These avoid the need for a read/modify/write.

This allows a lot of nice design patterns, and might later the the basis for capnp 3-party handoff within a machine.

E.g.:

    "foo"_kj

This literal will have type StringPtr. Although any string literal can implicitly cast to StringPtr, using the _kj suffix has the advantage that it can be constexpr.

Use case for me is Cloudflare's "Authenticated Origin Pulls", in which Cloudflare authenticates itself to the origin server using client certificates. Thus the origin server can ensure that it only accepts traffic through Cloudflare, without resorting to IP whitelists.

This really is more of a data structure than a resource type, and it's useful to be able to share it between threads and whatnot.

ubsan complains about the invalid reference even if it is unused.

Based on discussions in the Google group:

https://groups.google.com/forum/#!topic/capnproto/_1kBtRSC51s

The proxying code was responding to a `Close` message by ending the pump loop, which had the effect of immediately dropping the connection after a `Close` had been seen in each direction. This is arguably incorrect behavior: for proxying purposes, `Close` messages and underlying TCP disconnects should be treated as independent events, forwarded separately.

In practice this "bug" probably would never cause a problem and perhaps doesn't even violate spec (since `Close` was seen in both directions). But, OSX's implementation of shutdown() returns ENOTCONN if the connection has already been disconnected from the remote end. This is the case here, as the proxy dropped all connections immediately after sending the final `Close`.

This in turn led to a unit test failure.

The intended behavior was that the proxy would forward exactly what it saw: If a `Close` was sent, it would be forwarded, without changing the underlying connection state. If a TCP disconnect was detected, it would be "forwarded" by disconnecting the next leg. This change implements that behavior.

Due to differences in the way I/O events are queued on Windows, the timing of this test end up different, such that the two incoming pings are not both received before the large outgoing message is sent.

To fix this, I removed the dependency on native I/O altogether by implementing an in-memory pipe that does no buffering (it requires a read() and write() to rendezvous, then copies between their buffers).