Handle column count change in PDO MySQL

This has been fixed for PDO SQlite by GH-4313, however the same
issue also applied to PDO MySQL.

Move the column count setting function into the main PDO layer
(and export it) and then use it in both PDO SQLite and PDO MySQL.

Author: nikic

ext/pdo/pdo_stmt.c

@@ -173,6 +173,45 @@ int pdo_stmt_describe_columns(pdo_stmt_t *stmt) /* {{{ */
 }
 /* }}} */
 
+static void pdo_stmt_reset_columns(pdo_stmt_t *stmt) {
+	if (stmt->columns) {
+		int i;
+		struct pdo_column_data *cols = stmt->columns;
+
+		for (i = 0; i < stmt->column_count; i++) {
+			if (cols[i].name) {
+				zend_string_release_ex(cols[i].name, 0);
+			}
+		}
+		efree(stmt->columns);
+	}
+	stmt->columns = NULL;
+	stmt->column_count = 0;
+}
+
+/**
+ * Change the column count on the statement. If it differs from the previous one,
+ * discard existing columns information.
+ */
+PDO_API void php_pdo_stmt_set_column_count(pdo_stmt_t *stmt, int new_count)
+{
+	/* Columns not yet "described". */
+	if (!stmt->columns) {
+		stmt->column_count = new_count;
+		return;
+	}
+
+	/* The column count has not changed: No need to reload columns description.
+	 * Note: Do not handle attribute name change, without column count change. */
+	if (new_count == stmt->column_count) {
+		return;
+	}
+
+	/* Free previous columns to force reload description. */
+	pdo_stmt_reset_columns(stmt);
+	stmt->column_count = new_count;
+}
+
 static void get_lazy_object(pdo_stmt_t *stmt, zval *return_value) /* {{{ */
 {
 	if (Z_ISUNDEF(stmt->lazy_object_ref)) {
@@ -1910,20 +1949,7 @@ PHP_METHOD(PDOStatement, setFetchMode)
 
 static bool pdo_stmt_do_next_rowset(pdo_stmt_t *stmt)
 {
-	/* un-describe */
-	if (stmt->columns) {
-		int i;
-		struct pdo_column_data *cols = stmt->columns;
-
-		for (i = 0; i < stmt->column_count; i++) {
-			if (cols[i].name) {
-				zend_string_release_ex(cols[i].name, 0);
-			}
-		}
-		efree(stmt->columns);
-		stmt->columns = NULL;
-		stmt->column_count = 0;
-	}
+	pdo_stmt_reset_columns(stmt);
 
 	if (!stmt->methods->next_rowset(stmt)) {
 		/* Set the executed flag to 0 to reallocate columns on next execute */
@@ -2156,19 +2182,7 @@ PDO_API void php_pdo_free_statement(pdo_stmt_t *stmt)
 		efree(stmt->query_string);
 	}
 
-	if (stmt->columns) {
-		int i;
-		struct pdo_column_data *cols = stmt->columns;
-
-		for (i = 0; i < stmt->column_count; i++) {
-			if (cols[i].name) {
-				zend_string_release_ex(cols[i].name, 0);
-				cols[i].name = NULL;
-			}
-		}
-		efree(stmt->columns);
-		stmt->columns = NULL;
-	}
+	pdo_stmt_reset_columns(stmt);
 
 	if (!Z_ISUNDEF(stmt->fetch.into) && stmt->default_fetch_type == PDO_FETCH_INTO) {
 		zval_ptr_dtor(&stmt->fetch.into);

ext/pdo/php_pdo_driver.h

@@ -690,7 +690,7 @@ PDO_API void php_pdo_dbh_addref(pdo_dbh_t *dbh);
 PDO_API void php_pdo_dbh_delref(pdo_dbh_t *dbh);
 
 PDO_API void php_pdo_free_statement(pdo_stmt_t *stmt);
-
+PDO_API void php_pdo_stmt_set_column_count(pdo_stmt_t *stmt, int new_count);
 
