Waitress

Waitress is meant to be a production-quality pure-Python WSGI server with very acceptable performance. It has no dependencies except ones which live in the Python standard library. It runs on CPython on Unix and Windows under Python 3.7+. It is also known to run on PyPy 3 (python version 3.7+) on UNIX. It supports HTTP/1.0 and HTTP/1.1.

Extended Documentation

Usage

The following code will run waitress on port 8080 on all available IP addresses, both IPv4 and IPv6.

from waitress import serve
serve(wsgiapp, listen='*:8080')

Press Ctrl-C (or Ctrl-Break on Windows) to exit the server.

The following will run waitress on port 8080 on all available IPv4 addresses, but not IPv6.

from waitress import serve
serve(wsgiapp, host='0.0.0.0', port=8080)

By default Waitress binds to any IPv4 address on port 8080. You can omit the host and port arguments and just call serve with the WSGI app as a single argument:

from waitress import serve
serve(wsgiapp)

If you want to serve your application through a UNIX domain socket (to serve a downstream HTTP server/proxy such as nginx, lighttpd, and so on), call serve with the unix_socket argument:

from waitress import serve
serve(wsgiapp, unix_socket='/path/to/unix.sock')

Needless to say, this configuration won't work on Windows.

Exceptions generated by your application will be shown on the console by default. See Access Logging to change this.

There's an entry point for PasteDeploy (egg:waitress#main) that lets you use Waitress's WSGI gateway from a configuration file, e.g.:

[server:main]
use = egg:waitress#main
listen = 127.0.0.1:8080

Using host and port is also supported:

[server:main]
host = 127.0.0.1
port = 8080

The PasteDeploy syntax for UNIX domain sockets is analagous:

[server:main]
use = egg:waitress#main
unix_socket = /path/to/unix.sock

You can find more settings to tweak (arguments to waitress.serve or equivalent settings in PasteDeploy) in Arguments to waitress.serve.

Additionally, there is a command line runner called waitress-serve, which can be used in development and in situations where the likes of PasteDeploy is not necessary:

# Listen on both IPv4 and IPv6 on port 8041
waitress-serve --listen=*:8041 myapp:wsgifunc

# Listen on only IPv4 on port 8041
waitress-serve --port=8041 myapp:wsgifunc

Heroku

Waitress can be used to serve WSGI apps on Heroku, include waitress in your requirements.txt file a update the Procfile as following:

web: waitress-serve \
    --listen "*:$PORT" \
    --trusted-proxy '*' \
    --trusted-proxy-headers 'x-forwarded-for x-forwarded-proto x-forwarded-port' \
    --log-untrusted-proxy-headers \
    --clear-untrusted-proxy-headers \
    --threads ${WEB_CONCURRENCY:-4} \
    myapp:wsgifunc

The proxy config informs Waitress to trust the forwarding headers set by the Heroku load balancer. It also allows for setting the standard WEB_CONCURRENCY environment variable to tweak the number of requests handled by Waitress at a time.

Note that Waitress uses a thread-based model and careful effort should be taken to ensure that requests do not take longer than 30 seconds or Heroku will inform the client that the request failed even though the request is still being processed by Waitress and occupying a thread until it completes.

For more information on this, see waitress-serve.

Access Logging

The WSGI design is modular. Waitress logs error conditions, debugging output, etc., but not web traffic. For web traffic logging, Paste provides TransLogger middleware. TransLogger produces logs in the Apache Combined Log Format.

Logging to the Console Using Python

waitress.serve calls logging.basicConfig() to set up logging to the console when the server starts up. Assuming no other logging configuration has already been done, this sets the logging default level to logging.WARNING. The Waitress logger will inherit the root logger's level information (it logs at level WARNING or above).

Waitress sends its logging output (including application exception renderings) to the Python logger object named waitress. You can influence the logger level and output stream using the normal Python logging module API. For example:

import logging
logger = logging.getLogger('waitress')
logger.setLevel(logging.INFO)

Within a PasteDeploy configuration file, you can use the normal Python logging module .ini file format to change similar Waitress logging options. For example:

[logger_waitress]
level = INFO

Logging to the Console Using PasteDeploy

TransLogger will automatically setup a logging handler to the console when called with no arguments. It "just works" in environments that don't configure logging. This is by virtue of its default configuration setting of setup_console_handler = True.

Logging to a File Using PasteDeploy

TransLogger does not write to files, and the Python logging system must be configured to do this. The Python class FileHandler logging handler can be used alongside TransLogger to create an access.log file similar to Apache's.

Like any standard middleware with a Paste entry point, TransLogger can be configured to wrap your application using .ini file syntax. First add a [filter:translogger] section, then use a [pipeline:main] section file to form a WSGI pipeline with both the translogger and your application in it. For instance, if you have this:

[app:wsgiapp]
use = egg:mypackage#wsgiapp

[server:main]
use = egg:waitress#main
host = 127.0.0.1
port = 8080

Add this:

[filter:translogger]
use = egg:Paste#translogger
setup_console_handler = False

[pipeline:main]
pipeline = translogger
           wsgiapp

Using PasteDeploy this way to form and serve a pipeline is equivalent to wrapping your app in a TransLogger instance via the bottom of the main function of your project's __init__ file:

from mypackage import wsgiapp
from waitress import serve
from paste.translogger import TransLogger
serve(TransLogger(wsgiapp, setup_console_handler=False))

Note

TransLogger will automatically set up a logging handler to the console when called with no arguments, so it "just works" in environments that don't configure logging. Since our logging handlers are configured, we disable the automation via setup_console_handler = False.

With the filter in place, TransLogger's logger (named the wsgi logger) will propagate its log messages to the parent logger (the root logger), sending its output to the console when we request a page:

00:50:53,694 INFO [wsgiapp] Returning: Hello World!
                  (content-type: text/plain)
00:50:53,695 INFO [wsgi] 192.168.1.111 - - [11/Aug/2011:20:09:33 -0700] "GET /hello
HTTP/1.1" 404 - "-"
"Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8.1.6) Gecko/20070725
Firefox/2.0.0.6"

To direct TransLogger to an access.log FileHandler, we need the following to add a FileHandler (named accesslog) to the list of handlers, and ensure that the wsgi logger is configured and uses this handler accordingly:

# Begin logging configuration

[loggers]
keys = root, wsgiapp, wsgi

[handlers]
keys = console, accesslog

[logger_wsgi]
level = INFO
handlers = accesslog
qualname = wsgi
propagate = 0

[handler_accesslog]
class = FileHandler
args = ('%(here)s/access.log','a')
level = INFO
formatter = generic

As mentioned above, non-root loggers by default propagate their log records to the root logger's handlers (currently the console handler). Setting propagate to 0 (False) here disables this; so the wsgi logger directs its records only to the accesslog handler.

Finally, there's no need to use the generic formatter with TransLogger, as TransLogger itself provides all the information we need. We'll use a formatter that passes-through the log messages as is. Add a new formatter called accesslog by including the following in your configuration file:

[formatters]
keys = generic, accesslog

[formatter_accesslog]
format = %(message)s

Finally alter the existing configuration to wire this new accesslog formatter into the FileHandler:

[handler_accesslog]
class = FileHandler
args = ('%(here)s/access.log','a')
level = INFO
formatter = accesslog

Using Behind a Reverse Proxy

Often people will set up "pure Python" web servers behind reverse proxies, especially if they need TLS support (Waitress does not natively support TLS). Even if you don't need TLS support, it's not uncommon to see Waitress and other pure-Python web servers set up to only handle requests behind a reverse proxy; these proxies often have lots of useful deployment knobs.

