Open Source WebSocket Servers
Sort By:
WebSocket Servers
View 8592 business solutionsBrowse free open source WebSocket Servers and projects below. Use the toggles on the left to filter open source WebSocket Servers by OS, license, language, programming language, and project status.
-
Orchestrate Your AI Agents with ZenflowZenflow orchestrates AI agents like a real engineering system. With parallel execution, spec-driven workflows, and deep multi-repo understanding, agents plan, implement, test, and verify end-to-end. Upgrade to AI workflows that work the way your team does.
-
Auth0 for AI Agents now in GAConnect your AI agents to apps and data more securely, give users control over the actions AI agents can perform and the data they can access, and enable human confirmation for critical agent actions.
-
1
websocat
Command-line client for WebSockets, like netcat (or curl)
Netcat, curl and socat for WebSockets. Command-line client for WebSockets, like netcat (or curl) for ws:// with advanced socat-like functions. Connecting to and serving WebSockets from the command line. Executing external program and making it communicate to WebSocket using stdin/stdout. Text and binary modes, converting between lines (or null-terminated records) and messages. Inetd mode, UNIX sockets (including abstract namespaced on Linux). Integration with Nginx using TCP or UNIX sockets. Directly using unauthenticated SOCKS5 servers for connecting to WebSockets and listening WebSocket connections. Auto-reconnect and connection-reuse modes. Linux, Windows, and Mac support, with pre-built executables. Low-level WebSocket clients and servers with an overridable underlying transport connection, e.g. calling an external program to serve as a transport for websocat (for SSL, proxying, etc.). -
2
Mongoose Embedded Web Server
An embedded web server
Mongoose is a networking library for C/C++. It implements event-driven non-blocking APIs for TCP, UDP, HTTP, WebSocket, MQTT. It is designed for connecting devices and bringing them online. On the market since 2004, used by vast number of open source and commercial products - it even runs on the International Space Station! Mongoose makes embedded network programming fast, robust, and easy. Cross-platform, works on Linux/UNIX, MacOS, Windows, Android, FreeRTOS, etc. Supported embedded architectures: ESP32, NRF52, STM32, NXP, and more. Built-in protocols: plain TCP/UDP, HTTP, MQTT, Websocket. SSL/TLS support: mbedTLS, OpenSSL or custom (via API). Used to solve a wide range of business needs, like implementing Web UI interface on devices, RESTful API services, telemetry data exchange, remote control for a product, remote software updates, remote monitoring, and others. -
3
Java WebSockets
A barebones WebSocket client and server implementation
This repository contains a barebones WebSocket server and client implementation written in 100% Java. The underlying classes are implemented java.nio, which allows for a non-blocking event-driven model (similar to the WebSocket API for web browsers). The org.java_websocket.server.WebSocketServer abstract class implements the server-side of the WebSocket Protocol. A WebSocket server by itself doesn't do anything except establish socket connections though HTTP. After that it's up to your subclass to add purpose. The org.java_websocket.client.WebSocketClient abstract class can connect to valid WebSocket servers. The constructor expects a valid ws:// or wss:// URI to connect to. Important events onOpen, onClose, onMessage and onError get fired throughout the life of the WebSocketClient, and must be implemented in your subclass. -
4
WebSocket ++
C++ websocket client/server library
WebSocket++'s goal is to provide a flexible set of tools for building a wide variety of WebSocket based applications wrapped by low or zero overhead abstractions. It is not opinionated. If something can be practically replacable (with low overhead) based on the user's preference then it is. It accomplishes this via a policy based design built using C++ template metaprogramming. WebSocket++ is a cross platform open source (BSD license) header only C++ library that implements RFC6455 (The WebSocket Protocol) and RFC7692 (Compression Extensions for WebSocket). It allows integrating WebSocket client and server functionality into C++ programs. In its most common configuration full featured network I/O is provided by the Asio Networking Library. Bundled config packages provide sane defaults so most users can get started quickly. As they understand their solution better and want to optimize, the default components can be reconfigured or replaced entirely and transparently. -
Incredable is the first DLT-secured platform that allows you to save time, eliminate errors, and ensure your organization is compliant all in one place.Incredable streamlines and simplifies the complex process of medical credentialing for hospitals and medical facilities, helping you save valuable time, reduce costs, and minimize risks. With Incredable, you can effortlessly manage all your healthcare providers and their credentials within a single, unified platform. Our state-of-the-art technology ensures top-notch data security, giving you peace of mind.
