Fix getColumnMeta() for GH-15287 Pdo\Pgsql::setAttribute(PDO::ATTR_PREFETCH, 0)

ext/pdo_pgsql/pgsql_driver.c

@@ -256,6 +256,11 @@ static void pgsql_handle_closer(pdo_dbh_t *dbh) /* {{{ */
 			PQfinish(H->server);
 			H->server = NULL;
 		}
+		if (H->cached_table_name) {
+			H->cached_table_oid = InvalidOid;
+			efree(H->cached_table_name);
+			H->cached_table_name = NULL;
+		}
 		if (H->einfo.errmsg) {
 			pefree(H->einfo.errmsg, dbh->is_persistent);
 			H->einfo.errmsg = NULL;
@@ -1542,6 +1547,7 @@ static int pdo_pgsql_handle_factory(pdo_dbh_t *dbh, zval *driver_options) /* {{{
 
 	H->attached = 1;
 	H->pgoid = -1;
+	H->cached_table_oid = InvalidOid;
 
 	dbh->methods = &pgsql_methods;
 	dbh->alloc_own_columns = 1;

ext/pdo_pgsql/pgsql_statement.c

@@ -195,6 +195,10 @@ static void pgsql_stmt_finish(pdo_pgsql_stmt *S, int fin_mode)
 
 		S->is_prepared = false;
 	}
+
+	if ((fin_mode & (FIN_CLOSE|FIN_ABORT)) && H->running_stmt == S) {
+		H->running_stmt = NULL;
+	}
 }
 
 static int pgsql_stmt_dtor(pdo_stmt_t *stmt)
@@ -204,10 +208,6 @@ static int pgsql_stmt_dtor(pdo_stmt_t *stmt)
 
 	pgsql_stmt_finish(S, FIN_DISCARD|(server_obj_usable ? FIN_CLOSE|FIN_ABORT : 0));
 
-	if (server_obj_usable && S->H->running_stmt == S) {
-		S->H->running_stmt = NULL;
-	}
-
 	if (S->stmt_name) {
 		efree(S->stmt_name);
 		S->stmt_name = NULL;
@@ -271,9 +271,8 @@ static int pgsql_stmt_execute(pdo_stmt_t *stmt)
 	 * and returns a PGRES_FATAL_ERROR when PQgetResult gets called for stmt 2 if DEALLOCATE
 	 * was called for stmt 1 inbetween
 	 * (maybe it will change with pipeline mode in libpq 14?) */
-	if (S->is_unbuffered && H->running_stmt) {
+	if (H->running_stmt && H->running_stmt->is_unbuffered) {
 		pgsql_stmt_finish(H->running_stmt, FIN_CLOSE);
-		H->running_stmt = NULL;
 	}
 	/* ensure that we free any previous unfetched results */
 	pgsql_stmt_finish(S, 0);
@@ -814,12 +813,35 @@ static int pgsql_stmt_get_col(pdo_stmt_t *stmt, int colno, zval *result, enum pd
 	return 1;
 }
 
-static zend_always_inline char * pdo_pgsql_translate_oid_to_table(Oid oid, PGconn *conn)
+static zend_always_inline char * pdo_pgsql_translate_oid_to_table(Oid oid, pdo_pgsql_db_handle *H)
 {
+	PGconn *conn = H->server;
 	char *table_name = NULL;
 	PGresult *tmp_res;
 	char *querystr = NULL;
 
+	if (oid == InvalidOid) {
+		/* InvalidOid is emitted when not selecting from a table (e.g. "SELECT 1"). No need of
+		 * a database roundtrip.
+		 */
+		return NULL;
+	}
+	if (oid == H->cached_table_oid) {
+		return H->cached_table_name ? estrdup(H->cached_table_name) : NULL;
+	}
+
+	if (H->running_stmt && H->running_stmt->is_unbuffered) {
+		/* in single-row mode, libpq forbids passing a new query
+		 * while we're still flushing the current one's result */
+		return NULL;
+	}
+
+	if (H->cached_table_name) {
+		efree(H->cached_table_name);
+		H->cached_table_name = NULL;
+		H->cached_table_oid = InvalidOid;
+	}
+
 	spprintf(&querystr, 0, "SELECT RELNAME FROM PG_CLASS WHERE OID=%d", oid);
 
 	if ((tmp_res = PQexec(conn, querystr)) == NULL || PQresultStatus(tmp_res) != PGRES_TUPLES_OK) {
@@ -836,6 +858,8 @@ static zend_always_inline char * pdo_pgsql_translate_oid_to_table(Oid oid, PGcon
 		return 0;
 	}
 
+	H->cached_table_oid = oid;
+	H->cached_table_name = estrdup(table_name);
 	table_name = estrdup(table_name);
 
 	PQclear(tmp_res);
@@ -864,7 +888,7 @@ static int pgsql_stmt_get_column_meta(pdo_stmt_t *stmt, zend_long colno, zval *r
 
 	table_oid = PQftable(S->result, colno);
 	add_assoc_long(return_value, "pgsql:table_oid", table_oid);
-	table_name = pdo_pgsql_translate_oid_to_table(table_oid, S->H->server);
+	table_name = pdo_pgsql_translate_oid_to_table(table_oid, S->H);
 	if (table_name) {
 		add_assoc_string(return_value, "table", table_name);
 		efree(table_name);
@@ -906,6 +930,10 @@ 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 && S->H->running_stmt->is_unbuffered) {
+				/* 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/php_pdo_pgsql_int.h

@@ -41,6 +41,8 @@ typedef struct {
 	unsigned 	_reserved:31;
 	pdo_pgsql_error_info	einfo;
 	Oid 		pgoid;
+	Oid cached_table_oid;
+	char *cached_table_name;
 	unsigned int	stmt_counter;
 	bool		emulate_prepares;
 	bool		disable_prepares;

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