Fallback to md5sum when uname fails

sshfs/spec.py

@@ -8,6 +8,8 @@
 from typing import Optional
 
 import asyncssh
+from asyncssh import ProcessError
+from asyncssh.misc import ChannelOpenError
 from asyncssh.sftp import SFTPOpUnsupported
 from fsspec.asyn import (
     AsyncFileSystem,
@@ -343,19 +345,20 @@ async def _rm(self, path, recursive=False, **kwargs):
 
     @wrap_exceptions
     async def _checksum(self, path):
-        system = await self._get_system()
+        try:
+            system = await self._get_system()
+        except (ChannelOpenError, ProcessError):
+            system = "Linux"
+
         if system == "Linux":
-            command = "md5sum"
+            result = await self._execute(f"md5sum {shlex.quote(path)}")
             part = 0
         elif system == "Darwin":
-            command = "md5"
+            result = await self._execute(f"md5 {shlex.quote(path)}")
             part = -1
         else:
             raise ValueError(f"{system!r} doesn't support checksum operation")
 
-        cmd = f"{command} {shlex.quote(path)}"
-        result = await self._execute(cmd)
-
         parts = result.stdout.strip().split()
         assert len(parts) >= 1
 

tests/test_sshfs.py

@@ -1,3 +1,4 @@
+import asyncio
 import hashlib
 import posixpath
 import secrets
@@ -10,6 +11,7 @@
 
 import fsspec
 import pytest
+from asyncssh.misc import ChannelOpenError
 from asyncssh.sftp import SFTPAttrs, SFTPFailure
 from importlib_metadata import entry_points
 
@@ -239,6 +241,25 @@ def test_checksum(fs, remote_dir):
     assert fs.checksum(remote_dir + "/a.txt") == checksum
 
 
+def test_checksum_falls_back_to_md5sum_when_uname_session_fails():
+    checksum = "0123456789abcdef0123456789abcdef"
+    calls = []
+
+    class DummyFS:
+        async def _get_system(self):
+            raise ChannelOpenError(None, None)
+
+        async def _execute(self, command):
+            calls.append(command)
+            return SimpleNamespace(stdout=f"{checksum}  /tmp/a.txt\n")
+
+    assert (
+        asyncio.run(SSHFileSystem._checksum(DummyFS(), "/tmp/a.txt"))
+        == checksum
+    )
+    assert calls == ["md5sum /tmp/a.txt"]
+
+
 def test_ls(fs, remote_dir):
     fs.mkdir(remote_dir + "dir/")
     files = set()