-
5
IXWebSocket
websocket and http client and server library, with TLS support
IXWebSocket is a C++ library for WebSocket client and server development. It has minimal dependencies (no boost), is very simple to use and support everything you'll likely need for websocket dev (SSL, deflate compression, compiles on most platforms, etc...). HTTP client and server code is also available, but it hasn't received as much testing. It is been used on big mobile video game titles sending and receiving tons of messages since 2017 (iOS and Android). It was tested on macOS, iOS, Linux, Android, Windows and FreeBSD. Two important design goals are simplicity and correctness. -
6
WebSockets
Implementation of the WebSocket protocol, along with client and server
Implementation of the WebSocket protocol, along with client and server integration components. -
7
AnyCable
Polyglot replacement for Ruby WebSocket servers with Action Cable
Notifications, chats, real-time updates, GPS trackers, collaboration tools, and other real-time features are essential for every modern app. And you should be able to build them in the comfort of your core framework: owning the data, using resources efficiently, and writing clean, maintainable code. AnyCable transforms your Rails application’s real-time performance, making it on par with Go, Elixir, and Node.js–based solutions so you can focus on implementing the business logic. Scale efficiently with AnyCable by leveraging its much lower RAM usage and better CPU utilization than Action Cable. Like with any data, being strategic when handling real-time data is super important. With AnyCable, you remain the owner: you store and access all the data directly, and you never send it to a 3rd-party. Simple and secure. -
8
Netty-socketio
Socket.IO server implemented on Java
This project is an open-source Java implementation of Socket.IO server. Based on Netty server framework. Supports 0.7...0.9.16 (netty-socketio 1.6.6) and 1.0+ (netty-socketio latest version) version of Socket.IO-client. Supports distributed broadcast across netty-socketio nodes (Redisson, Hazelcast). Supports OSGi, supports Spring, lock-free and thread-safe implementation, and declarative handler configuration via annotations. YourKit is kindly supporting this open source project with its full-featured Java Profiler. YourKit, LLC is the creator of innovative and intelligent tools for profiling Java and .NET applications. CentOS, 1 CPU, 4GB RAM runned on VM, CPU 10%, Memory 15%, 6000 xhr-long polling sessions or 15000 websockets sessions, 4000 messages per second. -
9
Proxyee
HTTP proxy server,support HTTPS & websocket
Proxyee is a JAVA-written HTTP proxy server library that supports HTTP, HTTPS, and WebSocket protocols, and supports MITM (Man-in-the-middle), which can capture and tamper with HTTP, and HTTPS packets. The CA certificate (src/resources/ca.crt) from the project needs to be imported to a trusted root certificate authority. The CA certificate (src/resources/ca.crt) from the project needs to be imported to a trusted root certificate authority. You can use the CertDownIntercept interceptor to enable the web certificate download feature. -
Total Network Visibility for Network Engineers and IT ManagersThis means every device on your network, and every interface on every device is automatically analyzed for performance, errors, QoS, and configuration.