If you're using Waitress behind a reverse proxy, you'll almost always want your reverse proxy to pass along the Host header sent by the client to Waitress, in either case, as it will be used by most applications to generate correct URLs. You may also use the proxy headers if passing Host directly is not possible, or there are multiple proxies involved.

For example, when using nginx as a reverse proxy, you might add the following lines in a location section.

proxy_set_header        Host $host;

The Apache directive named ProxyPreserveHost does something similar when used as a reverse proxy.

Unfortunately, even if you pass the Host header, the Host header does not contain enough information to regenerate the original URL sent by the client. For example, if your reverse proxy accepts HTTPS requests (and therefore URLs which start with https://), the URLs generated by your application when used behind a reverse proxy served by Waitress might inappropriately be http://foo rather than https://foo. To fix this, you'll want to change the wsgi.url_scheme in the WSGI environment before it reaches your application. You can do this in one of three ways:

  1. You can pass a url_scheme configuration variable to the waitress.serve function.
  2. You can pass certain well known proxy headers from your proxy server and use waitress's trusted_proxy support to automatically configure the WSGI environment.

Using url_scheme to set wsgi.url_scheme

You can have the Waitress server use the https url scheme by default.:

from waitress import serve
serve(wsgiapp, listen='0.0.0.0:8080', url_scheme='https')

This works if all URLs generated by your application should use the https scheme.

Passing the proxy headers to setup the WSGI environment

If your proxy accepts both HTTP and HTTPS URLs, and you want your application to generate the appropriate url based on the incoming scheme, you'll want to pass waitress X-Forwarded-Proto, however Waitress is also able to update the environment using X-Forwarded-Proto, X-Forwarded-For, X-Forwarded-Host, and X-Forwarded-Port:

proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Host $host:$server_port;
proxy_set_header X-Forwarded-Port $server_port;

when using Apache, mod_proxy automatically forwards the following headers:

X-Forwarded-For
X-Forwarded-Host
X-Forwarded-Server

You will also want to add to Apache:

RequestHeader set X-Forwarded-Proto https

Configure waitress's trusted_proxy_headers as appropriate:

trusted_proxy_headers = "x-forwarded-for x-forwarded-host x-forwarded-proto x-forwarded-port"

At this point waitress will set up the WSGI environment using the information specified in the trusted proxy headers. This will setup the following variables:

HTTP_HOST
SERVER_NAME
SERVER_PORT
REMOTE_ADDR
REMOTE_PORT (if available)
wsgi.url_scheme

Waitress also has support for the Forwarded (RFC7239) HTTP header which is better defined than the ad-hoc X-Forwarded-*, however support is not nearly as widespread yet. Forwarded supports similar functionality as the different individual headers, and is mutually exclusive to using the X-Forwarded-* headers.

To configure waitress to use the Forwarded header, set:

trusted_proxy_headers = "forwarded"

Note

You must also configure the Waitress server's trusted_proxy to contain the IP address of the proxy.

Using url_prefix to influence SCRIPT_NAME and PATH_INFO

You can have the Waitress server use a particular url prefix by default for all URLs generated by downstream applications that take SCRIPT_NAME into account.:

from waitress import serve
serve(wsgiapp, listen='0.0.0.0:8080', url_prefix='/foo')

Setting this to any value except the empty string will cause the WSGI SCRIPT_NAME value to be that value, minus any trailing slashes you add, and it will cause the PATH_INFO of any request which is prefixed with this value to be stripped of the prefix. This is useful in proxying scenarios where you wish to forward all traffic to a Waitress server but need URLs generated by downstream applications to be prefixed with a particular path segment.

Design

Waitress uses a combination of asynchronous and synchronous code to do its job. It handles I/O to and from clients using the wasyncore, which is asyncore vendored into Waitress. It services requests via threads.

Note

asyncore has been deprecated since Python 3.6. Work continues on its inevitable removal from the Python standard library. Its recommended replacement is asyncio.

Although asyncore has been vendored into Waitress as wasyncore, you may see references to "asyncore" in this documentation's code examples and API. The terms are effectively the same and may be used interchangeably.

The wasyncore module:

  • Uses the select.select function to wait for connections from clients and determine if a connected client is ready to receive output.
  • Creates a channel whenever a new connection is made to the server.
  • Executes methods of a channel whenever it believes data can be read from or written to the channel.

A "channel" is created for each connection from a client to the server. The channel handles all requests over the same connection from that client. A channel will handle some number of requests during its lifetime: zero to how ever many HTTP requests are sent to the server by the client over a single connection. For example, an HTTP/1.1 client may issue a theoretically infinite number of requests over the same connection; each of these will be handled by the same channel. An HTTP/1.0 client without a "Connection: keep-alive" header will request usually only one over a single TCP connection, however, and when the request has completed, the client disconnects and reconnects (which will create another channel). When the connection related to a channel is closed, the channel is destroyed and garbage collected.

When a channel determines the client has sent at least one full valid HTTP request, it schedules a "task" with a "thread dispatcher". The thread dispatcher maintains a fixed pool of worker threads available to do client work (by default, 4 threads). If a worker thread is available when a task is scheduled, the worker thread runs the task. The task has access to the channel, and can write back to the channel's output buffer. When all worker threads are in use, scheduled tasks will wait in a queue for a worker thread to become available.

I/O is always done asynchronously (by wasyncore) in the main thread. Worker threads never do any I/O. This means that

  1. a large number of clients can be connected to the server at once, and
  2. worker threads will never be hung up trying to send data to a slow client.

No attempt is made to kill a "hung thread". It's assumed that when a task (application logic) starts that it will eventually complete. If for some reason WSGI application logic never completes and spins forever, the worker thread related to that WSGI application will be consumed "forever", and if enough worker threads are consumed like this, the server will stop responding entirely.

Periodic maintenance is done by the main thread (the thread handling I/O). If a channel hasn't sent or received any data in a while, the channel's connection is closed, and the channel is destroyed.

Differences from zope.server

  • Has no non-stdlib dependencies.
  • No support for non-WSGI servers (no FTP, plain-HTTP, etc); refactorings and slight interface changes as a result. Non-WSGI-supporting code removed.
  • Slight cleanup in the way application response headers are handled (no more "accumulated headers").
  • Supports the HTTP 1.1 "expect/continue" mechanism (required by WSGI spec).
  • Calls "close()" on the app_iter object returned by the WSGI application.
  • Allows trusted proxies to override wsgi.url_scheme for particular requests by supplying the X_FORWARDED_PROTO header.
  • Supports an explicit wsgi.url_scheme parameter for ease of deployment behind SSL proxies.
  • Different adjustment defaults (less conservative).
  • Python 3 compatible.
  • More test coverage (unit tests added, functional tests refactored and more added).
  • Supports convenience waitress.serve function (e.g. from waitress import serve; serve(app) and convenience server.run() function.
  • Returns a "real" write method from start_response.
  • Provides a getsockname method of the server FBO figuring out which port the server is listening on when it's bound to port 0.
  • Warns when app_iter bytestream numbytes less than or greater than specified Content-Length.
  • Set content-length header if len(app_iter) == 1 and none provided.
  • Raise an exception if start_response isnt called before any body write.
  • channel.write does not accept non-byte-sequences.
  • Put maintenance check on server rather than channel to avoid a class of DOS.
  • wsgi.multiprocess set (correctly) to False.
  • Ensures header total can not exceed a maximum size.
  • Ensures body total can not exceed a maximum size.
  • Broken chunked encoding request bodies don't crash the server.
  • Handles keepalive/pipelining properly (no out of order responses, no premature channel closes).
  • Send a 500 error to the client when a task raises an uncaught exception (with optional traceback rendering via "expose_traceback" adjustment).
  • Supports HTTP/1.1 chunked responses when application doesn't set a Content-Length header.
  • Dont hang a thread up trying to send data to slow clients.
  • Supports wsgi.file_wrapper protocol.

