Method resolveObject

plumbing/format/packfile/parser.go:513–568

resolveObject resolves an object from base, using information provided by o. This call has the side-effect of changing field values from the object info o: - Type: OFSDeltaObject may become the target type (e.g. Blob). - Size: The size may be update with the target size. - Hash: Zero hashes will be

(
	w io.Writer,
	o *objectInfo,
	base io.ReaderAt,
)

// delta object may lead to going backs and forths within base,
// which is not supported by io.Reader.
func (p *Parser) resolveObject(
	w io.Writer,
	o *objectInfo,
	base io.ReaderAt,
) error {
	if !o.DiskType.IsDelta() {
		return nil
	}
	buf := sync.GetBytesBuffer()
	defer sync.PutBytesBuffer(buf)
	err := p.readData(buf, o)
	if err != nil {
		return err
	}

	writers := []io.Writer{w}
	var obj *plumbing.MemoryObject
	var lwh objectHeaderWriter

	if p.storage != nil {
		if low, ok := p.storage.(lazyObjectWriter); ok {
			ow, wh, err := low.LazyWriter()
			if err != nil {
				return err
			}
			lwh = wh

			defer ow.Close()
			writers = append(writers, ow)
		} else {
			obj = new(plumbing.MemoryObject)
			ow, err := obj.Writer()
			if err != nil {
				return err
			}

			writers = append(writers, ow)
		}
	}

	mw := io.MultiWriter(writers...)

	err = applyPatchBase(o, base, buf, mw, lwh)
	if err != nil {
		return err
	}

	if obj != nil {
		obj.SetType(o.Type)
		obj.SetSize(o.Size()) // Size here is correct as it was populated by applyPatchBase.
		if _, err := p.storage.SetEncodedObject(obj); err != nil {
			return err
		}
	}
	return err
}

func (p *Parser) readData(w io.Writer, o *objectInfo) error {