restic/internal/backend/mem/mem_backend.go

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package mem
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import (
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"bytes"
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"context"
"encoding/base64"
"fmt"
"hash"
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"io"
"net/http"
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"sync"
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"github.com/cespare/xxhash/v2"
"github.com/restic/restic/internal/backend"
"github.com/restic/restic/internal/backend/location"
"github.com/restic/restic/internal/backend/util"
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"github.com/restic/restic/internal/debug"
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"github.com/restic/restic/internal/errors"
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)
type memMap map[backend.Handle][]byte
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// make sure that MemoryBackend implements backend.Backend
var _ backend.Backend = &MemoryBackend{}
// NewFactory creates a persistent mem backend
func NewFactory() location.Factory {
be := New()
return location.NewHTTPBackendFactory[struct{}, *MemoryBackend](
"mem",
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func(_ string) (*struct{}, error) {
return &struct{}{}, nil
},
location.NoPassword,
func(_ context.Context, _ struct{}, _ http.RoundTripper) (*MemoryBackend, error) {
return be, nil
},
func(_ context.Context, _ struct{}, _ http.RoundTripper) (*MemoryBackend, error) {
return be, nil
},
)
}
var errNotFound = fmt.Errorf("not found")
var errTooSmall = errors.New("access beyond end of file")
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const connectionCount = 2
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// MemoryBackend is a mock backend that uses a map for storing all data in
// memory. This should only be used for tests.
type MemoryBackend struct {
data memMap
m sync.Mutex
}
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// New returns a new backend that saves all data in a map in memory.
func New() *MemoryBackend {
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be := &MemoryBackend{
data: make(memMap),
}
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debug.Log("created new memory backend")
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return be
}
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// IsNotExist returns true if the file does not exist.
func (be *MemoryBackend) IsNotExist(err error) bool {
return errors.Is(err, errNotFound)
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}
func (be *MemoryBackend) IsPermanentError(err error) bool {
return be.IsNotExist(err) || errors.Is(err, errTooSmall)
}
// Save adds new Data to the backend.
func (be *MemoryBackend) Save(ctx context.Context, h backend.Handle, rd backend.RewindReader) error {
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be.m.Lock()
defer be.m.Unlock()
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h.IsMetadata = false
if h.Type == backend.ConfigFile {
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h.Name = ""
}
if _, ok := be.data[h]; ok {
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return errors.New("file already exists")
}
buf, err := io.ReadAll(rd)
if err != nil {
return err
}
// sanity check
if int64(len(buf)) != rd.Length() {
return errors.Errorf("wrote %d bytes instead of the expected %d bytes", len(buf), rd.Length())
}
beHash := be.Hasher()
// must never fail according to interface
_, err = beHash.Write(buf)
if err != nil {
panic(err)
}
if !bytes.Equal(beHash.Sum(nil), rd.Hash()) {
return errors.Errorf("invalid file hash or content, got %s expected %s",
base64.RawStdEncoding.EncodeToString(beHash.Sum(nil)),
base64.RawStdEncoding.EncodeToString(rd.Hash()),
)
}
be.data[h] = buf
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return ctx.Err()
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}
// Load runs fn with a reader that yields the contents of the file at h at the
// given offset.
func (be *MemoryBackend) Load(ctx context.Context, h backend.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
return util.DefaultLoad(ctx, h, length, offset, be.openReader, fn)
}
func (be *MemoryBackend) openReader(ctx context.Context, h backend.Handle, length int, offset int64) (io.ReadCloser, error) {
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be.m.Lock()
defer be.m.Unlock()
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h.IsMetadata = false
if h.Type == backend.ConfigFile {
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h.Name = ""
}
if _, ok := be.data[h]; !ok {
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return nil, errNotFound
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}
buf := be.data[h]
if offset+int64(length) > int64(len(buf)) {
return nil, errTooSmall
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}
buf = buf[offset:]
if length > 0 {
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buf = buf[:length]
}
return io.NopCloser(bytes.NewReader(buf)), ctx.Err()
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}
// Stat returns information about a file in the backend.
func (be *MemoryBackend) Stat(ctx context.Context, h backend.Handle) (backend.FileInfo, error) {
be.m.Lock()
defer be.m.Unlock()
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h.IsMetadata = false
if h.Type == backend.ConfigFile {
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h.Name = ""
}
e, ok := be.data[h]
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if !ok {
return backend.FileInfo{}, errNotFound
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}
return backend.FileInfo{Size: int64(len(e)), Name: h.Name}, ctx.Err()
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}
// Remove deletes a file from the backend.
func (be *MemoryBackend) Remove(ctx context.Context, h backend.Handle) error {
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be.m.Lock()
defer be.m.Unlock()
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h.IsMetadata = false
if _, ok := be.data[h]; !ok {
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return errNotFound
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}
delete(be.data, h)
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return ctx.Err()
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}
// List returns a channel which yields entries from the backend.
func (be *MemoryBackend) List(ctx context.Context, t backend.FileType, fn func(backend.FileInfo) error) error {
entries := make(map[string]int64)
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be.m.Lock()
for entry, buf := range be.data {
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if entry.Type != t {
continue
}
entries[entry.Name] = int64(len(buf))
}
be.m.Unlock()
for name, size := range entries {
fi := backend.FileInfo{
Name: name,
Size: size,
}
if ctx.Err() != nil {
return ctx.Err()
}
err := fn(fi)
if err != nil {
return err
}
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if ctx.Err() != nil {
return ctx.Err()
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}
}
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return ctx.Err()
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}
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func (be *MemoryBackend) Connections() uint {
return connectionCount
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}
// Hasher may return a hash function for calculating a content hash for the backend
func (be *MemoryBackend) Hasher() hash.Hash {
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return xxhash.New()
}
// HasAtomicReplace returns whether Save() can atomically replace files
func (be *MemoryBackend) HasAtomicReplace() bool {
return false
}
// Delete removes all data in the backend.
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func (be *MemoryBackend) Delete(ctx context.Context) error {
be.m.Lock()
defer be.m.Unlock()
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if ctx.Err() != nil {
return ctx.Err()
}
be.data = make(memMap)
return nil
}
// Close closes the backend.
func (be *MemoryBackend) Close() error {
return nil
}