putback

        # Encoding::Converter.putback

(from ruby core)
### Implementation from Converter
---
    ec.putback                    -> string
    ec.putback(max_numbytes)      -> string

---

Put back the bytes which will be converted.

The bytes are caused by invalid_byte_sequence error. When
invalid_byte_sequence error, some bytes are discarded and some bytes are
buffered to be converted later. The latter bytes can be put back. It can
be observed by Encoding::InvalidByteSequenceError#readagain_bytes and
Encoding::Converter#primitive_errinfo.

    ec = Encoding::Converter.new("utf-16le", "iso-8859-1")
    src = "\x00\xd8\x61\x00"
    dst = ""
    p ec.primitive_convert(src, dst)   #=> :invalid_byte_sequence
    p ec.primitive_errinfo     #=> [:invalid_byte_sequence, "UTF-16LE", "UTF-8", "\x00\xD8", "a\x00"]
    p ec.putback               #=> "a\x00"
    p ec.putback               #=> ""          # no more bytes to put back