Make sure parsed body is an array when expecting Sequence

Changelog.md

@@ -4,6 +4,7 @@
 - Fixes encoding query parameters in an array before joining them.(PR [#382](https://github.com/Azure/ms-rest-js/pull/382))
 - Replace public usage of `RequestPolicyOptions` to an interface `RequestPolicyOptionsLike` to avoid compatibility issues with private members.
 - Fix issue with null/undefined values in array and tabs/space delimiter arrays during sendOperationRequest. [PR #390](https://github.com/Azure/ms-rest-js/pull/390)
+- Fix in flattenResponse when expecting an array, checking for parsedBody to be an array before proceeding with flattening. (PR [#385](https://github.com/Azure/ms-rest-js/pull/385))
 
 ## 2.0.6 - 2020-04-15
 - A new interface `WebResourceLike` was introduced to avoid a direct dependency on the class `WebResource` in public interfaces. `HttpHeadersLike` was also added to replace references to `HttpHeaders`.  This change was added to improve compatibility between `@azure/core-http` and `@azure/ms-rest-nodeauth`.

lib/serviceClient.ts

@@ -556,7 +556,13 @@ export function flattenResponse(_response: HttpOperationResponse, responseSpec:
     const modelProperties = typeName === "Composite" && (bodyMapper as CompositeMapper).type.modelProperties || {};
     const isPageableResponse = Object.keys(modelProperties).some(k => modelProperties[k].serializedName === "");
     if (typeName === "Sequence" || isPageableResponse) {
-      const arrayResponse = [...(_response.parsedBody || [])] as RestResponse & any[];
+      // We're expecting a sequece(array) make sure that the response body is in the
+      // correct format, if not make it an empty array []
+      const parsedBody =
+        Array.isArray(_response.parsedBody)
+          ? _response.parsedBody
+          : [];
+      const arrayResponse = [...parsedBody] as RestResponse & any[];
 
       for (const key of Object.keys(modelProperties)) {
         if (modelProperties[key].serializedName) {

test/serviceClientTests.ts

@@ -219,6 +219,79 @@ describe("ServiceClient", function () {
     assert.deepStrictEqual(res.slice(), [1, 2, 3]);
   });
 
+  it("should deserialize response bodies with undefined array", async function () {
+    let request: WebResourceLike;
+    const httpClient: HttpClient = {
+      sendRequest: (req) => {
+        request = req;
+        return Promise.resolve({
+          request,
+          status: 200,
+          headers: new HttpHeaders(),
+          bodyAsText: JSON.stringify({ nextLink: "mockLink" }),
+        });
+      },
+    };
+
+    const client1 = new ServiceClient(undefined, {
+      httpClient,
+      requestPolicyFactories: [deserializationPolicy()],
+    });
+
+    const res = (await client1.sendOperationRequest(
+      {},
+      {
+        serializer: new Serializer(),
+        httpMethod: "GET",
+        baseUrl: "httpbin.org",
+        responses: {
+          "200": {
+            bodyMapper: {
+              type: {
+                name: "Composite",
+                modelProperties: {
+                  value: {
+                    serializedName: "",
+                    type: {
+                      name: "Sequence",
+                      element: {
+                        type: { name: "String" },
+                      },
+                    },
+                  },
+                  nextLink: {
+                    serializedName: "nextLink",
+                    type: { name: "String" },
+                  },
+                },
+              },
+            },
+          },
+          default: {
+            bodyMapper: {
+              serializedName: "ErrorResponse",
+              type: {
+                name: "Composite",
+                className: "ErrorResponse",
+                modelProperties: {
+                  code: { serializedName: "code", type: { name: "String" } },
+                  message: {
+                    serializedName: "message",
+                    type: { name: "String" },
+                  },
+                },
+              },
+            },
+          },
+        },
+      }
+    )) as any;
+
+    assert.strictEqual(res._response.status, 200);
+    assert.deepStrictEqual(res.nextLink, "mockLink");
+    assert.deepStrictEqual(res, []);
+  });
+
   it("should use userAgent header name value from options", async function () {
     const httpClient: HttpClient = {
       sendRequest: (request: WebResourceLike) => {