Java InputStream's read(byte[]) method

Question

First some background. Its not needed to answer the actual question, but maybe it\'ll help put things in perspective.

I have written an mp3 library in java (h) which

Answer 1

Your conclusions are sound, take a look at the documentation for InputStream.read(byte[]):

Reads some number of bytes from the input stream and stores them into the buffer array b. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.

There is no guarantee that read(byte[]) will fill the array you have provided, only that it will either read at least 1 byte (provided your array's length is > 0), or it will return -1 to signal the EOS. This means that if you want to read bytes from an InputStream correctly, you must use a loop.

The loop you currently have has one bug in it. On the first iteration of the loop, you will read a certain number of bytes into your buffer, but on the second iteration you will overwrite some, or all, of those bytes. Take a look at InputStream.read(byte[], int, int).

Answer 2

And hence my question is: In general, can I not assume that the InputStream's read(byte[]) method will block until the entire number of bytes has been read (or EOF is reached)?

No. That's why the documentation says "The number of bytes actually read" and "there is an attempt to read at least one byte."

I need to put the call in a loop and keep reading bytes until the desired number of bytes have been read

Rather than reinvent the wheel, you can get an already-tested wheel at Jakarta Commons IO.