-
10
SockJS-client
WebSocket emulation and Javascript client
SockJS is a browser JavaScript library that provides a WebSocket-like object. SockJS gives you a coherent, cross-browser, Javascript API which creates a low latency, full duplex, cross-domain communication channel between the browser and the web server. Under the hood SockJS tries to use native WebSockets first. If that fails it can use a variety of browser-specific transport protocols and presents them through WebSocket-like abstractions. SockJS is intended to work for all modern browsers and in environments which don't support the WebSocket protocol, for example, behind restrictive corporate proxies. SockJS-client does require a server counterpart, such as SockJS-node, which is a SockJS server for Node.js. The API should follow HTML5 Websockets API as closely as possible. All the transports must support cross domain connections out of the box. It's possible and recommended to host a SockJS server on a different server than your main web site. -
11
Soketi
Just another simple, fast, and resilient open-source WebSockets server
Ever dreamed about Serverless WebSockets? Soketi can be deployed to Cloudflare Workers. All around the world, closer to your users. Same Pusher protocol. Powered by Cloudflare's Durable Objects and KV, you can achieve great speeds at edge for your users. -
12
rpc-websockets
JSON-RPC 2.0 implementation over WebSockets for Node.js
The rpc-websockets library enables developers to easily implement their business logic that includes messaging between users, machines or any devices. It provides a possibility to send and receive JSON data through the WebSocket communication protocol in order to support two-way notification push, running RPC methods and firing any types of event signalling. Only clients can call RPC methods and not vice versa at the moment. Both frontend (HTML/JS-based) and backend (Node.js-based) development environments are supported. -
13
socket.io
Realtime application framework (Node.JS server)
socket.io is a JavaScript library that allows for realtime, bi-directional communication between web clients and servers. It is composed of two parts: a Node.js server and a JavaScript client library that runs in the browser. socket.io is focused on both reliability and speed, delivering an immensely powerful, fast and yet easy to use realtime engine that’s used by just about everyone: from Microsoft Office and Zendesk to hackathon winners and small startups. It’s considered one of the most depended-upon npm modules, and works on every platform, browser or device. -
14
libhv
Network library for developing TCP/UDP/SSL/HTTP/WebSocket/MQTT client
Like libevent, libev, and libuv, libhv provides event loop with non-blocking IO and timer, but simpler api and richer protocols. Cross-platform (Linux, Windows, MacOS, BSD, Solaris, Android, iOS) High-performance EventLoop (IO, timer, idle, custom) TCP/UDP client/server/proxy. TCP supports heartbeat, reconnect, upstream, MultiThread-safe write and close, etc. Built-in common unpacking modes (FixedLength, Delimiter, LengthField) RUDP support: WITH_KCP. SSL/TLS support: (via WITH_OPENSSL or WITH_GNUTLS or WITH_MBEDTLS) HTTP client/server (support https http1/x http2 grpc). HTTP supports static service, indexof service, proxy service, sync/async API handler. HTTP supports RESTful, router, middleware, keep-alive, chunked, SSE, etc. WebSocket client/server. -
15
uWebSockets.js
μWebSockets for Node.js back-ends
µWebSockets.js is a web server bypass for Node.js that reimplements eventing, networking, encryption, web protocols, routing and pub/sub in highly optimized C++. As such, µWebSockets.js delivers web serving for Node.js, 8.5x that of Fastify and at least 10x that of Socket.IO. It is also the built-in web server of Bun. -
16
Bloatless PHP WebSockets
Simple WebSocket server implemented in PHP
Simple WebSocket server implemented in PHP. -
17
HyperExpress
High performance Node.js webserver with a simple-to-use API
HyperExpress aims to be a simple yet performant HTTP & Websocket Server. Combined with the power of uWebsockets.js, a Node.js binding of uSockets written in C++, HyperExpress allows developers to unlock higher throughput for their web applications with their existing hardware. This can allow many web applications to become much more performant on optimized data serving endpoints without having to scale hardware. High-performance Node.js webserver with a simple-to-use API powered by uWebsockets.js under the hood. -
18
Laravel WebSockets
Websockets for Laravel
Laravel WebSockets is a package for Laravel 5.7 and up that will get your application started with WebSockets in no time. It has a drop-in Pusher API replacement, a debug dashboard, real-time statistics and even allows you to create custom WebSocket controllers. -
19
Ratchet WebSocket
Asynchronous WebSocket server
Ratchet is a loosely coupled PHP library providing developers with tools to create real time, bi-directional applications between clients and servers over WebSockets. Write your own chat (aka "Hello World!" for sockets) application in a matter of minutes. After understanding "the new flow", event driven programming, compared to traditional HTTP request/response - writing any application on top of Ratchet becomes fast and easy. Ratchet provides many components for you to pick and choose from to easily add functionality. The component architecture allows you to focus on functionality with the ability to reuse and add or remove other component functionality. Ratchet is fully PSR-4 compliant, so it naturally plays well with others. Leveraging components from Symfony2, development should feel similar to many. Ratchet passes all WebSocket tests to ensure it works on all supported browsers. -
20
Sandstone
PHP microframework designed to build a RestApi
PHP micro-framework designed to build a RestApi working together with a WebSocket server. Build a real-time RestApi! -
