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