feat(captp): handle send rejections

packages/captp/NEWS.md

@@ -1,5 +1,9 @@
 User-visible changes in `@endo/captp`:
 
+# Unreleased
+
+- Relax typing of `send` to allow `async` functions, and abort the connection if the `send` function returns a rejected promise.
+
 # v3.1.0 (2023-04-14)
 
 - Disable GC by default to work around known issues with dropping

packages/captp/src/captp.js

@@ -66,7 +66,7 @@ const reverseSlot = slot => {
  * Create a CapTP connection.
  *
  * @param {string} ourId our name for the current side
- * @param {(obj: Record<string, any>) => void} rawSend send a JSONable packet
+ * @param {((obj: Record<string, any>) => void) | ((obj: Record<string, any>) => PromiseLike<void>)} rawSend send a JSONable packet
  * @param {any} bootstrapObj the object to export to the other side
  * @param {CapTPOptions} opts options to the connection
  */
@@ -196,8 +196,10 @@ export const makeCapTP = (
       return;
     }
 
-    // Actually send the message, in the next turn.
-    rawSend(obj);
+    // Actually send the message.
+    Promise.resolve(rawSend(obj))
+      // eslint-disable-next-line no-use-before-define
+      .catch(abort); // Abort if rawSend returned a rejection.
   };
 
   /**
@@ -727,7 +729,7 @@ export const makeCapTP = (
         quietReject(obj.reason, false);
         unplug = reason;
         // Deliver the object, even though we're unplugged.
-        rawSend(obj);
+        Promise.resolve(rawSend(obj)).catch(sink);
       }
       // We no longer wish to subscribe to object finalization.
       slotToImported.clearWithoutFinalizing();