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.

2 files changed, 99 insertions, 28 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index fec1c6f..fcd548d 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -6,6 +6,7 @@ import os
 import abc
 import codecs
 import warnings
+import errno
 # Import _thread instead of threading to reduce startup cost
 try:
     from _thread import allocate_lock as Lock
@@ -717,8 +718,11 @@ class _BufferedIOMixin(BufferedIOBase):
 
     def close(self):
         if self.raw is not None and not self.closed:
-            self.flush()
-            self.raw.close()
+            try:
+                # may raise BlockingIOError or BrokenPipeError etc
+                self.flush()
+            finally:
+                self.raw.close()
 
     def detach(self):
         if self.raw is None:
@@ -1077,13 +1081,9 @@ class BufferedWriter(_BufferedIOMixin):
             # XXX we can implement some more tricks to try and avoid
             # partial writes
             if len(self._write_buf) > self.buffer_size:
-                # We're full, so let's pre-flush the buffer
-                try:
-                    self._flush_unlocked()
-                except BlockingIOError as e:
-                    # We can't accept anything else.
-                    # XXX Why not just let the exception pass through?
-                    raise BlockingIOError(e.errno, e.strerror, 0)
+                # We're full, so let's pre-flush the buffer.  (This may
+                # raise BlockingIOError with characters_written == 0.)
+                self._flush_unlocked()
             before = len(self._write_buf)
             self._write_buf.extend(b)
             written = len(self._write_buf) - before
@@ -1114,22 +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")
+            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 --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 318f7a7..5954999 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -42,7 +42,10 @@ try:
     import threading
 except ImportError:
     threading = None
-
+try:
+    import fcntl
+except ImportError:
+    fcntl = None
 
 def _default_chunk_size():
     """Get the default TextIOWrapper chunk size"""
@@ -242,9 +245,14 @@ class MockNonBlockWriterIO:
             except ValueError:
                 pass
             else:
-                self._blocker_char = None
-                self._write_stack.append(b[:n])
-                raise self.BlockingIOError(0, "test blocking", n)
+                if n > 0:
+                    # write data up to the first blocker
+                    self._write_stack.append(b[:n])
+                    return n
+                else:
+                    # cancel blocker and indicate would block
+                    self._blocker_char = None
+                    return None
         self._write_stack.append(b)
         return len(b)
 
@@ -2753,6 +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