tests: use $HTTP_DATE$ for Date header Support for the $HTTP_DATE$ substitution was recently added. Let's adopt it more widely. We had to tweak the substitution to be case insensitive, since HTTP headers are case insensitive. I also found a minor test issue not globbing over the length of the Server response header. Differential Revision: https://phab.mercurial-scm.org/D2839

debugcommands: introduce actions to perform deterministic reads "readavailable" is useful as a debugging device to see what data is available on a pipe. But the mechanism isn't deterministic because what's available on a pipe is highly conditional on timing, system load, OS behavior, etc. This makes it not suitable for tests. We introduce "ereadline," "read," and "eread" for performing deterministic I/O operations (at least on blocking file descriptors). We stop short of converting existing consumers of "readavailable" in tests because we're working out race conditions and deadlocks on Windows. But the goal is to eventually move tests away from "readavailable" to these new APIs. Differential Revision: https://phab.mercurial-scm.org/D2720

httppeer: refactor how httppeer is created (API) Previously, we passed a bunch of arguments to httppeer.__init__, validated them, then possibly constructed a valid instance. A short while ago, we refactored sshpeer so all the validation and setup work occurs before the constructor. We introduced a makepeer() to hold most of this logic. This commit gives httppeer the same treatment. As a sign that the previous design was poor, __del__ no longer conditionally checks for the presence of an attribute that may not be defined (it is always defined in the new code). .. api:: httppeer.httppeer.__init__ now takes additional arguments. Instances should be obtained by calling httppeer.instance() or httppeer.makepeer() instead. Differential Revision: https://phab.mercurial-scm.org/D2725