WSGI Helpers

The following classes and functions are designed to make working withthe WSGI specification easier or operate on the WSGI layer. All thefunctionality from this module is available on the high-levelRequest/Response classes.

Iterator / Stream Helpers

These classes and functions simplify working with the WSGI applicationiterator and the input stream.

  • class _werkzeug.wsgi.ClosingIterator(_iterable, callbacks=None)
  • The WSGI specification requires that all middlewares and gatewaysrespect the close callback of an iterator. Because it is useful to addanother close action to a returned iterator and adding a custom iteratoris a boring task this class can be used for that:
  1. return ClosingIterator(app(environ, start_response), [cleanup_session,
  2.                                                       cleanup_locals])

If there is just one close function it can be passed instead of the list.

A closing iterator is not needed if the application uses response objectsand finishes the processing if the response is started:

  1. try:
  2.     return response(environ, start_response)
  3. finally:
  4.     cleanup_session()
  5.     cleanup_locals()
  • class _werkzeug.wsgi.FileWrapper(_file, buffer_size=8192)
  • This class can be used to convert a file-like object intoan iterable. It yields buffer_size blocks until the file is fullyread.

You should not use this class directly but rather use thewrap_file() function that uses the WSGI server’s file wrappersupport if it’s available.

0.5 新版功能.

If you’re using this object together with a BaseResponse you haveto use the direct_passthrough mode.

参数:

  • file – a file-like object with a read() method.
  • buffer_size – number of bytes for one iteration.
  • class _werkzeug.wsgi.LimitedStream(_stream, limit)
  • Wraps a stream so that it doesn’t read more than n bytes. If thestream is exhausted and the caller tries to get more bytes from iton_exhausted() is called which by default returns an emptystring. The return value of that function is forwardedto the reader function. So if it returns an empty stringread() will return an empty string as well.

The limit however must never be higher than what the stream canoutput. Otherwise readlines() will try to read past thelimit.

Note on WSGI compliance

calls to readline() and readlines() are notWSGI compliant because it passes a size argument to thereadline methods. Unfortunately the WSGI PEP is not safelyimplementable without a size argument to readline()because there is no EOF marker in the stream. As a resultof that the use of readline() is discouraged.

For the same reason iterating over the LimitedStreamis not portable. It internally calls readline().

We strongly suggest using read() only or using themake_line_iter() which safely iterates line-basedover a WSGI input stream.

参数:

  • stream – the stream to wrap.
  • limit – the limit for the stream, must not be longer thanwhat the string can provide if the stream does notend with EOF (like wsgi.input)
  • exhaust(chunk_size=65536)
  • Exhaust the stream. This consumes all the data left until thelimit is reached.

参数:chunk_size – the size for a chunk. It will read the chunkuntil the stream is exhausted and throw awaythe results.

  • is_exhausted

  • If the stream is exhausted this attribute is True.

  • on_disconnect()

  • What should happen if a disconnect is detected? The returnvalue of this function is returned from read functions in casethe client went away. By default aClientDisconnected exception is raised.

  • on_exhausted()

  • This is called when the stream tries to read past the limit.The return value of this function is returned from the readingfunction.

  • read(size=None)

  • Read size bytes or if size is not provided everything is read.

参数:size – the number of bytes read.

  • readline(size=None)

  • Reads one line from the stream.

  • readlines(size=None)

  • Reads a file into a list of strings. It calls readline()until the file is read to the end. It does support the optionalsize argument if the underlaying stream supports it forreadline.

  • tell()

  • Returns the position of the stream.

0.9 新版功能.

  • werkzeug.wsgi.makeline_iter(_stream, limit=None, buffer_size=10240)
  • Safely iterates line-based over an input stream. If the input streamis not a LimitedStream the limit parameter is mandatory.

This uses the stream’s read() method internally as oppositeto the readline() method that is unsafe and can only be usedin violation of the WSGI specification. The same problem applies to theiter function of the input stream which calls readline()without arguments.

If you need line-by-line processing it’s strongly recommended to iterateover the input stream using this helper function.

在 0.8 版更改: This function now ensures that the limit was reached.

0.9 新版功能: added support for iterators as input stream.

参数:

  • stream – the stream or iterate to iterate over.
  • limit – the limit in bytes for the stream. (Usuallycontent length. Not necessary if the _stream_is a LimitedStream.
  • buffer_size – The optional buffer size.
  • werkzeug.wsgi.makechunk_iter(_stream, separator, limit=None, buffer_size=10240)
  • Works like make_line_iter() but accepts a separatorwhich divides chunks. If you want newline based processingyou should use make_line_iter() instead as itsupports arbitrary newline markers.

