# HG changeset patch
# User Matt Harbison <matt_harbison@yahoo.com>
# Date 1428460225 14400
# Node ID 232bf0028596fcc25d6a5f905e58cd7fbf67a6dd
# Parent  67241ee427cfb457d7728e44fc772572c1555c2e
win32: add a method to fetch the available pipe data size

This will be used in the next patch to do nonblocking reads from the child
process, like on posix platforms.  See that for why os.fstat() is insufficient.

diff -r 67241ee427cf -r 232bf0028596 mercurial/win32.py
--- a/mercurial/win32.py	Tue Apr 07 20:43:04 2015 -0700
+++ b/mercurial/win32.py	Tue Apr 07 22:30:25 2015 -0400
@@ -5,7 +5,7 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
-import ctypes, errno, os, subprocess, random
+import ctypes, errno, msvcrt, os, subprocess, random
 
 _kernel32 = ctypes.windll.kernel32
 _advapi32 = ctypes.windll.advapi32
@@ -26,6 +26,7 @@
 _ERROR_SUCCESS = 0
 _ERROR_NO_MORE_FILES = 18
 _ERROR_INVALID_PARAMETER = 87
+_ERROR_BROKEN_PIPE = 109
 _ERROR_INSUFFICIENT_BUFFER = 122
 
 # WPARAM is defined as UINT_PTR (unsigned type)
@@ -211,6 +212,10 @@
 _kernel32.CreateToolhelp32Snapshot.argtypes = [_DWORD, _DWORD]
 _kernel32.CreateToolhelp32Snapshot.restype = _BOOL
 
+_kernel32.PeekNamedPipe.argtypes = [_HANDLE, ctypes.c_void_p, _DWORD,
+    ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p]
+_kernel32.PeekNamedPipe.restype = _BOOL
+
 _kernel32.Process32First.argtypes = [_HANDLE, ctypes.c_void_p]
 _kernel32.Process32First.restype = _BOOL
 
@@ -260,6 +265,19 @@
     res2 = _getfileinfo(path2)
     return res1.dwVolumeSerialNumber == res2.dwVolumeSerialNumber
 
+def peekpipe(pipe):
+    handle = msvcrt.get_osfhandle(pipe.fileno())
+    avail = _DWORD()
+
+    if not _kernel32.PeekNamedPipe(handle, None, 0, None, ctypes.byref(avail),
+                                   None):
+        err = _kernel32.GetLastError()
+        if err == _ERROR_BROKEN_PIPE:
+            return 0
+        raise ctypes.WinError(err)
+
+    return avail.value
+
 def testpid(pid):
     '''return True if pid is still running or unable to
     determine, False otherwise'''