使用nchan构建全站推送

2022-04-08 nchan在实现 presence 相关方面是有欠缺的无法实现拉取当前所有联系人不方便跟踪房间进出详情在经过调研后，决定弃用，使用 centrifugo-v3.1.1 来实现相关推送能力

nchan 官站

Nchan is a scalable, flexible pub/sub server for the modern web, built as a module for the Nginx web server. It can be configured as a standalone server, or as a shim between your application and hundreds, thousands, or millions of live subscribers. It can buffer messages in memory, on-disk, or via Redis. All connections are handled asynchronously and distributed among any number of worker processes. It can also scale to many Nginx servers with Redis.

Messages are published to channels with HTTP POST requests or Websocket, and subscribed also through Websocket, long-polling, EventSource (SSE), old-fashioned interval polling, and more.

In a web browser, you can use Websocket or EventSource natively, or the NchanSubscriber.js wrapper library. It supports Long-Polling, EventSource, and resumable Websockets, and has a few other added convenience options. It's also available on NPM.

Features

RESTful, HTTP-native API.
Supports Websocket, EventSource (Server-Sent Events), Long-Polling and other HTTP-based subscribers.
Per-channel configurable message buffers with no-repeat, no-loss message delivery guarantees.
Subscribe to hundreds of channels over a single subscriber connection.
HTTP request callbacks and hooks for easy integration.
Introspection with channel events and url for monitoring performance statistics.
Channel group usage accounting and limits.
Fast, nonblocking shared-memory local message storage and optional, slower, persistent storage with Redis.
Horizontally scalable (using Redis).
Auto-failover and high availability with no single point of failure using Redis Cluster.

简介

以nginx module模式工作，高性能、可扩容、pub/sub推送服务。
subscribe客户端协议：websocket, sse, long-polling, http raw stream 等
扩容模型是基于redis（单机性能会下降，但使用redis后总体支持连接数可线性扩容）

工作模型

架构图

客户端发送消息可以有2种方式：

直接使用客户端通过websocket发送上行消息
通过http post到接口，然后通过接口再次转发回到nchan进行广播

通过websocket发上行消息

sequenceDiagram

participant client as 客户端设备
participant im as nchanim
participant lemon as lemon

client ->> im: 建立连接
im ->> lemon: auth request
lemon -->> im: 200
im ->> lemon: nchan_subscribe_request/nchan_unsubscribe_request
client ->> im: websock send msg
im ->> lemon: nchan_publisher_upstream_request: msg forward auth

通过api发上行消息

sequenceDiagram

participant client as 客户端设备
participant im as nchanim
participant lemon as lemon

client ->> im: 建立连接
im ->> lemon: auth request
lemon -->> im: 200
im ->> lemon: nchan_subscribe_request/nchan_unsubscribe_request
client ->> api: post msg
api -->> api: spam check
api -->> im: pub msg
im -->> client: pub msg

特定逻辑详细分析

如何做用户在线
如何跟踪用户离线