http_client.go

package server

import (
	"context"
	"fmt"
	"net"
	"net/http"
	"time"
)

const (
	requestTimeoutSecs = 60
)

var (
	dialer   = &net.Dialer{}
	resolver = &net.Resolver{}
)

func publicUnicastOnlyDialContext(ctx context.Context, network, addr string) (net.Conn, error) {
	host, port, err := net.SplitHostPort(addr)
	if err != nil {
		return nil, err
	}

	ip := net.ParseIP(host)

	var ipAddrs []string
	if ip != nil {
		ipAddrs = append(ipAddrs, ip.String())
	} else {
		ipAddrs, err = resolver.LookupHost(ctx, host)
		if err != nil {
			return nil, fmt.Errorf("failed to lookup host: %w", err)
		}
	}

	var dialErrs []error
	connectTimeout := requestTimeoutSecs * time.Second / time.Duration(len(ipAddrs)+1)
	for _, ipAddr := range ipAddrs {
		ip = net.ParseIP(ipAddr)
		switch {
		case !ip.IsGlobalUnicast() || ip.IsPrivate():
			dialErrs = append(dialErrs, fmt.Errorf("forbidden address: %s", ipAddr))
			continue
		}

		connCtx, cancel := context.WithTimeout(ctx, connectTimeout)
		conn, err := dialer.DialContext(connCtx, network, net.JoinHostPort(ipAddr, port))
		cancel()
		if nil == err {
			return conn, nil
		}
		dialErrs = append(dialErrs, fmt.Errorf("failed to dial '%s:%s': %w", ipAddr, port, err))
	}

	return nil, fmt.Errorf("failed to dial: %q", dialErrs)
}

type WithUserAgent struct {
	http.RoundTripper
	UserAgent string
}

func (w *WithUserAgent) RoundTrip(r *http.Request) (*http.Response, error) {
	r.Header.Set("User-Agent", w.UserAgent)
	return w.RoundTripper.RoundTrip(r)
}