Fix Connection.escape() with Unicode input (#608)

After aed1dd2, Connection.escape() used ASCII to escape Unicode input.
This commit makes it uses connection encoding instead.

src/MySQLdb/_mysql.c

@@ -943,7 +943,7 @@ _mysql_escape_string(
 {
     PyObject *str;
     char *in, *out;
-    int len;
+    unsigned long len;
     Py_ssize_t size;
     if (!PyArg_ParseTuple(args, "s#:escape_string", &in, &size)) return NULL;
     str = PyBytes_FromStringAndSize((char *) NULL, size*2+1);
@@ -980,35 +980,52 @@ _mysql_string_literal(
     _mysql_ConnectionObject *self,
     PyObject *o)
 {
-    PyObject *str, *s;
-    char *in, *out;
-    unsigned long len;
-    Py_ssize_t size;
+    PyObject *s; // input string or bytes. need to decref.
 
     if (self && PyModule_Check((PyObject*)self))
         self = NULL;
 
     if (PyBytes_Check(o)) {
         s = o;
         Py_INCREF(s);
-    } else {
-        s = PyObject_Str(o);
-        if (!s) return NULL;
-        {
-            PyObject *t = PyUnicode_AsASCIIString(s);
-            Py_DECREF(s);
-            if (!t) return NULL;
+    }
+    else {
+        PyObject *t = PyObject_Str(o);
+        if (!t) return NULL;
+
+        const char *encoding = (self && self->open) ?
+            _get_encoding(&self->connection) : utf8;
+        if (encoding == utf8) {
             s = t;
         }
+        else {
+            s = PyUnicode_AsEncodedString(t, encoding, "strict");
+            Py_DECREF(t);
+            if (!s) return NULL;
+        }
     }
-    in = PyBytes_AsString(s);
-    size = PyBytes_GET_SIZE(s);
-    str = PyBytes_FromStringAndSize((char *) NULL, size*2+3);
+
+    // Prepare input string (in, size)
+    const char *in;
+    Py_ssize_t size;
+    if (PyUnicode_Check(s)) {
+        in = PyUnicode_AsUTF8AndSize(s, &size);
+    } else {
+        assert(PyBytes_Check(s));
+        in = PyBytes_AsString(s);
+        size = PyBytes_GET_SIZE(s);
+    }
+
+    // Prepare output buffer (str, out)
+    PyObject *str = PyBytes_FromStringAndSize((char *) NULL, size*2+3);
     if (!str) {
         Py_DECREF(s);
         return PyErr_NoMemory();
     }
-    out = PyBytes_AS_STRING(str);
+    char *out = PyBytes_AS_STRING(str);
+
+    // escape
+    unsigned long len;
     if (self && self->open) {
 #if MYSQL_VERSION_ID >= 50707 && !defined(MARIADB_BASE_VERSION) && !defined(MARIADB_VERSION_ID)
         len = mysql_real_escape_string_quote(&(self->connection), out+1, in, size, '\'');
@@ -1018,10 +1035,14 @@ _mysql_string_literal(
     } else {
         len = mysql_escape_string(out+1, in, size);
     }
-    *out = *(out+len+1) = '\'';
-    if (_PyBytes_Resize(&str, len+2) < 0) return NULL;
+
     Py_DECREF(s);
-    return (str);
+    *out = *(out+len+1) = '\'';
+    if (_PyBytes_Resize(&str, len+2) < 0) {
+        Py_DECREF(str);
+        return NULL;
+    }
+    return str;
 }
 
 static PyObject *
@@ -1499,8 +1520,9 @@ _mysql_ResultObject_discard(
         // do nothing
     }
     Py_END_ALLOW_THREADS
-    if (mysql_errno(self->conn)) {
-        return _mysql_Exception(self->conn);
+    _mysql_ConnectionObject *conn = (_mysql_ConnectionObject *)self->conn;
+    if (mysql_errno(&conn->connection)) {
+        return _mysql_Exception(conn);
     }
     Py_RETURN_NONE;
 }