From 30e123a418a7cdd0faf96a724a39e29537517be5 Mon Sep 17 00:00:00 2001
From: Franck Royer <franck@royer.one>
Date: Thu, 23 Sep 2021 16:08:06 +1000
Subject: [PATCH] Add API to retrieve signers on a message

---
 .../src/application_metadata_message.ts       | 13 ++++++++
 packages/status-communities/src/identity.ts   |  7 ++++
 .../status-communities/src/messenger.spec.ts  | 33 +++++++++++++++++--
 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/packages/status-communities/src/application_metadata_message.ts b/packages/status-communities/src/application_metadata_message.ts
index 63d56587..bfd5c954 100644
--- a/packages/status-communities/src/application_metadata_message.ts
+++ b/packages/status-communities/src/application_metadata_message.ts
@@ -1,4 +1,7 @@
+import { keccak256 } from "js-sha3";
+import { utils } from "js-waku";
 import { Reader } from "protobufjs";
+import secp256k1 from "secp256k1";
 
 import { ChatMessage } from "./chat_message";
 import { Identity } from "./identity";
@@ -58,4 +61,14 @@ export class ApplicationMetadataMessage {
 
     return ChatMessage.decode(this.payload);
   }
+
+  public get signer(): Uint8Array | undefined {
+    if (!this.signature || !this.payload) return;
+
+    const signature = this.signature.slice(0, 64);
+    const recid = this.signature.slice(64)[0];
+    const hash = keccak256(this.payload);
+
+    return secp256k1.ecdsaRecover(signature, recid, utils.hexToBuf(hash));
+  }
 }
diff --git a/packages/status-communities/src/identity.ts b/packages/status-communities/src/identity.ts
index 2d4c4ae7..88ec6e80 100644
--- a/packages/status-communities/src/identity.ts
+++ b/packages/status-communities/src/identity.ts
@@ -26,4 +26,11 @@ export class Identity {
 
     return Buffer.concat([signature, Buffer.from([recid])]);
   }
+
+  /**
+   * Returns the compressed public key.
+   */
+  public get publicKey(): Uint8Array {
+    return secp256k1.publicKeyCreate(this.privateKey, true);
+  }
 }
diff --git a/packages/status-communities/src/messenger.spec.ts b/packages/status-communities/src/messenger.spec.ts
index dd074b8f..fa93e2c9 100644
--- a/packages/status-communities/src/messenger.spec.ts
+++ b/packages/status-communities/src/messenger.spec.ts
@@ -1,4 +1,5 @@
 import { expect } from "chai";
+import { utils } from "js-waku";
 
 import { ApplicationMetadataMessage } from "./application_metadata_message";
 import { Identity } from "./identity";
@@ -9,12 +10,14 @@ const testChatId = "test-chat-id";
 describe("Messenger", () => {
   let messengerAlice: Messenger;
   let messengerBob: Messenger;
+  let identityAlice: Identity;
+  let identityBob: Identity;
 
   beforeEach(async function () {
     this.timeout(10_000);
 
-    const identityAlice = Identity.generate();
-    const identityBob = Identity.generate();
+    identityAlice = Identity.generate();
+    identityBob = Identity.generate();
 
     [messengerAlice, messengerBob] = await Promise.all([
       Messenger.create(identityAlice),
@@ -44,7 +47,7 @@ describe("Messenger", () => {
     ]);
   });
 
-  it("Sends & Receive message in public chat", async function () {
+  it("Sends & Receive public chat messages", async function () {
     this.timeout(10_000);
 
     await messengerAlice.joinChat(testChatId);
@@ -66,6 +69,30 @@ describe("Messenger", () => {
     expect(receivedMessage.chatMessage?.text).to.eq(text);
   });
 
+  it("public chat messages have signers", async function () {
+    this.timeout(10_000);
+
+    await messengerAlice.joinChat(testChatId);
+    await messengerBob.joinChat(testChatId);
+
+    const text = "This is a message.";
+
+    const receivedMessagePromise: Promise<ApplicationMetadataMessage> =
+      new Promise((resolve) => {
+        messengerBob.addObserver((message) => {
+          resolve(message);
+        }, testChatId);
+      });
+
+    await messengerAlice.sendMessage(text, testChatId);
+
+    const receivedMessage = await receivedMessagePromise;
+
+    expect(utils.bufToHex(receivedMessage.signer!)).to.eq(
+      utils.bufToHex(identityAlice.publicKey)
+    );
+  });
+
   afterEach(async function () {
     this.timeout(5000);
     await messengerAlice.stop();