21
Starscream
Websockets in swift for iOS and OSX
Starscream is a conforming WebSocket (RFC 6455) library in Swift. Once imported, you can open a connection to your WebSocket server. Note that socket is probably best as a property, so it doesn't get deallocated right after being setup. After you are connected, there is either a delegate or closure you can use for process WebSocket events. The writeData method gives you a simple way to send Data (binary) data to the server. The writeString method is the same as writeData, but sends text/string. The writePing method is the same as write, but sends a ping control frame. Starscream will automatically respond to incoming ping control frames so you do not need to manually send pongs. You can override the default websocket headers, add your own custom ones and set a timeout. Update docs on how to load certificates and public keys into an app bundle, use the builtin pinner and TrustKit. -
22
WebSocket Kit
WebSocket client library built on SwiftNIO
WebSocket client library built on SwiftNIO. WebSockets allow for two-way communication between a client and server. Unlike HTTP, which has a request and response pattern, WebSocket peers can send an arbitrary number of messages in either direction. Vapor's WebSocket API allows you to create both clients and servers that handle messages asynchronously. -
23
WebSocket Ruby
Universal Ruby library to handle WebSocket protocol
Universal Ruby library to handle WebSocket protocol. It focuses on providing abstraction layer over WebSocket API instead of providing server or client functionality. WebSocket Ruby has no external dependencies, so it can be installed from source or directly from rubygems. -
24
arduinoWebSockets
arduinoWebSockets
A WebSocket Server and Client for Arduino based on RFC6455. -
25
gev
Gev is a lightweight, fast non-blocking TCP network library
Gev is a lightweight, fast non-blocking TCP network library / websocket server based on Reactor mode. Support custom protocols to quickly and easily build high-performance servers. Support custom protocols to quickly and easily build high-performance servers. High-performance event loop based on epoll and kqueue. Support multi-core and multi-threading. Dynamic expansion of read and write buffers implemented by Ring Buffer. Asynchronous read and write. SO_REUSEPORT port reuse support. Automatically clean up idle connections. Support WebSocket/Protobuf, custom protocols. Support for scheduled tasks and delayed tasks. High-performance web socket server.
Guide to Open Source WebSocket Servers
Open source websocket servers are an important part of web development, as they provide a way to connect browsers and web applications with each other in real-time. They can be used for a variety of purposes, from streaming data to creating multiplayer games. A websocket server is essentially a TCP server that runs over the web and uses the websocket protocol to communicate with clients. This allows for two-way communication between connected browsers and servers, allowing them to exchange messages in real time without having to reload the page. Some of the most popular open source websocket servers include Socket.io, Ratchet, WAMP, Faye and WebSocketClientServer.
Socket.io is one of the most widely used open source websocket servers due to its powerful features such as robust event handling and support for multiple transport protocols like XHR polling, HTML streaming and more. It also provides easy access to popular libraries like jQuery and Backbone so developers can quickly build interactive applications using these frameworks. Additionally, it has many built-in features such as connection persistence and binary data support which makes it convenient for developers working on complex projects.
Ratchet is another popular open source websocket server designed specifically for PHP applications. It supports multiple protocols including its own native protocol known as WAMP (Websockets Application Messaging Protocol) along with HTTP Streaming Protocols including HTTTP 1/1 upgrade mechanism that allows browser clients to upgrade their connection requests when needed during long connections. It also provides API hooks which make it easier for developers to integrate their own custom authentication methods into their existing applications or create their own messaging systems from scratch using Ratchet’s library of components.
WAMP (Websockets Application Messaging Protocol) is an open protocol that enables communication between client-server applications over WebSockets connections while supporting both RPC (Remote Procedure Calls) scripting across different programming languages such as JavaScript on the client side and Python or PHP on the server side. Additionally, WAMP includes traditional Unix signal handlers which allow developers greater control over how incoming messages are handled by application logic written on either side without needing special code each time a message arrives at either end point. Thanks this flexibility, WAMP avoids unnecessary message flooding due to misconfigured tools or software bugs making it perfect choice for large scale distributed systems.
Faye is another high performance open source websocket server offering publish/subscribe messaging features, enabling efficient one-to-many communications through backend services. Its architecture design allows users who subscribe topics receive updates whenever messages published onto those topic are received by Faye server. Furthermore, Faye provide application level security measures via token based authentication along with TLS encryption support ensuring secure transmission transmissions between clients. Lastly, Faye supports many commonly used transports including WebSockets, XMLHttpRequest, JSONP & SSE making it easier than ever before integrate component into existing system architectures effectively.
