http file system directed to stream by an "Accept-Ranges": "none" response

fsspec/implementations/http.py

@@ -358,9 +358,10 @@ def _open(
         kw = self.kwargs.copy()
         kw["asynchronous"] = self.asynchronous
         kw.update(kwargs)
-        size = size or self.info(path, **kwargs)["size"]
+        info = self.info(path, **kwargs)
+        size = size or info["size"]
         session = sync(self.loop, self.set_session)
-        if block_size and size:
+        if block_size and size and info.get("partial", True):
             return HTTPFile(
                 self,
                 path,
@@ -834,10 +835,6 @@ async def _file_info(url, session, size_policy="head", **kwargs):
     async with r:
         r.raise_for_status()
 
-        # TODO:
-        #  recognise lack of 'Accept-Ranges',
-        #                 or 'Accept-Ranges': 'none' (not 'bytes')
-        #  to mean streaming only, no random access => return None
         if "Content-Length" in r.headers:
             # Some servers may choose to ignore Accept-Encoding and return
             # compressed content, in which case the returned size is unreliable.
@@ -852,6 +849,11 @@ async def _file_info(url, session, size_policy="head", **kwargs):
         if "Content-Type" in r.headers:
             info["mimetype"] = r.headers["Content-Type"].partition(";")[0]
 
+        if r.headers.get("Accept-Ranges") == "none":
+            # Some servers may explicitly discourage partial content requests, but
+            # the lack of "Accept-Ranges" does not always indicate they would fail
+            info["partial"] = False
+
         info["url"] = str(r.url)
 
         for checksum_field in ["ETag", "Content-MD5", "Digest"]:

fsspec/implementations/tests/test_http.py

@@ -237,18 +237,22 @@ def test_random_access(server, headers):
 @pytest.mark.parametrize(
     "headers",
     [
-        {"ignore_range": "true", "head_ok": "true", "head_give_length": "true"},
+        # HTTPFile seeks, response headers lack size, assumed no range support
+        {"head_ok": "true", "head_give_length": "true"},
+        # HTTPFile seeks, response is not a range
         {"ignore_range": "true", "give_length": "true"},
         {"ignore_range": "true", "give_range": "true"},
+        # HTTPStreamFile does not seek (past 0)
+        {"accept_range": "none", "head_ok": "true", "give_length": "true"},
     ],
 )
 def test_no_range_support(server, headers):
     h = fsspec.filesystem("http", headers=headers)
     url = server + "/index/realfile"
     with h.open(url, "rb") as f:
         # Random access is not possible if the server doesn't respect Range
-        f.seek(5)
         with pytest.raises(ValueError):
+            f.seek(5)
             f.read(10)
 
         # Reading from the beginning should still work

fsspec/tests/conftest.py

@@ -135,10 +135,10 @@ def read_chunks(self):
             self.rfile.readline()
 
     def do_HEAD(self):
+        r_headers = {}
         if "head_not_auth" in self.headers:
-            return self._respond(
-                403, {"Content-Length": 123}, b"not authorized for HEAD request"
-            )
+            r_headers["Content-Length"] = 123
+            return self._respond(403, r_headers, b"not authorized for HEAD request")
         elif "head_ok" not in self.headers:
             return self._respond(405)
 
@@ -148,23 +148,23 @@ def do_HEAD(self):
             return self._respond(404)
 
         if ("give_length" in self.headers) or ("head_give_length" in self.headers):
-            response_headers = {"Content-Length": len(file_data)}
             if "zero_length" in self.headers:
-                response_headers["Content-Length"] = 0
+                r_headers["Content-Length"] = 0
             elif "gzip_encoding" in self.headers:
                 file_data = gzip.compress(file_data)
-                response_headers["Content-Encoding"] = "gzip"
-                response_headers["Content-Length"] = len(file_data)
-
-            self._respond(200, response_headers)
+                r_headers["Content-Encoding"] = "gzip"
+                r_headers["Content-Length"] = len(file_data)
+            else:
+                r_headers["Content-Length"] = len(file_data)
         elif "give_range" in self.headers:
-            self._respond(
-                200, {"Content-Range": f"0-{len(file_data) - 1}/{len(file_data)}"}
-            )
+            r_headers["Content-Range"] = f"0-{len(file_data) - 1}/{len(file_data)}"
         elif "give_etag" in self.headers:
-            self._respond(200, {"ETag": "xxx"})
-        else:
-            self._respond(200)  # OK response, but no useful info
+            r_headers["ETag"] = "xxx"
+
+        if self.headers.get("accept_range") == "none":
+            r_headers["Accept-Ranges"] = "none"
+
+        self._respond(200, r_headers)
 
 
 @contextlib.contextmanager