bpo-28557: error message for bad raw readinto

Author: davidszotten

Lib/test/test_io.py

@@ -1531,6 +1531,22 @@ def test_args_error(self):
         with self.assertRaisesRegex(TypeError, "BufferedReader"):
             self.tp(io.BytesIO(), 1024, 1024, 1024)
 
+    def test_bad_readinto_value(self):
+        rawio = io.BufferedReader(io.BytesIO(b"12"))
+        rawio.readinto = lambda buf: -1
+        bufio = self.tp(rawio)
+        with self.assertRaises(OSError) as cm:
+            bufio.readline()
+        assert cm.exception.__cause__ is None
+
+    def test_bad_readinto_type(self):
+        rawio = io.BufferedReader(io.BytesIO(b"12"))
+        rawio.readinto = lambda buf: b''
+        bufio = self.tp(rawio)
+        with self.assertRaises(TypeError) as cm:
+            bufio.readline()
+        assert isinstance(cm.exception.__cause__, TypeError)
+
 
 class PyBufferedReaderTest(BufferedReaderTest):
     tp = pyio.BufferedReader

Misc/ACKS

@@ -1581,6 +1581,7 @@ Péter Szabó
 John Szakmeister
 Piotr Szczepaniak
 Amir Szekely
+David Szotten
 Maciej Szulik
 Joel Taddei
 Arfrever Frehtes Taifersar Arahesis

Misc/NEWS.d/next/Library/2018-06-07-22-04-01.bpo-28557.ViNJnK.rst

@@ -0,0 +1 @@
+Improve the error message for a misbehaving ``rawio.readinto``

Modules/_io/bufferedio.c

@@ -1488,6 +1488,14 @@ _bufferedreader_raw_read(buffered *self, char *start, Py_ssize_t len)
     }
     n = PyNumber_AsSsize_t(res, PyExc_ValueError);
     Py_DECREF(res);
+
+    if (n == -1 && PyErr_Occurred()) {
+        _PyErr_TrySetFromCause(
+            "raw readinto() returned invalid value"
+        );
+        return -1;
+    }
+
     if (n < 0 || n > len) {
         PyErr_Format(PyExc_OSError,
                      "raw readinto() returned invalid length %zd "