waitress API

serve(app, listen='0.0.0.0:8080', unix_socket=None, unix_socket_perms='600', threads=4, url_scheme='http', url_prefix='', ident='waitress', backlog=1024, recv_bytes=8192, send_bytes=1, outbuf_overflow=104856, outbuf_high_watermark=16777216, inbuf_overflow=52488, connection_limit=1000, cleanup_interval=30, channel_timeout=120, log_socket_errors=True, max_request_header_size=262144, max_request_body_size=1073741824, expose_tracebacks=False)

See Arguments to waitress.serve for more information.

Arguments to waitress.serve

Here are the arguments you can pass to the waitress.serve function or use in PasteDeploy configuration (interchangeably):

host

Hostname or IP address (string) on which to listen, default 0.0.0.0, which means "all IP addresses on this host".

Warning

May not be used with listen

port

TCP port (integer) on which to listen, default 8080

Warning

May not be used with listen

listen

Tell waitress to listen on combinations of host:port arguments. Combinations should be a quoted, space-delimited list, as in the following examples.

listen="127.0.0.1:8080 [::1]:8080"
listen="*:8080 *:6543"

A wildcard for the hostname is also supported and will bind to both IPv4/IPv6 depending on whether they are enabled or disabled.

IPv6 IP addresses are supported by surrounding the IP address with brackets.

New in version 1.0.

server_name

This is the value that will be placed in the WSGI environment as SERVER_NAME, the only time that this value is used in the WSGI environment for a request is if the client sent a HTTP/1.0 request without a Host header set, and no other proxy headers.

The default is value is waitress.invalid, if your WSGI application is creating URL's that include this as the hostname and you are using a reverse proxy setup, you may want to validate that your reverse proxy is sending the appropriate headers.

In most situations you will not need to set this value.

Default: waitress.invalid

New in version 2.0.

ipv4
Enable or disable IPv4 (boolean)
ipv6
Enable or disable IPv6 (boolean)
unix_socket

Path of Unix socket (string). If a socket path is specified, a Unix domain socket is made instead of the usual inet domain socket.

Not available on Windows.

Default: None

unix_socket_perms

Octal permissions to use for the Unix domain socket (string). Only used if unix_socket is not None.

Default: '600'

sockets

A list of sockets. The sockets can be either Internet or UNIX sockets and have to be bound. Internet and UNIX sockets cannot be mixed. If the socket list is not empty, waitress creates one server for each socket.

Default: []

New in version 1.1.1.

Warning

May not be used with listen, host, port or unix_socket

threads

The number of threads used to process application logic (integer).

Default: 4

trusted_proxy

IP address of a remote peer allowed to override various WSGI environment variables using proxy headers.

For unix sockets, set this value to localhost instead of an IP address.

Default: None

trusted_proxy_count

How many proxies we trust when chained. For example,

X-Forwarded-For: 192.0.2.1, "[2001:db8::1]"

or

Forwarded: for=192.0.2.1, For="[2001:db8::1]"

means there were (potentially), two proxies involved. If we know there is only 1 valid proxy, then that initial IP address "192.0.2.1" is not trusted and we completely ignore it.

If there are two trusted proxies in the path, this value should be set to 2. If there are more proxies, this value should be set higher.

Default: 1

New in version 1.2.0.

trusted_proxy_headers

Which of the proxy headers should we trust, this is a set where you either specify "forwarded" or one or more of "x-forwarded-host", "x-forwarded-for", "x-forwarded-proto", "x-forwarded-port", "x-forwarded-by".

This list of trusted headers is used when trusted_proxy is set and will allow waitress to modify the WSGI environment using the values provided by the proxy.

New in version 1.2.0.

Warning

If trusted_proxy is set, the default is x-forwarded-proto to match older versions of Waitress. Users should explicitly opt-in by selecting the headers to be trusted as future versions of waitress will use an empty default.

Warning

It is an error to set this value without setting trusted_proxy.

log_untrusted_proxy_headers

Should waitress log warning messages about proxy headers that are being sent from upstream that are not trusted by trusted_proxy_headers but are being cleared due to clear_untrusted_proxy_headers?

This may be useful for debugging if you expect your upstream proxy server to only send specific headers.

Default: False

New in version 1.2.0.

Warning

It is a no-op to set this value without also setting clear_untrusted_proxy_headers and trusted_proxy

clear_untrusted_proxy_headers

This tells Waitress to remove any untrusted proxy headers ("Forwarded", "X-Forwared-For", "X-Forwarded-By", "X-Forwarded-Host", "X-Forwarded-Port", "X-Forwarded-Proto") not explicitly allowed by trusted_proxy_headers.

Default: False

New in version 1.2.0.

Warning

The default value is set to False for backwards compatibility. In future versions of Waitress this default will be changed to True. Warnings will be raised unless the user explicitly provides a value for this option, allowing the user to opt-in to the new safety features automatically.

Warning

It is an error to set this value without setting trusted_proxy.

url_scheme

The value of wsgi.url_scheme in the environ. This can be overridden per-request by the value of the X_FORWARDED_PROTO header, but only if the client address matches trusted_proxy.

Default: http

ident

Server identity (string) used in "Server:" header in responses.

Default: waitress

backlog

The value waitress passes to pass to socket.listen() (integer). This is the maximum number of incoming TCP connections that will wait in an OS queue for an available channel. From listen(1): "If a connection request arrives when the queue is full, the client may receive an error with an indication of ECONNREFUSED or, if the underlying protocol supports retransmission, the request may be ignored so that a later reattempt at connection succeeds."

Default: 1024

recv_bytes

The argument waitress passes to socket.recv() (integer).

Default: 8192

send_bytes

The number of bytes to send to socket.send() (integer). Multiples of 9000 should avoid partly-filled TCP packets, but don't set this larger than the TCP write buffer size. In Linux, /proc/sys/net/ipv4/tcp_wmem controls the minimum, default, and maximum sizes of TCP write buffers.

Default: 1

Deprecated since version 1.3.

outbuf_overflow

A tempfile should be created if the pending output is larger than outbuf_overflow, which is measured in bytes. The default is conservative.

Default: 1048576 (1MB)

outbuf_high_watermark

The app_iter will pause when pending output is larger than this value and will resume once enough data is written to the socket to fall below this threshold.

Default: 16777216 (16MB)

inbuf_overflow

A tempfile should be created if the pending input is larger than inbuf_overflow, which is measured in bytes. The default is conservative.

