What's Next for Cap'n Proto?

Cap'n Proto supports streaming!

{% highlight capnp %} interface FileStore { get @0 (name :Text, stream :Stream); put @1 (name :Text) -> (stream :Stream); }

interface Stream { write @0 (data :Data); end @1 (); } {% endhighlight %}

But flow control is up to the app.

Let's build it in.

{% highlight capnp %} interface Stream { write @0 (data :Data) -> bulk; end @1 (); } {% endhighlight %}

What about realtime streams?

{% highlight capnp %} interface VideoCallStream { sendFrame @0 (frame :Frame) -> realtime; } {% endhighlight %}

Best served on a UDP transport...

Forwarded request.

Where does response go?

Classic solution:

Proxy

Classic solution:

Redirect

Cap'n Proto:

3-Party Handoff

(aka 3PH)

Cap'n Proto:

3-Party Handoff

(aka 3PH)

... gonna need UDP

Cap'n Proto:

3-Party Handoff

(aka 3PH)

... gonna need UDP

... and 0-RT crypto

API: "Tail call"

{% highlight c++ %} kj::Promise<void> myRpc(MyRpcContext context) override { // Begin sub-request. auto subRequest = someCapability.someRpcRequest(); subRequest.setSomeParam(someValue);

// Send as a tail call. return context.tailCall(kj::mv(subRequest)); } {% endhighlight %}

Today: Will proxy Future: 3PH

KJ client networking, no TLS:

{% highlight c++ %} void send() { auto io = kj::setupAsyncIo(); auto& network = io.provider->getNetwork(); auto addr = network.parseAddress("capnproto.org", 80) .wait(io.waitScope); auto connection = addr->connect().wait(io.waitScope); connection->write("GET /", 5).wait(io.waitScope); } {% endhighlight %}

KJ client networking with TLS:

{% highlight c++ %} void send() { auto io = kj::setupAsyncIo(); kj::TlsContext tls; auto network = tls.wrapNetwork(io.provider->getNetwork()); auto addr = network->parseAddress("capnproto.org", 443) .wait(io.waitScope); auto connection = addr->connect().wait(io.waitScope); connection->write("GET /", 5).wait(io.waitScope); } {% endhighlight %}

Diff:

{% highlight c++ %} void send() {

kj::TlsContext tls; tls.wrapNetwork( );

} {% endhighlight %}

{% highlight c++ %} void receive() { auto io = kj::setupAsyncIo(); auto& network = io.provider->getNetwork(); auto addr = network.parseAddress("*", 80) .wait(io.waitScope); auto listener = addr->listen(); auto connection = listener->accept().wait(io.waitScope); connection->write("HTTP/1.1 404 Not Found\r\n\r\n", 26) .wait(io.waitScope); } {% endhighlight %}

{% highlight c++ %} void receive() { auto io = kj::setupAsyncIo(); kj::TlsKeypair keypair { KEY_PEM_TEXT, CERT_PEM_TEXT }; kj::TlsContext::Options options; options.defaultKeypair = keypair; kj::TlsContext tls(options); auto& network = io.provider->getNetwork(); auto addr = network.parseAddress("*", 443).wait(io.waitScope); auto listener = tls.wrapPort(addr->listen()); auto connection = listener->accept().wait(io.waitScope); connection->write("HTTP/1.1 404 Not Found\r\n\r\n", 26) .wait(io.waitScope); } {% endhighlight %}

{% highlight c++ %} void receive() {

kj::TlsKeypair keypair { KEY_PEM_TEXT, CERT_PEM_TEXT }; kj::TlsContext::Options options; options.defaultKeypair = keypair; kj::TlsContext tls(options);

              tls.wrapPort(              );

} {% endhighlight %}

{% highlight c++ %} auto io = kj::setupAsyncIo(); kj::HttpHeaderTable headerTable; auto client = kj::newHttpClient( *headerTable, io.provider->getNetwork());

kj::HttpHeaders headers(*headerTable); auto response = client->request( kj::HttpMethod::GET, "http://capnproto.org", headers) .response.wait(io.waitScope);

KJ_ASSERT(response.statusCode == 200); KJ_LOG(INFO, response.body->readAllText().wait(io.waitScope)); {% endhighlight %}

Headers identified by small numbers.

