From e8e56d903e5d356c41aedfd07fadf0d363c82476 Mon Sep 17 00:00:00 2001
From: "Mark S. Miller" <erights@gmail.com>
Date: Sun, 5 May 2024 22:00:23 -0700
Subject: [PATCH] feat(asyncFlow): E support

---
 packages/async-flow/src/replay-membrane.js | 50 ++++++++++++++++++----
 packages/async-flow/src/type-guards.js     | 14 +++---
 packages/async-flow/src/types.js           |  6 +++
 3 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/packages/async-flow/src/replay-membrane.js b/packages/async-flow/src/replay-membrane.js
index 9833ea81bfc0..e4639653f2e9 100644
--- a/packages/async-flow/src/replay-membrane.js
+++ b/packages/async-flow/src/replay-membrane.js
@@ -3,11 +3,10 @@ import { Fail, b, q } from '@endo/errors';
 import { Far, Remotable, getInterfaceOf } from '@endo/pass-style';
 import { E } from '@endo/eventual-send';
 import { getMethodNames } from '@endo/eventual-send/utils.js';
-import { makePromiseKit } from '@endo/promise-kit';
 import { makeEquate } from './equate.js';
 import { makeConvertKit } from './convert.js';
 
-const { fromEntries, defineProperties } = Object;
+const { fromEntries, defineProperties, assign } = Object;
 
 /**
  * @param {LogStore} log
@@ -195,6 +194,45 @@ export const makeReplayMembrane = (
     }
   };
 
+  // //////////////// Eventual Send ////////////////////////////////////////////
+
+  const guestHandler = harden({
+    applyMethod(guestTarget, verb, _guestArgs, _guestReturnedP) {
+      Fail`guest eventual send not yet supported:  ${guestTarget}.${b(verb)}(...)`;
+    },
+    applyFunction(guestTarget, _guestArgs, _guestReturnedP) {
+      Fail`guest eventual call not yet supported: ${guestTarget}`;
+    },
+    get(guestPresence, prop) {
+      Fail`guest eventual get not yet supported: ${guestPresence}.${b(prop)}`;
+    },
+  });
+
+  const makeGuestPresence = (iface, methodEntries) => {
+    let guestPresence;
+    void new HandledPromise((_res, _rej, resolveWithPresence) => {
+      guestPresence = resolveWithPresence(guestHandler);
+    }); // no unfulfilledHandler
+    if (typeof guestPresence !== 'object') {
+      throw Fail`presence expected to be object ${guestPresence}`;
+    }
+    assign(guestPresence, fromEntries(methodEntries));
+    const result = Remotable(iface, undefined, guestPresence);
+    result === guestPresence ||
+      Fail`Remotable expected to make presence in place: ${guestPresence} vs ${result}`;
+    return result;
+  };
+
+  const makeGuestPromiseKit = () => {
+    let resolve;
+    let reject;
+    const promise = new HandledPromise((res, rej, _resPres) => {
+      resolve = res;
+      reject = rej;
+    }, guestHandler);
+    return harden({ promise, resolve, reject });
+  };
+
   // //////////////// Converters ///////////////////////////////////////////////
 
   const makeGuestForHostRemotable = hRem => {
@@ -234,18 +272,14 @@ export const makeReplayMembrane = (
         name,
         makeGuestMethod(name),
       ]);
-      // TODO in order to support E *well*,
-      // use HandledPromise to make gRem a remote presence for hRem
-      gRem = Remotable(guestIface, undefined, fromEntries(guestMethods));
+      gRem = makeGuestPresence(guestIface, guestMethods);
     }
     return gRem;
   };
   harden(makeGuestForHostRemotable);
 
   const makeGuestForHostVow = hVow => {
-    // TODO in order to support E *well*,
-    // use HandledPromise to make `promise` a handled promise for hVow
-    const { promise, resolve, reject } = makePromiseKit();
+    const { promise, resolve, reject } = makeGuestPromiseKit();
     guestPromiseMap.set(promise, harden({ resolve, reject }));
 
     watchWake(hVow);
diff --git a/packages/async-flow/src/type-guards.js b/packages/async-flow/src/type-guards.js
index 65551bd5f89e..c3ebc5267391 100644
--- a/packages/async-flow/src/type-guards.js
+++ b/packages/async-flow/src/type-guards.js
@@ -42,13 +42,13 @@ export const LogEntryShape = M.or(
     M.arrayOf(M.any()),
     M.number(),
   ],
-  // [
-  //   'checkSend',
-  //   M.or(M.remotable('host target'), VowShape),
-  //   M.opt(PropertyKeyShape),
-  //   M.arrayOf(M.any()),
-  //   M.number(),
-  // ],
+  [
+    'checkSend',
+    M.or(M.remotable('host target'), VowShape),
+    M.opt(PropertyKeyShape),
+    M.arrayOf(M.any()),
+    M.number(),
+  ],
   // ['checkReturn', M.number(), M.any()],
   // ['checkThrow', M.number(), M.any()],
 );
diff --git a/packages/async-flow/src/types.js b/packages/async-flow/src/types.js
index 842574673906..cc5e5a1f315d 100644
--- a/packages/async-flow/src/types.js
+++ b/packages/async-flow/src/types.js
@@ -95,6 +95,12 @@
  *     optVerb: PropertyKey|undefined,
  *     args: Host[],
  *     callIndex: number
+ *   ] | [
+ *     op: 'checkSend',
+ *     target: Host,
+ *     optVerb: PropertyKey|undefined,
+ *     args: Host[],
+ *     callIndex: number
  *   ]} LogEntry
  */