Default: 524288 (512K)

connection_limit

Stop creating new channels if too many are already active (integer). Each channel consumes at least one file descriptor, and, depending on the input and output body sizes, potentially up to three, plus whatever file descriptors your application logic happens to open. The default is conservative, but you may need to increase the number of file descriptors available to the Waitress process on most platforms in order to safely change it (see ulimit -a "open files" setting). Note that this doesn't control the maximum number of TCP connections that can be waiting for processing; the backlog argument controls that.

Default: 100

cleanup_interval

Minimum seconds between cleaning up inactive channels (integer). See also channel_timeout.

Default: 30

channel_timeout

Maximum seconds to leave an inactive connection open (integer). "Inactive" is defined as "has received no data from a client and has sent no data to a client".

Default: 120

log_socket_errors

Set to False to not log premature client disconnect tracebacks.

Default: True

max_request_header_size

Maximum number of bytes of all request headers combined (integer).

Default: 262144 (256K)

max_request_body_size

Maximum number of bytes in request body (integer).

Default: 1073741824 (1GB)

expose_tracebacks

Set to True to expose tracebacks of unhandled exceptions to client.

Default: False

asyncore_loop_timeout

The timeout value (seconds) passed to asyncore.loop to run the mainloop.

Default: 1

New in version 0.8.3.

asyncore_use_poll

Set to True to switch from using select() to poll() in asyncore.loop. By default asyncore.loop() uses select() which has a limit of 1024 file descriptors. select() and poll() provide basically the same functionality, but poll() doesn't have the file descriptors limit.

Default: False

New in version 0.8.6.

url_prefix

String: the value used as the WSGI SCRIPT_NAME value. Setting this to anything except the empty string will cause the WSGI SCRIPT_NAME value to be the value passed minus any trailing slashes you add, and it will cause the PATH_INFO of any request which is prefixed with this value to be stripped of the prefix.

Default: ''

Support for wsgi.file_wrapper

Waitress supports the Python Web Server Gateway Interface v1.0 as specified in PEP 3333. Here's a usage example:

import os

here = os.path.dirname(os.path.abspath(__file__))

def myapp(environ, start_response):
    f = open(os.path.join(here, 'myphoto.jpg'), 'rb')
    headers = [('Content-Type', 'image/jpeg')]
    start_response(
        '200 OK',
        headers
        )
    return environ['wsgi.file_wrapper'](f, 32768)

The file wrapper constructor is accessed via environ['wsgi.file_wrapper']. The signature of the file wrapper constructor is (filelike_object, block_size). Both arguments must be passed as positional (not keyword) arguments. The result of creating a file wrapper should be returned as the app_iter from a WSGI application.

The object passed as filelike_object to the wrapper must be a file-like object which supports at least the read() method, and the read() method must support an optional size hint argument and the read() method must return bytes objects (never unicode). It should support the seek() and tell() methods. If it does not, normal iteration over the filelike_object using the provided block_size is used (and copying is done, negating any benefit of the file wrapper). It should support a close() method.

The specified block_size argument to the file wrapper constructor will be used only when the filelike_object doesn't support seek and/or tell methods. Waitress needs to use normal iteration to serve the file in this degenerate case (as per the WSGI pec), and this block size will be used as the iteration chunk size. The block_size argument is optional; if it is not passed, a default value 32768 is used.

Waitress will set a Content-Length header on behalf of an application when a file wrapper with a sufficiently file-like object is used if the application hasn't already set one.

The machinery which handles a file wrapper currently doesn't do anything particularly special using fancy system calls (it doesn't use sendfile for example); using it currently just prevents the system from needing to copy data to a temporary buffer in order to send it to the client. No copying of data is done when a WSGI app returns a file wrapper that wraps a sufficiently file-like object. It may do something fancier in the future.

waitress-serve

New in version 0.8.4: Waitress comes bundled with a thin command-line wrapper around the waitress.serve function called waitress-serve. This is useful for development, and in production situations where serving of static assets is delegated to a reverse proxy, such as nginx or Apache.

waitress-serve takes the very same arguments as the waitress.serve function, but where the function's arguments have underscores, waitress-serve uses hyphens. Thus:

import myapp

waitress.serve(myapp.wsgifunc, port=8041, url_scheme='https')

Is equivalent to:

waitress-serve --port=8041 --url-scheme=https myapp:wsgifunc

The full argument list is given below.

Boolean arguments are represented by flags. If you wish to explicitly set a flag, simply use it by its name. Thus the flag:

--expose-tracebacks

Is equivalent to passing expose_tracebacks=True to waitress.serve.

All flags have a negative equivalent. These are prefixed with no-; thus using the flag:

--no-expose-tracebacks

Is equivalent to passing expose_tracebacks=False to waitress.serve.

If at any time you want the full argument list, use the --help flag.

Applications are specified similarly to PasteDeploy, where the format is myapp.mymodule:wsgifunc. As some application frameworks use application objects, you can use dots to resolve attributes like so: myapp.mymodule:appobj.wsgifunc.

A number of frameworks, web.py being an example, have factory methods on their application objects that return usable WSGI functions when called. For cases like these, waitress-serve has the --call flag. Thus:

waitress-serve --call myapp.mymodule.app.wsgi_factory

Would load the myapp.mymodule module, and call app.wsgi_factory to get a WSGI application function to be passed to waitress.server.

Note

As of 0.8.6, the current directory is automatically included on sys.path.

Invocation

Usage:

waitress-serve [OPTS] MODULE:OBJECT

Common options:

--help
Show this information.
--call
Call the given object to get the WSGI application.
--host=ADDR
Hostname or IP address on which to listen, default is '0.0.0.0', which means "all IP addresses on this host".
--port=PORT
TCP port on which to listen, default is '8080'
--listen=host:port

Tell waitress to listen on an ip port combination.

Example:

--listen=127.0.0.1:8080 --listen=[::1]:8080 --listen=*:8080

This option may be used multiple times to listen on multipe sockets. A wildcard for the hostname is also supported and will bind to both IPv4/IPv6 depending on whether they are enabled or disabled.

--[no-]ipv4

Toggle on/off IPv4 support.

This affects wildcard matching when listening on a wildcard address/port combination.

--[no-]ipv6

Toggle on/off IPv6 support.

This affects wildcard matching when listening on a wildcard address/port combination.

--unix-socket=PATH

Path of Unix socket. If a socket path is specified, a Unix domain socket is made instead of the usual inet domain socket.

Not available on Windows.

--unix-socket-perms=PERMS
Octal permissions to use for the Unix domain socket, default is '600'.
--url-scheme=STR
Default wsgi.url_scheme value, default is 'http'.
--url-prefix=STR
The SCRIPT_NAME WSGI environment value. Setting this to anything except the empty string will cause the WSGI SCRIPT_NAME value to be the value passed minus any trailing slashes you add, and it will cause the PATH_INFO of any request which is prefixed with this value to be stripped of the prefix. Default is the empty string.
--ident=STR
Server identity used in the 'Server' header in responses. Default is 'waitress'.

Tuning options:

--threads=INT
Number of threads used to process application logic, default is 4.
--backlog=INT
Connection backlog for the server. Default is 1024.
--recv-bytes=INT
Number of bytes to request when calling socket.recv(). Default is 8192.
--send-bytes=INT

Number of bytes to send to socket.send(). Default is 1. Multiples of 9000 should avoid partly-filled TCP packets.

Deprecated since version 1.3.

