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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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) {
    // Use flow.Param() to retrieve the value of the named parameter from the
    // request context.
    name := flow.Param(r.Context(), "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 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 flow.Param("...").
mux.Handle("/static/...", exampleHandler)

// You can create route 'groups'.
mux.Group(func(mux *flow.Mux) {
    // Middleware declared within in 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.

Contributing

Bug fixes and documentation improvements are very welcome! For feature additions or behavioral changes, please open an issue to discuss the change before submitting a PR.

Thanks

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