Fixed logfile output to special files like /dev/stdout on Python 3. (Python 3.5.2 disallows open('/dev/stdout', 'a') but allows open('/dev/stdout', 'w').)

Author: Shane Hathaway

supervisor/loggers.py

@@ -9,6 +9,7 @@
 
 import os
 import errno
+import stat
 import sys
 import time
 import traceback
@@ -138,11 +139,29 @@ class FileHandler(Handler):
     """File handler which supports reopening of logs.
     """
 
-    def __init__(self, filename, mode="a"):
+    def __init__(self, filename, mode=None):
         Handler.__init__(self)
-        self.stream = open(filename, mode)
+        open_mode = mode or 'a'
+
+        try:
+            self.stream = open(filename, open_mode)
+        except OSError as e:
+            retried = False
+            if not mode:
+                if e.errno == errno.ESPIPE:
+                    st_mode = os.stat(filename).st_mode
+                    if stat.S_ISCHR(st_mode) or stat.S_ISFIFO(st_mode):
+                        # Python 3 can't open special files like
+                        # /dev/stdout in 'a' mode due to an implicit seek call
+                        # that fails with ESPIPE. Retry in 'w' mode.
+                        self.stream = open(filename, 'w')
+                        open_mode = 'w'
+                        retried = True
+            if not retried:
+                raise
+
         self.baseFilename = filename
-        self.mode = mode
+        self.mode = open_mode
 
     def reopen(self):
         self.close()

supervisor/tests/test_loggers.py

@@ -220,6 +220,22 @@ def test_emit_error(self):
         self.assertTrue(dummy_stderr.written.endswith('OSError\n'),
                         dummy_stderr.written)
 
+if os.path.exists('/dev/stdout'):
+    StdoutTestsBase = FileHandlerTests
+else:
+    # Skip the stdout tests on platforms that don't have /dev/stdout.
+    StdoutTestsBase = object
+
+class StdoutTests(StdoutTestsBase):
+    def test_ctor_with_dev_stdout(self):
+        handler = self._makeOne('/dev/stdout')
+        # Modes 'w' and 'a' have the same semantics when applied to
+        # character device files and fifos.
+        self.assertIn(handler.mode, ['w', 'a'])
+        self.assertEqual(handler.baseFilename, '/dev/stdout')
+        self.assertEqual(handler.stream.name, '/dev/stdout')
+        handler.close()
+
 class RotatingFileHandlerTests(FileHandlerTests):
 
     def _getTargetClass(self):