID, err := arch.Snapshot(ctx, []string{"."}, SnapshotOptions{Time: time.Now()})
if err != nil {
t.Logf("found expected error (%v)", err)
return
}
if snapshotID.IsNull() {
t.Fatalf("no error returned but found null id")
}
t.Fatalf("expected error not returned by archiver")
}
// TrackFS keeps track which files are opened. For some files, an error is injected.
type TrackFS struct {
fs.FS

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@ -33,6 +33,16 @@ func NewRetryBackend(be restic.Backend, maxTries int, report func(string, error,
}
func (be *RetryBackend) retry(ctx context.Context, msg string, f func() error) error {
// Don't do anything when called with an already cancelled context. There would be
// no retries in that case either, so be consistent and abort always.
// This enforces a strict contract for backend methods: Using a cancelled context
// will prevent any backup repository modifications. This simplifies ensuring that
// a backup repository is not modified any further after a context was cancelled.
// The 'local' backend for example does not provide this guarantee on its own.
if ctx.Err() != nil {
return ctx.Err()
}
err := backoff.RetryNotify(f,
backoff.WithContext(backoff.WithMaxRetries(backoff.NewExponentialBackOff(), uint64(be.MaxTries)), ctx),
func(err error, d time.Duration) {

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@ -236,3 +236,38 @@ func TestBackendLoadRetry(t *testing.T) {
test.Equals(t, data, buf)
test.Equals(t, 2, attempt)
}
func assertIsCanceled(t *testing.T, err error) {
test.Assert(t, err == context.Canceled, "got unexpected err %v", err)
}
func TestBackendCanceledContext(t *testing.T) {
// unimplemented mock backend functions return an error by default
// check that we received the expected context canceled error instead
retryBackend := NewRetryBackend(mock.NewBackend(), 2, nil)
h := restic.Handle{Type: restic.PackFile, Name: restic.NewRandomID().String()}
// create an already canceled context
ctx, cancel := context.WithCancel(context.Background())
cancel()
_, err := retryBackend.Test(ctx, h)
assertIsCanceled(t, err)
_, err = retryBackend.Stat(ctx, h)
assertIsCanceled(t, err)
err = retryBackend.Save(ctx, h, restic.NewByteReader([]byte{}))
assertIsCanceled(t, err)
err = retryBackend.Remove(ctx, h)
assertIsCanceled(t, err)
err = retryBackend.Load(ctx, restic.Handle{}, 0, 0, func(rd io.Reader) (err error) {
return nil
})
assertIsCanceled(t, err)
err = retryBackend.List(ctx, restic.PackFile, func(restic.FileInfo) error {
return nil
})
assertIsCanceled(t, err)
// don't test "Delete" as it is not used by normal code
}