RFR [9] Add blocking bulk read to java.io.InputStream

[Chris Hegarty]

On 23 Apr 2015, at 22:24, Roger Riggs <Roger.Riggs at oracle.com> wrote:

> Hi Pavel,
> 
> On 4/23/2015 5:12 PM, Pavel Rappo wrote:
>> Hey Roger,
>> 
>> 1. Good catch! This thing also applies to java.io.InputStream.read(byte[], int, int):

Yes, good catch indeed.

>>      * <p> In every case, elements <code>b[0]</code> through
>>      * <code>b[off]</code> and elements <code>b[off+len]</code> through
>>      * <code>b[b.length-1]</code> are unaffected.
>> 
>> I suppose the javadoc for the method proposed by Chris has started its life as a
>> copy of the javadoc read(byte[], int, int) which was assumed to be perfectly
>> polished. Unfortunately it was a false assumption.
> it happens...  many many people have read those descriptions  (or didn't because
> it was too obvious or thought to be redundant).

I propose this small amendment.

* <p> In the case where {@code off > 0}, elements {@code b[0]} through
* {@code b[off-1]} are unaffected. In every case, elements
* {@code b[off+len]} through {@code b[b.length-1]} are unaffected.

>> 
>> 2. About awkward sentences. This paragraph also has to be rephrased for the same reason:
>> 
>>      * <p> The first byte read is stored into element {@code b[off]}, the next
>>      * one in to {@code b[off+1]}, and so on. The number of bytes read is, at
>>      * most, equal to {@code len}. Let <i>k</i> be the number of bytes actually
>>      * read; these bytes will be stored in elements {@code b[off]} through
>>      * {@code b[off+}<i>k</i>{@code -1]}, leaving elements {@code b[off+}<i>k</i>
>>      * {@code ]} through {@code b[off+len-1]} unaffected.
>> 
>> If k == 0 then spec claims to store values in b[off]... b[off - 1].

Reading the whole method description leads to be believe that 'k' cannot equal 0 at this point. The previous paragraph handles the case where len is 0. The previous paragraph to that handles the EOF case. This paragraph implicitly implies that k is greater than 0, “The first byte read”, and “the number of actual bytes read”, neither of which can be 0 at this point.

I included below [*] the latest version of this method, including all comments so far. 

> If one concludes that's an empty interval then its ok; it just reads oddly and can
> make the reader think its wrong.
> In some cases it is easier if the upper bound is defined to be exclusive.
> Then if lower == upper, its empty.
> 
> If better language were constructed for the new method then perhaps it could
> be worked back into methods with similar behavior later.  If the wording changes
> in any significant way, the conformance team will have to go back and re-evaluate
> it in detail to see if it really has changed.  So I'd leave it alone.
> 
> Roger

-Chris.

[*]

/**
 * Reads some bytes from the input stream into the given byte array. This
 * method blocks until {@code len} bytes of input data have been read, end
 * of stream is detected, or an exception is thrown. The number of bytes
 * actually read, possibly zero, is returned. This method does not close
 * the input stream.
 *
 * <p> In the case where end of stream is reached before {@code len} bytes
 * have been read, then the actual number of bytes read will be returned.
 * When this stream reaches end of stream, further invocations of this
 * method will return zero.
 *
 * <p> If {@code len} is zero, then no bytes are read and {@code 0} is
 * returned; otherwise, there is an attempt to read up to {@code len} bytes.
 *
 * <p> The first byte read is stored into element {@code b[off]}, the next
 * one in to {@code b[off+1]}, and so on. The number of bytes read is, at
 * most, equal to {@code len}. Let <i>k</i> be the number of bytes actually
 * read; these bytes will be stored in elements {@code b[off]} through
 * {@code b[off+}<i>k</i>{@code -1]}, leaving elements {@code b[off+}<i>k</i>
 * {@code ]} through {@code b[off+len-1]} unaffected.
 *
 * <p> In the case where {@code off > 0}, elements {@code b[0]} through
 * {@code b[off-1]} are unaffected. In every case, elements
 * {@code b[off+len]} through {@code b[b.length-1]} are unaffected.
 *
 * <p> In every case, elements {@code b[0]} through {@code b[off-1]} and
 * elements {@code b[off+len]} through {@code b[b.length-1]} are unaffected.
 *
 * <p> The behavior for the case where the input stream is <i>asynchronously
 * closed</i>, or the thread interrupted during the read, is highly input
 * stream specific, and therefore not specified.
 *
 * <p> If an I/O error occurs reading from the input stream, then it may do
 * so after some, but not all, bytes of {@code b} have been updated with
 * data from the input stream. Consequently the input stream and {@code b}
 * may be in an inconsistent state. It is strongly recommended that the
 * stream be promptly closed if an I/O error occurs.
 *
 * @param  b the buffer into which the data is read
 * @param  off the start offset in {@code b} at which the data is written
 * @param  len the maximum number of bytes to read
 * @return the actual number of bytes read into the buffer
 * @throws IOException if an I/O error occurs
 * @throws NullPointerException if {@code b} is {@code null}
 * @throws IndexOutOfBoundsException If {@code off} is negative, {@code len}
 *                is negative, or {@code len} is greater than {@code b.length - off}
 *
 * @since 1.9
 */
public int readNBytes(byte[] b, int off, int len) throws IOException {
    Objects.requireNonNull(b);
    if (off < 0 || len < 0 || len > b.length - off)
        throw new IndexOutOfBoundsException();
    int n = 0;
    while (n < len) {
        int count = read(b, off + n, len - n);
        if (count < 0)
            break;
        n += count;
    }
    return n;
}