# HG changeset patch
# Parent 2b79b4848f44ea7dfea85a7e9ae7f471483c7401
Make rawiobase_read() read directly to bytes object instead of copying.

diff -r 2b79b4848f44 Lib/test/test_io.py
--- a/Lib/test/test_io.py	Thu Sep 13 17:27:15 2012 +0100
+++ b/Lib/test/test_io.py	Mon Sep 17 21:13:33 2012 +0100
@@ -616,6 +616,7 @@
         # readinto() internally).
         rawio = self.MockRawIOWithoutRead((b"abc", b"d", None, b"efg", None))
         self.assertEqual(rawio.read(2), b"ab")
+        self.assertEqual(rawio.read(0), b"")
         self.assertEqual(rawio.read(2), b"c")
         self.assertEqual(rawio.read(2), b"d")
         self.assertEqual(rawio.read(2), None)
@@ -623,6 +624,9 @@
         self.assertEqual(rawio.read(2), b"g")
         self.assertEqual(rawio.read(2), None)
         self.assertEqual(rawio.read(2), b"")
+        rawio = self.MockRawIOWithoutRead((b"abc", b"d", b"efg"))
+        self.assertEqual(rawio.read(-1), b"abcdefg")
+        self.assertEqual(rawio.read(-1), b"")
 
     def test_types_have_dict(self):
         test = (
diff -r 2b79b4848f44 Modules/_io/iobase.c
--- a/Modules/_io/iobase.c	Thu Sep 13 17:27:15 2012 +0100
+++ b/Modules/_io/iobase.c	Mon Sep 17 21:13:33 2012 +0100
@@ -781,8 +781,8 @@
 static PyObject *
 rawiobase_read(PyObject *self, PyObject *args)
 {
-    Py_ssize_t n = -1;
-    PyObject *b, *res;
+    Py_ssize_t n = -1, view_refcount;
+    PyObject *b, *view, *res;
 
     if (!PyArg_ParseTuple(args, "|n:read", &n)) {
         return NULL;
@@ -794,13 +794,19 @@
         return _PyObject_CallMethodId(self, &PyId_readall, NULL);
     }
 
-    /* TODO: allocate a bytes object directly instead and manually construct
-       a writable memoryview pointing to it. */
-    b = PyByteArray_FromStringAndSize(NULL, n);
+    b = PyBytes_FromStringAndSize(NULL, n);
     if (b == NULL)
         return NULL;
 
-    res = PyObject_CallMethodObjArgs(self, _PyIO_str_readinto, b, NULL);
+    view = PyMemoryView_FromMemory(PyBytes_AS_STRING(b), n, PyBUF_WRITE);
+    if (view == NULL) {
+        Py_DECREF(b);
+        return NULL;
+    }
+
+    res = PyObject_CallMethodObjArgs(self, _PyIO_str_readinto, view, NULL);
+    view_refcount = Py_REFCNT(view);
+    Py_DECREF(view);
     if (res == NULL || res == Py_None) {
         Py_DECREF(b);
         return res;
@@ -813,7 +819,21 @@
         return NULL;
     }
 
-    res = PyBytes_FromStringAndSize(PyByteArray_AsString(b), n);
+    if (n == PyBytes_GET_SIZE(b))
+        return b;
+
+    if (n > PyBytes_GET_SIZE(b) || n < 0) {
+        Py_DECREF(b);
+        PyErr_SetString(PyExc_RuntimeError, "readinto() returned bad value");
+        return NULL;
+    }
+
+    if (view_refcount == 1 && Py_REFCNT(b) == 1) {
+        _PyBytes_Resize(&b, n);
+        return b;
+    }
+
+    res = PyBytes_FromStringAndSize(PyBytes_AS_STRING(b), n);
     Py_DECREF(b);
     return res;
 }