Add PrefixFileSystem

The PrefixFileSystem is a filesystem-wrapper. It assumes every path it is dealing with
is relative to the `prefix`. After performing the necessary paths operation it delegates
everything to the wrapped filesystem.

Resolves #395

fsspec/implementations/prefix.py

@@ -0,0 +1,135 @@
+import os
+from pathlib import Path
+from typing import Any, Iterable, Sequence, Union
+
+import fsspec
+from fsspec import AbstractFileSystem
+from fsspec.core import split_protocol
+from fsspec.utils import stringify_path
+
+
+class PrefixFileSystem(AbstractFileSystem):
+    def __init__(
+        self,
+        prefix: str,
+        filesystem: fsspec.AbstractFileSystem,
+        *args,
+        **storage_options,
+    ) -> None:
+        super().__init__(*args, **storage_options)
+        self.prefix = prefix
+        self.filesystem = filesystem
+
+    def _add_fs_prefix(self, path: Union[str, Path]) -> Union[str, Sequence[str]]:
+        if isinstance(path, (str, Path)):
+            path = stringify_path(path)
+            protocol, path = split_protocol(path)
+            path = os.path.join(self.prefix, path)
+            return protocol + "://" + path if protocol is not None else path
+        elif isinstance(path, Iterable):
+            return [self._add_fs_prefix(x) for x in path]
+        assert False
+
+    def _remove_fs_prefix(self, path: Union[str, Path]) -> Union[str, Sequence[str]]:
+        if isinstance(path, (str, Path)):
+            path = stringify_path(path)
+            protocol, path = split_protocol(path)
+            path = os.path.relpath(path, start=self.prefix)
+            return protocol + "://" + path if protocol is not None else path
+        elif isinstance(path, Iterable):
+            return [self._remove_fs_prefix(x) for x in path]
+        assert False
+
+    def mkdir(self, path: str, create_parents: bool = True, **kwargs) -> None:
+        path = self._add_fs_prefix(path)
+        return self.filesystem.mkdir(path=path, create_parents=create_parents, **kwargs)
+
+    def makedirs(self, path: str, exist_ok: bool = False):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.mkdirs(path=path, exist_ok=exist_ok)
+
+    def rmdir(self, path: str):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.rmdir(path=path)
+
+    def ls(
+        self,
+        path: str,
+        detail=False,
+        **kwargs,
+    ) -> Sequence[str]:
+        path = self._add_fs_prefix(path)
+        ls_out = self.filesystem.ls(path=path, detail=detail, **kwargs)
+        if detail:
+            for out in ls_out:
+                out["name"] = self._remove_fs_prefix(out["name"])
+            return ls_out
+        return self._remove_fs_prefix(ls_out)
+
+    def glob(self, path: str, **kwargs):
+        path = self._add_fs_prefix(path)
+        glob_out = self.filesystem.glob(path=path, **kwargs)
+        return [self._remove_fs_prefix(x) for x in glob_out]
+
+    def info(self, path: str, **kwargs):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.info(path=path, **kwargs)
+
+    def cp_file(self, path1: str, path2: str, **kwargs):
+        path1 = self._add_fs_prefix(path1)
+        path2 = self._add_fs_prefix(path2)
+        return self.filesystem.cp_file(path1, path2, **kwargs)
+
+    def get_file(self, path1: str, path2: str, callback=None, **kwargs):
+        path1 = self._add_fs_prefix(path1)
+        path2 = self._add_fs_prefix(path2)
+        return self.filesystem.get_file(path1, path2, callback, **kwargs)
+
+    def put_file(self, path1: str, path2: str, callback=None, **kwargs):
+        path1 = self._add_fs_prefix(path1)
+        path2 = self._add_fs_prefix(path2)
+        return self.filesystem.put_file(path1, path2, callback, **kwargs)
+
+    def mv_file(self, path1: str, path2: str, **kwargs):
+        path1 = self._add_fs_prefix(path1)
+        path2 = self._add_fs_prefix(path2)
+        return self.filesystem.mv_file(path1, path2, **kwargs)
+
+    def rm_file(self, path: str):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.rm_file(path)
+
+    def rm(self, path: str, recursive=False, maxdepth=None):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.rm(path, recursive=False, maxdepth=None)
+
+    def touch(self, path: str, **kwargs):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.touch(path, **kwargs)
+
+    def created(self, path: str):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.created(path)
+
+    def modified(self, path: str):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.modified(path)
+
+    def sign(self, path: str, expiration=100, **kwargs):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.sign(path, expiration=100, **kwargs)
+
+    def cat(
+        self,
+        path: str,
+        recursive: bool = False,
+        on_error: str = "raise",
+        **kwargs: Any,
+    ):
+        path = self._add_fs_prefix(path)
+        return self.filesystem.cat(
+            path, recursive=recursive, on_error=on_error, **kwargs
+        )
+
+    def __repr__(self) -> str:
+        return f"{self.__class__.__qualname__}(prefix='{self.prefix}', filesystem={self.filesystem})"

