How to make BufferedReader's peek more reliable?

Question

There's convenient peek function in io.BufferedReader. But

peek([n])
    Return 1 (or n if specified) bytes from a buffer without advancing
the position. Only a single read on the raw stream is done to satisfy
the call. The number of bytes returned may be less than requested since
at most all the buffer’s bytes from the current position to the end are
returned.

it is returning too few bytes.

Where shall I get reliable multi-byte peek (without using read and disrupting other code nibbling the stream byte by byte and interpreting data from it)?

Answer 1

It depends on what you mean by reliable. The buffered classes are specifically tailored to prevent I/O as much as possible (as that is the whole point of a buffer) so they only guarantee that it will do 1 read of the buffer at most. The amount of data returned depends exclusively on the amount of data that the buffer already has in it.

If you need an exact amount of data, you will need to alter the underlying structures. In particular, you will probably need to re-open the stream with a bigger buffer.

If that is not an option, you could provide a wrapper class so that you can intercept the reads that you need and provide the data transparently to other code that actually want to consume the data.