fix: raise UnsupportedOperation exception in fsspec.BufferedFile impl

obstore/python/obstore/fsspec.py

@@ -36,6 +36,7 @@
 import warnings
 from collections import defaultdict
 from functools import cached_property, lru_cache
+from io import UnsupportedOperation
 from pathlib import Path
 from typing import TYPE_CHECKING, Literal, overload
 from urllib.parse import urlparse
@@ -721,7 +722,7 @@ def read(self, length: int = -1) -> bytes:
 
         """
         if self.mode != "rb":
-            raise ValueError("File not in read mode")
+            raise UnsupportedOperation("File not in read mode")
         if length < 0:
             length = self.size - self.tell()
         if self.closed:
@@ -736,15 +737,15 @@ def read(self, length: int = -1) -> bytes:
     def readline(self) -> bytes:
         """Read until first occurrence of newline character."""
         if self.mode != "rb":
-            raise ValueError("File not in read mode")
+            raise UnsupportedOperation("File not in read mode")
 
         out = self._reader.readline()
         return out.to_bytes()
 
     def readlines(self) -> list[bytes]:
         """Return all data, split by the newline character."""
         if self.mode != "rb":
-            raise ValueError("File not in read mode")
+            raise UnsupportedOperation("File not in read mode")
 
         out = self._reader.readlines()
         return [b.to_bytes() for b in out]
@@ -775,7 +776,7 @@ def seek(self, loc: int, whence: int = 0) -> int:
 
         """
         if self.mode != "rb":
-            raise ValueError("Seek only available in read mode.")
+            raise UnsupportedOperation("Seek only available in read mode.")
 
         return self._reader.seek(loc, whence)
 
@@ -787,7 +788,7 @@ def write(self, data: bytes) -> int:
 
         """
         if not self.writable():
-            raise ValueError("File not in write mode")
+            raise UnsupportedOperation("File not in write mode")
         if self.closed:
             raise ValueError("I/O operation on closed file.")
         if self.forced:

tests/test_fsspec.py

@@ -2,6 +2,7 @@
 
 import gc
 import os
+import zipfile
 from pathlib import Path
 from tempfile import TemporaryDirectory
 from typing import TYPE_CHECKING
@@ -172,6 +173,24 @@ def test_buffered_file_forwards_size_to_open_reader():
         assert len(data) == 500
 
 
+def test_zipfile_write_mode():
+    """Ensure a write-mode file can fall back to ZipFile non-seekable code path."""
+    register("memory")
+    fs: FsspecStore = fsspec.filesystem("memory")
+
+    with (
+        fs._open("archive.zip", mode="wb") as filelike,
+        zipfile.ZipFile(filelike, "w") as zf,
+    ):
+        zf.writestr("hello.txt", "hello world")
+
+    with (
+        fs._open("archive.zip") as filelike,
+        zipfile.ZipFile(filelike) as zf,
+    ):
+        assert zf.read("hello.txt") == b"hello world"
+
+
 def test_construct_store_cache_diff_bucket_name(
     minio_bucket: tuple[S3Config, ClientConfig],
 ):