make OutgoingMessage interface an abstract class and add setIdentifier

ts/session/messages/outgoing/Message.ts

@@ -1,3 +1,20 @@
-export interface Message {
-  timestamp: number;
+export abstract class Message {
+  public readonly timestamp: number;
+  public identifier: string;
+
+
+  constructor({ timestamp, identifier }: { timestamp: number; identifier: string }) {
+    if (identifier.length === 0) {
+      throw new Error('Cannot set empty identifier');
+    }
+    this.timestamp = timestamp;
+    this.identifier = identifier;
+  }
+
+  public setIdentifier(identifier: string) {
+    if (identifier.length === 0) {
+      throw new Error('Cannot set empty identifier');
+    }
+    this.identifier = identifier;
+  }
 }

ts/session/messages/outgoing/OpenGroupMessage.ts

@@ -2,21 +2,30 @@ import { Message } from './Message';
 import { AttachmentType } from '../../../types/Attachment';
 import { QuotedAttachmentType } from '../../../components/conversation/Quote';
 
-export class OpenGroupMessage implements Message {
-  public readonly timestamp: number;
+interface OpenGroupMessageParams {
+  timestamp: number;
+  identifier: string;
+  server: string;
+  attachments: [AttachmentType];
+  body?: string;
+  quote?: QuotedAttachmentType;
+}
+
+export class OpenGroupMessage extends Message {
   public readonly server: string;
   public readonly body?: string;
   public readonly attachments: [AttachmentType]; // TODO: Not sure if we should only use a subset of this type
   public readonly quote?: QuotedAttachmentType;
 
-  constructor(
-    timestamp: number,
-    server: string,
-    attachments: [AttachmentType],
-    body?: string,
-    quote?: QuotedAttachmentType
-  ) {
-    this.timestamp = timestamp;
+  constructor({
+      identifier,
+      timestamp,
+      server,
+      attachments,
+      body,
+      quote,
+    } : OpenGroupMessageParams) {
+    super({ timestamp, identifier });
     this.server = server;
     this.body = body;
     this.attachments = attachments;

ts/session/messages/outgoing/content/ContentMessage.ts

@@ -1,13 +1,10 @@
 import { Message } from '../Message';
 import { SignalService } from '../../../../protobuf';
 
-export abstract class ContentMessage implements Message {
-  public readonly timestamp: number;
-  public readonly identifier: string;
+export abstract class ContentMessage extends Message {
 
   constructor({ timestamp, identifier }: { timestamp: number; identifier: string }) {
-    this.timestamp = timestamp;
-    this.identifier = identifier;
+    super({timestamp, identifier});
   }
 
   public plainTextBuffer(): Uint8Array {