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restic/internal/backend/backend_retry.go
Alexander Neumann 99f7fd74e3 backend: Improve Save()
As mentioned in issue [#1560](https://github.com/restic/restic/pull/1560#issuecomment-364689346)
this changes the signature for `backend.Save()`. It now takes a
parameter of interface type `RewindReader`, so that the backend
implementations or our `RetryBackend` middleware can reset the reader to
the beginning and then retry an upload operation.

The `RewindReader` interface also provides a `Length()` method, which is
used in the backend to get the size of the data to be saved. This
removes several ugly hacks we had to do to pull the size back out of the
`io.Reader` passed to `Save()` before. In the `s3` and `rest` backend
this is actively used.
2018-03-03 15:49:44 +01:00

148 lines
4.3 KiB
Go

package backend
import (
"context"
"fmt"
"io"
"time"
"github.com/cenkalti/backoff"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/restic"
)
// RetryBackend retries operations on the backend in case of an error with a
// backoff.
type RetryBackend struct {
restic.Backend
MaxTries int
Report func(string, error, time.Duration)
}
// statically ensure that RetryBackend implements restic.Backend.
var _ restic.Backend = &RetryBackend{}
// NewRetryBackend wraps be with a backend that retries operations after a
// backoff. report is called with a description and the error, if one occurred.
func NewRetryBackend(be restic.Backend, maxTries int, report func(string, error, time.Duration)) *RetryBackend {
return &RetryBackend{
Backend: be,
MaxTries: maxTries,
Report: report,
}
}
func (be *RetryBackend) retry(ctx context.Context, msg string, f func() error) error {
err := backoff.RetryNotify(f,
backoff.WithContext(backoff.WithMaxTries(backoff.NewExponentialBackOff(), uint64(be.MaxTries)), ctx),
func(err error, d time.Duration) {
if be.Report != nil {
be.Report(msg, err, d)
}
},
)
return err
}
// Save stores the data in the backend under the given handle.
func (be *RetryBackend) Save(ctx context.Context, h restic.Handle, rd restic.RewindReader) error {
return be.retry(ctx, fmt.Sprintf("Save(%v)", h), func() error {
err := rd.Rewind()
if err != nil {
return err
}
err = be.Backend.Save(ctx, h, rd)
if err == nil {
return nil
}
debug.Log("Save(%v) failed with error, removing file: %v", h, err)
rerr := be.Backend.Remove(ctx, h)
if rerr != nil {
debug.Log("Remove(%v) returned error: %v", h, err)
}
// return original error
return err
})
}
// Load returns a reader that yields the contents of the file at h at the
// given offset. If length is larger than zero, only a portion of the file
// is returned. rd must be closed after use. If an error is returned, the
// ReadCloser must be nil.
func (be *RetryBackend) Load(ctx context.Context, h restic.Handle, length int, offset int64, consumer func(rd io.Reader) error) (err error) {
return be.retry(ctx, fmt.Sprintf("Load(%v, %v, %v)", h, length, offset),
func() error {
return be.Backend.Load(ctx, h, length, offset, consumer)
})
}
// Stat returns information about the File identified by h.
func (be *RetryBackend) Stat(ctx context.Context, h restic.Handle) (fi restic.FileInfo, err error) {
err = be.retry(ctx, fmt.Sprintf("Stat(%v)", h),
func() error {
var innerError error
fi, innerError = be.Backend.Stat(ctx, h)
return innerError
})
return fi, err
}
// Remove removes a File with type t and name.
func (be *RetryBackend) Remove(ctx context.Context, h restic.Handle) (err error) {
return be.retry(ctx, fmt.Sprintf("Remove(%v)", h), func() error {
return be.Backend.Remove(ctx, h)
})
}
// Test a boolean value whether a File with the name and type exists.
func (be *RetryBackend) Test(ctx context.Context, h restic.Handle) (exists bool, err error) {
err = be.retry(ctx, fmt.Sprintf("Test(%v)", h), func() error {
var innerError error
exists, innerError = be.Backend.Test(ctx, h)
return innerError
})
return exists, err
}
// List runs fn for each file in the backend which has the type t. When an
// error is returned by the underlying backend, the request is retried. When fn
// returns an error, the operation is aborted and the error is returned to the
// caller.
func (be *RetryBackend) List(ctx context.Context, t restic.FileType, fn func(restic.FileInfo) error) error {
// create a new context that we can cancel when fn returns an error, so
// that listing is aborted
listCtx, cancel := context.WithCancel(ctx)
defer cancel()
listed := make(map[string]struct{}) // remember for which files we already ran fn
var innerErr error // remember when fn returned an error, so we can return that to the caller
err := be.retry(listCtx, fmt.Sprintf("List(%v)", t), func() error {
return be.Backend.List(ctx, t, func(fi restic.FileInfo) error {
if _, ok := listed[fi.Name]; ok {
return nil
}
listed[fi.Name] = struct{}{}
innerErr = fn(fi)
if innerErr != nil {
// if fn returned an error, listing is aborted, so we cancel the context
cancel()
}
return innerErr
})
})
// the error fn returned takes precedence
if innerErr != nil {
return innerErr
}
return err
}