![]() It will return an error if the system's secure random // number generator fails to function correctly, in which // case the caller should not continue. Satisfying Go’s existing http.Import ( "crypto/rand" "encoding/base64" ) // GenerateRandomBytes returns securely generated random bytes. ![]() We were able to build a flexible, re-usable middleware component by: a trace ID), or specific response headers, we could easily do that by extending the call to logger.Log as needed in our own version of the middleware. If we wanted to log more information - such as *Request.Host, a value from *Request.Context() (e.g. # Make a request with: curl localhost:8000/ ts =T18:30:58.8816186Z loc =server.go:62 status =0 method =GET path =/ duration =7.6µs If we run this server, and then make a request against it, we’ll see our log line output to stderr: The only method required to satisfy http.Handler is ServeHTTP(http.ResponseWriter, *http.Request) - and the concrete http.HandlerFunc type means that you can convert any type with a matching signature into a type that satisfies http.Handler.įunc ExampleMiddleware ( next http. Go’s net/http library defines the http.Handler interface, and satisfying this makes it easy to write portable HTTP handling code. Handlers should be usable by any HTTP-speaking Go service: if team A chooses net/http, team B chooses gorilla/mux, and team C wants to use Twirp, then our middleware shouldn’t force a choice or be constrained within a particular framework. One thing that’s important when writing any middleware is that it be loosely coupled from your choice of framework or router-specific APIs. With this in mind, let’s see how defining “re-usable” middleware in Go actually works. Testing becomes simpler, as we can draw clearer boundaries around each component: noting that integration testing is still important for end-to-end validation.Similar to authn & authz, we can define a set of re-usable logging, metrics & tracing middleware for our applications, so that troubleshooting across services and/or teams isn’t a pot-luck.Separating this can make adding new authentication providers easier, or (importantly) fixing potential security issues easier as a team grows. Authentication and authorization (“authn” and “authz”) can be handled uniformly: we can both keep it separate from our primary business logic, and/or share the same authn/authz handling across our organization.Middleware allows us to separate concerns and write composable applications-and in a world of micro-services, allow clearer lines of ownership for specific components. If you’ve been writing Go for a while, you can skip to the code at the end of this post. Logging just happens to be one of the most common use-cases and makes for a great example. The patterns in this guide can be extended to any HTTP middleware use-cases, including authentication & authorization, metrics, tracing, and web security. Further, and especially in mux’s case, logging is not the focus of the library, and writing your own logging “middleware” can be simpler than you expect. Many of the asks are for different things, since “what” to log, how much to log, and which library to use are not agreed-upon by all. I’ve had a number of requests to add a built-in logger to gorilla/mux and to extend what is logged by gorilla/handlers, and they’re hard to triage. ![]() This is an opinionated guide on how to write extensible logging middleware for Go web services. A Guide To Writing Logging Middleware in Go
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