RFR: 8266078: Reader.read(CharBuffer) advances Reader position for read-only Charbuffers

[Brian Burkhalter]

On Tue, 27 Apr 2021 19:31:40 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Please consider this request to modify `Reader.read(CharBuffer)` to check whether the buffer is read-only before reading any characters from the character stream. This can happen now if the buffer is read-only. Character are first read thereby advancing the stream before an attempt is made to put them in the `CharBuffer` thus incorrectly advancing the stream position.
>
> src/java.base/share/classes/java/io/Reader.java line 202:
> 
>> 200:             if (target.isReadOnly())
>> 201:                 throw new ReadOnlyBufferException();
>> 202:             int len = target.remaining();
> 
> It seems like the other branch of the if should also check for read-only and throw.
> Or can the target not have an array if it is readonly.
> It might return -1 for a readonly target if the source was used up. The always throw.
> 
> Moving the `if (target.isReadOnly())`  to the line 188: would be unambiguous.

It can't have an array if it is read-only.

Returns:
    true if, and only if, this buffer is backed by an array and is not read-only

https://docs.oracle.com/en/java/javase/16/docs/api/java.base/java/nio/CharBuffer.html#hasArray()

> test/jdk/java/io/Reader/ReadIntoReadOnlyBuffer.java line 52:
> 
>> 50:         try {
>> 51:             r.read(b);
>> 52:             throw new RuntimeException();
> 
> A helpful message would make it clearer what failed, when/if it fails.

Agreed.

-------------

PR: https://git.openjdk.java.net/jdk/pull/3725