WebSocketClientServer is another great open source WebSocketServer implementation that provides an easy interface allowing developers easily get up running without having learn too much new technology stack from scratch. It utilizes Java NIO techniques utilizing non blocking IO techniques providing efficient memory usage within backend services while still maintaining low latency communication performances even under extreme load scenarios thanks careful multi threading management implemented within underlying codebase itself. Furthermore, unlike some other server alternatives mentioned here, this library provides ability customize header information sent back forth between clients further enhancing potential security aspects when necessary terms of certain projects demands arise from client requirements if needed be done properly.
In conclusion, open source websocket servers provide an efficient way to connect browsers and web applications in real time. There are a variety of popular open source websocket servers available that offer different features and advantages making them suitable for various projects. Some of the most popular include Socket.io, Ratchet, WAMP, Faye and WebSocketClientServer.
Open Source WebSocket Servers Features
- Authentication: Open source websocket servers provide support for authentication, allowing the server to confirm the identity of each connection and ensuring that only authorized users are able to communicate with it.
- Encryption: Communication between connected clients is encrypted by open source websocket servers, protecting sensitive data from being accessed by unauthorized third parties.
- Low Latency Messages: Websockets allow for significantly lower latency communication than traditional web technologies like HTTP or AJAX. This allows for real-time events and updates and makes applications more responsive.
- Publish/Subscribe Messaging System: Publish/subscribe messaging systems allow clients to subscribe to topics so that they can receive messages about specific topics without having to actively request them from the server each time.
- Push Notifications: Open source websocket servers allow applications to push notifications directly to a client’s browser, providing an instant notification system when new content is available or an event has occurred.
- Scalability: Websockets provide a high level of scalability as they are designed with concurrent connections in mind and can handle large numbers of active connections at once without affecting performance.
- Cross-Domain Communication: Websockets provide the ability to communicate with other domains with minimal overhead, making it easier to develop distributed applications.
What Are the Different Types of Open Source WebSocket Servers?
- Ratchet: Ratchet is a PHP-based websocket server that enables real-time, bi-directional communication between multiple clients. It works with various versions of PHP and WAMP.
- Node.js: Node.js is an open source JavaScript runtime environment that lets developers create highly scalable web applications quickly and easily. It has built-in support for websockets, allowing real-time data transfer between clients in an asynchronous way.
- Autobahn: Autobahn is an open source framework for creating websocket applications. It allows developers to put together both client and server components, which makes it easier to create interactive web applications. It also supports WebSockets and HTML5 technologies such as Server Sent Events (SSE) and EventSource API.
- Socket.io: Socket.io is a popular JavaScript library that simplifies real-time web application development by enabling bidirectional event-based communication between the browser and server over websockets or long polling HTTP connections.
- Jetty Websocket Server: The Jetty Websocket Server provides a low level but highly extensible infrastructure to build custom websocket solutions on top of the Java platform. It was designed from the ground up to scale efficiently while reducing system resource consumption, making it ideal for high performance environments with limited system resources.
- Netty Websocket Server: Netty is a Java-based, asynchronous I/O (input/output) framework that allows developers to rapidly build high-performance web and enterprise applications. It includes an integrated websocket server that makes it easy to create real-time web applications with low latency and scalability requirements.
- Glassfish Websocket Server: Glassfish is an open source application server developed by Oracle for use in creating enterprise applications written in Java. It includes integrated support for websockets, making it easy to develop highly interactive web experiences quickly and easily.
Benefits of Open Source WebSocket Servers
- Increased Flexibility: Open source websocket servers provide significantly more flexibility than their proprietary counterparts. This flexibility allows developers to customize the server with additional features and functions to meet their specific needs.
- Reduced Costs: Since open source websocket servers are free to use, they can save organizations a significant amount of money compared to the cost of using commercial, proprietary software.
- Higher Quality: Open source websocket servers tend to be of higher quality than many commercial products because they are developed by teams of dedicated open source contributors who often have extensive experience in both development and networking.
- Increased Security: Open source websockets offer greater levels of security as there is a larger number of eyes that can help detect potential bugs or vulnerabilities as well as suggest ways to fix them quickly if any arise.
- Better Support: The development team behind an open source project is usually very active in providing support for users via various channels, such as mailing lists, forums, IRC channels, etc., which ensures that users get accurate and timely answers when they need them.
