s3: implement isfile()

dvc/remote/s3.py

@@ -207,17 +207,24 @@ class RemoteS3(RemoteBASE):
     def list_cache_paths(self):
         return self._list_paths(self.path_info)
 
+    def isfile(self, path_info):
+        if path_info.path.endswith("/"):
+            return False
+
+        try:
+            self.get_head_object(self.s3, path_info.bucket, path_info.path)
+        except DvcException:
+            return False
+
+        return True
+
     def exists(self, path_info):
-        dir_path = path_info / ""
+        """Check if the blob exists. If it does not exist,
+        it could be a part of a directory path.
 
-        if self.isdir(dir_path):
-            return True
-
-        for fname in self._list_paths(path_info):
-            if path_info.path == fname:
-                return True
-
-        return False
+        eg: if `data/file.txt` exists, check for `data` should return True
+        """
+        return True if self.isfile(path_info) else self.isdir(path_info)
 
     def makedirs(self, path_info):
         # We need to support creating empty directories, which means

tests/unit/remote/test_s3.py

@@ -118,3 +118,23 @@ def test_makedirs(remote):
     assert not remote.exists(empty_dir)
     remote.makedirs(empty_dir)
     assert remote.exists(empty_dir)
+
+
+def test_isfile(remote):
+    test_cases = [
+        (False, "empty_dir/"),
+        (True, "empty_file"),
+        (True, "foo"),
+        (True, "data/alice"),
+        (True, "data/alpha"),
+        (True, "data/subdir/1"),
+        (True, "data/subdir/2"),
+        (True, "data/subdir/3"),
+        (False, "data/subdir/empty_dir/"),
+        (False, "data/subdir/1/"),
+        (False, "something-that-does-not-exist"),
+        (False, "empty_dir"),
+    ]
+
+    for expected, path in test_cases:
+        assert remote.isfile(remote.path_info / path) == expected