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HTTP & REST APIs

net/http Handlers

Build handlers with http.HandlerFunc, ResponseWriter, Request, ServeMux, and server timeouts.

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The Handler Interface

Go's net/http package defines a single interface for handling requests: Handler. It has one method, ServeHTTP(ResponseWriter, Request). Every HTTP handler in Go implements this interface, either directly or through the convenience type http.HandlerFunc.

Gohandler-vs-handlerfunc.go

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HandlerFunc is an adapter that lets ordinary functions satisfy the Handler interface. Most Go HTTP handlers use this pattern.

Handlers are the unit of composition

In Go, every endpoint is a handler. Middleware wraps handlers. Routers map paths to handlers. Everything revolves around this single abstraction.

ResponseWriter

ResponseWriter is how you write the HTTP response. You set the status code, add headers, and write the body. The order matters: call WriteHeader before Write, or Write will implicitly send 200 OK.

Goresponsewriter-patterns.go

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Headers must be set before WriteHeader or Write is called. After the first Write, Go sends the headers automatically.

Request Object

The Request object gives you access to everything about the incoming request: method, URL, headers, body, query parameters, path parameters (from routers), and the context for cancellation and deadlines.

Goaccessing-request-fields.go

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Always defer r.Body.Close() after reading the body. The context from r.Context() is how middleware passes values like user IDs to handlers.

ServeMux Routing

Go 1.22 enhanced ServeMux with method matching and path parameters. For most applications, the standard library router is sufficient. For more complex routing, use chi or Gin.

Gogo-1.22+-servemux-with-methods-and-path-params.go

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Go 1.22 ServeMux supports method-based routing and path variables. This eliminates the need for third-party routers in many cases.

Server Timeouts

Without timeouts, slow clients can hold connections open forever, exhausting your server's resources. Configure ReadTimeout, WriteTimeout, and IdleTimeout to prevent this.

Goproduction-server-with-timeouts.go

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ReadTimeout limits how long to read the full request. WriteTimeout limits how long to write the response. IdleTimeout limits how long keep-alive connections persist.

Always set WriteTimeout

Without WriteTimeout, a handler that blocks forever will leak a goroutine and hold a connection indefinitely. This is one of the most common causes of resource exhaustion in Go HTTP servers.

Full Server Example

Gominimal-production-server.go

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This is the foundation. Every production Go HTTP server starts with this structure: define handlers, configure timeouts, and start listening.

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