0.8 新版功能.

0.9 新版功能: added support for iterators as input stream.

参数:

  • stream – the stream or iterate to iterate over.
  • separator – the separator that divides chunks.
  • limit – the limit in bytes for the stream. (Usuallycontent length. Not necessary if the _stream_is otherwise already limited).
  • buffer_size – The optional buffer size.
  • werkzeug.wsgi.wrapfile(_environ, file, buffer_size=8192)
  • Wraps a file. This uses the WSGI server’s file wrapper if availableor otherwise the generic FileWrapper.

0.5 新版功能.

If the file wrapper from the WSGI server is used it’s important to notiterate over it from inside the application but to pass it throughunchanged. If you want to pass out a file wrapper inside a responseobject you have to set directpassthrough to _True.

More information about file wrappers are available in PEP 333.

参数:

  • file – a file-like object with a read() method.
  • buffer_size – number of bytes for one iteration.

Environ Helpers

These functions operate on the WSGI environment. They extract usefulinformation or perform common manipulations:

  • werkzeug.wsgi.gethost(_environ, trusted_hosts=None)
  • Return the real host for the given WSGI environment. This takes careof the X-Forwarded-Host header. Optionally it verifies that the hostis in a list of trusted hosts. If the host is not in there it will raisea SecurityError.

参数:

  • environ – the WSGI environment to get the host of.
  • trusted_hosts – a list of trusted hosts, see host_is_trusted()for more information.
  • werkzeug.wsgi.getcontent_length(_environ)
  • Returns the content length from the WSGI environment asinteger. If it’s not available None is returned.

0.9 新版功能.

参数:environ – the WSGI environ to fetch the content length from.

  • werkzeug.wsgi.getinput_stream(_environ, safe_fallback=True)
  • Returns the input stream from the WSGI environment and wraps itin the most sensible way possible. The stream returned is not theraw WSGI stream in most cases but one that is safe to read fromwithout taking into account the content length.

0.9 新版功能.

参数:

  • environ – the WSGI environ to fetch the stream from.
  • safe – indicates weather the function should use an emptystream as safe fallback or just return the originalWSGI input stream if it can’t wrap it safely. Thedefault is to return an empty string in those cases.
  • werkzeug.wsgi.getcurrent_url(_environ, root_only=False, strip_querystring=False, host_only=False, trusted_hosts=None)
  • A handy helper function that recreates the full URL for the currentrequest or parts of it. Here an example:
  1. >>> from werkzeug.test import create_environ
  2. >>> env = create_environ("/?param=foo", "http://localhost/script")
  3. >>> get_current_url(env)
  4. 'http://localhost/script/?param=foo'
  5. >>> get_current_url(env, root_only=True)
  6. 'http://localhost/script/'
  7. >>> get_current_url(env, host_only=True)
  8. 'http://localhost/'
  9. >>> get_current_url(env, strip_querystring=True)
  10. 'http://localhost/script/'

This optionally it verifies that the host is in a list of trusted hosts.If the host is not in there it will raise aSecurityError.

参数:

  • environ – the WSGI environment to get the current URL from.
  • root_only – set True if you only want the root URL.
  • strip_querystring – set to True if you don’t want the querystring.
  • host_only – set to True if the host URL should be returned.
  • trusted_hosts – a list of trusted hosts, see host_is_trusted()for more information.
  • werkzeug.wsgi.getquery_string(_environ)
  • Returns the QUERY_STRING from the WSGI environment. This also takescare about the WSGI decoding dance on Python 3 environments as anative string. The string returned will be restricted to ASCIIcharacters.

0.9 新版功能.

参数:environ – the WSGI environment object to get the query string from.

  • werkzeug.wsgi.getscript_name(_environ, charset='utf-8', errors='replace')
  • Returns the SCRIPT_NAME from the WSGI environment and properlydecodes it. This also takes care about the WSGI decoding danceon Python 3 environments. if the charset is set to None abytestring is returned.

0.9 新版功能.

