add range download method (#1769)

Author: Hitenjain14

core/sys/util.go

@@ -290,10 +290,18 @@ func (pf *PipeFile) Close() error {
 	return pf.w.Close()
 }
 
+func (pf *PipeFile) CloseWithError(err error) {
+	pf.w.CloseWithError(err)
+}
+
 func (pf *PipeFile) Read(p []byte) (int, error) {
 	return pf.r.Read(p)
 }
 
+func (pf *PipeFile) Reader() io.ReadCloser {
+	return pf.r
+}
+
 func (pf *PipeFile) Stat() (fs.FileInfo, error) {
 	return nil, nil
 }
@@ -303,5 +311,39 @@ func (pf *PipeFile) Sync() error {
 }
 
 func (pf *PipeFile) Seek(offset int64, whence int) (int64, error) {
-	return 0, nil
+	if whence != io.SeekStart {
+		return 0, os.ErrInvalid
+	}
+	if offset < 0 {
+		return 0, os.ErrInvalid
+	}
+	return io.CopyN(io.Discard, pf.r, offset)
+}
+
+type LimitedReaderCloser struct {
+	R io.ReadCloser // underlying reader
+	N int64         // max bytes remaining
+}
+
+func NewLimitedReaderCloser(r io.ReadCloser, n int64) *LimitedReaderCloser {
+	return &LimitedReaderCloser{
+		R: r,
+		N: n,
+	}
+}
+
+func (l *LimitedReaderCloser) Read(p []byte) (n int, err error) {
+	if l.N <= 0 {
+		return 0, io.EOF
+	}
+	if int64(len(p)) > l.N {
+		p = p[0:l.N]
+	}
+	n, err = l.R.Read(p)
+	l.N -= int64(n)
+	return
+}
+
+func (l *LimitedReaderCloser) Close() error {
+	return l.R.Close()
 }

zboxcore/sdk/allocation.go

@@ -3405,6 +3405,75 @@ func (a *Allocation) DownloadDirectory(ctx context.Context, remotePath, localPat
 	return nil
 }
 
+func (a *Allocation) DownloadObject(ctx context.Context, remotePath string, rangeStart, rangeEnd int64) (io.ReadCloser, error) {
+	fm, err := a.GetFileMeta(remotePath)
+	if err != nil {
+		return nil, err
+	}
+	if fm.Type != fileref.FILE {
+		return nil, errors.New("invalid_file_type", "Invalid file type. Expected file type")
+	}
+	var (
+		startBlock, endBlock int64
+	)
+	effectiveChunkSize := a.GetChunkReadSize(fm.EncryptedKey != "")
+	fileRangeSize := rangeEnd - rangeStart + 1
+	if rangeEnd < rangeStart {
+		fileRangeSize = fm.ActualFileSize
+	}
+	if rangeEnd >= rangeStart {
+		startBlock = int64(rangeStart / effectiveChunkSize)
+		if startBlock == 0 {
+			startBlock = 1
+		}
+		if rangeEnd < fileRangeSize {
+			endBlock = (fileRangeSize + effectiveChunkSize - 1) / effectiveChunkSize
+		} else {
+			endBlock = int64(rangeEnd+effectiveChunkSize-1) / effectiveChunkSize
+		}
+	} else {
+		startBlock = 1
+		endBlock = 0
+	}
+
+	if rangeEnd == -1 {
+		endBlock = 0
+		startBlock = int64(rangeStart / effectiveChunkSize)
+		if startBlock == 0 {
+			startBlock = 1
+		}
+		fileRangeSize = fm.ActualFileSize - rangeStart
+	}
+	pipeFile := sys.NewPipeFile()
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+	downloadStatusBar := &StatusBar{
+		wg: wg,
+	}
+	err = a.DownloadByBlocksToFileHandler(pipeFile, remotePath, startBlock, endBlock, numBlockDownloads, false, downloadStatusBar, true)
+	if err != nil {
+		return nil, err
+	}
+	go func() {
+		wg.Wait()
+		if downloadStatusBar.err != nil {
+			pipeFile.CloseWithError(downloadStatusBar.err) //nolint: errcheck
+		} else {
+			pipeFile.Close() //nolint: errcheck
+		}
+	}()
+	startOffset := rangeStart - (startBlock-1)*effectiveChunkSize
+
+	if startOffset > 0 {
+		_, err = pipeFile.Seek(startOffset, io.SeekStart)
+		if err != nil {
+			return nil, err
+		}
+	}
+	lr := sys.NewLimitedReaderCloser(pipeFile.Reader(), fileRangeSize)
+	return lr, nil
+}
+
 // contextCanceled returns whether a context is canceled.
 func contextCanceled(ctx context.Context) bool {
 	select {