 PDO_API void pdo_throw_exception(unsigned int driver_errcode, char *driver_errmsg, pdo_error_type *pdo_error);
 #endif /* PHP_PDO_DRIVER_H */

ext/pdo_mysql/mysql_statement.c

@@ -144,7 +144,7 @@ static int pdo_mysql_fill_stmt_from_result(pdo_stmt_t *stmt) /* {{{ */
 		}
 
 		stmt->row_count = (zend_long) mysql_num_rows(S->result);
-		stmt->column_count = (int) mysql_num_fields(S->result);
+		php_pdo_stmt_set_column_count(stmt, (int) mysql_num_fields(S->result));
 		S->fields = mysql_fetch_fields(S->result);
 	} else {
 		/* this was a DML or DDL query (INSERT, UPDATE, DELETE, ... */
@@ -194,7 +194,7 @@ static int pdo_mysql_stmt_execute_prepared_libmysql(pdo_stmt_t *stmt) /* {{{ */
 				efree(S->out_length);
 			}
 
-			stmt->column_count = (int)mysql_num_fields(S->result);
+			php_pdo_stmt_set_column_count(stmt, (int)mysql_num_fields(S->result));
 			S->bound_result = ecalloc(stmt->column_count, sizeof(MYSQL_BIND));
 			S->out_null = ecalloc(stmt->column_count, sizeof(my_bool));
 			S->out_length = ecalloc(stmt->column_count, sizeof(zend_ulong));
@@ -290,7 +290,7 @@ static int pdo_mysql_stmt_execute_prepared_mysqlnd(pdo_stmt_t *stmt) /* {{{ */
 	}
 
 	/* for SHOW/DESCRIBE and others the column/field count is not available before execute */
-	stmt->column_count = mysql_stmt_field_count(S->stmt);
+	php_pdo_stmt_set_column_count(stmt, mysql_stmt_field_count(S->stmt));
 	for (i = 0; i < stmt->column_count; i++) {
 		mysqlnd_stmt_bind_one_result(S->stmt, i);
 	}
@@ -378,7 +378,7 @@ static int pdo_mysql_stmt_next_rowset(pdo_stmt_t *stmt) /* {{{ */
 			/* for SHOW/DESCRIBE and others the column/field count is not available before execute */
 			int i;
 
-			stmt->column_count = mysql_stmt_field_count(S->stmt);
+			php_pdo_stmt_set_column_count(stmt, mysql_stmt_field_count(S->stmt));
 			for (i = 0; i < stmt->column_count; i++) {
 				mysqlnd_stmt_bind_one_result(S->stmt, i);
 			}
@@ -407,9 +407,6 @@ static int pdo_mysql_stmt_next_rowset(pdo_stmt_t *stmt) /* {{{ */
 /* ensure that we free any previous unfetched results */
 #ifndef PDO_USE_MYSQLND
 	if (S->stmt) {
-		if (S->result) {
-			stmt->column_count = (int)mysql_num_fields(S->result);
-		}
 		mysql_stmt_free_result(S->stmt);
 	}
 #endif

