Fix capnproto serialisation of undefined values, closes #371 (#377)

Author: mrbbot

packages/tre/src/runtime/config/index.ts

@@ -1,5 +1,5 @@
 import { Data, List, Message, Struct } from "capnp-ts";
-import { Config } from "./sserve-conf";
+import { Config, kVoid } from "./sserve-conf";
 import { Config as CapnpConfig } from "./sserve-conf.capnp.js";
 
 function capitalize<S extends string>(str: S): Capitalize<S> {
@@ -8,10 +8,14 @@ function capitalize<S extends string>(str: S): Capitalize<S> {
   ) as Capitalize<S>;
 }
 
-// TODO(important): this will fail if someone sets `{ script: undefined }` or
-//  something manually, where we're expecting an optional string, need a better
-//  solution
-function encodeCapnpStruct(obj: any, struct: Struct, padding = "") {
+// Dynamically encode a capnp struct based on keys and the types of values.
+// `obj` should be an instance of a type in `./sserve-conf.ts`. The safety of
+// this function relies on getting `./sserve-conf.ts` correct, TypeScript's type
+// safety guarantees, and us validating all user input with zod.
+//
+// TODO: generate `./sserve-conf.ts` and corresponding encoders automatically
+//  from the `.capnp` file.
+function encodeCapnpStruct(obj: any, struct: Struct) {
   const anyStruct = struct as any;
   for (const [key, value] of Object.entries(obj)) {
     const capitalized = capitalize(key);
@@ -22,17 +26,19 @@ function encodeCapnpStruct(obj: any, struct: Struct, padding = "") {
       const newList: List<any> = anyStruct[`init${capitalized}`](value.length);
       for (let i = 0; i < value.length; i++) {
         if (typeof value[i] === "object") {
-          encodeCapnpStruct(value[i], newList.get(i), padding + "  ");
+          encodeCapnpStruct(value[i], newList.get(i));
         } else {
           newList.set(i, value[i]);
         }
       }
     } else if (typeof value === "object") {
       const newStruct: Struct = anyStruct[`init${capitalized}`]();
-      encodeCapnpStruct(value, newStruct, padding + "  ");
-    } else {
-      // TODO: could we catch here if value is actually undefined, but meant to
-      //  be a different type
+      encodeCapnpStruct(value, newStruct);
+    } else if (value === kVoid) {
+      anyStruct[`set${capitalized}`]();
+    } else if (value !== undefined) {
+      // Ignore all `undefined` values, explicitly `undefined` values should use
+      // kVoid symbol instead.
       anyStruct[`set${capitalized}`](value);
     }
   }