This will allow for e.g. xous on riscv32-imac but not a precursor
target, for example: by using feature selectors we get to have
a bigger range of targets that we support, such as for implementations
that haven't been upstreamed or have official target-triples.
The downsides are:
- patch override libraries don't absorb feature flags. so, for
example, the AES crate that is used to patch other crates won't
be aware of the target features without modifying the referencing
crates.
- features are normally meant to be additive, but target features
are mutually exclusive. The mutex is enforced by a check in
utralib that throws a panic on build if two targets are accidentally
selected at the same time.
It's crappy because it uses a busy wait loop to poll the udp
rx socket in order to accurately emulate the Xous async callback
feature (which is _not_ emulated for Tcp, for example).
It's more accurate because this emulation happens. But it's a lot
more complicated to implement it because zero-cost async UDP callbacks
aren't really a host-native feature (but they are a Xous-native feature!),
and I didn't want to .. pull in tokio or mio code surface into
the Xous hosted mode, seemed a bit like crushing a fly by dropping
a house on it. Maybe that's a fine solution in Oz, but Xous doesn't live in Oz.
Total bodge -- we lop off the TCP stack at the Xous API level, and
substitute it with a native host TCP stack.
Caveat hacker: this means that a lot of OS-specific net properties
will carry through to the hosted mode emulation. This is adequate
for "smoke testing" a build but do not be shocked, *shocked* if
there are more bugs to be found because of some weird host integration
issue.
Good enough so that if you type `net server` and you hit the IP
address of the device, it'll respond with something like
Hello from Precursor!
I have been up for 86087 ms.
There's still all kinds of bugs, I'm sure. But ... I'm also not
sure /why/ you would want a web server on Precursor. This is more
just to make sure that the TCP stack isn't totally broken.
The "web server" as it may be is quite broken and doesn't parse
any headers and probably sends a bogus amount of data because
I can't figure out if the content length includes some new lines
or not. But really, this just isn't in scope. Works with Chrome,
Firefox shows the status page and then says "connection reset" and hides
all the information. Whatever, browser compatibility is well beyond
my pay grade!
