MySQL Bugs: #95210: ClassCastException in BlobFromLocator when connecting as jdbc:mysql:replication

Bug #95210	ClassCastException in BlobFromLocator when connecting as jdbc:mysql:replication
Submitted:	30 Apr 2019 16:36	Modified:	26 Jun 2019 16:35
Reporter:	matt m	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / J	Severity:	S2 (Serious)
Version:	8.0.15	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
When using a connection that supports replication of the form
   
jdbc:mysql:replication://server1:6600,server2:6601/db?useCursorFetch=true&emulateLocators=true&enableQueryTimeouts=false&alwaysSendSetIsolation=false&autoClosePStmtStreams=true&nullCatalogMeansCurrent=true&pinGlobalTxToPhysicalConnection=true&sslMode=DISABLED 

calling read() on the stream returned from BlobFromLocator.getBinaryStream () results in a ClassCastException:

 java.lang.ClassCastException: com.sun.proxy.$Proxy110 cannot be cast to com.mysql.cj.jdbc.result.ResultSetImpl
	at com.mysql.cj.jdbc.BlobFromLocator.getBytesInternal(BlobFromLocator.java:482) ~[mysql-connector-java.jar:8.0.15]
	at com.mysql.cj.jdbc.BlobFromLocator$LocatorInputStream.read(BlobFromLocator.java:560) ~[mysql-connector-java.jar:8.0.15]
	at java.io.BufferedInputStream.fill(BufferedInputStream.java:246) ~[?:1.8.0_202]
	at java.io.BufferedInputStream.read1(BufferedInputStream.java:286) ~[?:1.8.0_202]
	at java.io.BufferedInputStream.read(BufferedInputStream.java:345) ~[?:1.8.0_202]

How to repeat:

Retrieve data from any BlobFromLocator utilizing a replicated (and I suspect loadbalanced) connection.

Suggested fix:
Workaround: don't use emulateLocators=true on loadbalanced connections.

Fix: Remove the cast since getBytes(int) is defined in the java.sql.ResultSet interface.

Hi Matt,

Thanks for the report and working solution!

Posted by developer:
 
Added the following entry to the Connector/J 8.0.17 changelog:

"When using a replication connection, retrieving data from a BlobFromLocator resulted in a ClassCastException. It was due to some wrong and unnecessary casting, which has been removed by this fix."