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New to the subject of realtime APIs? This article is the place to start! There are four common realtime API mechanisms:. The best APIs offer simple connectivity. This means your API should make use of the above mechanisms in a way that is easy for your consumers to understand and that allows access via generic tools e.
HTTP streaming provides a long-lived connection for instant and continuous data push. Twitter , DataSift , Superfeedr , Gitter. A client makes a request to an HTTP endpoint in the usual way along with possibly authentication information, again in the usual way , and the server replies with a response of indefinite length. Response data often comes in two flavors: The former is slightly easier for typical application developers to parse, while the latter enables browsers to consume the stream using EventSource.
When to use it: HTTP streaming is a great for pushing data frequently more than once per minute to the same receiver. If the client needs to be able to rapidly change what it is listening to, this will require adding or recreating HTTP streaming connections.
Consider WebSockets in this case. HTTP long-polling provides a long-lived connection for instant data push. It is the easiest mechanism to consume and also the easiest to make reliable. A client makes a request to an HTTP endpoint in the usual way, with the intention of requesting data it has not yet received. If there is no new data available, then the server holds the request open until data becomes available to respond with.
If enough time passes without new data becoming available, then the server sends a timeout response. The length of time the server waits may be specified by the client for example, via a header or query parameter , or the server may use a fixed default. After receiving a response whether new data or timeout , the transaction is complete.
The client may create a new request to listen for further data. HTTP long-polling is great for making reliable APIs, because sync and listen actions can be combined into the same request. Uses more bandwidth than other mechanisms, particularly if you push data to the same receiver more frequently than the request timeout. If you push extremely often faster than the round trip latency with the client , then expect a batching effect as well.
A WebSocket provides a long-lived connection for exchanging messages between client and server. Messages may flow in either direction for full-duplex communication. Commandline access is possible with wscat. A client creates a WebSocket connection to a server, using a WebSocket client library.
WebSocket libraries are generally available in every language, and of course browsers support it natively using the WebSocket JavaScript object. The connection negotiation uses an HTTP-like exchange, and a successful negotiation is indicated with status code After the negotiation response is sent, the connection remains open to be used for exchanging message frames in either binary or unicode string format. Peers may also exchange close frames to perform a clean close.
While WebSockets as a technology is not exactly new, it is still relatively new in the context of APIs. Also, there is no standard support in WebSocket messages for the things we love about HTTP such as status codes and headers. WebSockets are a great addition to a realtime API, but they should probably not be the sole access mechanism. Webhooks are a simple way of sending data between servers. No long-lived connections are needed. The sender makes an HTTP request to the receiver when there is data to push.
GitHub , Facebook , Stripe , Zapier. The request method is usually POST. Others offer programmatic registration. You may also consider PubSubHubbub if you are sending feed updates. Webhooks are great for pushing data to other servers. You can easily make HTTP requests directly from your server code, without setting up any new components or changing programming languages. Webhooks are also harder to test compared to just running curl or wscat , but tools like ngrok , RequestBin and WebhookInbox can help with this.
Use any or all, whichever makes most sense for your API. It is not uncommon for APIs to offer more than one realtime access mechanism, though. We hope you find this guide handy as your API enters the brave new world of realtime! Sign up for the Fanout Newsletter: