Method Seek

api-get-object.go:547–629

Seek sets the offset for the next Read or Write to offset, interpreted according to whence: 0 means relative to the origin of the file, 1 means relative to the current offset, and 2 means relative to the end. Seek returns the new offset and an error, if any. Seeking to a negative offset is an error

(offset int64, whence int)

// offset is legal, subsequent io operations succeed until the
// underlying object is not closed.
func (o *Object) Seek(offset int64, whence int) (n int64, err error) {
	if o == nil {
		return 0, errInvalidArgument("Object is nil")
	}

	// Locking.
	o.mutex.Lock()
	defer o.mutex.Unlock()

	// At EOF seeking is legal allow only io.EOF, for any other errors we return.
	if o.prevErr != nil && o.prevErr != io.EOF {
		return 0, o.prevErr
	}

	// Negative offset is valid for whence of '2'.
	if offset < 0 && whence != 2 {
		return 0, errInvalidArgument(fmt.Sprintf("Negative position not allowed for %d", whence))
	}

	// This is the first request. So before anything else
	// get the ObjectInfo.
	if !o.isStarted || !o.objectInfoSet {
		// Create the new Seek request.
		seekReq := getRequest{
			isReadOp:   false,
			Offset:     offset,
			isFirstReq: true,
		}
		// Send and receive from the seek request.
		_, err := o.doGetRequest(seekReq)
		if err != nil {
			// Save the error.
			o.prevErr = err
			return 0, err
		}
	}

	newOffset := o.currOffset

	// Switch through whence.
	switch whence {
	default:
		return 0, errInvalidArgument(fmt.Sprintf("Invalid whence %d", whence))
	case 0:
		if o.objectInfo.Size > -1 && offset > o.objectInfo.Size {
			return 0, io.EOF
		}
		newOffset = offset
	case 1:
		if o.objectInfo.Size > -1 && o.currOffset+offset > o.objectInfo.Size {
			return 0, io.EOF
		}
		newOffset += offset
	case 2:
		// If we don't know the object size return an error for io.SeekEnd
		if o.objectInfo.Size < 0 {
			return 0, errInvalidArgument("Whence END is not supported when the object size is unknown")
		}