Improve error messages

README.md

@@ -20,14 +20,14 @@ Afterwards replace `PubSub` with `PostgresPubSub`:
 
 ```js
 // Before
-import { PubSub } from 'graphql-subscriptions';
+import { PubSub } from "graphql-subscriptions";
 
 export const pubsub = new PubSub();
 ```
 
 ```js
 // After
-import { PostgresPubSub } from 'graphql-postgres-subscriptions';
+import { PostgresPubSub } from "graphql-postgres-subscriptions";
 
 export const pubsub = new PostgresPubSub();
 ```
@@ -43,7 +43,7 @@ You can also pass [node-postgres connection options](https://node-postgres.com/f
 You can instantiate your own `client` and pass it to `PostgresPubSub`. Like this:
 
 ```js
-import { PostgresPubSub } from 'graphql-postgres-subscriptions';
+import { PostgresPubSub } from "graphql-postgres-subscriptions";
 import { Client } from "pg";
 
 const client = new Client();
@@ -53,11 +53,29 @@ const pubsub = new PostgresPubSub({ client });
 
 **Important**: Don't pass clients from `pg`'s `Pool` to `PostgresPubSub`. As [node-postgres creator states in this StackOverflow answer](https://stackoverflow.com/questions/8484404/what-is-the-proper-way-to-use-the-node-js-postgresql-module), the client needs to be around and not shared so pg can properly handle `NOTIFY` messages (which this library uses under the hood)
 
+## Error handling
+
+`PostgresPubSub` instances emit a special event called `"error"`. This event's payload is an instance of Javascript's `Error`. You can get the error's text using `error.message`.
+
+```js
+const ps = new PostgresPubSub({ client });
+
+ps.subscribe("error", err => {
+  console.log(err.message); // -> "payload string too long"
+}).then(() => ps.publish("a", "a".repeat(9000)));
+```
+
+For example you can log all error messages (including stack traces and friends) using something like this:
+
+```js
+ps.subscribe("error", console.error);
+```
+
 ## Development
 
 This project has an integration test suite that uses [`jest`](https://facebook.github.io/jest/) to make sure everything works correctly.
 
 We use Docker to spin up a PostgreSQL instance before running the tests. To run them, type the following commands:
 
-* `docker-compose build`
-* `docker-compose run test`
+- `docker-compose build`
+- `docker-compose run test`

package.json

@@ -1,6 +1,6 @@
 {
   "name": "graphql-postgres-subscriptions",
-  "version": "1.0.2",
+  "version": "1.0.3",
   "main": "index.js",
   "license": "MIT",
   "engines": {

postgres-pubsub.js

@@ -21,7 +21,9 @@ class PostgresPubSub extends PubSub {
     return true;
   }
   subscribe(triggerName, onMessage) {
-    const callback = ({ payload }) => onMessage(payload);
+    const callback = message => {
+      onMessage(message instanceof Error ? message : message.payload);
+    };
     this.ee.on(triggerName, callback);
     this.subIdCounter = this.subIdCounter + 1;
     this.subscriptions[this.subIdCounter] = [triggerName, callback];

postgres-pubsub.test.js

@@ -14,36 +14,36 @@ describe("PostgresPubSub", () => {
   test("PostgresPubSub can subscribe when instantiated without a client", function(done) {
     const ps = new PostgresPubSub();
     ps.subscribe("a", payload => {
-        expect(payload).toEqual("test");
-        done();
+      expect(payload).toEqual("test");
+      done();
     }).then(() => {
-        const succeed = ps.publish("a", "test");
-        expect(succeed).toBe(true);
-      });
+      const succeed = ps.publish("a", "test");
+      expect(succeed).toBe(true);
+    });
   });
 
   test("PostgresPubSub can subscribe and is called when events happen", function(done) {
     const ps = new PostgresPubSub({ client });
     ps.subscribe("a", payload => {
-        expect(payload).toEqual("test");
-        done();
+      expect(payload).toEqual("test");
+      done();
     }).then(() => {
-        const succeed = ps.publish("a", "test");
-        expect(succeed).toBe(true);
-      });
+      const succeed = ps.publish("a", "test");
+      expect(succeed).toBe(true);
+    });
   });
 
   test("PostgresPubSub can subscribe when instantiated with connection options but without a client", function(done) {
     const ps = new PostgresPubSub({
       connectionString: process.env.DATABASE_URL
     });
     ps.subscribe("a", payload => {
-        expect(payload).toEqual("test");
-        done();
+      expect(payload).toEqual("test");
+      done();
     }).then(() => {
-        const succeed = ps.publish("a", "test");
-        expect(succeed).toBe(true);
-      });
+      const succeed = ps.publish("a", "test");
+      expect(succeed).toBe(true);
+    });
   });
 
   test("should send notification event after calling publish", done => {
@@ -53,24 +53,39 @@ describe("PostgresPubSub", () => {
       done();
     });
     ps.subscribe("a", payload => {
-        expect(payload).toEqual("test");
+      expect(payload).toEqual("test");
     }).then(() => {
-        const succeed = ps.publish("a", "test");
-        expect(succeed).toBe(true);
-      });
+      const succeed = ps.publish("a", "test");
+      expect(succeed).toBe(true);
+    });
   });
 
   test("PostgresPubSub can unsubscribe", function(done) {
     const ps = new PostgresPubSub({ client });
     ps.subscribe("a", payload => {
-        expect(false).toBe(true); // Should not reach this point
+      expect(false).toBe(true); // Should not reach this point
     }).then(subId => {
-        ps.unsubscribe(subId);
-        const succeed = ps.publish("a", "test");
-        expect(succeed).toBe(true); // True because publish success is not
-        // indicated by trigger having subscriptions
-        done(); // works because pubsub is synchronous
-      });
+      ps.unsubscribe(subId);
+      const succeed = ps.publish("a", "test");
+      expect(succeed).toBe(true); // True because publish success is not
+      // indicated by trigger having subscriptions
+      done(); // works because pubsub is synchronous
+    });
+  });
+
+  test("Should emit error when payload exceeds Postgres 8000 character limit", done => {
+    const ps = new PostgresPubSub({ client });
+    ps.subscribe("a", () => {
+      expect(false).toBe(true); // Should not reach this point
+      done();
+    });
+    ps.subscribe("error", err => {
+      expect(err.message).toEqual("payload string too long");
+      done();
+    }).then(() => {
+      const succeed = ps.publish("a", "a".repeat(9000));
+      expect(succeed).toBe(true);
+    });
   });
 
   test("AsyncIterator should expose valid asyncIterator for a specific event", () => {
@@ -130,10 +145,10 @@ describe("PostgresPubSub", () => {
     iterator
       .next()
       .then(result => {
-      expect(result).not.toBeUndefined();
-      expect(result.value).not.toBeUndefined();
-      expect(result.done).toBe(false);
-    });
+        expect(result).not.toBeUndefined();
+        expect(result.value).not.toBeUndefined();
+        expect(result.done).toBe(false);
+      });
 
     ps.publish(eventName, { test: true });