remote: adds support for s3.list_objects

Optionally use list_objects, useful for ceph and other s3 emulators
fixes: #1476

dvc/config.py

@@ -193,6 +193,7 @@ class Config(object):  # pylint: disable=too-many-instance-attributes
     SECTION_AWS_STORAGEPATH = "storagepath"
     SECTION_AWS_CREDENTIALPATH = "credentialpath"
     SECTION_AWS_ENDPOINT_URL = "endpointurl"
+    SECTION_AWS_LIST_OBJECTS = "listobjects"
     SECTION_AWS_REGION = "region"
     SECTION_AWS_PROFILE = "profile"
     SECTION_AWS_USE_SSL = "use_ssl"
@@ -202,6 +203,9 @@ class Config(object):  # pylint: disable=too-many-instance-attributes
         Optional(SECTION_AWS_PROFILE): str,
         Optional(SECTION_AWS_CREDENTIALPATH): str,
         Optional(SECTION_AWS_ENDPOINT_URL): str,
+        Optional(SECTION_AWS_LIST_OBJECTS, default=False): And(
+            str, is_bool, Use(to_bool)
+        ),
         Optional(SECTION_AWS_USE_SSL, default=True): And(
             str, is_bool, Use(to_bool)
         ),
@@ -239,6 +243,9 @@ class Config(object):  # pylint: disable=too-many-instance-attributes
         Optional(SECTION_AWS_PROFILE): str,
         Optional(SECTION_AWS_CREDENTIALPATH): str,
         Optional(SECTION_AWS_ENDPOINT_URL): str,
+        Optional(SECTION_AWS_LIST_OBJECTS, default=False): And(
+            str, is_bool, Use(to_bool)
+        ),
         Optional(SECTION_AWS_USE_SSL, default=True): And(
             str, is_bool, Use(to_bool)
         ),

dvc/remote/s3.py

@@ -55,6 +55,8 @@ class RemoteS3(RemoteBase):
 
         self.endpoint_url = config.get(Config.SECTION_AWS_ENDPOINT_URL)
 
+        self.list_objects = config.get(Config.SECTION_AWS_LIST_OBJECTS)
+
         self.use_ssl = config.get(Config.SECTION_AWS_USE_SSL, True)
 
         shared_creds = config.get(Config.SECTION_AWS_CREDENTIALPATH)
@@ -125,27 +127,17 @@ class RemoteS3(RemoteBase):
         )
 
     def _list_paths(self, bucket, prefix):
+        """ Read config for list object api, paginate through list objects."""
         s3 = self.s3
-
         kwargs = {"Bucket": bucket, "Prefix": prefix}
-        while True:
-            # NOTE: list_objects_v2() is 90% faster than head_object [1]
-            #
-            # [1] https://www.peterbe.com/plog/
-            #     fastest-way-to-find-out-if-a-file-exists-in-s3
-            resp = s3.list_objects_v2(**kwargs)
-            contents = resp.get("Contents", None)
-            if not contents:
-                break
-
-            for obj in contents:
-                yield obj["Key"]
-
-            token = resp.get("NextContinuationToken", None)
-            if not token:
-                break
-
-            kwargs["ContinuationToken"] = token
+        if self.list_objects:
+            list_objects_api = "list_objects"
+        else:
+            list_objects_api = "list_objects_v2"
+        paginator = s3.get_paginator(list_objects_api)
+        for page in paginator.paginate(**kwargs):
+            for item in page["Contents"]:
+                yield item["Key"]
 
     def list_cache_paths(self):
         return self._list_paths(self.bucket, self.prefix)