Roll back Cap'n Proto to where it was in the previous release.

Some people have reported Etherpad being broken. Although I cannot reproduce this, @zenhack found that rolling back Cap'n Proto fixed it.

The problem is most likely this: https://github.com/capnproto/capnproto/pull/1571

This is actually a bug that was *fixed*, but apps would still be using the old version with the bug. Unfortuntaely the old buggy behavior interacts badly with the new cancellation impelementation on the callee side.

(This also reverts "Update for Cap'n Proto allowCancellation and CallHints changes.", commit 1563fa81942fe4dd230d52850e378d33f6f35459.)

src/sandstorm/sandstorm-http-bridge.c++

@@ -1223,7 +1223,7 @@ public:
 
       // We need to verify the capability is still connected. Send a dummy call to check. We'll
       // use a known-invalid type ID / method number and expect to get an UNIMPLEMENTED error.
-      auto ping = identity.typelessRequest(0, 65535, capnp::MessageSize { 4, 0 }, {});
+      auto ping = identity.typelessRequest(0, 65535, capnp::MessageSize { 4, 0 });
       ping.initAsAnyStruct(0, 0);
       return ping.send().then([identity](auto&&) mutable -> kj::Promise<Identity::Client> {
         // Weird, we shouldn't get here.

src/sandstorm/supervisor.c++

@@ -2204,6 +2204,8 @@ public:
   }
 
   kj::Promise<void> getWwwFileHack(GetWwwFileHackContext context) override {
+    context.allowCancellation();
+
     auto params = context.getParams();
     auto path = params.getPath();
 

src/sandstorm/supervisor.capnp

@@ -18,8 +18,7 @@
 # This file contains interfaces defining communication between a Sandstorm grain supervisor and
 # other components of the system. These interfaces are NOT used by Sandstorm applications.
 
-using Cxx = import "/capnp/c++.capnp";
-$Cxx.namespace("sandstorm");
+$import "/capnp/c++.capnp".namespace("sandstorm");
 
 using Util = import "util.capnp";
 using Grain = import "grain.capnp";
@@ -82,8 +81,7 @@ interface Supervisor {
     notFound @2;
   }
 
-  getWwwFileHack @9 (path :Text, stream :Util.ByteStream) -> (status :WwwFileStatus)
-      $Cxx.allowCancellation;
+  getWwwFileHack @9 (path :Text, stream :Util.ByteStream) -> (status :WwwFileStatus);
   # Reads a file from under the grain's "/var/www" directory. If the path refers to a regular
   # file, the contents are written to `stream`, and `status` is returned as `file`. If the path
   # refers to a directory or is not found, then `stream` is NOT called at all and the method

src/sandstorm/util.c++

@@ -893,7 +893,7 @@ capnp::Capability::Server::DispatchCallResult CapRedirector::dispatchCall(
     uint64_t interfaceId, uint16_t methodId,
     capnp::CallContext<capnp::AnyPointer, capnp::AnyPointer> context) {
   capnp::AnyPointer::Reader params = context.getParams();
-  auto req = target.typelessRequest(interfaceId, methodId, params.targetSize(), {});
+  auto req = target.typelessRequest(interfaceId, methodId, params.targetSize());
   req.set(params);
 
   auto oldIteration = iteration;
@@ -915,7 +915,7 @@ capnp::Capability::Server::DispatchCallResult CapRedirector::dispatchCall(
     // OK, this disconnect is new to us. We need to determine if this disconnected capability
     // is our direct target or something else that was accessed as part of the call. So, send
     // a dummy call to check.
-    auto ping = target.typelessRequest(0, 65535, capnp::MessageSize { 4, 0 }, {});
+    auto ping = target.typelessRequest(0, 65535, capnp::MessageSize { 4, 0 });
     ping.initAsAnyStruct(0, 0);
     return ping.send().then([](auto&&) -> void {
       KJ_LOG(ERROR, "dummy ping request should have failed with UNIMPLEMENTED");