--outbuf-overflow=INT
A temporary file should be created if the pending output is larger than this. Default is 1048576 (1MB).
--outbuf-high-watermark=INT
The app_iter will pause when pending output is larger than this value and will resume once enough data is written to the socket to fall below this threshold. Default is 16777216 (16MB).
--inbuf-overflow=INT
A temporary file should be created if the pending input is larger than this. Default is 524288 (512KB).
--connection-limit=INT
Stop creating new channels if too many are already active. Default is 100.
--cleanup-interval=INT
Minimum seconds between cleaning up inactive channels. Default is 30. See --channel-timeout.
--channel-timeout=INT
Maximum number of seconds to leave inactive connections open. Default is 120. 'Inactive' is defined as 'has received no data from the client and has sent no data to the client'.
--[no-]log-socket-errors
Toggle whether premature client disconnect tracebacks ought to be logged. On by default.
--max-request-header-size=INT
Maximum size of all request headers combined. Default is 262144 (256KB).
--max-request-body-size=INT
Maximum size of request body. Default is 1073741824 (1GB).
--[no-]expose-tracebacks
Toggle whether to expose tracebacks of unhandled exceptions to the client. Off by default.
--asyncore-loop-timeout=INT
The timeout value in seconds passed to asyncore.loop(). Default is 1.
--asyncore-use-poll
The use_poll argument passed to asyncore.loop(). Helps overcome open file descriptors limit. Default is False.

Socket Activation

While waitress does not support the various implementations of socket activation, for example using systemd or launchd, it is prepared to receive pre-bound sockets from init systems, process and socket managers, or other launchers that can provide pre-bound sockets.

The following shows a code example starting waitress with two pre-bound Internet sockets.

import socket
import waitress


def app(environ, start_response):
    content_length = environ.get('CONTENT_LENGTH', None)
    if content_length is not None:
        content_length = int(content_length)
    body = environ['wsgi.input'].read(content_length)
    content_length = str(len(body))
    start_response(
        '200 OK',
        [('Content-Length', content_length), ('Content-Type', 'text/plain')]
    )
    return [body]


if __name__ == '__main__':
    sockets = [
        socket.socket(socket.AF_INET, socket.SOCK_STREAM),
        socket.socket(socket.AF_INET, socket.SOCK_STREAM)]
    sockets[0].bind(('127.0.0.1', 8080))
    sockets[1].bind(('127.0.0.1', 9090))
    waitress.serve(app, sockets=sockets)
    for socket in sockets:
        socket.close()

Generally, to implement socket activation for a given init system, a wrapper script uses the init system specific libraries to retrieve the sockets from the init system. Afterwards it starts waitress, passing the sockets with the parameter sockets. Note that the sockets have to be bound, which all init systems supporting socket activation do.

Glossary

asyncore

A Python standard library module for asynchronous communications. See asyncore.

Changed in version 1.2.0: Waitress has now "vendored" asyncore into itself as waitress.wasyncore. This is to cope with the eventuality that asyncore will be removed from the Python standard library in Python 3.8 or so.

middleware
Middleware is a WSGI concept. It is a WSGI component that acts both as a server and an application. Interesting uses for middleware exist, such as caching, content-transport encoding, and other functions. See WSGI.org or PyPI to find middleware for your application.
PasteDeploy
A system for configuration of WSGI web components in declarative .ini format. See https://docs.pylonsproject.org/projects/pastedeploy/en/latest/.
wasyncore

Changed in version 1.2.0: Waitress has now "vendored" asyncore into itself as waitress.wasyncore. This is to cope with the eventuality that asyncore will be removed from the Python standard library in Python 3.8 or so.

WSGI
Web Server Gateway Interface. This is a Python standard for connecting web applications to web servers, similar to the concept of Java Servlets. Waitress requires that your application be served as a WSGI application.

Change History

2.1.0

Python Version Support

  • Python 3.6 is no longer supported by Waitress
  • Python 3.10 is fully supported by Waitress

Bugfix

Features

  • When the WSGI app starts sending data to the output buffer, we now attempt to send data directly to the socket. This avoids needing to wake up the main thread to start sending data. Allowing faster transmission of the first byte. See https://github.com/Pylons/waitress/pull/364

    With thanks to Michael Merickel for being a great rubber ducky!

  • Add REQUEST_URI to the WSGI environment.

    REQUEST_URI is similar to request_uri in nginx. It is a string that contains the request path before separating the query string and decoding %-escaped characters.

2.0.0 (2021-03-07)

Friendly Reminder

This release still contains a variety of deprecation notices about defaults that can be set for a variety of options.

Please note that this is your last warning, and you should update your configuration if you do NOT want to use the new defaults.

See the arguments documentation page for all supported options, and pay attention to the warnings:

https://docs.pylonsproject.org/projects/waitress/en/stable/arguments.html

Without further ado, here's a short list of great changes thanks to our contributors!

Bugfixes/Features

  • Fix a crash on startup when listening to multiple interfaces. See https://github.com/Pylons/waitress/pull/332

  • Waitress no longer attempts to guess at what the server_name should be for a listen socket, instead it always use a new adjustment/argument named server_name.

    Please see the documentation for server_name in https://docs.pylonsproject.org/projects/waitress/en/latest/arguments.html and see https://github.com/Pylons/waitress/pull/329

  • Allow tasks to notice if the client disconnected.

    This inserts a callable waitress.client_disconnected into the environment that allows the task to check if the client disconnected while waiting for the response at strategic points in the execution and to cancel the operation.

    It requires setting the new adjustment channel_request_lookahead to a value larger than 0, which continues to read requests from a channel even if a request is already being processed on that channel, up to the given count, since a client disconnect is detected by reading from a readable socket and receiving an empty result.

    See https://github.com/Pylons/waitress/pull/310

  • Drop Python 2.7 and 3.5 support

  • The server now issues warning output when it there are enough open connections (controlled by "connection_limit"), that it is no longer accepting new connections. This situation was previously difficult to diagnose. See https://github.com/Pylons/waitress/pull/322

1.4.4 (2020-06-01)

  • Fix an issue with keep-alive connections in which memory usage was higher than expected because output buffers were being reused across requests on a long-lived connection and each buffer would not be freed until it was full or the connection was closed. Buffers are now rotated per-request to stabilize their behavior.

    See https://github.com/Pylons/waitress/pull/300

  • Waitress threads have been updated to contain their thread number. This will allow loggers that use that information to print the thread that the log is coming from.

    See https://github.com/Pylons/waitress/pull/302

1.4.3 (2020-02-02)

Security Fixes

  • In Waitress version 1.4.2 a new regular expression was added to validate the headers that Waitress receives to make sure that it matches RFC7230. Unfortunately the regular expression was written in a way that with invalid input it leads to catastrophic backtracking which allows for a Denial of Service and CPU usage going to a 100%.

    This was reported by Fil Zembowicz to the Pylons Project. Please see https://github.com/Pylons/waitress/security/advisories/GHSA-73m2-3pwg-5fgc for more information.

1.4.2 (2020-01-02)

Security Fixes

  • This is a follow-up to the fix introduced in 1.4.1 to tighten up the way Waitress strips whitespace from header values. This makes sure Waitress won't accidentally treat non-printable characters as whitespace and lead to a potental HTTP request smuggling/splitting security issue.

    Thanks to ZeddYu Lu for the extra test cases.

