[PATCH STABLE] posix: insert seek between reads and writes on Solaris (issue4943)

[Adrian Buehlmann]

On 2015-11-16 00:34, Adrian Buehlmann wrote:
> On 2015-11-15 23:21, Gregory Szorc wrote:
>> Yes, we copied a large block of source code. This is not ideal.
>> However, posix.py and windows.py are very low level modules. There
>> is no obvious existing module we could add the function to without
>> introducing an import cycle. A new module will likely need to be
>> invented. I'm not comfortable doing that on the stable branch.
>> Once this patch is merged into @, we should clean up the duplicated
>> code.
> 
> Perhaps you could move mixedfilemodewrapper to util.py and do the
> wrapping there for the Solaris and Windows cases.
> 
> Likely not appropriate for stable indeed...

I was thinking of something like this (completely untested):

diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -24,6 +24,7 @@
 import gc
 import bz2
 import zlib
+import platform as pyplatform
 
 if os.name == 'nt':
     import windows as platform
@@ -91,6 +92,78 @@
 def safehasattr(thing, attr):
     return getattr(thing, attr, _notset) is not _notset
 
+class mixedfilemodewrapper(object):
+    """Wraps a file handle when it is opened in read/write mode.
+
+    This class wraps posixfile instances when the file is opened in read/write
+    mode and automatically adds checks or inserts appropriate file positioning
+    calls when necessary.
+    """
+    OPNONE = 0
+    OPREAD = 1
+    OPWRITE = 2
+
+    def __init__(self, fp):
+        object.__setattr__(self, '_fp', fp)
+        object.__setattr__(self, '_lastop', 0)
+
+    def __getattr__(self, name):
+        return getattr(self._fp, name)
+
+    def __setattr__(self, name, value):
+        return self._fp.__setattr__(name, value)
+
+    def _noopseek(self):
+        self._fp.seek(0, os.SEEK_CUR)
+
+    def seek(self, *args, **kwargs):
+        object.__setattr__(self, '_lastop', self.OPNONE)
+        return self._fp.seek(*args, **kwargs)
+
+    def write(self, d):
+        if self._lastop == self.OPREAD:
+            self._noopseek()
+
+        object.__setattr__(self, '_lastop', self.OPWRITE)
+        return self._fp.write(d)
+
+    def writelines(self, *args, **kwargs):
+        if self._lastop == self.OPREAD:
+            self._noopeseek()
+
+        object.__setattr__(self, '_lastop', self.OPWRITE)
+        return self._fp.writelines(*args, **kwargs)
+
+    def read(self, *args, **kwargs):
+        if self._lastop == self.OPWRITE:
+            self._noopseek()
+
+        object.__setattr__(self, '_lastop', self.OPREAD)
+        return self._fp.read(*args, **kwargs)
+
+    def readline(self, *args, **kwargs):
+        if self._lastop == self.OPWRITE:
+            self._noopseek()
+
+        object.__setattr__(self, '_lastop', self.OPREAD)
+        return self._fp.readline(*args, **kwargs)
+
+    def readlines(self, *args, **kwargs):
+        if self._lastop == self.OPWRITE:
+            self._noopseek()
+
+        object.__setattr__(self, '_lastop', self.OPREAD)
+        return self._fp.readlines(*args, **kwargs)
+
+def _wrappedposixfile(name, mode='r', buffering=-1):
+    fp = platform.posixfile(name, mode, buffering)
+    if '+' in mode:
+        return mixedfilemodewrapper(fp)
+    return fp
+
+if os.name == 'nt' or pyplatform.system() == 'SunOS'
+    posixfile = _wrappedposixfile
+
 from hashlib import md5, sha1
 
 DIGESTS = {
diff --git a/mercurial/windows.py b/mercurial/windows.py
--- a/mercurial/windows.py
+++ b/mercurial/windows.py
@@ -27,73 +27,6 @@
 
 umask = 0o022
 
-class mixedfilemodewrapper(object):
-    """Wraps a file handle when it is opened in read/write mode.
-
-    fopen() and fdopen() on Windows have a specific-to-Windows requirement
-    that files opened with mode r+, w+, or a+ make a call to a file positioning
-    function when switching between reads and writes. Without this extra call,
-    Python will raise a not very intuitive "IOError: [Errno 0] Error."
-
-    This class wraps posixfile instances when the file is opened in read/write
-    mode and automatically adds checks or inserts appropriate file positioning
-    calls when necessary.
-    """
-    OPNONE = 0
-    OPREAD = 1
-    OPWRITE = 2
-
-    def __init__(self, fp):
-        object.__setattr__(self, '_fp', fp)
-        object.__setattr__(self, '_lastop', 0)
-
-    def __getattr__(self, name):
-        return getattr(self._fp, name)
-
-    def __setattr__(self, name, value):
-        return self._fp.__setattr__(name, value)
-
-    def _noopseek(self):
-        self._fp.seek(0, os.SEEK_CUR)
-
-    def seek(self, *args, **kwargs):
-        object.__setattr__(self, '_lastop', self.OPNONE)
-        return self._fp.seek(*args, **kwargs)
-
-    def write(self, d):
-        if self._lastop == self.OPREAD:
-            self._noopseek()
-
-        object.__setattr__(self, '_lastop', self.OPWRITE)
-        return self._fp.write(d)
-
-    def writelines(self, *args, **kwargs):
-        if self._lastop == self.OPREAD:
-            self._noopeseek()
-
-        object.__setattr__(self, '_lastop', self.OPWRITE)
-        return self._fp.writelines(*args, **kwargs)
-
-    def read(self, *args, **kwargs):
-        if self._lastop == self.OPWRITE:
-            self._noopseek()
-
-        object.__setattr__(self, '_lastop', self.OPREAD)
-        return self._fp.read(*args, **kwargs)
-
-    def readline(self, *args, **kwargs):
-        if self._lastop == self.OPWRITE:
-            self._noopseek()
-
-        object.__setattr__(self, '_lastop', self.OPREAD)
-        return self._fp.readline(*args, **kwargs)
-
-    def readlines(self, *args, **kwargs):
-        if self._lastop == self.OPWRITE:
-            self._noopseek()
-
-        object.__setattr__(self, '_lastop', self.OPREAD)
-        return self._fp.readlines(*args, **kwargs)
 
 def posixfile(name, mode='r', buffering=-1):
     '''Open a file with even more POSIX-like semantics'''
@@ -105,9 +38,6 @@
         if 'a' in mode:
             fp.seek(0, os.SEEK_END)
 
-        if '+' in mode:
-            return mixedfilemodewrapper(fp)
-
         return fp
     except WindowsError as err:
         # convert to a friendlier exception