Reviving the old range request PR

This commit basically just adds the codes from the PR
https://github.com/micahflee/onionshare/pull/804/commits
on the newly structured and refactored code and also
fixes import dependencies and changed any code that was
relevant with the new code of onionshare

cli/tests/test_range_request.py

@@ -0,0 +1,41 @@
+import pytest
+import subprocess
+
+from tempfile import NamedTemporaryFile
+from werkzeug.exceptions import RequestedRangeNotSatisfiable
+
+from onionshare_cli.web.share_mode import parse_range_header
+
+
+VALID_RANGES = [
+    (None, 500, [(0, 499)]),
+    ('bytes=0', 500, [(0, 499)]),
+    ('bytes=100', 500, [(100, 499)]),
+    ('bytes=100-', 500, [(100, 499)]),  # not in the RFC, but how curl sends
+    ('bytes=0-99', 500, [(0, 99)]),
+    ('bytes=0-599', 500, [(0, 499)]),
+    ('bytes=0-0', 500, [(0, 0)]),
+    ('bytes=-100', 500, [(400, 499)]),
+    ('bytes=0-99,100-199', 500, [(0, 199)]),
+    ('bytes=0-100,100-199', 500, [(0, 199)]),
+    ('bytes=0-99,101-199', 500, [(0, 99), (101, 199)]),
+    ('bytes=0-199,100-299', 500, [(0, 299)]),
+    ('bytes=0-99,200-299', 500, [(0, 99), (200, 299)]),
+]
+
+
+INVALID_RANGES = [
+    'bytes=200-100',
+    'bytes=0-100,300-200',
+]
+
+
+def test_parse_ranges():
+    for case in VALID_RANGES:
+        (header, target_size, expected) = case
+        parsed = parse_range_header(header, target_size)
+        assert parsed == expected, case
+
+    for invalid in INVALID_RANGES:
+        with pytest.raises(RequestedRangeNotSatisfiable):
+            parse_range_header(invalid, 500)