astahlman opened a new pull request #4596: [AIRFLOW-2190] Fix TypeError when returning 404 URL: https://github.com/apache/airflow/pull/4596 Make sure you have checked _all_ steps below. ### Jira - [ X ] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR" - https://issues.apache.org/jira/browse/AIRFLOW-2190 ### Description - [ X ] Here are some details about my PR, including screenshots of any UI changes: When processing HTTP response headers, gunicorn checks that the name of each header is a string. Here's the relevant gunicorn code: From gunicorn/http/wsgi.py, line 257 def process_headers(self, headers): for name, value in headers: if not isinstance(name, string_types): raise TypeError('%r is not a string' % name) In Python3, `string_types` is set to the built-in `str`. For Python 2, it's set to `basestring`. Again, the relevant gunicorn code: From gunicorn/six.py, line 38: if PY3: string_types = str, ... else: string_types = basestring, On Python2 the `b''` syntax returns a `str`, but in Python3 it returns `bytes`. `bytes` != `str`, so we get the following error when returning a 404 on Python3: File "/usr/local/lib/python3.6/site-packages/airflow/www/app.py", line 166, in root_app resp(b'404 Not Found', [(b'Content-Type', b'text/plain')]) File "/usr/local/lib/python3.6/site-packages/gunicorn/http/wsgi.py", line 261, in start_response self.process_headers(headers) File "/usr/local/lib/python3.6/site-packages/gunicorn/http/wsgi.py", line 268, in process_headers raise TypeError('%r is not a string' % name) TypeError: b'Content-Type' is not a string Dropping the `b` prefix in favor of the single-quote string syntax should work for both Python2 and 3, as demonstrated below: Python 3.7.2 (default, Jan 13 2019, 12:50:15) [Clang 10.0.0 (clang-1000.11.45.5)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> isinstance('foo', str) True Python 2.7.15 (default, Jan 12 2019, 21:43:48) [GCC 4.2.1 Compatible Apple LLVM 10.0.0 (clang-1000.11.45.5)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> isinstance('foo', basestring) True ### Tests - [ ] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason: Not sure if there's a clean way to unit test this middleware - open to suggestions. FWIW, I ran the webserver and confirmed that this fixes the issue in AIRFLOW-2190. ### Commits - [ X ] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)": 1. Subject is separated from body by a blank line 1. Subject is limited to 50 characters (not including Jira issue reference) 1. Subject does not end with a period 1. Subject uses the imperative mood ("add", not "adding") 1. Body wraps at 72 characters 1. Body explains "what" and "why", not "how" ### Documentation - [ ] In case of new functionality, my PR adds documentation that describes how to use it. - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added. - All the public functions and the classes in the PR contain docstrings that explain what it does ### Code Quality - [ X ] Passes `flake8`
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