ext/pdo_mysql/tests/change_column_count.phpt

@@ -0,0 +1,60 @@
+--TEST--
+Change column count after statement has been prepared
+--SKIPIF--
+<?php
+if (!extension_loaded('pdo') || !extension_loaded('pdo_mysql')) die('skip not loaded');
+require_once(__DIR__ . DIRECTORY_SEPARATOR . 'skipif.inc');
+require_once(__DIR__ . DIRECTORY_SEPARATOR . 'mysql_pdo_test.inc');
+MySQLPDOTest::skip();
+?>
+--FILE--
+<?php
+require_once(__DIR__ . DIRECTORY_SEPARATOR . 'mysql_pdo_test.inc');
+
+$db = MySQLPDOTest::factory();
+$db->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
+
+$db->exec('DROP TABLE IF EXISTS test');
+$db->exec('CREATE TABLE test (id INTEGER PRIMARY KEY NOT NULL, name VARCHAR(255) NOT NULL)');
+
+$stmt = $db->prepare('INSERT INTO test (id, name) VALUES(:id, :name)');
+$stmt->execute([
+    'id'   => 10,
+    'name' => 'test',
+]);
+
+$stmt = $db->prepare('SELECT * FROM test WHERE id = :id');
+$stmt->execute(['id' => 10]);
+var_dump($stmt->fetchAll(\PDO::FETCH_ASSOC));
+
+$db->exec('ALTER TABLE test ADD new_col VARCHAR(255)');
+$stmt->execute(['id' => 10]);
+var_dump($stmt->fetchAll(\PDO::FETCH_ASSOC));
+
+?>
+--CLEAN--
+<?php
+require __DIR__ . '/mysql_pdo_test.inc';
+MySQLPDOTest::dropTestTable();
+?>
+--EXPECT--
+array(1) {
+  [0]=>
+  array(2) {
+    ["id"]=>
+    string(2) "10"
+    ["name"]=>
+    string(4) "test"
+  }
+}
+array(1) {
+  [0]=>
+  array(3) {
+    ["id"]=>
+    string(2) "10"
+    ["name"]=>
+    string(4) "test"
+    ["new_col"]=>
+    NULL
+  }
+}

ext/pdo_sqlite/sqlite_statement.c

@@ -39,46 +39,6 @@ static int pdo_sqlite_stmt_dtor(pdo_stmt_t *stmt)
 	return 1;
 }
 
-/**
- * Change the column count on the statement.
- *
- * Since PHP 7.2 sqlite3_prepare_v2 is used which auto recompile prepared statement on schema change.
- * Instead of raise an error on schema change, the result set will change, and the statement's columns must be updated.
- *
- * See bug #78192
- */
-static void pdo_sqlite_stmt_set_column_count(pdo_stmt_t *stmt, int new_count)
-{
-	/* Columns not yet "described" */
-	if (!stmt->columns) {
-		stmt->column_count = new_count;
-
-		return;
-	}
-
-	/*
-	 * The column count has not changed : no need to reload columns description
-	 * Note: Do not handle attribute name change, without column count change
-	 */
-	if (new_count == stmt->column_count) {
-		return;
-	}
-
-	/* Free previous columns to force reload description */
-	int i;
-
-	for (i = 0; i < stmt->column_count; i++) {
-		if (stmt->columns[i].name) {
-			zend_string_release(stmt->columns[i].name);
-			stmt->columns[i].name = NULL;
-		}
-	}
-
-	efree(stmt->columns);
-	stmt->columns = NULL;
-	stmt->column_count = new_count;
-}
-
 static int pdo_sqlite_stmt_execute(pdo_stmt_t *stmt)
 {
 	pdo_sqlite_stmt *S = (pdo_sqlite_stmt*)stmt->driver_data;
@@ -91,11 +51,11 @@ static int pdo_sqlite_stmt_execute(pdo_stmt_t *stmt)
 	switch (sqlite3_step(S->stmt)) {
 		case SQLITE_ROW:
 			S->pre_fetched = 1;
-			pdo_sqlite_stmt_set_column_count(stmt, sqlite3_data_count(S->stmt));
+			php_pdo_stmt_set_column_count(stmt, sqlite3_data_count(S->stmt));
 			return 1;
 
 		case SQLITE_DONE:
-			pdo_sqlite_stmt_set_column_count(stmt, sqlite3_column_count(S->stmt));
+			php_pdo_stmt_set_column_count(stmt, sqlite3_column_count(S->stmt));
 			stmt->row_count = sqlite3_changes(S->H->db);
 			sqlite3_reset(S->stmt);
 			S->done = 1;