fix(gateway): improve validation errors (#1347)

Thanks @vignesh07.

Co-authored-by: Vignesh <vignesh07@users.noreply.github.com>

src/gateway/protocol/index.test.ts

@@ -0,0 +1,65 @@
+import { describe, expect, it } from "vitest";
+import type { ErrorObject } from "ajv";
+
+import { formatValidationErrors } from "./index.js";
+
+const makeError = (overrides: Partial<ErrorObject>): ErrorObject => ({
+  keyword: "type",
+  instancePath: "",
+  schemaPath: "#/",
+  params: {},
+  message: "validation error",
+  ...overrides,
+});
+
+describe("formatValidationErrors", () => {
+  it("returns unknown validation error when missing errors", () => {
+    expect(formatValidationErrors(undefined)).toBe("unknown validation error");
+    expect(formatValidationErrors(null)).toBe("unknown validation error");
+  });
+
+  it("returns unknown validation error when errors list is empty", () => {
+    expect(formatValidationErrors([])).toBe("unknown validation error");
+  });
+
+  it("formats additionalProperties at root", () => {
+    const err = makeError({
+      keyword: "additionalProperties",
+      params: { additionalProperty: "token" },
+    });
+
+    expect(formatValidationErrors([err])).toBe("at root: unexpected property 'token'");
+  });
+
+  it("formats additionalProperties with instancePath", () => {
+    const err = makeError({
+      keyword: "additionalProperties",
+      instancePath: "/auth",
+      params: { additionalProperty: "token" },
+    });
+
+    expect(formatValidationErrors([err])).toBe("at /auth: unexpected property 'token'");
+  });
+
+  it("formats message with path for other errors", () => {
+    const err = makeError({
+      keyword: "required",
+      instancePath: "/auth",
+      message: "must have required property 'token'",
+    });
+
+    expect(formatValidationErrors([err])).toBe("at /auth: must have required property 'token'");
+  });
+
+  it("de-dupes repeated entries", () => {
+    const err = makeError({
+      keyword: "required",
+      instancePath: "/auth",
+      message: "must have required property 'token'",
+    });
+
+    expect(formatValidationErrors([err, err])).toBe(
+      "at /auth: must have required property 'token'",
+    );
+  });
+});