Add Camino service-backed custom fields

src/index.ts

@@ -34,6 +34,7 @@ export type CaminoClient = Client<typeof CaminoService>;
 export type { InvokeRequest, Value };
 
 export type Field<T> = {
+  get(): Promise<T | undefined>;
   set(value: T): Promise<void>;
 };
 
@@ -41,9 +42,25 @@ export type RuntimeHandler<Context> = (
   context: Context,
 ) => Promise<unknown> | unknown;
 
+export type FieldOperation<Context> = {
+  get?: RuntimeHandler<Context>;
+  set?: RuntimeHandler<Context>;
+  watchStart?: RuntimeHandler<Context>;
+  watchStop?: RuntimeHandler<Context>;
+};
+
+export const fieldOps = <Context>(
+  operation: FieldOperation<Context>,
+): FieldOperation<Context> => operation;
+
+export const derivedWithDeps = <Context>(operation: {
+  get: RuntimeHandler<Context>;
+}): FieldOperation<Context> => fieldOps(operation);
+
 export type RuntimeFunctionSpec<ExportName extends string = string> = {
   exportName: ExportName;
   symbol: string;
+  operation?: string;
 };
 
 const isRecord = (value: unknown): value is Record<string, unknown> =>
@@ -203,6 +220,10 @@ export const createField = <T>(
   objectId: string,
   fieldName: string,
 ): Field<T> => ({
+  async get() {
+    const response = await camino.getObject({ objectId });
+    return protoValueToJs(response.object?.fields[fieldName]) as T | undefined;
+  },
   async set(value) {
     await camino.setField({
       objectId,
@@ -221,7 +242,9 @@ export const serveQuixosPackageRuntime = <
   runtimeProtocolVersion: string;
   functions: Spec;
   implementation: {
-    [Name in Spec[number]["exportName"]]: RuntimeHandler<Context>;
+    [Name in Spec[number]["exportName"]]:
+      | RuntimeHandler<Context>
+      | FieldOperation<Context>;
   };
   createContext: (camino: CaminoClient, request: InvokeRequest) => Context;
 }) => {
@@ -242,6 +265,7 @@ export const serveQuixosPackageRuntime = <
       packageNamespace: params.packageNamespace,
       packageName: params.packageName,
       symbol: entry.symbol,
+      operation: entry.operation ?? "",
     }),
   );
 
@@ -261,19 +285,41 @@ export const serveQuixosPackageRuntime = <
           try {
             const symbol = request.function?.symbol ?? "";
             const spec = params.functions.find(
-              (entry) => entry.symbol === symbol,
+              (entry) =>
+                entry.symbol === symbol &&
+                (entry.operation ?? "") === (request.function?.operation ?? ""),
             );
             if (!spec) {
               throw new Error(
-                `Unknown ${params.packageName} function: ${symbol}`,
+                `Unknown ${params.packageName} function: ${symbol}${
+                  request.function?.operation
+                    ? `.${request.function.operation}`
+                    : ""
+                }`,
               );
             }
-            const runtimeFunction = (
-              params.implementation as Record<string, RuntimeHandler<Context>>
+            const implementationExport = (
+              params.implementation as Record<
+                string,
+                RuntimeHandler<Context> | FieldOperation<Context>
+              >
             )[spec.exportName];
+            const runtimeFunction =
+              spec.operation && typeof implementationExport === "object"
+                ? implementationExport[spec.operation as keyof FieldOperation<Context>]
+                : implementationExport;
             if (!runtimeFunction) {
               throw new Error(
-                `Missing ${params.packageName} implementation export: ${spec.exportName}`,
+                `Missing ${params.packageName} implementation export: ${spec.exportName}${
+                  spec.operation ? `.${spec.operation}` : ""
+                }`,
+              );
+            }
+            if (typeof runtimeFunction !== "function") {
+              throw new Error(
+                `${params.packageName} implementation export is not callable: ${spec.exportName}${
+                  spec.operation ? `.${spec.operation}` : ""
+                }`,
               );
             }
             return create(InvokeResponseSchema, {