fsspec/implementations/tests/test_prefix.py

@@ -0,0 +1,135 @@
+from __future__ import absolute_import, division, print_function
+
+import os
+import os.path
+import tempfile
+from contextlib import contextmanager
+
+import pytest
+
+import fsspec
+from fsspec.core import OpenFile
+from fsspec.implementations.local import make_path_posix
+from fsspec.implementations.prefix import PrefixFileSystem
+
+files = {
+    ".test.accounts.1.json": (
+        b'{"amount": 100, "name": "Alice"}\n'
+        b'{"amount": 200, "name": "Bob"}\n'
+        b'{"amount": 300, "name": "Charlie"}\n'
+        b'{"amount": 400, "name": "Dennis"}\n'
+    ),
+    ".test.accounts.2.json": (
+        b'{"amount": 500, "name": "Alice"}\n'
+        b'{"amount": 600, "name": "Bob"}\n'
+        b'{"amount": 700, "name": "Charlie"}\n'
+        b'{"amount": 800, "name": "Dennis"}\n'
+    ),
+}
+
+
+csv_files = {
+    ".test.fakedata.1.csv": (b"a,b\n" b"1,2\n"),
+    ".test.fakedata.2.csv": (b"a,b\n" b"3,4\n"),
+}
+odir = os.getcwd()
+
+
+@contextmanager
+def filetexts(d, open=open, mode="t"):
+    """Dumps a number of textfiles to disk
+
+    d - dict
+        a mapping from filename to text like {'a.csv': '1,1\n2,2'}
+
+    Since this is meant for use in tests, this context manager will
+    automatically switch to a temporary current directory, to avoid
+    race conditions when running tests in parallel.
+    """
+    dirname = tempfile.mkdtemp()
+    try:
+        os.chdir(dirname)
+        for filename, text in d.items():
+            f = open(filename, "w" + mode)
+            try:
+                f.write(text)
+            finally:
+                try:
+                    f.close()
+                except AttributeError:
+                    pass
+
+        yield list(d)
+
+        for filename in d:
+            if os.path.exists(filename):
+                try:
+                    os.remove(filename)
+                except (IOError, OSError):
+                    pass
+    finally:
+        os.chdir(odir)
+
+
+def test_cats():
+    with filetexts(csv_files, mode="b"):
+        fs = PrefixFileSystem(prefix=".", filesystem=fsspec.filesystem("file"))
+        assert fs.cat(".test.fakedata.1.csv") == b"a,b\n" b"1,2\n"
+        out = set(fs.cat([".test.fakedata.1.csv", ".test.fakedata.2.csv"]).values())
+        assert out == {b"a,b\n" b"1,2\n", b"a,b\n" b"3,4\n"}
+        assert fs.cat(".test.fakedata.1.csv", None, None) == b"a,b\n" b"1,2\n"
+        assert fs.cat(".test.fakedata.1.csv", start=1, end=6) == b"a,b\n" b"1,2\n"[1:6]
+        assert fs.cat(".test.fakedata.1.csv", start=-1) == b"a,b\n" b"1,2\n"[-1:]
+        assert (
+            fs.cat(".test.fakedata.1.csv", start=1, end=-2) == b"a,b\n" b"1,2\n"[1:-2]
+        )
+        out = set(
+            fs.cat(
+                [".test.fakedata.1.csv", ".test.fakedata.2.csv"], start=1, end=-1
+            ).values()
+        )
+        assert out == {b"a,b\n" b"1,2\n"[1:-1], b"a,b\n" b"3,4\n"[1:-1]}
+
+
+def test_not_found():
+    fn = "not-a-file"
+    fs = PrefixFileSystem(prefix=".", filesystem=fsspec.filesystem("file"))
+    with pytest.raises((FileNotFoundError, OSError)):
+        with OpenFile(fs, fn, mode="rb"):
+            pass
+
+
+def test_isfile():
+    fs = PrefixFileSystem(prefix=".", filesystem=fsspec.filesystem("file"))
+    with filetexts(files, mode="b"):
+        for f in files.keys():
+            assert fs.isfile(f)
+            assert fs.isfile("file://" + f)
+        assert not fs.isfile("not-a-file")
+        assert not fs.isfile("file://not-a-file")
+
+
+def test_isdir():
+    fs = PrefixFileSystem(prefix=".", filesystem=fsspec.filesystem("file"))
+    with filetexts(files, mode="b"):
+        for f in files.keys():
+            assert fs.isdir(os.path.dirname(os.path.abspath(f)))
+            assert not fs.isdir(f)
+        assert not fs.isdir("not-a-dir")
+
+
+@pytest.mark.parametrize("prefix", ["/", "/tmp"])
+def test_directories(tmpdir, prefix):
+    tmpdir = make_path_posix(str(tmpdir))
+    rel_tmpdir = os.path.relpath(tmpdir, prefix)
+
+    fs = PrefixFileSystem(prefix=prefix, filesystem=fsspec.filesystem("file"))
+
+    fs.mkdir(rel_tmpdir + "/dir")
+
+    assert not fs.ls(tmpdir + "/dir")
+
+    assert rel_tmpdir + "/dir" in fs.ls(rel_tmpdir)
+    assert fs.ls(rel_tmpdir, True)[0]["type"] == "directory"
+    fs.rmdir(rel_tmpdir + "/dir")
+    assert not fs.ls(rel_tmpdir)