Go net/http timeouts

https://blog.cloudflare.com/the-complete-guide-to-golang-net-http-timeouts

When writing an HTTP server or client in Go, timeouts are amongst the easiest and most subtle things to get wrong: there’s many to choose from, and a mistake can have no consequences for a long time, until the network glitches and the process hangs.

HTTP is a complex multi-stage protocol, so there’s no one-size fits all solution to timeouts. Think about a streaming endpoint versus a JSON API versus a Comet endpoint. Indeed, the defaults are often not what you want.

In this post I’ll take apart the various stages you might need to apply a timeout to, and look at the different ways to do it, on both the Server and the Client side.

SetDeadline

First, you need to know about the network primitive that Go exposes to implement timeouts: Deadlines.

Exposed by net.Conn with the Set[Read|Write]Deadline(time.Time) methods, Deadlines are an absolute time which when reached makes all I/O operations fail with a timeout error.

Deadlines are not timeouts. Once set they stay in force forever (or until the next call to SetDeadline), no matter if and how the connection is used in the meantime. So to build a timeout with SetDeadline you’ll have to call it before every Read/Write operation.

You probably don’t want to call SetDeadline yourself, and let net/http call it for you instead, using its higher level timeouts. However, keep in mind that all timeouts are implemented in terms of Deadlines, so they do NOT reset every time data is sent or received.

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