Check liveness in PDO_ODBC

PDO drivers allow for it, and procedural ODBC has its own facility for it, but PDO_ODBC doesn't. If a connection is severed (for example, on IBM i, ending a databse job, or killing the network connection elsewhere), a persistent connection could get stuck. This adapts the procedural ODBC code to PDO for handling connection liveness, so PDO can reconnect if needed. A discussion about the method to check liveness is linked; this might not be the best method, but it's what procedural ODBC uses, so it's consistent. Closes phpGH-6805.

Author: NattyNarwhal

ext/pdo_odbc/odbc_driver.c

@@ -372,6 +372,26 @@ static int odbc_handle_get_attr(pdo_dbh_t *dbh, zend_long attr, zval *val)
 return 0;
 }
 
+static zend_result odbc_handle_check_liveness(pdo_dbh_t *dbh)
+{
+RETCODE ret;
+UCHAR d_name[32];
+SQLSMALLINT len;
+pdo_odbc_db_handle *H = (pdo_odbc_db_handle *)dbh->driver_data;
+
+/*
+ * SQL_ATTR_CONNECTION_DEAD is tempting, but only in ODBC 3.5,
+ * and not all drivers implement it properly
+ */
+ret = SQLGetInfo(H->dbc, SQL_DATA_SOURCE_READ_ONLY, d_name,
+sizeof(d_name), &len);
+
+if (ret != SQL_SUCCESS || len == 0) {
+return FAILURE;
+}
+return SUCCESS;
+}
+
 static const struct pdo_dbh_methods odbc_methods = {
 odbc_handle_closer,
 odbc_handle_preparer,
@@ -384,7 +404,7 @@ static const struct pdo_dbh_methods odbc_methods = {
 NULL,/* last id */
 pdo_odbc_fetch_error_func,
 odbc_handle_get_attr,/* get attr */
-NULL, /* check_liveness */
+odbc_handle_check_liveness, /* check_liveness */
 NULL, /* get_driver_methods */
 NULL, /* request_shutdown */
 NULL, /* in transaction, use PDO's internal tracking mechanism */