terrymanu commented on issue #34972:
URL:
https://github.com/apache/shardingsphere/issues/34972#issuecomment-3642247010
## Understanding
In openGauss 7.0 + psycopg, running select … order by %s::int limit %s via
Proxy (extended query, prepare=False/binary=False) triggers
java.lang.ClassCastException: java.lang.Short cannot be cast to
java.lang.Integer. You’re checking whether Proxy mishandles int2
parameters.
## Root Cause
For LIMIT/OFFSET params, PaginationContext#getValue assumes Integer/Long;
when the client marks the param as int2 (OID 21),
PostgreSQLInt2BinaryProtocolValue returns a Short, and the subsequent (int) obj
cast throws CCE. The client usage is valid per PostgreSQL/
OpenGauss protocol; the incompatibility is on Proxy’s side for small
integer params.
## Analysis
- Protocol: PostgreSQL int2 binary encoding is a signed 2-byte integer
(official doc:
https://www.postgresql.org/docs/current/protocol-message-types.html). Switching
to payload.readInt2() would read as unsigned, breaking negative smallints, so
that isn’t a correct fix.
- Current code: PaginationContext#getValue only handles Long/Integer and
otherwise does (int) obj, so Short and other Number subtypes fail.
- Trigger: Any binary-bound param declared as int2 (or other non-int4
numeric) for LIMIT/ORDER BY becomes Short and hits the cast.
- Workaround: Explicitly cast the placeholder to ::int4 or send params as
text/INT4 to avoid the CCE temporarily; the server-side compatibility still
needs a fix.
## Conclusion
This is a Proxy compatibility gap for small integer pagination params, not
a misuse. A safer server-side fix is to accept any Number and widen it, while
keeping PostgreSQLInt2BinaryProtocolValue using readShort() to preserve signed
semantics. Example direction
(illustrative):
```java
// PaginationContext#getValue
if (paginationValueSegment instanceof
ParameterMarkerPaginationValueSegment) {
Object obj = params == null || params.isEmpty() ? 0L :
params.get(((ParameterMarkerPaginationValueSegment)
paginationValueSegment).getParameterIndex());
if (obj == null) {
return null;
}
if (obj instanceof Number) {
return ((Number) obj).longValue(); // unify Short/Integer/Long,
etc.
}
throw new IllegalArgumentException("Unsupported pagination param type:
" + obj.getClass());
}
```
We warmly welcome community contributors to submit a PR with this
compatibility fix and add tests covering int2 pagination parameters—thanks!
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