Make sure we get usable error messages when text could not be decoded when...

Make sure we get usable error messages when text could not be decoded when fetched from the database.

Lib/sqlite3/test/regression.py

@@ -79,6 +79,20 @@ class RegressionTests(unittest.TestCase):
         cur.fetchone()
         cur.fetchone()
 
+    def CheckErrorMsgDecodeError(self):
+        # When porting the module to Python 3.0, the error message about
+        # decoding errors disappeared. This verifies they're back again.
+        failure = None
+        try:
+            self.con.execute("select 'xxx' || ? || 'yyy' colname", (bytes(bytearray([250])),)).fetchone()
+            failure = "should have raised an OperationalError with detailed description"
+        except sqlite.OperationalError as e:
+            msg = e.args[0]
+            if not msg.startswith("Could not decode to UTF-8 column 'colname' with text 'xxx"):
+                failure = "OperationalError did not have expected description text"
+        if failure:
+            self.fail(failure)
+
 def suite():
     regression_suite = unittest.makeSuite(RegressionTests, "Check")
     return unittest.TestSuite((regression_suite,))

Modules/_sqlite/cursor.c

@@ -295,6 +295,8 @@ PyObject* _pysqlite_fetch_one_row(pysqlite_Cursor* self)
     const char* val_str;
     char buf[200];
     const char* colname;
+    PyObject* buf_bytes;
+    PyObject* error_obj;
 
     Py_BEGIN_ALLOW_THREADS
     numcols = sqlite3_data_count(self->statement->st);
@@ -363,7 +365,19 @@ PyObject* _pysqlite_fetch_one_row(pysqlite_Cursor* self)
                         }
                         PyOS_snprintf(buf, sizeof(buf) - 1, "Could not decode to UTF-8 column '%s' with text '%s'",
                                      colname , val_str);
-                        PyErr_SetString(pysqlite_OperationalError, buf);
+                        buf_bytes = PyBytes_FromStringAndSize(buf, strlen(buf)); 
+                        if (!buf_bytes) {
+                            PyErr_SetString(pysqlite_OperationalError, "Could not decode to UTF-8");
+                        } else {
+                            error_obj = PyUnicode_FromEncodedObject(buf_bytes, "ascii", "replace");
+                            if (!error_obj) {
+                                PyErr_SetString(pysqlite_OperationalError, "Could not decode to UTF-8");
+                                Py_DECREF(error_obj);
+                            } else {
+                                PyErr_SetObject(pysqlite_OperationalError, error_obj);
+                            }
+                            Py_DECREF(buf_bytes);
+                        }
                     }
                 } else if (self->connection->text_factory == (PyObject*)&PyString_Type) {
                     converted = PyString_FromString(val_str);