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tornado.netutil — Miscellaneous network utilities

Miscellaneous network utility code.

tornado.netutil.bind_sockets(port, address=None, family=<AddressFamily.AF_UNSPEC: 0>, backlog=128, flags=None, reuse_port=False)[source]

Creates listening sockets bound to the given port and address.

Returns a list of socket objects (multiple sockets are returned if the given address maps to multiple IP addresses, which is most common for mixed IPv4 and IPv6 use).

Address may be either an IP address or hostname. If it’s a hostname, the server will listen on all IP addresses associated with the name. Address may be an empty string or None to listen on all available interfaces. Family may be set to either socket.AF_INET or socket.AF_INET6 to restrict to IPv4 or IPv6 addresses, otherwise both will be used if available.

The backlog argument has the same meaning as for socket.listen().

flags is a bitmask of AI_* flags to getaddrinfo, like socket.AI_PASSIVE | socket.AI_NUMERICHOST.

reuse_port option sets SO_REUSEPORT option for every socket in the list. If your platform doesn’t support this option ValueError will be raised.

tornado.netutil.bind_unix_socket(file, mode=384, backlog=128)[source]

Creates a listening unix socket.

If a socket with the given name already exists, it will be deleted. If any other file with that name exists, an exception will be raised.

Returns a socket object (not a list of socket objects like bind_sockets)

tornado.netutil.add_accept_handler(sock, callback)[source]

Adds an IOLoop event handler to accept new connections on sock.

When a connection is accepted, callback(connection, address) will be run (connection is a socket object, and address is the address of the other end of the connection). Note that this signature is different from the callback(fd, events) signature used for IOLoop handlers.

A callable is returned which, when called, will remove the IOLoop event handler and stop processing further incoming connections.

Changed in version 5.0: The io_loop argument (deprecated since version 4.1) has been removed.

Changed in version 5.0: A callable is returned (None was returned before).


Returns true if the given string is a well-formed IP address.

Supports IPv4 and IPv6.

class tornado.netutil.Resolver[source]

Configurable asynchronous DNS resolver interface.

By default, a blocking implementation is used (which simply calls socket.getaddrinfo). An alternative implementation can be chosen with the Resolver.configure class method:


The implementations of this interface included with Tornado are

Changed in version 5.0: The default implementation has changed from BlockingResolver to DefaultExecutorResolver.

resolve(host, port, family=<AddressFamily.AF_UNSPEC: 0>, callback=None)[source]

Resolves an address.

The host argument is a string which may be a hostname or a literal IP address.

Returns a Future whose result is a list of (family, address) pairs, where address is a tuple suitable to pass to socket.connect (i.e. a (host, port) pair for IPv4; additional fields may be present for IPv6). If a callback is passed, it will be run with the result as an argument when it is complete.

IOError – if the address cannot be resolved.

Changed in version 4.4: Standardized all implementations to raise IOError.


Closes the Resolver, freeing any resources used.

New in version 3.1.

class tornado.netutil.DefaultExecutorResolver[source]

Resolver implementation using IOLoop.run_in_executor.

New in version 5.0.

class tornado.netutil.ExecutorResolver[source]

Resolver implementation using a concurrent.futures.Executor.

Use this instead of ThreadedResolver when you require additional control over the executor being used.

The executor will be shut down when the resolver is closed unless close_resolver=False; use this if you want to reuse the same executor elsewhere.

Changed in version 5.0: The io_loop argument (deprecated since version 4.1) has been removed.

Deprecated since version 5.0: The default Resolver now uses IOLoop.run_in_executor; use that instead of this class.

class tornado.netutil.BlockingResolver[source]

Default Resolver implementation, using socket.getaddrinfo.

The IOLoop will be blocked during the resolution, although the callback will not be run until the next IOLoop iteration.

Deprecated since version 5.0: The default Resolver now uses IOLoop.run_in_executor; use that instead of this class.

class tornado.netutil.ThreadedResolver[source]

Multithreaded non-blocking Resolver implementation.

Requires the concurrent.futures package to be installed (available in the standard library since Python 3.2, installable with pip install futures in older versions).

The thread pool size can be configured with:


Changed in version 3.1: All ThreadedResolvers share a single thread pool, whose size is set by the first one to be created.

Deprecated since version 5.0: The default Resolver now uses IOLoop.run_in_executor; use that instead of this class.

class tornado.netutil.OverrideResolver[source]

Wraps a resolver with a mapping of overrides.

This can be used to make local DNS changes (e.g. for testing) without modifying system-wide settings.

The mapping can be in three formats:

    # Hostname to host or ip
    "": "",

    # Host+port to host+port
    ("", 443): ("localhost", 1443),

    # Host+port+address family to host+port
    ("", 443, socket.AF_INET6): ("::1", 1443),

Changed in version 5.0: Added support for host-port-family triplets.


Try to convert an ssl_options dictionary to an SSLContext object.

The ssl_options dictionary contains keywords to be passed to ssl.wrap_socket. In Python 2.7.9+, ssl.SSLContext objects can be used instead. This function converts the dict form to its SSLContext equivalent, and may be used when a component which accepts both forms needs to upgrade to the SSLContext version to use features like SNI or NPN.

tornado.netutil.ssl_wrap_socket(socket, ssl_options, server_hostname=None, **kwargs)[source]

Returns an ssl.SSLSocket wrapping the given socket.

ssl_options may be either an ssl.SSLContext object or a dictionary (as accepted by ssl_options_to_context). Additional keyword arguments are passed to wrap_socket (either the SSLContext method or the ssl module function as appropriate).