fix TextIOWrapper.read() when the buffer is not readable #5628

Lib/_pyio.py

@@ -1696,6 +1696,7 @@ class TextIOWrapper(TextIOBase):
         return cookie
 
     def read(self, n=None):
+        self._checkReadable()
         if n is None:
             n = -1
         decoder = self._decoder or self._get_decoder()

Lib/test/test_io.py

@@ -1754,6 +1754,13 @@ class TextIOWrapperTest(unittest.TestCase):
             self.assertEquals(f.read(), data * 2)
             self.assertEquals(buf.getvalue(), (data * 2).encode(encoding))
 
+    def test_unreadable(self):
+        class UnReadable(self.BytesIO):
+            def readable(self):
+                return False
+        txt = self.TextIOWrapper(UnReadable())
+        self.assertRaises(IOError, txt.read)
+
     def test_read_one_by_one(self):
         txt = self.TextIOWrapper(self.BytesIO(b"AA\r\nBB"))
         reads = ""

Misc/NEWS

@@ -53,6 +53,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #5628: Fix io.TextIOWrapper.read() with a unreadable buffer.
+
 - Issue #5619: Multiprocessing children disobey the debug flag and causes
   popups on windows buildbots. Patch applied to work around this issue.
 

Modules/_textio.c

@@ -1348,6 +1348,11 @@ TextIOWrapper_read(PyTextIOWrapperObject *self, PyObject *args)
 
     CHECK_CLOSED(self);
 
+    if (self->decoder == NULL) {
+        PyErr_SetString(PyExc_IOError, "not readable");
+        return NULL;
+    }
+
     if (_TextIOWrapper_writeflush(self) < 0)
         return NULL;