{% highlight c++ %} kj::HttpHeaderTable::Builder builder; kj::HttpHeaderId userAgent = builder.add("User-Agent"); auto headerTable = builder.build();

kj::HttpHeaders headers(*headerTable); headers.set(kj::HttpHeaderId::HOST, "capnproto.org"); headers.set(userAgent, "kj-http/0.6"); {% endhighlight %}

Header parsing is zero-copy.

Ugly imperative code:

{% highlight c++ %} capnp::MallocMessageBuilder message;

auto root = message.initRoot<MyStruct>(); root.setFoo(123); root.setBar("foo"); auto inner = root.initBaz(); inner.setQux(true);

capnp::writeMessageToFd(fd, message); {% endhighlight %}

Nice declarative code:

{% highlight c++ %} using namespace capnp::init;

capnp::MallocMessageBuilder message; message.initRoot<MyStruct>( $foo = 123, $bar = "foo", $baz( $qux = true ) ); capnp::writeMessageToFd(fd, message); {% endhighlight %}

Even better:

{% highlight c++ %} using namespace capnp::init;

capnp::writeMessageToFd<MyStruct>(fd, $foo = 123, $bar = "foo", $baz( $qux = true ) ); {% endhighlight %}

{% highlight c++ %} struct { template <typename T> struct Setter { T value; template <typename U> void operator()(U& target) { target.setFoo(kj::fwd<T>(value)); } };

template <typename T> Setter<T> operator=(T&& value) { return { kj::fwd<T>(value) }; } } $foo; {% endhighlight %}

Not idiomatic:

{% highlight c++ %} capnp::MallocMessageBuilder message;

MyStruct::Builder root = message.initRoot<MyStruct>(); root.setFoo(123); root.setBar("foo"); InnerStruct::Builder inner = root.initBaz(); inner.setQux(true);

capnp::writeMessageToFd(fd, message); {% endhighlight %}

Plain Old C++ Structs?

{% highlight c++ %} MyStruct root; root.foo = 123; root.bar = "foo"; InnerStruct inner; inner.qux = true; root.baz = kj::mv(inner);

capnp::writeMessageToFd(fd, message); {% endhighlight %}

Caveat: No longer zero-copy.

{% highlight c++ %} capnp::MallocMessageBuilder message; capnp::readMessageCopy(input, message); auto root = message.getRoot<MyStruct>(); auto oldListOrphan = root.disownStructList(); auto oldList = oldListOrphan.getReader(); auto newList = root.initStructList(oldList.size() - 1); for (auto i: kj::indices(newList)) { newList.setWithCaveats(i, oldList[i < indexToRemove ? i : i + 1]); } capnp::MallocMessageBuilder message2; message2.setRoot(root.asReader()); capnp::writeMessage(output, message2); {% endhighlight %}

{% highlight c++ %} auto root = capnp::readMessageCopy<MyStruct>(input); root.structList.erase(indexToRemove); capnp::writeMessageCopy(output, root); {% endhighlight %}

{% highlight capnp %} interface AddressBook { getPerson @0 (id :UInt32 $httpPath) -> (person :Person $httpBody(type = json)) $http(method = get, route = "person");

GET /person/<id>

JSON response body

updatePerson @1 (id :UInt32 $httpPath, person :Person $httpBody(type = json)); $http(method = put, route = "person");

PUT /person/<id>

JSON request body

} {% endhighlight %}

{% highlight capnp %} addPerson @2 (person :Person $httpBody(type = json)) -> (id :UInt32 $httpBody(type = jsonField)); $http(method = post, route = "person");

POST /person

JSON request body

JSON response body (object containing field id)

getAll @3 (page :UInt32 = 0 $httpQuery) -> (people: List(Person) $httpBody(type = json)); $http(method = get);

GET /?page=<num>

Query is optional.

JSAN (JSON array) response body.

{% endhighlight %}

{% highlight capnp %} interface AddressBookService { getAddressBook @0 (key :String $httpPath) -> (result :AddressBook $httpPipeline); $http(route = "book");

GET /book/JrpmUduyHd8uW3x3TOXn2g/person/123

Becomes:

service.getAddressBook("JrpmUduyHd8uW3x3TOXn2g").send()

.getResult().getPerson(123).send()

GET /book/JrpmUduyHd8uW3x3TOXn2g

Becomes:

service.getAddressBook("JrpmUduyHd8uW3x3TOXn2g").send()

.getResult().getAll().send()

} {% endhighlight %}

Questions?