参数:

  • environ – the WSGI environment object to get the path from.
  • charset – the charset for the path, or None if nodecoding should be performed.
  • errors – the decoding error handling.
  • werkzeug.wsgi.getpath_info(_environ, charset='utf-8', errors='replace')
  • Returns the PATH_INFO from the WSGI environment and properlydecodes it. This also takes care about the WSGI decoding danceon Python 3 environments. if the charset is set to None abytestring is returned.

0.9 新版功能.

参数:

  • environ – the WSGI environment object to get the path from.
  • charset – the charset for the path info, or None if nodecoding should be performed.
  • errors – the decoding error handling.
  • werkzeug.wsgi.poppath_info(_environ, charset='utf-8', errors='replace')
  • Removes and returns the next segment of PATH_INFO, pushing it ontoSCRIPT_NAME. Returns None if there is nothing left on PATH_INFO.

If the charset is set to None a bytestring is returned.

If there are empty segments ('/foo//bar) these are ignored butproperly pushed to the SCRIPT_NAME:

  1. >>> env = {'SCRIPT_NAME': '/foo', 'PATH_INFO': '/a/b'}
  2. >>> pop_path_info(env)
  3. 'a'
  4. >>> env['SCRIPT_NAME']
  5. '/foo/a'
  6. >>> pop_path_info(env)
  7. 'b'
  8. >>> env['SCRIPT_NAME']
  9. '/foo/a/b'

0.5 新版功能.

在 0.9 版更改: The path is now decoded and a charset and encodingparameter can be provided.

参数:environ – the WSGI environment that is modified.

  • werkzeug.wsgi.peekpath_info(_environ, charset='utf-8', errors='replace')
  • Returns the next segment on the PATH_INFO or None if thereis none. Works like pop_path_info() without modifying theenvironment:
  1. >>> env = {'SCRIPT_NAME': '/foo', 'PATH_INFO': '/a/b'}
  2. >>> peek_path_info(env)
  3. 'a'
  4. >>> peek_path_info(env)
  5. 'a'

If the charset is set to None a bytestring is returned.

0.5 新版功能.

在 0.9 版更改: The path is now decoded and a charset and encodingparameter can be provided.

参数:environ – the WSGI environment that is checked.

  • werkzeug.wsgi.extractpath_info(_environ_or_baseurl, path_or_url, charset='utf-8', errors='replace', collapse_http_schemes=True)
  • Extracts the path info from the given URL (or WSGI environment) andpath. The path info returned is a unicode string, not a bytestringsuitable for a WSGI environment. The URLs might also be IRIs.

If the path info could not be determined, None is returned.

Some examples:

  1. >>> extract_path_info('http://example.com/app', '/app/hello')
  2. u'/hello'
  3. >>> extract_path_info('http://example.com/app',
  4. ...                   'https://example.com/app/hello')
  5. u'/hello'
  6. >>> extract_path_info('http://example.com/app',
  7. ...                   'https://example.com/app/hello',
  8. ...                   collapse_http_schemes=False) is None
  9. True

Instead of providing a base URL you can also pass a WSGI environment.

0.6 新版功能.

参数:

  • environ_or_baseurl – a WSGI environment dict, a base URL orbase IRI. This is the root of theapplication.
  • path_or_url – an absolute path from the server root, arelative path (in which case it’s the path info)or a full URL. Also accepts IRIs and unicodeparameters.
  • charset – the charset for byte data in URLs
  • errors – the error handling on decode
  • collapse_http_schemes – if set to False the algorithm doesnot assume that http and https on thesame server point to the sameresource.
  • werkzeug.wsgi.hostis_trusted(_hostname, trusted_list)
  • Checks if a host is trusted against a list. This also takes careof port normalization.

0.9 新版功能.

参数:

  • hostname – the hostname to check
  • trusted_list – a list of hostnames to check against. If ahostname starts with a dot it will match againstall subdomains as well.

Convenience Helpers

  • werkzeug.wsgi.responder(f)
  • Marks a function as responder. Decorate a function with it and itwill automatically call the return value as WSGI application.

Example:

  1. @responder
  2. def application(environ, start_response):
  3.     return Response('Hello World!')
  • werkzeug.testapp.testapp(_environ, start_response)
  • Simple test application that dumps the environment. You can useit to check if Werkzeug is working properly:
  1. >>> from werkzeug.serving import run_simple
  2. >>> from werkzeug.testapp import test_app
  3. >>> run_simple('localhost', 3000, test_app)
  4.  * Running on http://localhost:3000/

The application displays important information from the WSGI environment,the Python interpreter and the installed libraries.