public-ip-tracker/tracker/ip/ip.go

package ip

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

const ifconfigURL = "https://ifconfig.me"
const httpMaxRead = 100
const httpTimeout = 10 * time.Second

type IPGetter interface {
	GetCurrentPublicIP(ctx context.Context) (net.IP, error)
}

type concreteIPGetter struct {
	httpClt       *http.Client
	remoteAddress string
	timeout       time.Duration
}

func (c *concreteIPGetter) GetCurrentPublicIP(ctx context.Context) (net.IP, error) {
	reqCtx, cancel := context.WithTimeout(ctx, c.timeout)
	defer cancel()

	req, err := http.NewRequestWithContext(reqCtx, http.MethodGet, c.remoteAddress, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare public IP request: %w", err)
	}
	resp, err := c.httpClt.Do(req)
	if err != nil {
		return nil, fmt.Errorf("failed to get current IP from ifconfig: %w", err)
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("invalid returncode %d", resp.StatusCode)
	}
	if resp.ContentLength > httpMaxRead {
		return nil, fmt.Errorf("response too big: %d/%d", resp.ContentLength, httpMaxRead)
	}

	buf := bytes.NewBuffer([]byte{})
	if _, err := io.CopyN(buf, resp.Body, resp.ContentLength); err != nil {
		return nil, fmt.Errorf("error parsing body: %w", err)
	}

	content := string(buf.Bytes())
	res := net.ParseIP(content)
	if res == nil {
		return nil, fmt.Errorf("got an invalid public IP %q", content)
	}
	return res, nil
}

func New() IPGetter {
	return &concreteIPGetter{
		httpClt:       http.DefaultClient,
		remoteAddress: ifconfigURL,
		timeout:       httpTimeout,
	}
}