Feature Request: Filesystem middleware

[circa10a]

Issue Description

It would be very nice to have a filesystem middleware supported by echo. Fiber currently has one implemented that allows much easier integration of the new go embed directive.

With fiber, integration looks like this with the middleware:

package main

import (
	"embed"
	"log"
	"net/http"

	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/filesystem"
)

//go:embed index.html
var f embed.FS

func main() {
	app := fiber.New()
	app.Use("/", filesystem.New(filesystem.Config{
		Root: http.FS(f),
	}))
	log.Fatal(app.Listen(":3000"))
}

And the current way to get this working with echo looks like this:

package main

import (
	"embed"
	"net/http"

	"github.com/labstack/echo/v4"
)

//go:embed index.html
var f embed.FS

func main() {
	e := echo.New()
	frontendHttpFs := http.FS(f)
	frontendFileServer := http.FileServer(frontendHttpFs)
	e.GET("/*", echo.WrapHandler(frontendFileServer))
	e.Logger.Fatal(e.Start(":3000"))
}

Curious on your thoughts on this

[maciej-jezierski]

There is currently static middleware with the option to browse: https://echo.labstack.com/middleware/static

[aldas]

Related to #1755

Currently for Echo same thing is achievable with following line if embed.FS is needed.

        //go:embed public/*
...
        var content embed.FS
...
        e.GET("/*", echo.WrapHandler(http.FileServer(http.FS(content))))

We probably should tweak static middleware so user can pass in their FS with other options.

[aldas]

So I created locally branch to add support for fs.FS to serve files. But there is a problem - currently adding support for fs.FS for File() and Static() routes and static middleware is not that simple. For 1.16 it is but when we want to support also 1.15 there are problems as io/fs package does not exist in 1.15 and even with build flags currently go tools are not very happy about it

see: golang/go#44557 and golang/go#40067

Lets wait a little