Patch: Initializing Subscription WebSocket doesn't inherit custom headers

[vmcruz]

Hi!

I've used patch-package to patch aws-appsync-subscription-link@3.1.3 for the project I'm working on.

I found that the graphql_headers were not being passed down during the realtime handshake initialization. I needed a custom header in the Auth Lambda but I wasn't receiving it in the requestHeaders from the event object. After debugging, I found this line where the _initializeWebSocketConnection does the handshake:

aws-mobile-appsync-sdk-js/packages/aws-appsync-subscription-link/src/realtime-subscription-handshake-link.ts

Line 399 in ea05577

graphql_headers: () => { }

Here is the diff that solved my problem:

diff --git a/node_modules/aws-appsync-subscription-link/lib/realtime-subscription-handshake-link.js b/node_modules/aws-appsync-subscription-link/lib/realtime-subscription-handshake-link.js
index 612efd0..c8c669d 100644
--- a/node_modules/aws-appsync-subscription-link/lib/realtime-subscription-handshake-link.js
+++ b/node_modules/aws-appsync-subscription-link/lib/realtime-subscription-handshake-link.js
@@ -318,7 +318,8 @@ var AppSyncRealTimeSubscriptionHandshakeLink = /** @class */ (function (_super)
                                 authenticationType: authenticationType,
                                 region: region,
                                 credentials: credentials,
-                                token: token
+                                token: token,
+                                graphql_headers: graphql_headers
                             })];
                     case 3:
                         _g.sent();
@@ -362,7 +363,7 @@ var AppSyncRealTimeSubscriptionHandshakeLink = /** @class */ (function (_super)
     };
     AppSyncRealTimeSubscriptionHandshakeLink.prototype._initializeWebSocketConnection = function (_a) {
         var _this = this;
-        var appSyncGraphqlEndpoint = _a.appSyncGraphqlEndpoint, authenticationType = _a.authenticationType, apiKey = _a.apiKey, region = _a.region, credentials = _a.credentials, token = _a.token;
+        var appSyncGraphqlEndpoint = _a.appSyncGraphqlEndpoint, authenticationType = _a.authenticationType, apiKey = _a.apiKey, region = _a.region, credentials = _a.credentials, token = _a.token, graphql_headers = _a.graphql_headers;
         if (this.socketStatus === types_1.SOCKET_STATUS.READY) {
             return;
         }
@@ -388,7 +389,7 @@ var AppSyncRealTimeSubscriptionHandshakeLink = /** @class */ (function (_super)
                                 region: region,
                                 credentials: credentials,
                                 token: token,
-                                graphql_headers: function () { }
+                                graphql_headers: graphql_headers
                             })];
                     case 2:
                         headerString = _b.apply(_a, [_c.sent()]);

Now it works using setContext from Apollo:

  const customHeadersMiddleware = setContext((_, { headers }) => {
    return {
      headers: {
        ...headers,
        'x-custom-header': 'my-value',
      },
    };
  });

  const subscriptionLink = ApolloLink.from([
    customHeadersMiddleware,
    createAuthLink(subscriptionLinkParams),
    createSubscriptionHandshakeLink(subscriptionLinkParams),
  ]);

This should solve #630 #761 and maybe #585

This issue body was partially generated by patch-package.