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object_reader.go
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/
object_reader.go
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package object
import (
"bytes"
"context"
"encoding/json"
"io"
"github.com/pkg/errors"
"github.com/kopia/kopia/repo/compression"
"github.com/kopia/kopia/repo/content"
)
// Open creates new ObjectReader for reading given object from a repository.
func Open(ctx context.Context, r contentReader, objectID ID) (Reader, error) {
return openAndAssertLength(ctx, r, objectID, -1)
}
// VerifyObject ensures that all objects backing ObjectID are present in the repository
// and returns the content IDs of which it is composed.
func VerifyObject(ctx context.Context, cr contentReader, oid ID) ([]content.ID, error) {
tracker := &contentIDTracker{}
if err := verifyObjectInternal(ctx, cr, oid, tracker); err != nil {
return nil, err
}
return tracker.contentIDs(), nil
}
type objectReader struct {
ctx context.Context
cr contentReader
seekTable []indirectObjectEntry
currentPosition int64 // Overall position in the objectReader
totalLength int64 // Overall length
currentChunkIndex int // Index of current chunk in the seek table
currentChunkData []byte // Current chunk data
currentChunkPosition int // Read position in the current chunk
}
func (r *objectReader) Read(buffer []byte) (int, error) {
readBytes := 0
remaining := len(buffer)
if r.currentPosition >= r.totalLength {
return 0, io.EOF
}
for remaining > 0 {
if r.currentChunkData != nil {
toCopy := len(r.currentChunkData) - r.currentChunkPosition
if toCopy == 0 {
// EOF on current chunk
r.closeCurrentChunk()
r.currentChunkIndex++
continue
}
if toCopy > remaining {
toCopy = remaining
}
copy(buffer[readBytes:],
r.currentChunkData[r.currentChunkPosition:r.currentChunkPosition+toCopy])
r.currentChunkPosition += toCopy
r.currentPosition += int64(toCopy)
readBytes += toCopy
remaining -= toCopy
continue
}
if r.currentChunkIndex < len(r.seekTable) {
err := r.openCurrentChunk()
if err != nil {
return 0, err
}
} else {
break
}
}
if readBytes == 0 {
return readBytes, io.EOF
}
return readBytes, nil
}
func (r *objectReader) openCurrentChunk() error {
st := r.seekTable[r.currentChunkIndex]
rd, err := openAndAssertLength(r.ctx, r.cr, st.Object, st.Length)
if err != nil {
return err
}
defer rd.Close() //nolint:errcheck
b := make([]byte, st.Length)
if _, err := io.ReadFull(rd, b); err != nil {
return errors.Wrap(err, "error reading chunk")
}
r.currentChunkData = b
r.currentChunkPosition = 0
return nil
}
func (r *objectReader) closeCurrentChunk() {
r.currentChunkData = nil
}
func (r *objectReader) findChunkIndexForOffset(offset int64) (int, error) {
left := 0
right := len(r.seekTable) - 1
for left <= right {
middle := (left + right) / 2 //nolint:gomnd
if offset < r.seekTable[middle].Start {
right = middle - 1
continue
}
if offset >= r.seekTable[middle].endOffset() {
left = middle + 1
continue
}
return middle, nil
}
return 0, errors.Errorf("can't find chunk for offset %v", offset)
}
func (r *objectReader) Seek(offset int64, whence int) (int64, error) {
if whence == io.SeekCurrent {
return r.Seek(r.currentPosition+offset, 0)
}
if whence == io.SeekEnd {
return r.Seek(r.totalLength+offset, 0)
}
if offset >= r.totalLength {
r.currentChunkIndex = len(r.seekTable)
r.currentChunkData = nil
r.currentPosition = offset
return offset, nil
}
index, err := r.findChunkIndexForOffset(offset)
if err != nil {
return -1, errors.Wrapf(err, "invalid seek %v %v", offset, whence)
}
chunkStartOffset := r.seekTable[index].Start
if index != r.currentChunkIndex {
