Fix crash with COPY FROM and/or foreign partition routing operations.

COPY FROM and/or foreign partition routing code path in core assumes
that FDW has BeginForeignInsert() APIs present and thus later
executes ExecForeignInsert().  However, mysql_fdw does not support
routable foreign-table partitions and/or executing COPY FROM on
foreign tables and thus do not have BeginForeignInsert() API
implemented.  But as it has ExecForeignInsert() API, it gets called
for these operations and results in the server crash.  To fix this,
add the BeginForeignInsert() API that throws an error.  Also, add
EndForeignInsert() similar to the Begin API.

Reported on GitHub through issue #208 and an initial patch by
Ian Barwick (ibarwick).

FDW-224, patch further revised by Suraj Kharage, reviewed by
Jeevan Ladhe.

Author: jeevanchalke

mysql_fdw.c

@@ -188,6 +188,13 @@ static List *mysqlImportForeignSchema(ImportForeignSchemaStmt *stmt,
 									  Oid serverOid);
 #endif
 
+#if PG_VERSION_NUM >= 110000
+static void mysqlBeginForeignInsert(ModifyTableState *mtstate,
+									ResultRelInfo *resultRelInfo);
+static void mysqlEndForeignInsert(EState *estate,
+								  ResultRelInfo *resultRelInfo);
+#endif
+
 /*
  * Helper functions
  */
@@ -418,6 +425,12 @@ mysql_fdw_handler(PG_FUNCTION_ARGS)
 	fdwroutine->ImportForeignSchema = mysqlImportForeignSchema;
 #endif
 
+#if PG_VERSION_NUM >= 110000
+	/* Partition routing and/or COPY from */
+	fdwroutine->BeginForeignInsert = mysqlBeginForeignInsert;
+	fdwroutine->EndForeignInsert = mysqlEndForeignInsert;
+#endif
+
 	PG_RETURN_POINTER(fdwroutine);
 }
 
@@ -1873,6 +1886,39 @@ mysqlImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 }
 #endif
 
+#if PG_VERSION_NUM >= 110000
+/*
+ * mysqlBeginForeignInsert
+ * 		Prepare for an insert operation triggered by partition routing
+ * 		or COPY FROM.
+ *
+ * This is not yet supported, so raise an error.
+ */
+static void
+mysqlBeginForeignInsert(ModifyTableState *mtstate,
+						ResultRelInfo *resultRelInfo)
+{
+	ereport(ERROR,
+			(errcode(ERRCODE_FDW_UNABLE_TO_CREATE_EXECUTION),
+			 errmsg("COPY and foreign partition routing not supported in mysql_fdw")));
+}
+
+/*
+ * mysqlEndForeignInsert
+ * 		BeginForeignInsert() is not yet implemented, hence we do not
+ * 		have anything to cleanup as of now. We throw an error here just
+ * 		to make sure when we do that we do not forget to cleanup
+ * 		resources.
+ */
+static void
+mysqlEndForeignInsert(EState *estate, ResultRelInfo *resultRelInfo)
+{
+	ereport(ERROR,
+			(errcode(ERRCODE_FDW_UNABLE_TO_CREATE_EXECUTION),
+			 errmsg("COPY and foreign partition routing not supported in mysql_fdw")));
+}
+#endif
+
 /*
  * Prepare for processing of parameters used in remote query.
  */