Propagate uri to compression_wrapper (#842)

* Add ftp compression test

* Propagate uri to compression_wrapper

* Prefer name attribute in smart_open_lib

* Amend test to actually check for gzip bytes

* Add comments

integration-tests/test_ftp.py

@@ -1,4 +1,5 @@
 from __future__ import unicode_literals
+import gzip
 import pytest
 from smart_open import open
 import ssl
@@ -52,6 +53,39 @@ def test_binary(server_info):
         read_contents = f.read()
         assert read_contents == file_contents + appended_content1
 
+def test_compression(server_info):
+    server_type = server_info[0]
+    port_num = server_info[1]
+    file_contents = "Test Test \n new test \n another tests"
+    appended_content1 = "Added \n to end"
+
+    with open(f"{server_type}://user:123@localhost:{port_num}/file.gz", "w") as f:
+        f.write(file_contents)
+
+    with open(f"{server_type}://user:123@localhost:{port_num}/file.gz", "r") as f:
+        read_contents = f.read()
+        assert read_contents == file_contents
+
+    with open(f"{server_type}://user:123@localhost:{port_num}/file.gz", "a") as f:
+        f.write(appended_content1)
+
+    with open(f"{server_type}://user:123@localhost:{port_num}/file.gz", "r") as f:
+        read_contents = f.read()
+        assert read_contents == file_contents + appended_content1
+
+    # ftp socket makefile returns a file whose name attribute is fileno() which is int
+    # that can't be used to infer compression extension, so the calls above would
+    # silently not use any compression (neither reading nor writing) so they would pass
+    # pytest suppresses the logging.warning('unable to transparently decompress...')
+    # so check here explicitly that the bytes on server are gzip compressed
+    with open(
+        f"{server_type}://user:123@localhost:{port_num}/file.gz",
+        "rb",
+        compression='disable',
+    ) as f:
+        read_contents = gzip.decompress(f.read()).decode()
+        assert read_contents == file_contents + appended_content1
+
 def test_line_endings_non_binary(server_info):
     server_type = server_info[0]
     port_num = server_info[1]

smart_open/smart_open_lib.py

@@ -222,7 +222,19 @@ def open(
         raise NotImplementedError(ve.args[0])
 
     binary = _open_binary_stream(uri, binary_mode, transport_params)
-    decompressed = so_compression.compression_wrapper(binary, binary_mode, compression)
+    filename = (
+        binary.name
+        # if name attribute is not string-like (e.g. ftp socket fileno)...
+        if isinstance(getattr(binary, "name", None), (str, bytes))
+        # ...fall back to uri
+        else uri
+    )
+    decompressed = so_compression.compression_wrapper(
+        binary,
+        binary_mode,
+        compression,
+        filename=filename,
+    )
 
     if 'b' not in mode or explicit_encoding is not None:
         decoded = _encoding_wrapper(