MySQL Bugs: #99108: Zero-length branch qualifier causes SQL syntax error when starting transaction

Bug #99108	Zero-length branch qualifier causes SQL syntax error when starting transaction
Submitted:	30 Mar 2020 14:11	Modified:	4 May 2020 12:20
Reporter:	Viliam Durina	Email Updates:
Status:	Can't repeat	Impact on me:	None
Category:	Connector / J	Severity:	S3 (Non-critical)
Version:	8.0.12	OS:	Ubuntu
Assigned to:		CPU Architecture:	x86

Description:
Using JDBC we created a `Xid` with zero-length branch qualifier. When calling `XAResource.start(xid, TMNOFLAGS)`, this error was thrown:

Exception in thread "main" com.mysql.cj.jdbc.MysqlXAException: Undetermined error occurred in the underlying Connection - check your data for consistency
	at com.mysql.cj.jdbc.MysqlXAConnection.mapXAExceptionFromSQLException(MysqlXAConnection.java:347)
	at com.mysql.cj.jdbc.MysqlXAConnection.dispatchCommand(MysqlXAConnection.java:329)
	at com.mysql.cj.jdbc.MysqlXAConnection.start(MysqlXAConnection.java:290)
	at com.hazelcast.jet.contrib.xatests.JdbcXaTest.main(JdbcXaTest.java:66)
Caused by: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '0x,0x1' at line 1
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
	at com.mysql.cj.jdbc.StatementImpl.executeInternal(StatementImpl.java:764)
	at com.mysql.cj.jdbc.StatementImpl.execute(StatementImpl.java:648)
	at com.mysql.cj.jdbc.MysqlXAConnection.dispatchCommand(MysqlXAConnection.java:323)
	... 2 more 

How to repeat:
Use this `Xid` implementation:

public final class MyXid implements Xid, Serializable {

    private final byte trId;

    /** Constructor */
    public MyXid(int trId) {
        this.trId = (byte) trId;
    }

    @Override
    public int getFormatId() {
        return 1;
    }

    @Override
    public byte[] getGlobalTransactionId() {
        return new byte[]{trId};
    }

    @Override
    public byte[] getBranchQualifier() {
        return new byte[0];
    }
}

Then call this:

        XAConnection xaConn = factory.getXAConnection();
        Connection conn = xaConn.getConnection();
        XAResource xaRes = xaConn.getXAResource();
        Xid xid = new MyXid(1);
        // here it fails:
        xaRes.start(xid, XAResource.TMNOFLAGS);

I confirmed with the X/Open spec that the branch qualifier should have length between 1..64, so 0 isn't allowed. But other databases accept it so it can happen in the wild. The above error is very unspecific and took us a while to figure out the cause. JDBC driver version was 8.0.18.

Suggested fix:
I expect the code to throw "Branch qualifier must be between 1..64 bytes" or similar.

Hi Mr. Durina,

Thank you for your bug report.

When you created this report, you have set a category of "MySQL Server: XA transactions". However, your steps for repeating this behaviour are strictly related to Connector/JDBC.

Hence, if the category is correct, you can provide us with a test case in SQL ????

Last, but not least, you are using an outdated release. Hence, please download and use latest releases of our server and of Connector/JDBC. Let us know if it helps .......

I couldn't find a category for JDBC driver, that's why I've put it to the XA transactions category. I don't have a reproducer in plain SQL. Can you please change the category?

Regarding the version this is the newest version I have in my setup using testcontainers. It's rather minor issue and I searched for existing issues first, I don't believe it was fixed since then, though it's possible. I'm unable to try the newest release now.

Hi Mr. Durina,

I have now set a category that is correct.

Still, we do not test reports on the old releases. Please, try our latest server and latest Connector/J release.

Thanks in advance.

No feedback was provided for this bug for over a month, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".