Fix stdin bug

README.rst

@@ -184,6 +184,13 @@ To ensure that you get the correct ``zstandard`` version, you can specify the ``
 Changelog
 ---------
 
+in-development
+~~~~~~~~~~~~~~~~~~~
++ #158: Fixed a bug where reading from stdin and other pipes would discard the
+  first bytes from the input.
++ #156: Zstd files compressed with the ``--long=31`` files can now be opened
+  without throwing errors.
+
 v2.0.0 (2024-03-26)
 ~~~~~~~~~~~~~~~~~~~
 

src/xopen/__init__.py

@@ -10,6 +10,7 @@
 
 import dataclasses
 import gzip
+import stat
 import sys
 import io
 import os
@@ -701,8 +702,6 @@ def _file_or_path_to_binary_stream(
     file_or_path: FileOrPath, binary_mode: str
 ) -> Tuple[BinaryIO, bool]:
     assert binary_mode in ("rb", "wb", "ab")
-    if file_or_path == "-":
-        return _open_stdin_or_out(binary_mode), False
     if isinstance(file_or_path, (str, bytes)) or hasattr(file_or_path, "__fspath__"):
         return open(os.fspath(file_or_path), binary_mode), True  # type: ignore
     if isinstance(file_or_path, io.TextIOWrapper):
@@ -722,10 +721,22 @@ def _filepath_from_path_or_filelike(fileorpath: FileOrPath) -> str:
     except TypeError:
         pass
     if hasattr(fileorpath, "name"):
-        return fileorpath.name
+        name = fileorpath.name
+        if isinstance(name, str):
+            return name
+        elif isinstance(name, bytes):
+            return name.decode()
     return ""
 
 
+def _file_is_a_socket_or_pipe(filepath):
+    try:
+        mode = os.stat(filepath).st_mode
+        return stat.S_ISFIFO(mode) or stat.S_ISSOCK(mode) or stat.S_ISPORT(mode)
+    except (OSError, TypeError):  # Type error for unexpected types in stat.
+        return False
+
+
 @overload
 def xopen(
     filename: FileOrPath,
@@ -756,7 +767,7 @@ def xopen(
     ...
 
 
-def xopen(
+def xopen(  # noqa: C901
     filename: FileOrPath,
     mode: Literal["r", "w", "a", "rt", "rb", "wt", "wb", "at", "ab"] = "r",
     compresslevel: Optional[int] = None,
@@ -819,6 +830,13 @@ def xopen(
     binary_mode = mode[0] + "b"
     filepath = _filepath_from_path_or_filelike(filename)
 
+    # Open non-regular files such as pipes and sockets here to force opening
+    # them once.
+    if filename == "-":
+        filename = _open_stdin_or_out(binary_mode)
+    elif _file_is_a_socket_or_pipe(filename):
+        filename = open(filename, binary_mode)  # type: ignore
+
     if format not in (None, "gz", "xz", "bz2", "zst"):
         raise ValueError(
             f"Format not supported: {format}. "

tests/test_xopen.py

@@ -2,7 +2,9 @@
 Tests for the xopen.xopen function
 """
 import bz2
+import subprocess
 import sys
+import tempfile
 from contextlib import contextmanager
 import functools
 import gzip
@@ -634,3 +636,57 @@ def test_pass_bytesio_for_reading_and_writing(ext, threads):
     filelike.seek(0)
     with xopen(filelike, "rb", format=format, threads=threads) as fh:
         assert fh.readline() == first_line
+
+
+@pytest.mark.parametrize("threads", (0, 1))
+def test_xopen_stdin(monkeypatch, ext, threads):
+    if ext == ".zst" and zstandard is None:
+        return
+    # Add encoding to suppress encoding warnings
+    with open(TEST_DIR / f"file.txt{ext}", "rt", encoding="latin-1") as in_file:
+        monkeypatch.setattr("sys.stdin", in_file)
+        with xopen("-", "rt", threads=threads) as f:
+            data = f.read()
+        assert data == CONTENT
+
+
+def test_xopen_stdout(monkeypatch):
+    # Add encoding to suppress encoding warnings
+    with tempfile.TemporaryFile(mode="w+t", encoding="latin-1") as raw:
+        monkeypatch.setattr("sys.stdout", raw)
+        with xopen("-", "wt") as f:
+            f.write("Hello world!")
+        raw.seek(0)
+        data = raw.read()
+    assert data == "Hello world!"
+
+
+@pytest.mark.parametrize("threads", (0, 1))
+def test_xopen_read_from_pipe(ext, threads):
+    if ext == ".zst" and zstandard is None:
+        return
+    in_file = TEST_DIR / f"file.txt{ext}"
+    process = subprocess.Popen(("cat", str(in_file)), stdout=subprocess.PIPE)
+    with xopen(process.stdout, "rt", threads=threads) as f:
+        data = f.read()
+    process.wait()
+    process.stdout.close()
+    assert data == CONTENT
+
+
+@pytest.mark.parametrize("threads", (0, 1))
+def test_xopen_write_to_pipe(threads, ext):
+    if ext == ".zst" and zstandard is None:
+        return
+    format = ext.lstrip(".")
+    if format == "":
+        format = None
+    process = subprocess.Popen(("cat",), stdout=subprocess.PIPE, stdin=subprocess.PIPE)
+    with xopen(process.stdin, "wt", threads=threads, format=format) as f:
+        f.write(CONTENT)
+    process.stdin.close()
+    with xopen(process.stdout, "rt", threads=threads) as f:
+        data = f.read()
+    process.wait()
+    process.stdout.close()
+    assert data == CONTENT