Tornado: Add example how to connect via UNIX socket with httpclient

[spaceone]

It would be very nice if there would be an example in the documentation how one can connect to a UNIX socket with tornado.httpclient.
I currently could not figure out how to do this.

[ploxiln]

I don't think this is currently possible with tornado.

[spaceone]

@ploxiln I saw that tornado.httpclient has a curl implementation. Maybe it is possible by setting some curl options?

[spaceone]

https://curl.haxx.se/libcurl/c/CURLOPT_UNIX_SOCKET_PATH.html

[spaceone]

Yippieh! Got it:

import tornado.httpclient
import pycurl
tornado.httpclient.AsyncHTTPClient.configure('tornado.curl_httpclient.CurlAsyncHTTPClient')
client = tornado.httpclient.AsyncHTTPClient()
client.fetch('http://www.google.com', prepare_curl_callback=lambda curl: curl.setopt(pycurl.UNIX_SOCKET_PATH, '/tmp/1'))
tornado.ioloop.IOLoop.instance().run_sync(lambda *a: None)

(to start it run in bash socat unix-listen:/tmp/1 stdout)

[ploxiln]

ah, looks like that would do it :)

[friedcell]

An easier way to do it (and no need to use pycurl and the curl client) is to create a custom resolver that returns [(socket.AF_UNIX, "/path/to/socketfile")] when it matches a certain host (or host/port) combination.

class UnixResolver(Resolver):
    def initialize(self, resolver, unix_sockets, *args, **kwargs):
        self.resolver = resolver
        self.unix_sockets = unix_sockets

    def close(self):
        self.resolver.close()

    @gen.coroutine
    def resolve(self, host, port, *args, **kwargs):
        if host in self.unix_sockets:
            return [(socket.AF_UNIX, self.unix_sockets[host])]
        result = yield self.resolver.resolve(host, port, *args, **kwargs)
        return result

resolver = Resolver()
Resolver.configure(UnixResolver, resolver=resolver, unix_sockets={"host_on_socket": "/path/to/socketfile"})

[bdarnell]

This is pretty esoteric; I'm not sure it's worth adding to the docs without opening up a lot of questions about how and why you'd run an HTTP server on an address that's not URL-addressable anyway. And now this issue exists so people can find an answer by googling :)