add module "fs.filelike" with utils for building file-like objects.

This is a local copy of the guts of my "filelike" module, re-licensed under
the MIT license.

This commit also uses it to fix a few edge-cases in various filesystem
implementations (e.g. truncating StringIO objects).

ChangeLog

@@ -57,4 +57,6 @@
     * Added utils.isdir(fs,path,info) and utils.isfile(fs,path,info); these
       can often determine whether a path is a file or directory by inspecting
       the info dict and avoid an additional query to the filesystem.
+    * Added utility module 'fs.filelike' with some helpers for building and
+      manipulating file-like objects.
 

fs/contrib/bigfs/__init__.py

@@ -12,15 +12,13 @@ Contributed under the terms of the BSD License:
 http://www.opensource.org/licenses/bsd-license.php
 """
 
+from struct import pack, unpack
+
 from fs.base import *
 from fs.memoryfs import MemoryFS
-from fs.contrib.bigfs.subrangefile import SubrangeFile
+from fs.filelike import StringIO
 
-from struct import pack, unpack
-try:
-    from cStringIO import StringIO
-except ImportError:
-    from StringIO import StringIO
+from fs.contrib.bigfs.subrangefile import SubrangeFile
 
 class BIGEntry:
     def __init__(self, filename, offset, storedSize, isCompressed, realSize):

fs/expose/sftp.py

@@ -29,7 +29,6 @@ import stat as statinfo
 import time
 import SocketServer as sockserv
 import threading
-from StringIO import StringIO
 
 import paramiko
 
@@ -37,6 +36,7 @@ from fs.base import flags_to_mode
 from fs.path import *
 from fs.errors import *
 from fs.local_functools import wraps
+from fs.filelike import StringIO
 
 
 # Default host key used by BaseSFTPServer

fs/ftpfs.py

@@ -29,11 +29,6 @@ import re
 from socket import error as socket_error
 from fs.local_functools import wraps
 
-try:
-    from cStringIO import StringIO
-except ImportError:
-    from StringIO import StringIO
-
 import time
 import sys
 

fs/memoryfs.py

@@ -16,11 +16,7 @@ from fs.path import iteratepath, pathsplit, normpath
 from fs.base import *
 from fs.errors import *
 from fs import _thread_synchronize_default
-
-try:
-    from cStringIO import StringIO
-except ImportError:
-    from StringIO import StringIO
+from fs.filelike import StringIO
 
 
 def _check_mode(mode, mode_chars):

fs/multifs.py

@@ -3,9 +3,10 @@ fs.multifs
 ==========
 
 A MultiFS is a filesytem composed of a sequence of other filesystems, where
-the directory structure of each filesystem is overlaid over the previous filesystem.
-When you attempt to access a file from the MultiFS it will try each 'child'
-FS in order, until it either finds a path that exists or raises a ResourceNotFoundError.
+the directory structure of each filesystem is overlaid over the previous
+filesystem. When you attempt to access a file from the MultiFS it will try
+each 'child' FS in order, until it either finds a path that exists or raises a
+ResourceNotFoundError.
 
 One use for such a filesystem would be to selectively override a set of files,
 to customize behaviour. For example, to create a filesystem that could be used
@@ -61,11 +62,11 @@ from fs.errors import ResourceNotFoundError
 
 class MultiFS(FS):
 
-    """A MultiFS is a filesystem that delegates to a sequence of other filesystems.
-    Operations on the MultiFS will try each 'child' filesystem in order, until it
-    succeeds. In effect, creating a filesystem that combines the files and dirs of
-    its children.
+    """A filesystem that delegates to a sequence of other filesystems.
 
+    Operations on the MultiFS will try each 'child' filesystem in order, until
+    it succeeds. In effect, creating a filesystem that combines the files and
+    dirs of its children.
     """
 
     def __init__(self):

fs/rpcfs.py

@@ -14,17 +14,7 @@ from fs.base import *
 from fs.errors import *
 from fs.path import *
 
-from StringIO import StringIO
-if hasattr(StringIO,"__exit__"):
-    class StringIO(StringIO):
-        pass
-else:
-    class StringIO(StringIO):
-        def __enter__(self):
-            return self
-        def __exit__(self,exc_type,exc_value,traceback):
-            self.close()
-            return False
+from fs.filelike import StringIO
 
 
 def re_raise_faults(func):
@@ -173,14 +163,19 @@ class RPCFS(FS):
             f.seek(0,2)
         oldflush = f.flush
         oldclose = f.close
+        oldtruncate = f.truncate
         def newflush():
             oldflush()
             self.proxy.set_contents(path,xmlrpclib.Binary(f.getvalue()))
         def newclose():
             f.flush()
             oldclose()
+        def newtruncate(size=None):
+            oldtruncate(size)
+            f.flush()
         f.flush = newflush
         f.close = newclose
+        f.truncate = newtruncate
         return f
 
     def exists(self, path):

fs/tests/test_remote.py

@@ -109,7 +109,7 @@ class TestRemoteFileBuffer(unittest.TestCase, FSTestCases, ThreadingTestCases):
         
         f = self.fs.open('test.txt', 'rb')
         self.assertEquals(f.read(10), contents[:10])
-        f.file.seek(0, SEEK_END)
+        f.wrapped_file.seek(0, SEEK_END)
         self.assertEquals(f._rfile.tell(), 10)
         f.seek(20)
         self.assertEquals(f.tell(), 20)
@@ -136,9 +136,9 @@ class TestRemoteFileBuffer(unittest.TestCase, FSTestCases, ThreadingTestCases):
         f._rfile.seek(len(contents[:-5]))
         # Write 10 new characters (will make contents longer for 5 chars)
         f.write(u'1234567890')
+        f.flush()
         # We are on the end of file (and buffer not serve anything anymore)
         self.assertEquals(f.read(), '')
-        f.close()
         
         self.fakeOn()
         

fs/zipfs.py

@@ -11,15 +11,11 @@ import datetime
 from fs.base import *
 from fs.path import *
 from fs.errors import *
+from fs.filelike import StringIO
 
 from zipfile import ZipFile, ZIP_DEFLATED, ZIP_STORED, BadZipfile, LargeZipFile
 from memoryfs import MemoryFS
 
-try:
-    from cStringIO import StringIO
-except ImportError:
-    from StringIO import StringIO
-
 import tempfs