paste.lint – Check for the validity of WSGI requests and responses

Middleware to check for obedience to the WSGI specification.

Some of the things this checks:

• Signature of the application and start_response (including that keyword arguments are not used).
• Environment checks:
  • Environment is a dictionary (and not a subclass).
  • That all the required keys are in the environment: REQUEST_METHOD, SERVER_NAME, SERVER_PORT, wsgi.version, wsgi.input, wsgi.errors, wsgi.multithread, wsgi.multiprocess, wsgi.run_once
  • That HTTP_CONTENT_TYPE and HTTP_CONTENT_LENGTH are not in the environment (these headers should appear as CONTENT_LENGTH and CONTENT_TYPE).
  • Warns if QUERY_STRING is missing, as the cgi module acts unpredictably in that case.
  • That CGI-style variables (that don’t contain a .) have (non-unicode) string values
  • That wsgi.version is a tuple
  • That wsgi.url_scheme is ‘http’ or ‘https’ (@@: is this too restrictive?)
  • Warns if the REQUEST_METHOD is not known (@@: probably too restrictive).
  • That SCRIPT_NAME and PATH_INFO are empty or start with /
  • That at least one of SCRIPT_NAME or PATH_INFO are set.
  • That CONTENT_LENGTH is a positive integer.
  • That SCRIPT_NAME is not ‘/’ (it should be ‘’, and PATH_INFO should be ‘/’).
  • That wsgi.input has the methods read, readline, readlines, and __iter__
  • That wsgi.errors has the methods flush, write, writelines
• The status is a string, contains a space, starts with an integer, and that integer is in range (> 100).
• That the headers is a list (not a subclass, not another kind of sequence).
• That the items of the headers are tuples of strings.
• That there is no ‘status’ header (that is used in CGI, but not in WSGI).
• That the headers don’t contain newlines or colons, end in _ or -, or contain characters codes below 037.
• That Content-Type is given if there is content (CGI often has a default content type, but WSGI does not).
• That no Content-Type is given when there is no content (@@: is this too restrictive?)
• That the exc_info argument to start_response is a tuple or None.
• That all calls to the writer are with strings, and no other methods on the writer are accessed.
• That wsgi.input is used properly:
  • .read() is called with zero or one argument
  • That it returns a string
  • That readline, readlines, and __iter__ return strings
  • That .close() is not called
  • No other methods are provided
• That wsgi.errors is used properly:
  • .write() and .writelines() is called with a string
  • That .close() is not called, and no other methods are provided.
• The response iterator:
  • That it is not a string (it should be a list of a single string; a string will work, but perform horribly).
  • That .next() returns a string
  • That the iterator is not iterated over until start_response has been called (that can signal either a server or application error).
  • That .close() is called (doesn’t raise exception, only prints to sys.stderr, because we only know it isn’t called when the object is garbage collected).

Module Contents

paste.lint.middleware(application, global_conf=None)

When applied between a WSGI server and a WSGI application, this middleware will check for WSGI compliancy on a number of levels. This middleware does not modify the request or response in any way, but will throw an AssertionError if anything seems off (except for a failure to close the application iterator, which will be printed to stderr – there’s no way to throw an exception at that point).

exception paste.lint.WSGIWarning

Raised in response to WSGI-spec-related warnings