Issue #13322: Fix BufferedWriter.write() to ensure that BlockingIOError is

raised when the wrapped raw file is non-blocking and the write would block.
Previous code assumed that the raw write() would raise BlockingIOError, but
RawIOBase.write() is defined to returned None when the call would block.
Patch by sbt.

diff --cc Lib/_pyio.py
index fec1c6fab0a2ed84bc55251a70991448129bdb85,a2faeb32579b0b8b2b520a3e48316f18801e8e33..fcd548ddc388272e4e544f93ecdb3039cf7bc511
--- 1/Lib/_pyio.py
--- 2/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@@ -1114,22 -1117,23 +1114,21 @@@ class BufferedWriter(_BufferedIOMixin)
      def _flush_unlocked(self):
          if self.closed:
              raise ValueError("flush of closed file")
-         written = 0
-         try:
-             while self._write_buf:
-                 try:
-                     n = self.raw.write(self._write_buf)
-                 except InterruptedError:
-                     continue
-                 if n > len(self._write_buf) or n < 0:
-                     raise IOError("write() returned incorrect number of bytes")
-                 del self._write_buf[:n]
-                 written += n
-         except BlockingIOError as e:
-             n = e.characters_written
+         while self._write_buf:
+             try:
+                 n = self.raw.write(self._write_buf)
++            except InterruptedError:
++                continue
+             except BlockingIOError:
+                 raise RuntimeError("self.raw should implement RawIOBase: it "
+                                    "should not raise BlockingIOError")
 -            except IOError as e:
 -                if e.errno != EINTR:
 -                    raise
 -                continue
+             if n is None:
+                 raise BlockingIOError(
+                     errno.EAGAIN,
+                     "write could not complete without blocking", 0)
+             if n > len(self._write_buf) or n < 0:
+                 raise IOError("write() returned incorrect number of bytes")
              del self._write_buf[:n]
-             written += n
-             raise BlockingIOError(e.errno, e.strerror, written)
  
      def tell(self):
          return _BufferedIOMixin.tell(self) + len(self._write_buf)

diff --cc Lib/test/test_io.py
index 318f7a7571a07f104d6677577b327ca59a21264a,df7ca15f58fe06a0070f4434f8807b864654d9eb..5954999e6e9418f04a9d607cf0a77c5f995a1296
--- 1/Lib/test/test_io.py
--- 2/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@@ -2753,6 -2751,68 +2761,70 @@@ class MiscIOTest(unittest.TestCase)
                  with self.open(support.TESTFN, **kwargs) as f:
                      self.assertRaises(TypeError, pickle.dumps, f, protocol)
  
+     @unittest.skipUnless(fcntl, 'fcntl required for this test')
+     def test_nonblock_pipe_write_bigbuf(self):
+         self._test_nonblock_pipe_write(16*1024)
+ 
+     @unittest.skipUnless(fcntl, 'fcntl required for this test')
+     def test_nonblock_pipe_write_smallbuf(self):
+         self._test_nonblock_pipe_write(1024)
+ 
+     def _set_non_blocking(self, fd):
+         flags = fcntl.fcntl(fd, fcntl.F_GETFL)
+         self.assertNotEqual(flags, -1)
+         res = fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
+         self.assertEqual(res, 0)
+ 
+     def _test_nonblock_pipe_write(self, bufsize):
+         sent = []
+         received = []
+         r, w = os.pipe()
+         self._set_non_blocking(r)
+         self._set_non_blocking(w)
+ 
+         # To exercise all code paths in the C implementation we need
+         # to play with buffer sizes.  For instance, if we choose a
+         # buffer size less than or equal to _PIPE_BUF (4096 on Linux)
+         # then we will never get a partial write of the buffer.
+         rf = self.open(r, mode='rb', closefd=True, buffering=bufsize)
+         wf = self.open(w, mode='wb', closefd=True, buffering=bufsize)
+ 
+         with rf, wf:
+             for N in 9999, 73, 7574:
+                 try:
+                     i = 0
+                     while True:
+                         msg = bytes([i % 26 + 97]) * N
+                         sent.append(msg)
+                         wf.write(msg)
+                         i += 1
+ 
+                 except self.BlockingIOError as e:
+                     self.assertEqual(e.args[0], errno.EAGAIN)
++                    self.assertEqual(e.args[2], e.characters_written)
+                     sent[-1] = sent[-1][:e.characters_written]
+                     received.append(rf.read())
+                     msg = b'BLOCKED'
+                     wf.write(msg)
+                     sent.append(msg)
+ 
+             while True:
+                 try:
+                     wf.flush()
+                     break
+                 except self.BlockingIOError as e:
+                     self.assertEqual(e.args[0], errno.EAGAIN)
++                    self.assertEqual(e.args[2], e.characters_written)
+                     self.assertEqual(e.characters_written, 0)
+                     received.append(rf.read())
+ 
+             received += iter(rf.read, None)
+ 
+         sent, received = b''.join(sent), b''.join(received)
+         self.assertTrue(sent == received)
+         self.assertTrue(wf.closed)
+         self.assertTrue(rf.closed)
+ 
  class CMiscIOTest(MiscIOTest):
      io = io
  

diff --cc Misc/ACKS
Simple merge

diff --cc Misc/NEWS
Simple merge

diff --cc Modules/_io/bufferedio.c
Simple merge