Function copyWithBuffer

core/content/helpers.go:321–360

copyWithBuffer is very similar to io.CopyBuffer https://golang.org/pkg/io/#CopyBuffer but instead of using Read to read from the src, we use ReadAtLeast to make sure we have a full buffer before we do a write operation to dst to reduce overheads associated with the write operations of small buffers

(dst io.Writer, src io.Reader)

// a full buffer before we do a write operation to dst to reduce overheads associated
// with the write operations of small buffers.
func copyWithBuffer(dst io.Writer, src io.Reader) (written int64, err error) {
	// If the reader has a WriteTo method, use it to do the copy.
	// Avoids an allocation and a copy.
	if wt, ok := src.(io.WriterTo); ok {
		return wt.WriteTo(dst)
	}
	// Similarly, if the writer has a ReadFrom method, use it to do the copy.
	if rt, ok := dst.(io.ReaderFrom); ok {
		return rt.ReadFrom(src)
	}
	bufRef := bufPool.Get().(*[]byte)
	defer bufPool.Put(bufRef)
	buf := *bufRef
	for {
		nr, er := io.ReadAtLeast(src, buf, len(buf))
		if nr > 0 {
			nw, ew := dst.Write(buf[0:nr])
			if nw > 0 {
				written += int64(nw)
			}
			if ew != nil {
				err = ew
				break
			}
			if nr != nw {
				err = io.ErrShortWrite
				break
			}
		}
		if er != nil {
			// If an EOF happens after reading fewer than the requested bytes,
			// ReadAtLeast returns ErrUnexpectedEOF.
			if er != io.EOF && er != io.ErrUnexpectedEOF {
				err = er
			}
			break
		}
	}
	return
}

// Exists returns whether an attempt to access the content would not error out
// with an ErrNotFound error. It will return an encountered error if it was