<form action="/generate" method="POST"> <textarea name="body" cols="30" rows="10"></textarea> <button>Submit</button> </form>

getpost.go

package main

import (
        "github.com/codegangsta/martini"
        "github.com/russross/blackfriday"
        "net/http"
)

func main() {
        m := martini.Classic()

        m.Post("/generate", func(r *http.Request) []byte {
                body := r.FormValue("body")
                return blackfriday.MarkdownBasic([]byte(body))
        })

        m.Run()
}