wsgi: Fix handling partial writeswritelines-fix

Closes https://github.com/eventlet/eventlet/issues/295

3 files changed, 56 insertions, 3 deletions

diff --git a/eventlet/support/__init__.py b/eventlet/support/__init__.py
index 4c2b75d..de6b1e2 100644
--- a/eventlet/support/__init__.py
+++ b/eventlet/support/__init__.py
@@ -53,3 +53,16 @@ def capture_stderr():
     finally:
         sys.stderr = original
         stream.seek(0)
+
+
+if six.PY2:
+    def safe_writelines(fd, to_write):
+        fd.writelines(to_write)
+else:
+    def safe_writelines(fd, to_write):
+        # Standard Python 3 writelines() is not reliable because it doesn't care if it
+        # loses data. See CPython bug report: http://bugs.python.org/issue26292
+        for item in to_write:
+            written = 0
+            while written < len(item):
+                written += fd.write(item[written:])
diff --git a/eventlet/wsgi.py b/eventlet/wsgi.py
index 88e7752..66c7d4d 100644
--- a/eventlet/wsgi.py
+++ b/eventlet/wsgi.py
@@ -1,4 +1,5 @@
 import errno
+import functools
 import os
 import sys
 import time
@@ -11,7 +12,7 @@ from eventlet.green import socket
 from eventlet import greenio
 from eventlet import greenpool
 from eventlet import support
-from eventlet.support import six
+from eventlet.support import safe_writelines, six
 
 from eventlet.support.six.moves import urllib
 
@@ -112,7 +113,7 @@ class Input(object):
         # Blank line
         towrite.append(b'\r\n')
 
-        self.wfile.writelines(towrite)
+        safe_writelines(self.wfile, towrite)
 
         # Reinitialize chunk_length (expect more data)
         self.chunk_length = -1
@@ -385,7 +386,7 @@ class HttpProtocol(BaseHTTPServer.BaseHTTPRequestHandler):
         length = [0]
         status_code = [200]
 
-        def write(data, _writelines=wfile.writelines):
+        def write(data, _writelines=functools.partial(safe_writelines, wfile)):
             towrite = []
             if not headers_set:
                 raise AssertionError("write() before start_response()")
diff --git a/tests/wsgi_test.py b/tests/wsgi_test.py
index 50091eb..2c25553 100644
--- a/tests/wsgi_test.py
+++ b/tests/wsgi_test.py
@@ -10,6 +10,8 @@ import tempfile
 import traceback
 import unittest
 
+from nose.tools import eq_
+
 import eventlet
 from eventlet import debug
 from eventlet import event
@@ -444,6 +446,43 @@ class TestHttpd(_TestBase):
         # Require a CRLF to close the message body
         self.assertEqual(response, b'\r\n')
 
+    def test_partial_writes_are_handled(self):
+        # The bug was caused by the default writelines() implementaiton
+        # (used by the wsgi module) which doesn't check if write()
+        # successfully completed sending *all* data therefore data could be
+        # lost and the client could be left hanging forever.
+        #
+        # Eventlet issue: "Python 3: wsgi doesn't handle correctly partial
+        # write of socket send() when using writelines()",
+        # https://github.com/eventlet/eventlet/issues/295
+        #
+        # Related CPython issue: "Raw I/O writelines() broken",
+        # http://bugs.python.org/issue26292
+
+        # Piece of data large enough that we can reasonably expect it to not
+        # be sent in one piece. Is there a reliable way to determine this
+        # number without testing various sizes empirically?
+        data = b'a' * 10 ** 7
+
+        def application(env, start_response):
+            # Sending content-length is important here, otherwise chunked encoding
+            # is chosen
+            start_response('200 OK', [])
+            yield data
+
+        self.site.application = application
+
+        sock = eventlet.connect(('localhost', self.port))
+
+        # HTTP 1.0 is important here, this tells the server to close the socket
+        # after sending the data so that read_http() can safely read until EOF
+        # without hanging forever.
+        sock.sendall(b'GET / HTTP/1.0\r\nHost: localhost\r\n\r\n')
+        result = read_http(sock)
+
+        # This would previously fail because part of the data would be lost
+        eq_(len(result.body), len(data))
+
     @tests.skip_if_no_ssl
     def test_012_ssl_server(self):
         def wsgi_app(environ, start_response):