r.closeCurrentChunk()
r.currentChunkIndex = index
}
if r.currentChunkData == nil {
if err := r.openCurrentChunk(); err != nil {
return 0, err
}
}
r.currentChunkPosition = int(offset - chunkStartOffset)
r.currentPosition = offset
return r.currentPosition, nil
}
func (r *objectReader) Close() error {
return nil
}
func (r *objectReader) Length() int64 {
return r.totalLength
}
func openAndAssertLength(ctx context.Context, cr contentReader, objectID ID, assertLength int64) (Reader, error) {
if indexObjectID, ok := objectID.IndexObjectID(); ok {
// recursively calls openAndAssertLength
seekTable, err := loadSeekTable(ctx, cr, indexObjectID)
if err != nil {
return nil, err
}
totalLength := seekTable[len(seekTable)-1].endOffset()
return &objectReader{
ctx: ctx,
cr: cr,
seekTable: seekTable,
totalLength: totalLength,
}, nil
}
return newRawReader(ctx, cr, objectID, assertLength)
}
func verifyIndirectObjectInternal(ctx context.Context, cr contentReader, indexObjectID ID, tracker *contentIDTracker) error {
if err := verifyObjectInternal(ctx, cr, indexObjectID, tracker); err != nil {
return errors.Wrap(err, "unable to read index")
}
seekTable, err := loadSeekTable(ctx, cr, indexObjectID)
if err != nil {
return err
}
for _, m := range seekTable {
err := verifyObjectInternal(ctx, cr, m.Object, tracker)
if err != nil {
return err
}
}
return nil
}
func verifyObjectInternal(ctx context.Context, r contentReader, oid ID, tracker *contentIDTracker) error {
if indexObjectID, ok := oid.IndexObjectID(); ok {
return verifyIndirectObjectInternal(ctx, r, indexObjectID, tracker)
}
if contentID, _, ok := oid.ContentID(); ok {
if _, err := r.ContentInfo(ctx, contentID); err != nil {
return errors.Wrapf(err, "error getting content info for %v", contentID)
}
tracker.addContentID(contentID)
return nil
}
return errors.Errorf("unrecognized object type: %v", oid)
}
type indirectObject struct {
StreamID string `json:"stream"`
Entries []indirectObjectEntry `json:"entries"`
}
func loadSeekTable(ctx context.Context, cr contentReader, indexObjectID ID) ([]indirectObjectEntry, error) {
r, err := openAndAssertLength(ctx, cr, indexObjectID, -1)
if err != nil {
return nil, err
}
defer r.Close() //nolint:errcheck
var ind indirectObject
if err := json.NewDecoder(r).Decode(&ind); err != nil {
return nil, errors.Wrap(err, "invalid indirect object")
}
return ind.Entries, nil
}
func newRawReader(ctx context.Context, cr contentReader, objectID ID, assertLength int64) (Reader, error) {
contentID, compressed, ok := objectID.ContentID()
if !ok {
return nil, errors.Errorf("unsupported object ID: %v", objectID)
}
payload, err := cr.GetContent(ctx, contentID)
if errors.Is(err, content.ErrContentNotFound) {
return nil, errors.Wrapf(ErrObjectNotFound, "content %v not found", contentID)
}
if err != nil {
return nil, errors.Wrap(err, "unexpected content error")
}
if compressed {
var b bytes.Buffer
if err = compression.DecompressByHeader(&b, bytes.NewReader(payload)); err != nil {
return nil, errors.Wrap(err, "decompression error")
}
payload = b.Bytes()
}
if assertLength != -1 && int64(len(payload)) != assertLength {
return nil, errors.Errorf("unexpected chunk length %v, expected %v", len(payload), assertLength)
}
return newObjectReaderWithData(payload), nil
}
type readerWithData struct {
io.ReadSeeker
length int64
}
func (rwd *readerWithData) Close() error {
return nil
}
func (rwd *readerWithData) Length() int64 {
return rwd.length
}
func newObjectReaderWithData(data []byte) Reader {
return &readerWithData{
ReadSeeker: bytes.NewReader(data),
length: int64(len(data)),
}
}