GH-15750 Pdo\Pgsql with ATTR_PREFETCH = 0: fix getColumnMeta()

doing an (internal) query to fetch metadata from the server broke the currently-running query

Author: outtersg

ext/pdo_pgsql/pgsql_statement.c

@@ -713,6 +713,12 @@ static zend_always_inline char * pdo_pgsql_translate_oid_to_table(Oid oid, pdo_p
 		return H->cached_table_name;
 	}
 
+	if (H->running_stmt) {
+		/* in single-row mode, libpq forbids passing a new query
+		 * while we're still flushing the current one's */
+		return 0;
+	}
+
 	if (H->cached_table_name) {
 		efree(H->cached_table_name);
 		H->cached_table_oid = InvalidOid;
@@ -805,6 +811,10 @@ static int pgsql_stmt_get_column_meta(pdo_stmt_t *stmt, zend_long colno, zval *r
 			break;
 		default:
 			/* Fetch metadata from Postgres system catalogue */
+			if (S->H->running_stmt) {
+				/* libpq forbids calling a query while we're still reading the preceding one's */
+				break;
+			}
 			spprintf(&q, 0, "SELECT TYPNAME FROM PG_TYPE WHERE OID=%u", S->cols[colno].pgsql_type);
 			res = PQexec(S->H->server, q);
 			efree(q);

ext/pdo_pgsql/tests/gh15287.phpt

@@ -132,6 +132,17 @@ $res = []; while (($re = $stmt->fetch())) $res[] = $re; display($res);
 $stmt->execute([ 0 ]);
 $res = []; for ($i = -1; ++$i < 2;) $res[] = $stmt->fetch(); display($res);
 display($pdo->query("select * from t2")->fetchAll());
+
+// Metadata calls the server for some operations (notably table oid-to-name conversion).
+// This will break libpq (that forbids a second PQexec before we consumed the first one).
+// Instead of either letting libpq return an error, or blindly forbid this call, we expect
+// being transparently provided at least attributes which do not require a server roundtrip.
+// And good news: column name is one of those "local" attributes.
+echo "=== meta ===\n";
+$stmt = $pdo->query("select * from t limit 2");
+echo "Starting with column " . $stmt->getColumnMeta(0)['name'] . ":\n";
+display($stmt->fetchAll());
+
 ?>
 --EXPECTF--
 === non regression ===
@@ -181,3 +192,7 @@ multiple calls to the same prepared statement, some interrupted before having re
 0
 1
 678	ok
+=== meta ===
+Starting with column n:
+0	original
+1	non original