Do not export SOURCE from port-util

Sometimes there was some confusion between the `source` in the
`window#postMessage` context and the property in the message sent
through it. We believe it is better to replace the `SOURCE` by the
'hypothesis' string.

src/shared/port-finder.js

 import { ListenerCollection } from './listener-collection';
-import { isMessageEqual, SOURCE as source } from './port-util';
+import { isMessageEqual } from './port-util';
 
 const MAX_WAIT_FOR_PORT = 1000 * 30;
 const POLLING_INTERVAL_FOR_PORT = 250;
@@ -59,7 +59,10 @@ export class PortFinder {
       }
 
       function postRequest() {
-        hostFrame.postMessage({ channel, port, source, type: 'request' }, '*');
+        hostFrame.postMessage(
+          { channel, port, source: 'hypothesis', type: 'request' },
+          '*'
+        );
       }
 
       const intervalId = setInterval(
@@ -78,7 +81,14 @@ export class PortFinder {
       // TODO: It would be nice to remove the listener after receiving the port.
       this._listeners.add(window, 'message', event => {
         const { data, ports } = /** @type {MessageEvent} */ (event);
-        if (isMessageEqual(data, { channel, port, source, type: 'offer' })) {
+        if (
+          isMessageEqual(data, {
+            channel,
+            port,
+            source: 'hypothesis',
+            type: 'offer',
+          })
+        ) {
           clearInterval(intervalId);
           clearTimeout(timeoutId);
           resolve(ports[0]);

src/shared/port-provider.js

 import { TinyEmitter } from 'tiny-emitter';
 
 import { ListenerCollection } from './listener-collection';
-import { isMessageEqual, SOURCE as source } from './port-util';
+import { isMessageEqual } from './port-util';
 
 /**
  * @typedef {import('../types/config').SidebarConfig} SidebarConfig
@@ -220,7 +220,7 @@ export class PortProvider {
         const allowedMessage = {
           channel,
           port,
-          source,
+          source: 'hypothesis',
           type: 'request',
         };
 

src/shared/port-util.js

@@ -3,7 +3,7 @@
 // message and avoid listening to messages that could have the same properties
 // but different source. This is not a security feature but an
 // anti-collision mechanism.
-export const SOURCE = 'hypothesis';
+const SOURCE = 'hypothesis';
 
 /**
  * These types are the used in by `PortProvider` and `PortFinder` for the
@@ -15,7 +15,7 @@ export const SOURCE = 'hypothesis';
  * @prop {Channel} channel
  * @prop {Port} port
  * @prop {'offer'|'request'}  type
- * @prop {SOURCE} source
+ * @prop {SOURCE} source -
  */
 
 /**

src/shared/test/port-finder-test.js

 import { delay } from '../../test-util/wait';
 import { PortFinder } from '../port-finder';
-import { SOURCE as source } from '../port-util';
 
 describe('PortFinder', () => {
   let portFinder;
@@ -44,7 +43,7 @@ describe('PortFinder', () => {
           .catch(e => (error = e));
         portFinder.destroy();
         sendMessage({
-          data: { channel, port, source, type: 'offer' },
+          data: { channel, port, source: 'hypothesis', type: 'offer' },
           ports: [port1],
         });
         clock.tick(30000);
@@ -100,7 +99,7 @@ describe('PortFinder', () => {
           })
           .then(port => (resolvedPort = port));
         sendMessage({
-          data: { channel, port, source, type: 'offer' },
+          data: { channel, port, source: 'hypothesis', type: 'offer' },
           ports: [port1],
         });
         await delay(0);
@@ -131,7 +130,7 @@ describe('PortFinder', () => {
       assert.callCount(window.postMessage, 121);
       assert.alwaysCalledWithExactly(
         window.postMessage,
-        { channel, port, source, type: 'request' },
+        { channel, port, source: 'hypothesis', type: 'request' },
         '*'
       );
 

src/shared/test/port-provider-test.js

 import { delay } from '../../test-util/wait';
 import { PortProvider } from '../port-provider';
-import { SOURCE as source } from '../port-util';
+
+const source = 'hypothesis';
 
 describe('PortProvider', () => {
   let portProvider;

src/shared/test/port-util-test.js

-import { isMessageEqual, SOURCE as source } from '../port-util';
+import { isMessageEqual } from '../port-util';
+
+const source = 'hypothesis';
 
 describe('port-util', () => {
   describe('isMessageEqual', () => {