utils: proper file interface for HashedStreamReader (#5508)

dvc/utils/stream.py

@@ -1,6 +1,8 @@
 import hashlib
 import io
 
+from funcy import cached_property
+
 from dvc.hash_info import HashInfo
 from dvc.istextfile import istextblock
 from dvc.utils import dos2unix
@@ -61,17 +63,30 @@ class IterStream(io.RawIOBase):
         return self.leftover[:n]
 
 
-class HashedStreamReader:
+class HashedStreamReader(io.IOBase):
 
     PARAM_CHECKSUM = "md5"
 
     def __init__(self, fobj):
+        self.fobj = fobj
         self.md5 = hashlib.md5()
         self.is_text_file = None
-        self.reader = fobj.read1 if hasattr(fobj, "read1") else fobj.read
+        super().__init__()
+
+    def readable(self):
+        return True
+
+    def tell(self):
+        return self.fobj.tell()
+
+    @cached_property
+    def _reader(self):
+        if hasattr(self.fobj, "read1"):
+            return self.fobj.read1
+        return self.fobj.read
 
     def read(self, n=-1):
-        chunk = self.reader(n)
+        chunk = self._reader(n)
         if self.is_text_file is None:
             self.is_text_file = istextblock(chunk)
 

tests/unit/utils/test_stream.py

@@ -9,7 +9,15 @@ def test_hashed_stream_reader(tmp_dir):
     foo = tmp_dir / "foo"
     with open(foo, "rb") as fobj:
         stream_reader = HashedStreamReader(fobj)
-        assert stream_reader.read(3) == b"foo"
+
+        assert stream_reader.readable()
+        assert not stream_reader.seekable()
+
+        assert stream_reader.read(2) == b"fo"
+        assert stream_reader.tell() == 2
+
+        assert stream_reader.read(1) == b"o"
+        assert stream_reader.tell() == 3
 
     hex_digest = file_md5(foo, LocalFileSystem(None, {}))
     assert stream_reader.is_text_file
@@ -20,13 +28,21 @@ def test_hashed_stream_reader_as_chunks(tmp_dir):
     tmp_dir.gen({"foo": b"foo \x00" * 16})
 
     foo = tmp_dir / "foo"
+
+    actual_size = len(foo.read_bytes())
     with open(foo, "rb") as fobj:
         stream_reader = HashedStreamReader(fobj)
+
+        total_read = 0
         while True:
             chunk = stream_reader.read(16)
+            total_read += len(chunk)
+            assert stream_reader.tell() == total_read
             if not chunk:
                 break
 
+        assert stream_reader.tell() == actual_size == total_read
+
     hex_digest = file_md5(foo, LocalFileSystem(None, {}))
     assert not stream_reader.is_text_file
     assert hex_digest == stream_reader.hash_info.value