<div dir="ltr"><div><div><div><div><div><div><div><div>I am fascinated by the new WSGI - HTTP/2 discussions. I don't have much to contribute, because my own experience with web development is either very old (when CGI was new and exciting) or uses corporate frameworks where there's a huge set of layers between the app code and the external network (e.g. Google, Dropbox).<br><br>I have strong emotional responses to some of the discussion topics (e.g. I feel that REMOTE_ADDR should represent the public IP address from which the request originated, not the internal address of a reverse proxy, since my use cases for it are all about blocking or rate-limiting specific clients, and I assume the network between the reverse proxy and the app server is secure) but I am sure there are already enough voices here and I trust that the sig will come up with the right answers (even if they override my gut feelings!).<br><br></div>My most recent foray into web stuff was writing a small web crawler as an example for asyncio (PEP 3156, a.k.a. tulip). The crawler is written in Python 3 and the source code is here: <a href="https://github.com/aosabook/500lines/blob/master/crawler/crawling.py">https://github.com/aosabook/500lines/blob/master/crawler/crawling.py</a> and it supports several advanced HTTP features: TLS, connection reuse, chunked transfer encoding, redirects (but not compression -- I think it would be straightforward to add, but the code would then exceed the 500 lines limit imposed by the book).<br><br></div>Perhaps the main lesson I learned from writing this is how different yet similar web code looks when you use an asynchronous framework. Which makes me wonder -- can there be a future where you can write your web app as an asyncio coroutine?<br><br></div><div>It looks like the WSGI protocol already supports asynchronously producing the response (using yield), and I don't think asyncio would have a problem with converting this convention to its own "yield from" convention. However, the situation is different for reading the request body. The app can read this in dribs and drabs if it wants to, by reading limited amounts of data from environ['wsgi.input'], but in an asyncio-driven world reading operations should really be marked with "yield from" (or perhaps just yield -- again, I'm sure an adaptor won't have a problem with this).<br><br>I'm wondering if a small extension to the WSGI protocol might be sufficient to support this: the special environ variable "wsgi.async_input" could optionally be tied to a standard asyncio stream reader (<a href="https://docs.python.org/3/library/asyncio-stream.html#streamreader">https://docs.python.org/3/library/asyncio-stream.html#streamreader</a>), from which bytes can be read using "yield from stream.read([nbytes])" or "yield from stream.readline()".<br><br></div><div>Thinking a little more about this, it might be better if an async app could be a regular asyncio coroutine. In this case it might be better if start_response() were to return an asyncio stream writer (<a href="https://docs.python.org/3/library/asyncio-stream.html#streamwriter">https://docs.python.org/3/library/asyncio-stream.html#streamwriter</a>) and if it was expected to produce all its output by writing to this stream.<br><br></div><div>Anyway, I think I'm getting ahead of myself, but I do think it would be nice if the next WSGI standard supported asyncio. For older Python versions it could then instead support Trollius (<a href="https://pypi.python.org/pypi/trollius">https://pypi.python.org/pypi/trollius</a>), a backport of asyncio that supports Python 2.7 and 3.2 (and newer).<br clear="all"></div></div></div></div></div></div><div><div><div><div><div><div><div><div><div><div><br>-- <br>--Guido van Rossum (<a href="http://python.org/~guido">python.org/~guido</a>)
</div></div></div></div></div></div></div></div></div></div></div>