templatefuncs: do not stringify result of if*() expression Returning a generator means that the result is a byte string. I can't find any reason to make the "if" condition lazy since it is evaluated anyway when {if()} has to be evaluated. So let's simply make if*() return an input expression unmodified.

templater: add brief doc about internal data types Hopefully this will help reviewing upcoming my series. Start small.

debugcommands: support sending HTTP requests with debugwireproto We implement an action that can issue an HTTP request. We can define headers via arguments and specify a file to use for the HTTP request body. The request uses the HTTP peer's opener, which is already configured for auth, etc. This is both good and bad. Good in that we get some nice behavior out of the box. Bad in that some HTTP request headers are added automatically. Differential Revision: https://phab.mercurial-scm.org/D2841

debugcommands: support connecting to HTTP peers Now that we have the plumbing for logging socket activity, let's hook it up to `hg debugwireproto` so we can collect low-level activity on sockets. The new code is a bit incomplete. But it is better than nothing: `hg debugwireproto` is still heavily evolving. The added test demonstrates some interesting behavior. For example, we're calling socket.makefile() and doing I/O on that. TIL. We're also sending an "Accept-Encoding: identity" request header. Differential Revision: https://phab.mercurial-scm.org/D2726

url: add HTTP handler that uses a proxied socket Now that we have a socket proxy that can log I/O, we need to teach mechanisms that open URLs how to use it. We invent a custom HTTP handler class that knows how to proxy sockets as soon as they are opened. We teach the high-level opener() to accept logging arguments so a logging HTTP handler can be constructed. We don't yet support intercepting HTTPS sockets because I don't want to go down that rabbit hole. For the record, the urllib API is crazy and it took way too long to figure out at what levels I needed to plug in to modify the socket. # no-check-commit because we must name http_open that way Differential Revision: https://phab.mercurial-scm.org/D2722

util: observable proxy objects for sockets We previously introduced proxy objects and observers for file objects to help implement low-level tests for the SSH wire protocol. In this commit, we do the same for sockets in order to help test the HTTP server. We only proxy/observe some socket methods. I didn't feel like implementing all the methods because there are so many of them and implementing them will provide no short term value. We can always implement them later. # no-check-commit because we implement foo_bar methods on stdlib types Differential Revision: https://phab.mercurial-scm.org/D2721