Issue #9971: Write an optimized implementation of BufferedReader.readinto().

Patch by John O'Connor.

Lib/test/test_io.py

@@ -794,6 +794,12 @@ class BufferedReaderTest(unittest.TestCase, CommonBufferedTests):
         self.assertEqual(b, b"gf")
         self.assertEqual(bufio.readinto(b), 0)
         self.assertEqual(b, b"gf")
+        rawio = self.MockRawIO((b"abc", None))
+        bufio = self.tp(rawio)
+        self.assertEqual(bufio.readinto(b), 2)
+        self.assertEqual(b, b"ab")
+        self.assertEqual(bufio.readinto(b), 1)
+        self.assertEqual(b, b"cb")
 
     def test_readlines(self):
         def bufio():

Misc/ACKS

@@ -645,6 +645,7 @@ Neal Norwitz
 Michal Nowikowski
 Steffen Daode Nurpmeso
 Nigel O'Brian
+John O'Connor
 Kevin O'Connor
 Tim O'Malley
 Pascal Oberndoerfer

Misc/NEWS

@@ -142,6 +142,10 @@ Core and Builtins
 
 Library
 -------
+
+- Issue #9971: Write an optimized implementation of BufferedReader.readinto().
+  Patch by John O'Connor.
+
 - Issue #1028: Tk returns invalid Unicode null in %A: UnicodeDecodeError.
   With Tk < 8.5 _tkinter.c:PythonCmd() raised UnicodeDecodeError, caused
   IDLE to exit.  Converted to valid Unicode null in PythonCmd().

Modules/_io/bufferedio.c

@@ -596,7 +596,8 @@ static PyObject *
 _bufferedreader_read_fast(buffered *self, Py_ssize_t);
 static PyObject *
 _bufferedreader_read_generic(buffered *self, Py_ssize_t);
-
+static Py_ssize_t
+_bufferedreader_raw_read(buffered *self, char *start, Py_ssize_t len);
 
 /*
  * Helpers
@@ -912,23 +913,75 @@ end:
 static PyObject *
 buffered_readinto(buffered *self, PyObject *args)
 {
+    Py_buffer buf;
+    Py_ssize_t n, written = 0, remaining;
     PyObject *res = NULL;
 
     CHECK_INITIALIZED(self)
 
-    /* TODO: use raw.readinto() instead! */
-    if (self->writable) {
-        if (!ENTER_BUFFERED(self))
+    if (!PyArg_ParseTuple(args, "w*:readinto", &buf))
         return NULL;
+
+    n = Py_SAFE_DOWNCAST(READAHEAD(self), Py_off_t, Py_ssize_t);
+    if (n > 0) {
+        if (n >= buf.len) {
+            memcpy(buf.buf, self->buffer + self->pos, buf.len);
+            self->pos += buf.len;
+            res = PyLong_FromSsize_t(buf.len);
+            goto end_unlocked;
+        }
+        memcpy(buf.buf, self->buffer + self->pos, n);
+        self->pos += n;
+        written = n;
+    }
+
+    if (!ENTER_BUFFERED(self))
+        goto end_unlocked;
+
+    if (self->writable) {
         res = _bufferedwriter_flush_unlocked(self, 0);
-        LEAVE_BUFFERED(self)
         if (res == NULL)
             goto end;
-        Py_DECREF(res);
+        Py_CLEAR(res);
+    }
+
+    _bufferedreader_reset_buf(self);
+    self->pos = 0;
+
+    for (remaining = buf.len - written;
+         remaining > 0;
+         written += n, remaining -= n) {
+        /* If remaining bytes is larger than internal buffer size, copy
+         * directly into caller's buffer. */
+        if (remaining > self->buffer_size) {
+            n = _bufferedreader_raw_read(self, buf.buf + written, remaining);
+        }
+        else {
+            n = _bufferedreader_fill_buffer(self);
+            if (n > 0) {
+                if (n > remaining)
+                    n = remaining;
+                memcpy(buf.buf + written, self->buffer + self->pos, n);
+                self->pos += n;
+                continue; /* short circuit */
+            }
+        }
+        if (n == 0 || (n == -2 && written > 0))
+            break;
+        if (n < 0) {
+            if (n == -2) {
+                Py_INCREF(Py_None);
+                res = Py_None;
+            }
+            goto end;
         }
-    res = bufferediobase_readinto((PyObject *)self, args);
+    }
+    res = PyLong_FromSsize_t(written);
 
 end:
+    LEAVE_BUFFERED(self);
+end_unlocked:
+    PyBuffer_Release(&buf);
     return res;
 }
 
@@ -1573,6 +1626,7 @@ static PyMethodDef bufferedreader_methods[] = {
     {"read", (PyCFunction)buffered_read, METH_VARARGS},
     {"peek", (PyCFunction)buffered_peek, METH_VARARGS},
     {"read1", (PyCFunction)buffered_read1, METH_VARARGS},
+    {"readinto", (PyCFunction)buffered_readinto, METH_VARARGS},
     {"readline", (PyCFunction)buffered_readline, METH_VARARGS},
     {"seek", (PyCFunction)buffered_seek, METH_VARARGS},
     {"tell", (PyCFunction)buffered_tell, METH_NOARGS},