get_data: fix SPI fetch order and portal leak on zero-row input

include/cpp_common/get_data.hpp

@@ -134,23 +134,53 @@ std::vector<Data_type> get_data(
 
     while (moredata == true) {
         SPI_cursor_fetch(SPIportal, true, tuple_limit);
+        long fetched = SPI_processed;
         auto tuptable = SPI_tuptable;
-        auto tupdesc = SPI_tuptable->tupdesc;
-        if (total_tuples == 0) fetch_column_info(tupdesc, info);
+        auto tupdesc = tuptable ? tuptable->tupdesc : nullptr;
+
+        if (fetched <= 0) {
+            /*
+             * Zero-row batch: validate schema when a descriptor is
+             * available so typos still raise a clean error, then exit
+             * with whatever was collected so far (possibly empty).
+             */
+            if (tupdesc && total_tuples == 0) {
+                try {
+                    fetch_column_info(tupdesc, info);
+                } catch (...) {
+                    if (tuptable) SPI_freetuptable(tuptable);
+                    SPI_cursor_close(SPIportal);
+                    throw;
+                }
+            }
+            if (tuptable) SPI_freetuptable(tuptable);
+            moredata = false;
+            break;
+        }
 
-        size_t ntuples = SPI_processed;
-        total_tuples += ntuples;
+        if (!tuptable || !tupdesc) {
+            if (tuptable) SPI_freetuptable(tuptable);
+            moredata = false;
+            break;
+        }
+
+        try {
+            if (total_tuples == 0) fetch_column_info(tupdesc, info);
+
+            size_t ntuples = static_cast<size_t>(fetched);
+            total_tuples += ntuples;
 
-        if (ntuples > 0) {
             tuples.reserve(total_tuples);
             for (size_t t = 0; t < ntuples; t++) {
                 tuples.push_back(func(tuptable->vals[t], tupdesc, info,
                         &default_id,
                         &valid_pgtuples, flag));
             }
             SPI_freetuptable(tuptable);
-        } else {
-            moredata = false;
+        } catch (...) {
+            SPI_freetuptable(tuptable);
+            SPI_cursor_close(SPIportal);
+            throw;
         }
     }
 

pgtap/dijkstra/dijkstra/no_crash_test.pg

@@ -7,10 +7,17 @@ BEGIN;
 
 
 UPDATE edges SET cost = sign(cost), reverse_cost = sign(reverse_cost);
-SELECT CASE WHEN min_version('3.1.0') THEN plan(82) ELSE plan(69) END;
+SELECT CASE WHEN min_version('3.1.0') THEN plan(84) ELSE plan(71) END;
 
 SELECT no_crash_dijkstra('pgr_dijkstra');
 SELECT throw_on_empty_edges_sql('pgr_dijkstra', ',1,2');
+SELECT is_empty(
+    $$SELECT * FROM pgr_dijkstra('SELECT id, source, target, cost FROM edges WHERE false', 1, 2)$$,
+    'zero-row edges_sql returns empty set without crashing');
+SELECT throws_ok(
+    $$SELECT * FROM pgr_dijkstra('SELECT id, source FROM edges WHERE false', 1, 2)$$,
+    'XX000', 'Column ''cost'' not Found',
+    'zero-row edges_sql with missing column raises a clean error');
 
 SELECT finish();