feat: return all catalogs for getCatalogs metadata query (#2949) (#2953)

Use the pg.catalog.pg_database table present in all catalogs to return
the list of available catalogs, instead of just the current one the
connection uses. The table is filtered to include only the
catalogs that can be connected to.

closes #2949

Co-authored-by: Papp István Péter <pip25@sonrisa.hu>

pgjdbc/src/main/java/org/postgresql/jdbc/PgDatabaseMetaData.java

@@ -1457,20 +1457,11 @@ public ResultSet getSchemas(@Nullable String catalog, @Nullable String schemaPat
     return createMetaDataStatement().executeQuery(sql);
   }
 
-  /**
-   * PostgreSQL does not support multiple catalogs from a single connection, so to reduce confusion
-   * we only return the current catalog. {@inheritDoc}
-   */
   @Override
   public ResultSet getCatalogs() throws SQLException {
-    Field[] f = new Field[1];
-    List<Tuple> v = new ArrayList<Tuple>();
-    f[0] = new Field("TABLE_CAT", Oid.VARCHAR);
-    byte[] @Nullable [] tuple = new byte[1][];
-    tuple[0] = connection.encodeString(connection.getCatalog());
-    v.add(new Tuple(tuple));
-
-    return ((BaseStatement) createMetaDataStatement()).createDriverResultSet(f, v);
+    String sql = "SELECT datname AS TABLE_CAT FROM pg_catalog.pg_database"
+        + " WHERE datallowconn = true";
+    return createMetaDataStatement().executeQuery(sql);
   }
 
   @Override

pgjdbc/src/test/java/org/postgresql/test/jdbc2/DatabaseMetaDataTest.java

@@ -1065,9 +1065,26 @@ public void testProcedures() throws SQLException {
   public void testCatalogs() throws SQLException {
     DatabaseMetaData dbmd = con.getMetaData();
     ResultSet rs = dbmd.getCatalogs();
-    assertTrue(rs.next());
-    assertEquals(con.getCatalog(), rs.getString(1));
-    assertTrue(!rs.next());
+
+    boolean foundDefault = false;
+    boolean foundTest = false;
+    int count;
+
+    for (count = 0; rs.next(); count++) {
+      String catalog = rs.getString("TABLE_CAT");
+      if ("test".equals(catalog)) {
+        foundTest = true;
+      }
+      if ("postgres".equals(catalog)) {
+        foundDefault = true;
+      }
+    }
+
+    rs.close();
+
+    assertTrue(count >= 2);
+    assertTrue(foundDefault);
+    assertTrue(foundTest);
   }
 
   @Test