# `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