Correctly handle reading/writing pipes via file

- make numBytes argument optional
- open real pipe as file and store it if needed
- fixes #661

3 files changed, 19 insertions, 6 deletions

diff --git a/CHANGES.md b/CHANGES.md
index 36da884..9cbfb8d 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -6,6 +6,8 @@ The released versions correspond to PyPi releases.
 ### Fixes
 * correctly handle file system space for files opened in write mode
   (see [#660](../../issues/660))
+* correctly handle reading/writing pipes via file
+  (see [#661](../../issues/661)) 
 
 ## [Version 4.5.4](https://pypi.python.org/pypi/pyfakefs/4.5.4) (2022-01-12)
 Minor bugfix release.
diff --git a/pyfakefs/fake_filesystem.py b/pyfakefs/fake_filesystem.py
index 2a863d1..758e46f 100644
--- a/pyfakefs/fake_filesystem.py
+++ b/pyfakefs/fake_filesystem.py
@@ -5383,7 +5383,7 @@ class StandardStreamWrapper:
             return self.filedes
         raise OSError(errno.EBADF, 'Invalid file descriptor')
 
-    def read(self, n: int) -> bytes:
+    def read(self, n: int = -1) -> bytes:
         return cast(bytes, self._stream_object.read())
 
     def close(self) -> None:
@@ -5427,12 +5427,16 @@ class FakePipeWrapper:
     used in open files list.
     """
 
-    def __init__(self, filesystem: FakeFilesystem, fd: int, can_write: bool):
+    def __init__(self, filesystem: FakeFilesystem,
+                 fd: int, can_write: bool, mode: str = ''):
         self._filesystem = filesystem
         self.fd = fd  # the real file descriptor
         self.can_write = can_write
         self.file_object = None
         self.filedes: Optional[int] = None
+        self.real_file = None
+        if mode:
+            self.real_file = open(fd, mode)
 
     def __enter__(self) -> 'FakePipeWrapper':
         """To support usage of this fake pipe with the 'with' statement."""
@@ -5454,8 +5458,10 @@ class FakePipeWrapper:
             return self.filedes
         raise OSError(errno.EBADF, 'Invalid file descriptor')
 
-    def read(self, numBytes: int) -> bytes:
+    def read(self, numBytes: int = -1) -> bytes:
         """Read from the real pipe."""
+        if self.real_file:
+            return self.real_file.read(numBytes)
         return os.read(self.fd, numBytes)
 
     def flush(self) -> None:
@@ -5464,6 +5470,8 @@ class FakePipeWrapper:
 
     def write(self, contents: bytes) -> int:
         """Write to the real pipe."""
+        if self.real_file:
+            return self.real_file.write(contents)
         return os.write(self.fd, contents)
 
     def close(self) -> None:
@@ -5472,7 +5480,10 @@ class FakePipeWrapper:
         open_files = self._filesystem.open_files[self.filedes]
         assert open_files is not None
         open_files.remove(self)
-        os.close(self.fd)
+        if self.real_file:
+            self.real_file.close()
+        else:
+            os.close(self.fd)
 
     def readable(self) -> bool:
         """The pipe end can either be readable or writable."""
@@ -5571,7 +5582,7 @@ class FakeFileOpen:
             existing_wrapper = wrappers[0]
             assert isinstance(existing_wrapper, FakePipeWrapper)
             wrapper = FakePipeWrapper(self.filesystem, existing_wrapper.fd,
-                                      existing_wrapper.can_write)
+                                      existing_wrapper.can_write, mode)
             file_des = self.filesystem._add_open_file(wrapper)
             wrapper.filedes = file_des
             return wrapper
diff --git a/pyfakefs/tests/fake_os_test.py b/pyfakefs/tests/fake_os_test.py
index fa923d7..7408d17 100644
--- a/pyfakefs/tests/fake_os_test.py
+++ b/pyfakefs/tests/fake_os_test.py
@@ -2750,7 +2750,7 @@ class FakeOsModuleTest(FakeOsModuleTestBase):
             with self.open(write_fd, 'wb') as f:
                 self.assertEqual(4, f.write(b'test'))
             with self.open(read_fd, 'rb') as f:
-                self.assertEqual(b'test', f.read(4))
+                self.assertEqual(b'test', f.read())
         for fd in fds:
             self.os.close(fd)