Add publig IP getter

Ref #3

This commit uses a GET query to ifconfig.me in order to get the current
public IP. It also modifies the initialization message to send the
current public IP to the Telegram channel instead of a simple message.

tracker/bot/bot.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"git.faercol.me/faercol/public-ip-tracker/tracker/config"
+	"git.faercol.me/faercol/public-ip-tracker/tracker/ip"
 	"github.com/ahugues/go-telegram-api/bot"
 )
 
@@ -14,10 +15,16 @@ type Notifier struct {
 	cancel       context.CancelFunc
 	tgBot        *bot.ConcreteBot
 	notifChannel int64
+	ipGetter     ip.Getter
 }
 
 func (n *Notifier) SendInitMessage() error {
-	initMsg := fmt.Sprintf("Public IP tracked initialized at %v", time.Now())
+	publicIP, err := n.ipGetter.GetCurrentPublicIP(n.ctx)
+	if err != nil {
+		return fmt.Errorf("failed to get current public IP: %w", err)
+	}
+
+	initMsg := fmt.Sprintf("Public IP tracker initialized at %v, public IP is %s", time.Now(), publicIP)
 	if err := n.tgBot.SendMessage(n.ctx, n.notifChannel, initMsg); err != nil {
 		return fmt.Errorf("failed to send initialization message: %w", err)
 	}
@@ -33,5 +40,6 @@ func New(ctx context.Context, config *config.Config) *Notifier {
 		cancel:       cancel,
 		tgBot:        tgBot,
 		notifChannel: config.Telegram.ChannelID,
+		ipGetter:     ip.New(),
 	}
 }

tracker/ip/ip.go

@@ -0,0 +1,52 @@
+package ip
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+)
+
+const ifconfigURL = "https://ifconfig.me"
+const httpMaxRead = 100
+
+// TODO: use a struct, but a baseHTTPClient inside it to perform unit tests
+type Getter interface {
+	GetCurrentPublicIP(ctx context.Context) (net.IP, error)
+}
+
+type concreteIPGetter struct {
+}
+
+func (c *concreteIPGetter) GetCurrentPublicIP(ctx context.Context) (net.IP, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, ifconfigURL, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to prepare public IP request: %w", err)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get current IP from ifconfig: %w", err)
+	}
+
+	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() *concreteIPGetter {
+	return &concreteIPGetter{}
+}