A delightfully tiny but powerful HTTP router for Go web applications

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Flow packs in a bunch of features that you'll probably like:

• Use named parameters, wildcards and (optionally) regexp patterns in your routes.
• Create route groups which use different middleware (a bit like chi).
• Customizable handlers for 404 Not Found and 405 Method Not Allowed responses.
• Automatic handling of OPTIONS and HEAD requests.
• Works with http.Handler, http.HandlerFunc, and standard Go middleware.
• Zero dependencies.
• Tiny, readable, codebase (~160 lines of code).

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Project status

This package has reached a stable status. It is actively maintained with ongoing bug fixes and essential updates, but significant alterations to the API or behavior are not expected.

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Installation

$ go get github.com/alexedwards/flow@latest

Basic example

package main

import (
    "fmt"
    "log"
    "net/http"

    "github.com/alexedwards/flow"
)

func main() {
    // Initialize a new router.
    mux := flow.New()

    // Add a `GET /greet/:name` route. The : character is used to denote a 
    // named parameter in the URL path, which acts like a 'wildcard'.
    mux.HandleFunc("/greet/:name", greet, "GET")

    err := http.ListenAndServe(":2323", mux)
    log.Fatal(err)
}

func greet(w http.ResponseWriter, r *http.Request) {
    // Retrieve the value of the named parameter from the request.
    name := r.PathValue("name")

    fmt.Fprintf(w, "Hello %s", name)
}

Kitchen-sink example

mux := flow.New()

// The Use() method can be used to register middleware. Middleware declared at
// the top level will be used on all routes (including error handlers and OPTIONS
// responses).
mux.Use(exampleMiddleware1)

// Routes can use multiple HTTP methods.
mux.HandleFunc("/profile/:name", exampleHandlerFunc1, "GET", "POST")

// Optionally, regular expressions can be used to enforce a specific pattern
// for a named parameter.
mux.HandleFunc("/profile/:name/:age|^[0-9]{1,3}$", exampleHandlerFunc2, "GET")

// The wildcard ... can be used to match the remainder of a request path.
// Notice that HTTP methods are also optional (if not provided, all HTTP
// methods will match the route). The value of the wildcard can be retrieved 
// by calling r.PathValue("...").
mux.Handle("/static/...", exampleHandler)

// You can create route 'groups'.
mux.Group(func(mux *flow.Mux) {
    // Middleware declared within the group will only be used on the routes
    // in the group.
    mux.Use(exampleMiddleware2)

    mux.HandleFunc("/admin", exampleHandlerFunc3, "GET")

    // Groups can be nested.
    mux.Group(func(mux *flow.Mux) {
        mux.Use(exampleMiddleware3)

        mux.HandleFunc("/admin/passwords", exampleHandlerFunc4, "GET")
    })
})

Notes

• Conflicting routes are permitted (e.g. /posts/:id and posts/new). Routes are matched in the order that they are declared.
• Trailing slashes are significant (/profile/:id and /profile/:id/ are not the same).
• An Allow header is automatically set for all OPTIONS and 405 Method Not Allowed responses (including when using custom handlers).
• Once the flow.Mux type is being used by your server, it is not safe to add more middleware or routes concurrently.
• Middleware must be declared before a route in order to be used by that route. Any middleware declared after a route won't act on that route. For example:

mux := flow.New()
mux.Use(middleware1)
mux.HandleFunc("/foo", ...) // This route will use middleware1 only.
mux.Use(middleware2)
mux.HandleFunc("/bar", ...) // This route will use both middleware1 and middleware2.

Thanks

The pattern matching logic for Flow was heavily inspired by matryer/way.