    Please see the security advisory for more information: https://github.com/Pylons/waitress/security/advisories/GHSA-m5ff-3wj3-8ph4

    CVE-ID: CVE-2019-16789

Bugfixes

1.4.1 (2019-12-24)

Security Fixes

  • Waitress did not properly validate that the HTTP headers it received were properly formed, thereby potentially allowing a front-end server to treat a request different from Waitress. This could lead to HTTP request smuggling/splitting.

    Please see the security advisory for more information: https://github.com/Pylons/waitress/security/advisories/GHSA-m5ff-3wj3-8ph4

    CVE-ID: CVE-2019-16789

1.4.0 (2019-12-20)

Bugfixes

  • Waitress used to slam the door shut on HTTP pipelined requests without setting the Connection: close header as appropriate in the response. This is of course not very friendly. Waitress now explicitly sets the header when responding with an internally generated error such as 400 Bad Request or 500 Internal Server Error to notify the remote client that it will be closing the connection after the response is sent.
  • Waitress no longer allows any spaces to exist between the header field-name and the colon. While waitress did not strip the space and thereby was not vulnerable to any potential header field-name confusion, it should have sent back a 400 Bad Request. See https://github.com/Pylons/waitress/issues/273

Security Fixes

  • Waitress implemented a "MAY" part of the RFC7230 (https://tools.ietf.org/html/rfc7230#section-3.5) which states:

    Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR.

    Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message.

    For more information I can highly recommend the blog post by ZeddYu Lu https://blog.zeddyu.info/2019/12/08/HTTP-Smuggling-en/

    Please see the security advisory for more information: https://github.com/Pylons/waitress/security/advisories/GHSA-pg36-wpm5-g57p

    CVE-ID: CVE-2019-16785

  • Waitress used to treat LF the same as CRLF in Transfer-Encoding: chunked requests, while the maintainer doesn't believe this could lead to a security issue, this is no longer supported and all chunks are now validated to be properly framed with CRLF as required by RFC7230.

  • Waitress now validates that the Transfer-Encoding header contains only transfer codes that it is able to decode. At the moment that includes the only valid header value being chunked.

    That means that if the following header is sent:

    Transfer-Encoding: gzip, chunked

    Waitress will send back a 501 Not Implemented with an error message stating as such, as while Waitress supports chunked encoding it does not support gzip and it is unable to pass that to the underlying WSGI environment correctly.

    Waitress DOES NOT implement support for Transfer-Encoding: identity eventhough identity was valid in RFC2616, it was removed in RFC7230. Please update your clients to remove the Transfer-Encoding header if the only transfer coding is identity or update your client to use Transfer-Encoding: chunked instead of Transfer-Encoding: identity, chunked.

    Please see the security advisory for more information: https://github.com/Pylons/waitress/security/advisories/GHSA-g2xc-35jw-c63p

    CVE-ID: CVE-2019-16786

  • While validating the Transfer-Encoding header, Waitress now properly handles line-folded Transfer-Encoding headers or those that contain multiple comma seperated values. This closes a potential issue where a front-end server may treat the request as being a chunked request (and thus ignoring the Content-Length) and Waitress using the Content-Length as it was looking for the single value chunked and did not support comma seperated values.

  • Waitress used to explicitly set the Content-Length header to 0 if it was unable to parse it as an integer (for example if the Content-Length header was sent twice (and thus folded together), or was invalid) thereby allowing for a potential request to be split and treated as two requests by HTTP pipelining support in Waitress. If Waitress is now unable to parse the Content-Length header, a 400 Bad Request is sent back to the client.

    Please see the security advisory for more information: https://github.com/Pylons/waitress/security/advisories/GHSA-4ppp-gpcr-7qf6

1.3.1 (2019-08-27)

Bugfixes

1.3.0 (2019-04-22)

Deprecations

Features

Bugfixes

1.2.1 (2019-01-25)

Bugfixes

1.2.0 (2019-01-15)

No changes since the last beta release. Enjoy Waitress!

1.2.0b3 (2019-01-07)

Bugfixes

1.2.0b2 (2019-02-02)

Bugfixes

  • Fixed logic to no longer warn on writes where the output is required to have a body but there may not be any data to be written. Solves issue posted on the Pylons Project mailing list with 1.2.0b1.

1.2.0b1 (2018-12-31)

Happy New Year!

Features

  • Setting the trusted_proxy setting to '*' (wildcard) will allow all upstreams to be considered trusted proxies, thereby allowing services behind Cloudflare/ELBs to function correctly whereby there may not be a singular IP address that requests are received from.

    Using this setting is potentially dangerous if your server is also available from anywhere on the internet, and further protections should be used to lock down access to Waitress. See https://github.com/Pylons/waitress/pull/224

  • Waitress has increased its support of the X-Forwarded-* headers and includes Forwarded (RFC7239) support. This may be used to allow proxy servers to influence the WSGI environment. See https://github.com/Pylons/waitress/pull/209

    This also provides a new security feature when using Waitress behind a proxy in that it is possible to remove untrusted proxy headers thereby making sure that downstream WSGI applications don't accidentally use those proxy headers to make security decisions.

    The documentation has more information, see the following new arguments:

    • trusted_proxy_count
    • trusted_proxy_headers
    • clear_untrusted_proxy_headers
    • log_untrusted_proxy_headers (useful for debugging)

    Be aware that the defaults for these are currently backwards compatible with older versions of Waitress, this will change in a future release of waitress. If you expect to need this behaviour please explicitly set these variables in your configuration, or pin this version of waitress.

    Documentation: https://docs.pylonsproject.org/projects/waitress/en/latest/reverse-proxy.html

  • Waitress can now accept a list of sockets that are already pre-bound rather than creating its own to allow for socket activation. Support for init systems/other systems that create said activated sockets is not included. See https://github.com/Pylons/waitress/pull/215

  • Server header can be omitted by specifying ident=None or ident=''. See https://github.com/Pylons/waitress/pull/187

Bugfixes

Compatibility

  • Waitress has now "vendored" asyncore into itself as waitress.wasyncore. This is to cope with the eventuality that asyncore will be removed from the Python standard library in 3.8 or so.

Documentation

1.1.0 (2017-10-10)

Features

  • Waitress now has a __main__ and thus may be called with python -mwaitress

Bugfixes

1.0.2 (2017-02-04)

Features

  • Python 3.6 is now officially supported in Waitress

Bugfixes

  • Add a work-around for libc issue on Linux not following the documented standards. If getnameinfo() fails because of DNS not being available it should return the IP address instead of the reverse DNS entry, however instead getnameinfo() raises. We catch this, and ask getnameinfo() for the same information again, explicitly asking for IP address instead of reverse DNS hostname. See https://github.com/Pylons/waitress/issues/149 and https://github.com/Pylons/waitress/pull/153

1.0.1 (2016-10-22)

Bugfixes

  • IPv6 support on Windows was broken due to missing constants in the socket module. This has been resolved by setting the constants on Windows if they are missing. See https://github.com/Pylons/waitress/issues/138
  • A ValueError was raised on Windows when passing a string for the port, on Windows in Python 2 using service names instead of port numbers doesn't work with getaddrinfo. This has been resolved by attempting to convert the port number to an integer, if that fails a ValueError will be raised. See https://github.com/Pylons/waitress/issues/139

1.0.0 (2016-08-31)

Bugfixes

  • Removed AI_ADDRCONFIG from the call to getaddrinfo, this resolves an issue whereby getaddrinfo wouldn't return any addresses to bind to on hosts where there is no internet connection but localhost is requested to be bound to. See https://github.com/Pylons/waitress/issues/131 for more information.

