[GitHub] astahlman opened a new pull request #4596: [AIRFLOW-2190] Fix TypeError when returning 404

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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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