Bryan Pendleton created DERBY-6997:
--------------------------------------
Summary: Confusing code in NetworkServerControlImpl could be
improved
Key: DERBY-6997
URL: https://issues.apache.org/jira/browse/DERBY-6997
Project: Derby
Issue Type: Improvement
Components: Network Server
Affects Versions: 10.14.2.0
Reporter: Bryan Pendleton
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:
{code:java}
private void writeShort(int value) throws Exception
{
try {
commandOs.writeByte((byte)((value & 0xf0) >> 8 ));
commandOs.writeByte((byte)(value & 0x0f));
}
catch (IOException e)
{
clientSocketError(e);
}
}
{code}
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:
{code:java}
private void writeShort(int value) throws Exception
{
try {
commandOs.writeByte((byte)((value & 0xff00) >> 8 ));
commandOs.writeByte((byte)(value & 0x00ff));
}
catch (IOException e)
{
clientSocketError(e);
}
}
{code}
or perhaps
{code:java}
private void writeShort(int value) throws Exception
{
try {
commandOs.writeByte((byte)((value >> 8 ));
commandOs.writeByte((byte)value);
}
catch (IOException e)
{
clientSocketError(e);
}
}
{code}
or some such, but really I don't understand it at all.
And, very close to this code is a very similar method:
{code:java}
private void writeByte(int value) throws Exception
{
try {
commandOs.writeByte((byte)(value & 0x0f));
}
catch (IOException e)
{
clientSocketError(e);
}
}
{code}
which I think might be damaged for any value in the
range 17-255? It seems like it should probably be:
{code:java}
private void writeByte(int value) throws Exception
{
try {
commandOs.writeByte((byte)(value & 0xff));
}
catch (IOException e)
{
clientSocketError(e);
}
}
{code}
or maybe just:
{code:java}
private void writeByte(int value) throws Exception
{
try {
commandOs.writeByte((byte)value);
}
catch (IOException e)
{
clientSocketError(e);
}
}
{code}
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