Deprecations

  • Python 2.6 is no longer supported.

Features

  • IPv6 support

  • Waitress is now able to listen on multiple sockets, including IPv4 and IPv6. Instead of passing in a host/port combination you now provide waitress with a space delineated list, and it will create as many sockets as required.

    from waitress import serve
serve(wsgiapp, listen='0.0.0.0:8080 [::]:9090 *:6543')

Security

0.9.0 (2016-04-15)

Deprecations

  • Python 3.2 is no longer supported by Waitress.
  • Python 2.6 will no longer be supported by Waitress in future releases.

Security/Protections

Bugfixes

0.8.10 (2015-09-02)

  • Add support for Python 3.4, 3.5b2, and PyPy3.
  • Use a nonglobal asyncore socket map by default, trying to prevent conflicts with apps and libs that use the asyncore global socket map ala https://github.com/Pylons/waitress/issues/63. You can get the old use-global-socket-map behavior back by passing asyncore.socket_map to the create_server function as the map argument.
  • Waitress violated PEP 3333 with respect to reraising an exception when start_response was called with an exc_info argument. It would reraise the exception even if no data had been sent to the client. It now only reraises the exception if data has actually been sent to the client. See https://github.com/Pylons/waitress/pull/52 and https://github.com/Pylons/waitress/issues/51
  • Add a docs section to tox.ini that, when run, ensures docs can be built.
  • If an application value of None is supplied to the create_server constructor function, a ValueError is now raised eagerly instead of an error occuring during runtime. See https://github.com/Pylons/waitress/pull/60
  • Fix parsing of multi-line (folded) headers. See https://github.com/Pylons/waitress/issues/53 and https://github.com/Pylons/waitress/pull/90
  • Switch from the low level Python thread/_thread module to the threading module.
  • Improved exception information should module import go awry.

0.8.9 (2014-05-16)

  • Fix tests under Windows. NB: to run tests under Windows, you cannot run "setup.py test" or "setup.py nosetests". Instead you must run python.exe -c "import nose; nose.main()". If you try to run the tests using the normal method under Windows, each subprocess created by the test suite will attempt to run the test suite again. See https://github.com/nose-devs/nose/issues/407 for more information.
  • Give the WSGI app_iter generated when wsgi.file_wrapper is used (ReadOnlyFileBasedBuffer) a close method. Do not call close on an instance of such a class when it's used as a WSGI app_iter, however. This is part of a fix which prevents a leakage of file descriptors; the other part of the fix was in WebOb (https://github.com/Pylons/webob/commit/951a41ce57bd853947f842028bccb500bd5237da).
  • Allow trusted proxies to override wsgi.url_scheme via a request header, X_FORWARDED_PROTO. Allows proxies which serve mixed HTTP / HTTPS requests to control signal which are served as HTTPS. See https://github.com/Pylons/waitress/pull/42.

0.8.8 (2013-11-30)

  • Fix some cases where the creation of extremely large output buffers (greater than 2GB, suspected to be buffers added via wsgi.file_wrapper) might cause an OverflowError on Python 2. See https://github.com/Pylons/waitress/issues/47.
  • When the url_prefix adjustment starts with more than one slash, all slashes except one will be stripped from its beginning. This differs from older behavior where more than one leading slash would be preserved in url_prefix.
  • If a client somehow manages to send an empty path, we no longer convert the empty path to a single slash in PATH_INFO. Instead, the path remains empty. According to RFC 2616 section "5.1.2 Request-URI", the scenario of a client sending an empty path is actually not possible because the request URI portion cannot be empty.
  • If the url_prefix adjustment matches the request path exactly, we now compute SCRIPT_NAME and PATH_INFO properly. Previously, if the url_prefix was /foo and the path received from a client was /foo, we would set both SCRIPT_NAME and PATH_INFO to /foo. This was incorrect. Now in such a case we set PATH_INFO to the empty string and we set SCRIPT_NAME to /foo. Note that the change we made has no effect on paths that do not match the url_prefix exactly (such as /foo/bar); these continue to operate as they did. See https://github.com/Pylons/waitress/issues/46
  • Preserve header ordering of headers with the same name as per RFC 2616. See https://github.com/Pylons/waitress/pull/44
  • When waitress receives a Transfer-Encoding: chunked request, we no longer send the TRANSFER_ENCODING nor the HTTP_TRANSFER_ENCODING value to the application in the environment. Instead, we pop this header. Since we cope with chunked requests by buffering the data in the server, we also know when a chunked request has ended, and therefore we know the content length. We set the content-length header in the environment, such that applications effectively never know the original request was a T-E: chunked request; it will appear to them as if the request is a non-chunked request with an accurate content-length.
  • Cope with the fact that the Transfer-Encoding value is case-insensitive.
  • When the --unix-socket-perms option was used as an argument to waitress-serve, a TypeError would be raised. See https://github.com/Pylons/waitress/issues/50.

0.8.7 (2013-08-29)

  • The HTTP version of the response returned by waitress when it catches an exception will now match the HTTP request version.
  • Fix: CONNECTION header will be HTTP_CONNECTION and not CONNECTION_TYPE (see https://github.com/Pylons/waitress/issues/13)

0.8.6 (2013-08-12)

  • Do alternate type of checking for UNIX socket support, instead of checking for platform == windows.
  • Functional tests now use multiprocessing module instead of subprocess module, speeding up test suite and making concurrent execution more reliable.
  • Runner now appends the current working directory to sys.path to support running WSGI applications from a directory (i.e., not installed in a virtualenv).
  • Add a url_prefix adjustment setting. You can use it by passing script_name='/foo' to waitress.serve or you can use it in a PasteDeploy ini file as script_name = /foo. This will cause the WSGI SCRIPT_NAME value to be the value passed minus any trailing slashes you add, and it will cause the PATH_INFO of any request which is prefixed with this value to be stripped of the prefix. You can use this instead of PasteDeploy's prefixmiddleware to always prefix the path.

0.8.5 (2013-05-27)

  • Fix runner multisegment imports in some Python 2 revisions (see https://github.com/Pylons/waitress/pull/34).
  • For compatibility, WSGIServer is now an alias of TcpWSGIServer. The signature of BaseWSGIServer is now compatible with WSGIServer pre-0.8.4.

0.8.4 (2013-05-24)

  • Add a command-line runner called waitress-serve to allow Waitress to run WSGI applications without any addional machinery. This is essentially a thin wrapper around the waitress.serve() function.
  • Allow parallel testing (e.g., under detox or nosetests --processes) using PID-dependent port / socket for functest servers.
  • Fix integer overflow errors on large buffers. Thanks to Marcin Kuzminski for the patch. See: https://github.com/Pylons/waitress/issues/22
  • Add support for listening on Unix domain sockets.

0.8.3 (2013-04-28)

Features

  • Add an asyncore_loop_timeout adjustment value, which controls the timeout value passed to asyncore.loop; defaults to 1.

