git-p4: check free space during streaming

git-p4 will just halt if there is not enough disk space while
streaming content from P4 to Git. Add a check to ensure at least
4 times (arbitrarily chosen) the size of a streamed file is available.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -104,6 +104,16 @@ def chdir(path, is_client_path=False):
         path = os.getcwd()
     os.environ['PWD'] = path
 
+def calcDiskFree():
+    """Return free space in bytes on the disk of the given dirname."""
+    if platform.system() == 'Windows':
+        free_bytes = ctypes.c_ulonglong(0)
+        ctypes.windll.kernel32.GetDiskFreeSpaceExW(ctypes.c_wchar_p(os.getcwd()), None, None, ctypes.pointer(free_bytes))
+        return free_bytes.value
+    else:
+        st = os.statvfs(os.getcwd())
+        return st.f_bavail * st.f_frsize
+
 def die(msg):
     if verbose:
         raise Exception(msg)
@@ -2263,6 +2273,14 @@ class P4Sync(Command, P4UserMap):
             if marshalled["code"] == "error":
                 if "data" in marshalled:
                     err = marshalled["data"].rstrip()
+
+        if not err and 'fileSize' in self.stream_file:
+            required_bytes = int((4 * int(self.stream_file["fileSize"])) - calcDiskFree())
+            if required_bytes > 0:
+                err = 'Not enough space left on %s! Free at least %i MB.' % (
+                    os.getcwd(), required_bytes/1024/1024
+                )
+
         if err:
             f = None
             if self.stream_have_file_info: