fields.go

package rest

import (
	"flag"
	"io/ioutil"
	"net/url"

	"github.com/artyom/autoflags"
)

// parseFields fills dst struct with values provided using flag parsing logic
// relying on autoflags package. dst must be a pointer to struct. Only the first
// value of each key from provided url.Values are used.
func parseFields(dst interface{}, vals url.Values) error {
	fs := new(flag.FlagSet)
	fs.SetOutput(ioutil.Discard)
	autoflags.DefineFlagSet(fs, dst)
	args := make([]string, 0, len(vals)*2)
	for k := range vals {
		args = append(args, "-"+k, vals.Get(k))
	}
	return fs.Parse(args)
}

real-world-example.go

package main

import (
	"flag"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"

	"github.com/artyom/autoflags"
)

// parseFields fills dst struct with values provided using flag parsing logic
// relying on autoflags package. dst must be a pointer to struct. Only the first
// value of each key from provided url.Values are used.
func parseFields(dst interface{}, vals url.Values) error {
	fs := new(flag.FlagSet)
	fs.SetOutput(ioutil.Discard)
	autoflags.DefineFlagSet(fs, dst)
	args := make([]string, 0, len(vals)*2)
	for k := range vals {
		args = append(args, "-"+k, vals.Get(k))
	}
	return fs.Parse(args)
}

func parseArgs(dst interface{}, r *http.Request) error {
	if err := r.ParseForm(); err != nil {
		return err
	}
	return parseFields(dst, r.Form)
}

func main() {
	log.Fatal(http.ListenAndServe("localhost:8080", http.HandlerFunc(example)))
}

func example(w http.ResponseWriter, r *http.Request) {
	args := &struct {
		Name string `flag:"name"`
		Age  uint64 `flag:"age"`
	}{}
	if err := parseArgs(args, r); err != nil {
		http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
		return
	}
	fmt.Fprintf(w, "%s is %d years old\n", args.Name, args.Age)
}