[
http://issues.apache.org/jira/browse/DERBY-1516?page=comments#action_12425568 ]
Dag H. Wanvik commented on DERBY-1516:
--------------------------------------
If you are modelling this on the java.lang.String modulo indexing, it
seems to me that this is slightly wrong:
"The position must be between 1 and the last position of the Lob".
I think it should be
"The position must be between 1 and the last position + 1 of the Lob",
cf. this example which does not throw exceptions. In the substring of
t2, the position is *one past* the final position of the string, final
position being 0.
String t1 = "";
String t2 = "a";
String t3;
try {
System.out.println("t1.substring(0,0) = '" +
t1.substring(0,0) +
"'");
} catch (IndexOutOfBoundsException e) {
System.out.println("t1.substring(0,0) throws");
}
try {
System.out.println("t2.substring(1,1) = '" +
t2.substring(1,1) +
"'");
} catch (IndexOutOfBoundsException e) {
System.out.println("t2.substring(1,1) throws");
}
}
that is, you can always request an empty string from the position
*immediately after* the last byte, but not further out. This would
remove the asymmetry you have in the code, too:
if (this.length() == 0) {
if (pos > 1) {
throw new SqlException(agent_.logWriter_,
new ClientMessageId(SQLState.BLOB_POSITION_TOO_LARGE),
new Long(pos));
}
} else { // this.length() > 0
if (pos > this.length()) {
throw new SqlException(agent_.logWriter_,
new ClientMessageId(SQLState.BLOB_POSITION_TOO_LARGE),
new Long(pos));
}
}
would reduce to:
if (pos > this.length() + 1) {
throw new SqlException(agent_.logWriter_,
new ClientMessageId(SQLState.BLOB_POSITION_TOO_LARGE),
new Long(pos));
}
I also think this is the symmetry one would want for programming
convenience, like you have mentioned.
> Inconsistent behavior for getBytes and getSubString for embedded versus
> network
> -------------------------------------------------------------------------------
>
> Key: DERBY-1516
> URL: http://issues.apache.org/jira/browse/DERBY-1516
> Project: Derby
> Issue Type: Bug
> Components: JDBC
> Reporter: Craig Russell
> Assigned To: Craig Russell
> Priority: Minor
> Attachments: DERBY-1516.patch, DERBY-1516.patch, DERBY-1516.patch,
> DERBY-1516.patch
>
>
> org.apache.derby.client.am.Clob.getSubString(pos, length) and
> org.apache.derby.client.am.Blob.getBytes(pos, length) check the length for
> less than zero.
> if ((pos <= 0) || (length < 0)) {
> throw new SqlException(agent_.logWriter_, "Invalid position "
> + pos + " or length " + length);
> But org.apache.derby.impl.jdbc.EmbedClob(pos, length) and
> org.apache.derby.impl.jdbc.EmbedBlob(pos, length) check the length for less
> than or equal to zero.
> if (length <= 0)
> throw Util.generateCsSQLException(
> SQLState.BLOB_NONPOSITIVE_LENGTH, new Integer(length));
> The specification does not disallow length of zero, so zero length should be
> allowed. I believe that the implementation in org.apache.derby.client.am is
> correct, and the implementation in org.apache.derby.impl.jdbc is incorrect.
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