Merge pull request #506 from tibber/feature/deserializer-context-with-docs

Expose channel and pattern to deserialize callback (with docs)

Author: davidyaha

README.md

@@ -172,6 +172,28 @@ const pubsub = new RedisPubSub({
 
 You can learn more on the `ioredis` package [here](https://github.com/luin/ioredis).
 
+## Using a custom serializer/deserializer
+
+By default, Javascript objects are (de)serialized using the `JSON.stringify` and `JSON.parse` methods.
+You may pass your own serializer and/or deserializer function(s) as part of the options.
+
+The `deserializer` will be called with an extra context object containing `pattern` (if available) and `channel` properties, allowing you to access this information when subscribing to a pattern.
+
+```javascript
+import { RedisPubSub } from 'graphql-redis-subscriptions';
+import { someSerializer, someDeserializer } from 'some-serializer-library';
+
+const serialize = (source) => {
+  return someSerializer(source);
+};
+
+const deserialize = (sourceOrBuffer, { channel, pattern }) => {
+  return someDeserializer(sourceOrBuffer, channel, pattern);
+};
+
+const pubSub = new RedisPubSub({ ..., serializer: serialize, deserializer: deserialize });
+```
+
 ## Using a custom reviver
 
 By default, Javascript objects are serialized using the `JSON.stringify` and `JSON.parse` methods.

src/redis-pubsub.ts

@@ -4,6 +4,7 @@ import {PubSubAsyncIterator} from './pubsub-async-iterator';
 
 type RedisClient = Redis | Cluster;
 type OnMessage<T> = (message: T) => void;
+type DeserializerContext = { channel: string, pattern?: string };
 
 export interface PubSubRedisOptions {
   connection?: RedisOptions;
@@ -178,7 +179,9 @@ export class RedisPubSub implements PubSubEngine {
 
     let parsedMessage;
     try {
-      parsedMessage = this.deserializer ? this.deserializer(message) : JSON.parse(message, this.reviver);
+      parsedMessage = this.deserializer
+        ? this.deserializer(message, { pattern, channel })
+        : JSON.parse(message, this.reviver);
     } catch (e) {
       parsedMessage = message;
     }
@@ -198,4 +201,4 @@ export type TriggerTransform = (
 ) => string;
 export type Reviver = (key: any, value: any) => any;
 export type Serializer = (source: any) => string;
-export type Deserializer = (source: string | Buffer) => any;
+export type Deserializer = (source: string | Buffer, context: DeserializerContext) => any;