How can Tornado serve a single static file at an arbitrary location?

Question

I am developing a simple web app with Tornado. It serves some dynamic files and some static ones. The dynamic ones are not a problem, but I am having trouble serving a static file. What I am looking to do is to serve the file /path/to/foo.json when the /foo.json URL is accessed.

Note that /path/to/foo.json is outside the document root. In Apache I would just set up an Alias. With Tornado I have:

app = tornado.web.Application([
    (r'/dynamic\.html', MyService, dict(param = 12345)),
    (r'/(foo\.json)', tornado.web.StaticFileHandler, {'path': '/path/to/foo.json'})
    ])

I added the regex group operator () to satisfy Tornado, which threw an exception otherwise. But now, when I access /foo.json, I get a 404: File Not Found.

Tests reveal that Tornado is attempting to use the path provided as a root directory to which it appends foo.json, implying my file could be found if it were at /path/to/foo.json/foo.json. Close, but not quite.

I suppose I could shorten my path to simply "/path/to", which will trigger a fetch of /path/to/foo.json upon the /foo.json URL, but this forces me to use the same name in the URL as on the filesystem. How can I just do a simple, arbitrary, URL to file mapping?

I have done some research on this, reading the documentation for tornado.web.Application and tornado.web.StaticFilehandler, plus some other SO questions. Nothing is quite my use case.

So by arbitrary file mapping what you want is to map, say, the URL `yourdomain.com/path/to/foo.json` to `yourfilesystem/path/to/bar.json`? I think you should include that in your question (i.e., use different name in the example, not using `foo.json` in both URL and file system) — justhalf, Jan 21 '14 at 02:57
I mention this in my second to last paragraph, @justhalf, but perhaps it could be clearer. — Randall Cook, Jan 21 '14 at 03:01
Yes, my point is to include what you refer to in your second last paragraph in your example. Because your example doesn't really represent your real question. — justhalf, Jan 21 '14 at 04:42

score 14 · Answer 1 · answered Nov 30 '14 at 11:50

14

StaticFileHandler expects two arguments, so if you want a single url (/foo.json) to be mapped to your file path you can use:

app = tornado.web.Application([
(r'/foo.json()', tornado.web.StaticFileHandler, {'path': '/path/to/foo.json'})
])

The regex will match /foo.json and send the empty capture group (), which will cause the filepath to be used as is. When the capture group is not empty, /path/to/foo.json will be treated as a directory /path/to/foo.json/, and the handler will try to match whatever is within the capture group to a file name in that directory.

answered Nov 30 '14 at 11:50

Mark

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Thanks, Mark. I like the simplicity of this approach. +1. – Randall Cook Nov 30 '14 at 18:42
Why not without the brackets? – WisdomPill Oct 10 '19 at 10:13

score 6 · Accepted Answer · answered Jan 21 '14 at 03:39

6

Something like this should work:

import os
import tornado.ioloop
import tornado.web


class MyFileHandler(tornado.web.StaticFileHandler):
    def initialize(self, path):
        self.dirname, self.filename = os.path.split(path)
        super(MyFileHandler, self).initialize(self.dirname)

    def get(self, path=None, include_body=True):
        # Ignore 'path'.
        super(MyFileHandler, self).get(self.filename, include_body)

app = tornado.web.Application([
    (r'/foo\.json', MyFileHandler, {'path': '/path/to/foo.json'})
])

app.listen(8888)
tornado.ioloop.IOLoop.current().start()

The URL pattern and the filename need not be related, you could do this and it would work just as well:

app = tornado.web.Application([
    (r'/jesse\.txt', MyFileHandler, {'path': '/path/to/foo.json'})
])

answered Jan 21 '14 at 03:39

A. Jesse Jiryu Davis

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Note that subclassing StaticFileHandler can be delicate, and it's better to leave `get()` alone. Instead, the classmethod `get_absolute_path` is a better method to override here (http://www.tornadoweb.org/en/stable/web.html#tornado.web.StaticFileHandler.get_absolute_path) – Ben Darnell Jan 21 '14 at 14:24
I like this approach, and it is working well for me. But I am intrigued by the approach of overriding `get_absolute_path`. @BenDarnell, can you provide an example? – Randall Cook Jan 22 '14 at 02:31
1

This is untested, but it illustrates the general idea: https://gist.github.com/bdarnell/8553378 – Ben Darnell Jan 22 '14 at 04:15
1

But get_absolute_path is a class method, there's no 'self'. – A. Jesse Jiryu Davis Jan 22 '14 at 13:31

score 6 · Answer 3 · answered Jan 21 '14 at 14:22

StaticFileHandler gets is file name from the regex capturing group and the directory name from its path argument. It will work if you use /path/to/ as the path:

(r'/(foo\.json)', tornado.web.StaticFileHandler, {'path': '/path/to/'})

StaticFileHandler is designed for cases where URLs and filenames match; if you can't arrange to have this file available on disk under the same name you want to serve it as you'll have to use a custom handler.

How can Tornado serve a single static file at an arbitrary location?

3 Answers3

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