json parsing

backend-assemblyscript/step-2-json-encoding/assembly/request.ts

@@ -0,0 +1,85 @@
+import {JSONDecoder, JSONHandler} from "../node_modules/assemblyscript-json/assembly/decoder";
+
+export enum Action {
+    Post,
+    Fetch,
+    Unknown
+    // Error
+}
+
+export abstract class Request {
+    public action: Action = Action.Unknown;
+}
+
+export class PostRequest extends Request {
+
+    public readonly msg: string;
+    public readonly handle: string;
+
+    constructor(msg: string, handle: string) {
+        super();
+        this.msg = msg;
+        this.handle = handle;
+        this.action = Action.Post;
+    }
+}
+
+export class FetchRequest extends Request {
+    constructor() {
+        super();
+        this.action = Action.Fetch;
+    }
+}
+
+export class UnknownRequest extends Request {
+    constructor() {
+        super();
+        this.action = Action.Unknown;
+    }
+}
+
+export function string2Bytes(str: string): Uint8Array {
+    return Uint8Array.wrap(String.UTF8.encode(str));
+}
+
+export function decode(input: string): Request {
+    let jsonHandler = new RequestJSONEventsHandler();
+    let decoder = new JSONDecoder<RequestJSONEventsHandler>(jsonHandler);
+
+    let bytes = string2Bytes(input);
+
+    decoder.deserialize(bytes);
+
+    let action = jsonHandler.action;
+
+    let request: Request;
+
+    if (action == "Fetch") {
+        request = new FetchRequest();
+    } else if (action == "Post") {
+        request = new PostRequest(jsonHandler.msg, jsonHandler.handle)
+    } else {
+        request = new UnknownRequest()
+    }
+
+    return request;
+}
+
+class RequestJSONEventsHandler extends JSONHandler {
+
+    public action: string;
+    public msg: string;
+    public handle: string;
+
+    setString(name: string, value: string): void {
+
+        if (name == "action") {
+            this.action = value;
+        } else if (name == "msg") {
+            this.msg = value;
+        } else if (name == "handle") {
+            this.handle = value;
+        }
+        // json scheme is not strict, so we won't throw an error on excess fields
+    }
+}