refactor: report undefined for no expected value() (#1230)

* refactor: report undefined for no expected value()

* Update packages/core/src/interaction-output.ts

Co-authored-by: Jan Romann <jan.romann@uni-bremen.de>

* fix: test by adding DataSchema

* refactor: make undefined return more explicitly

* refactor: remove unnecessary comment

* refactor: add test case for value() returning undefined if no DataSchema is provided

* refactor: add warn logging in case undefined is returned

* reword warning based on comment from @relu91

---------

Co-authored-by: Jan Romann <jan.romann@uni-bremen.de>

Author: danielpeintner

packages/core/src/interaction-output.ts

@@ -21,7 +21,7 @@ import { Content } from "./content";
 import Ajv from "ajv";
 import { createLoggers } from "./logger";
 
-const { debug } = createLoggers("core", "interaction-output");
+const { debug, warn } = createLoggers("core", "interaction-output");
 
 // Problem: strict mode ajv does not accept unknown keywords in schemas
 // however property affordances could contain all sort of fields
@@ -78,6 +78,14 @@ export class InteractionOutput implements WoT.InteractionOutput {
     }
 
     async value<T extends WoT.DataSchemaValue>(): Promise<T> {
+        // is there any value expected at all?
+        if (this.schema == null) {
+            warn(
+                `No schema defined. Hence undefined is reported for value() function. If you are invoking an action with no output that is on purpose, otherwise consider using arrayBuffer().`
+            );
+            return undefined as unknown as T;
+        }
+
         // the value has been already read?
         if (this.#value !== undefined) {
             return this.#value as T;
@@ -91,8 +99,8 @@ export class InteractionOutput implements WoT.InteractionOutput {
             throw new NotReadableError("No form defined");
         }
 
-        if (this.schema == null || this.schema.type == null) {
-            throw new NotReadableError("No schema defined");
+        if (this.schema.type == null) {
+            throw new NotReadableError("No schema type defined");
         }
 
         // is content type valid?

packages/core/test/InteractionOutputTest.ts

@@ -59,7 +59,7 @@ class InteractionOutputTests {
         const stream = Readable.from([1, 2, 3]);
         const content = new Content("application/json", stream);
 
-        const out = new InteractionOutput(content, {});
+        const out = new InteractionOutput(content, {}, { type: "string" });
         const result = [];
         const reader = out.data.getReader();
         expect(reader).not.to.be.undefined;
@@ -73,6 +73,20 @@ class InteractionOutputTests {
         return expect(out.value()).to.be.rejected;
     }
 
+    @test async "should return undefined for value call if no DataSchema is provided"() {
+        const stream = Readable.from([]);
+        const content = new Content("application/json", stream);
+
+        const out = new InteractionOutput(content, {});
+
+        const result1 = await out.value();
+        expect(result1).be.undefined;
+
+        // try a second time also
+        const result2 = await out.value();
+        expect(result2).be.undefined;
+    }
+
     @test async "should return the value"() {
         const stream = Readable.from(Buffer.from("true", "utf-8"));
         const content = new Content("application/json", stream);