- Improved Scalability: Open source websockets offer much better scalability than many commercially available solutions since they are designed from the ground up with scalability in mind and have been heavily tested before being released for public use.
- Increased Reliability: Open source websockets tend to be more reliable than their proprietary counterparts as they are developed by experienced professionals who have tested and optimized them for performance, ensuring that the server remains stable.
What Types of Users Use Open Source WebSocket Servers?
- Web Developers: Web developers who are using websockets to create websites and applications that use real-time communication.
- Mobile Developers: Mobile developers who are using websockets to create mobile apps that can communicate with other devices in real time.
- Game Developers: Game developers who are using websockets to make online multiplayer games that require real-time communication.
- System Administrators: System administrators who are setting up open source websocket servers for their organizations or clients, configuring them for optimal performance and security.
- DevOps Professionals: DevOps professionals who are managing web infrastructure at scale, automating websocket server deployments and maintenance tasks.
- Scientists: Scientists who are utilizing open source websocket servers for their research projects, enabling real-time data collection and analysis.
- Educators: Educators who use open source websocket servers as part of their teaching material for lessons related to networks or distributed systems engineering.
- IoT Device Manufacturers: IoT device manufacturers using open source websockets to enable quick setup of their devices on a network, allowing remote control and monitoring from anywhere in the world.
- Network Architects: Network architects who are using websockets to design secure and resilient networks that can handle large amounts of traffic, ensuring low latency and high throughput.
How Much Do Open Source WebSocket Servers Cost?
Open source web socket servers are available to download and use at no cost. That said, setting up and running a web socket server requires time and effort, as well as other technical resources such as hardware and software. So while the initial cost for an open source web socket server is free, there can be significant costs incurred downstream in terms of setup, maintenance, upgrade, troubleshooting, and security. Additionally, depending on the size of your organization's needs, there may be additional costs associated with larger data transfers or increased scalability. Finally, if you require specialized features or services not available in an open source solution there may be additional license fees for a commercial websocket product.
What Software Do Open Source WebSocket Servers Integrate With?
Open source websocket servers can integrate with a variety of software types. These include web applications, streaming solutions, messaging platforms, and chatbots such as Slack and Discord. For instance, an open source websocket server can be used to enable real-time communication between a web application's backend and its frontend. It also allows for the registration of client subscriptions and automatic messages when data changes are detected. Open source websocket servers can also be used to stream audio, video, or other types of media in real time to web clients. Additionally, they can power messaging platforms for different user groups such as team members within an organization or customers interacting with a business's customer service system. Finally, they can facilitate more complex interactions by powering chatbot systems that can respond to human input in natural language processing formats.
Recent Trends Related to Open Source WebSocket Servers
- Open source websocket servers are becoming increasingly popular due to their ability to provide real-time communication and allow for bi-directional data transfer between a web client and server.
- As more developers have become familiar with the concept of websockets, they have created a variety of open source websocket servers that can be used in various applications.
- Open source websocket servers offer many advantages over traditional web technologies such as scalability, greater performance, and easier maintenance.
- Furthermore, open source websocket servers are generally more secure than proprietary solutions because the code is open for public review and inspection.
- Finally, open source web socket servers are often free to use, which allows developers to rapidly experiment with ideas without having to invest money in expensive software licenses or development tools.
How Users Can Get Started With Open Source WebSocket Servers
Getting started with open source websocket servers can be a relatively simple process. First, you'll need to decide which websocket server to use.
Once you know which websocket server you want to use, the next step is downloading the appropriate files from their respective websites and installing them on your web server. Depending on which websocket server you're using, the installation instructions will vary; so make sure you read any accompanying documentation closely for best results.
Now that your websocket server is installed, it's time to configure it to suit your needs. You may need to write some code in order to further customize the settings of your websocket connection but this should be fairly straightforward if you've already downloaded all the necessary files and followed all of the setup instructions correctly.
Finally, when everything is configured properly and running as expected, it's time to put your open source web socket server into action by writing client-side JavaScript code that interacts with it. The exact JavaScript syntax will depend on which websocked server you are using; so once again check out each project's website for details about how their particular API works so you don't get lost along the way.
Following these steps should allow you to quickly and easily get started with open source web socket servers.