Bug Fixes

0.8.2 (2012-11-14)

Bug Fixes

  • https://corte.si/posts/code/pathod/pythonservers/index.html pointed out that sending a bad header resulted in an exception leading to a 500 response instead of the more proper 400 response without an exception.
  • Fix a race condition in the test suite.
  • Allow "ident" to be used as a keyword to serve() as per docs.
  • Add py33 to tox.ini.

0.8.1 (2012-02-13)

Bug Fixes

  • A brown-bag bug prevented request concurrency. A slow request would block subsequent the responses of subsequent requests until the slow request's response was fully generated. This was due to a "task lock" being declared as a class attribute rather than as an instance attribute on HTTPChannel. Also took the opportunity to move another lock named "outbuf lock" to the channel instance rather than the class. See https://github.com/Pylons/waitress/pull/1 .

0.8 (2012-01-31)

Features

  • Support the WSGI wsgi.file_wrapper protocol as per https://www.python.org/dev/peps/pep-0333/#optional-platform-specific-file-handling. Here's a usage example:

    import os

here = os.path.dirname(os.path.abspath(__file__))

def myapp(environ, start_response):
    f = open(os.path.join(here, 'myphoto.jpg'), 'rb')
    headers = [('Content-Type', 'image/jpeg')]
    start_response(
        '200 OK',
        headers
        )
    return environ['wsgi.file_wrapper'](f, 32768)

    The signature of the file wrapper constructor is (filelike_object, block_size). Both arguments must be passed as positional (not keyword) arguments. The result of creating a file wrapper should be returned as the app_iter from a WSGI application.

    The object passed as filelike_object to the wrapper must be a file-like object which supports at least the read() method, and the read() method must support an optional size hint argument. It should support the seek() and tell() methods. If it does not, normal iteration over the filelike object using the provided block_size is used (and copying is done, negating any benefit of the file wrapper). It should support a close() method.

    The specified block_size argument to the file wrapper constructor will be used only when the filelike_object doesn't support seek and/or tell methods. Waitress needs to use normal iteration to serve the file in this degenerate case (as per the WSGI spec), and this block size will be used as the iteration chunk size. The block_size argument is optional; if it is not passed, a default value``32768`` is used.

    Waitress will set a Content-Length header on the behalf of an application when a file wrapper with a sufficiently filelike object is used if the application hasn't already set one.

    The machinery which handles a file wrapper currently doesn't do anything particularly special using fancy system calls (it doesn't use sendfile for example); using it currently just prevents the system from needing to copy data to a temporary buffer in order to send it to the client. No copying of data is done when a WSGI app returns a file wrapper that wraps a sufficiently filelike object. It may do something fancier in the future.

0.7 (2012-01-11)

Features

  • Default send_bytes value is now 18000 instead of 9000. The larger default value prevents asyncore from needing to execute select so many times to serve large files, speeding up file serving by about 15%-20% or so. This is probably only an optimization for LAN communications, and could slow things down across a WAN (due to higher TCP overhead), but we're likely to be behind a reverse proxy on a LAN anyway if in production.
  • Added an (undocumented) profiling feature to the serve() command.

0.6.1 (2012-01-08)

Bug Fixes

  • Remove performance-sapping call to pull_trigger in the channel's write_soon method added mistakenly in 0.6.

0.6 (2012-01-07)

Bug Fixes

  • A logic error prevented the internal outbuf buffer of a channel from being flushed when the client could not accept the entire contents of the output buffer in a single succession of socket.send calls when the channel was in a "pending close" state. The socket in such a case would be closed prematurely, sometimes resulting in partially delivered content. This was discovered by a user using waitress behind an Nginx reverse proxy, which apparently is not always ready to receive data. The symptom was that he received "half" of a large CSS file (110K) while serving content via waitress behind the proxy.

0.5 (2012-01-03)

Bug Fixes

  • Fix PATH_INFO encoding/decoding on Python 3 (as per PEP 3333, tunnel bytes-in-unicode-as-latin-1-after-unquoting).

0.4 (2012-01-02)

Features

  • Added "design" document to docs.

Bug Fixes

  • Set default connection_limit back to 100 for benefit of maximal platform compatibility.
  • Normalize setting of last_activity during send.
  • Minor resource cleanups during tests.
  • Channel timeout cleanup was broken.

0.3 (2012-01-02)

Features

  • Dont hang a thread up trying to send data to slow clients.
  • Use self.logger to log socket errors instead of self.log_info (normalize).
  • Remove pointless handle_error method from channel.
  • Queue requests instead of tasks in a channel.

Bug Fixes

  • Expect: 100-continue responses were broken.

0.2 (2011-12-31)

Bug Fixes

  • Set up logging by calling logging.basicConfig() when serve is called (show tracebacks and other warnings to console by default).
  • Disallow WSGI applications to set "hop-by-hop" headers (Connection, Transfer-Encoding, etc).
  • Don't treat 304 status responses specially in HTTP/1.1 mode.
  • Remove out of date interfaces.py file.
  • Normalize logging (all output is now sent to the waitress logger rather than in degenerate cases some output being sent directly to stderr).

Features

  • Support HTTP/1.1 Transfer-Encoding: chunked responses.
  • Slightly better docs about logging.

0.1 (2011-12-30)

  • Initial release.

Known Issues

Support and Development

The Pylons Project web site is the main online source of Waitress support and development information.

To report bugs, use the issue tracker.

If you've got questions that aren't answered by this documentation, contact the Pylons-discuss maillist or join the #pyramid IRC channel.

Browse and check out tagged and trunk versions of Waitress via the Waitress GitHub repository. To check out the trunk via git, use this command:

git clone git@github.com:Pylons/waitress.git

To find out how to become a contributor to Waitress, please see the guidelines in contributing.md and How to Contribute Source Code and Documentation.

Why?

At the time of the release of Waitress, there are already many pure-Python WSGI servers. Why would we need another?

Waitress is meant to be useful to web framework authors who require broad platform support. It's neither the fastest nor the fanciest WSGI server available but using it helps eliminate the N-by-M documentation burden (e.g. production vs. deployment, Windows vs. Unix, Python 3 vs. Python 2, PyPy vs. CPython) and resulting user confusion imposed by spotty platform support of the current (2012-ish) crop of WSGI servers. For example, gunicorn is great, but doesn't run on Windows. paste.httpserver is perfectly serviceable, but doesn't run under Python 3 and has no dedicated tests suite that would allow someone who did a Python 3 port to know it worked after a port was completed. wsgiref works fine under most any Python, but it's a little slow and it's not recommended for production use as it's single-threaded and has not been audited for security issues.

At the time of this writing, some existing WSGI servers already claim wide platform support and have serviceable test suites. The CherryPy WSGI server, for example, targets Python 2 and Python 3 and it can run on UNIX or Windows. However, it is not distributed separately from its eponymous web framework, and requiring a non-CherryPy web framework to depend on the CherryPy web framework distribution simply for its server component is awkward. The test suite of the CherryPy server also depends on the CherryPy web framework, so even if we forked its server component into a separate distribution, we would have still needed to backfill for all of its tests. The CherryPy team has started work on Cheroot, which should solve this problem, however.

Waitress is a fork of the WSGI-related components which existed in zope.server. zope.server had passable framework-independent test coverage out of the box, and a good bit more coverage was added during the fork. zope.server has existed in one form or another since about 2001, and has seen production usage since then, so Waitress is not exactly "another" server, it's more a repackaging of an old one that was already known to work fairly well.