[DERBY-6997] Confusing code in NetworkServerControlImpl could be improved

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 10.14.2.0
• Component/s: Network Server
• Assignee: Unassigned
• Reporter: Bryan Pendleton
• Created: 05/May/18 15:30
• Updated: 05/May/18 15:30

Description

As was discussed on the derby-dev list here: http://mail-archives.apache.org/mod_mbox/db-derby-dev/201802.mbox/%3CCANi-yg8ru8BLNVxW0v6TT_ndPa8Y7_MD6zpgjiyQ6MQoT4Ca9g%40mail.gmail.com%3E

it seems like there is some confusing shifting-and-masking code in NetworkServerControlImpl that could be improved:

    private void writeShort(int value) throws Exception
    {
        try {
            commandOs.writeByte((byte)((value & 0xf0) >> 8 ));
            commandOs.writeByte((byte)(value & 0x0f));
        }
        catch (IOException e)
        {
            clientSocketError(e);
        }
    }

I'm not quite sure what this code is doing.

It seems to be mixing some combination of 8-bit shifting
and 4-bit value masking.

I think it might actually be losing/destroying 4 bits of
the 16-bit value (the high 4 bytes in the low byte of
the short).

For example if you call writeShort(23), it emits 0x00, 0x07,
when I think it should emit 0x00,0x17.

I suspect the code should read:

    private void writeShort(int value) throws Exception
    {
        try {
            commandOs.writeByte((byte)((value & 0xff00) >> 8 ));
            commandOs.writeByte((byte)(value & 0x00ff));
        }
        catch (IOException e)
        {
            clientSocketError(e);
        }
    }

or perhaps

    private void writeShort(int value) throws Exception
    {
        try {
            commandOs.writeByte((byte)((value >> 8 ));
            commandOs.writeByte((byte)value);
        }
        catch (IOException e)
        {
            clientSocketError(e);
        }
    }

or some such, but really I don't understand it at all.

And, very close to this code is a very similar method:

    private void writeByte(int value) throws Exception
    {
        try {
            commandOs.writeByte((byte)(value & 0x0f));
        }
        catch (IOException e)
        {
            clientSocketError(e);
        }
    }

which I think might be damaged for any value in the
range 17-255? It seems like it should probably be:

    private void writeByte(int value) throws Exception
    {
        try {
            commandOs.writeByte((byte)(value & 0xff));
        }
        catch (IOException e)
        {
            clientSocketError(e);
        }
    }

or maybe just:

    private void writeByte(int value) throws Exception
    {
        try {
            commandOs.writeByte((byte)value);
        }
        catch (IOException e)
        {
            clientSocketError(e);
        }
    }