fix(provider/pia): handle "port is busy" messages and retry port forwarding logic

internal/provider/privateinternetaccess/portforward.go

@@ -13,6 +13,7 @@ import (
 	"net/netip"
 	"net/url"
 	"os"
+	"regexp"
 	"strconv"
 	"strings"
 	"time"
@@ -79,13 +80,27 @@ func (p *Provider) PortForward(ctx context.Context,
 		}
 		durationToExpiration = data.Expiration.Sub(p.timeNow())
 	}
-	logger.Info("Port forwarded data expires in " + format.FriendlyDuration(durationToExpiration))
 
 	// First time binding
-	if err := bindPort(ctx, privateIPClient, p.apiIP, data); err != nil {
-		return nil, fmt.Errorf("binding port: %w", err)
+	for ctx.Err() == nil {
+		err = bindPort(ctx, privateIPClient, p.apiIP, data)
+		if err == nil {
+			break
+		} else if !errors.Is(err, errPortBusy) {
+			return nil, fmt.Errorf("binding port: %w", err)
+		}
+		logger.Warn("refreshing port forward data and trying again because " + err.Error())
+		client := objects.Client
+		data, err = refreshPIAPortForwardData(ctx, client, privateIPClient, p.apiIP,
+			p.portForwardPath, objects.Username, objects.Password)
+		if err != nil {
+			return nil, fmt.Errorf("refreshing port forward data: %w", err)
+		}
+		durationToExpiration = data.Expiration.Sub(p.timeNow())
 	}
 
+	logger.Info("Port forwarded data expires in " + format.FriendlyDuration(durationToExpiration))
+
 	return map[uint16]uint16{data.Port: data.Port}, nil
 }
 
@@ -393,6 +408,13 @@ func fetchPortForwardData(ctx context.Context, client *http.Client, apiIP netip.
 	return port, data.Signature, expiration, err
 }
 
+var errPortBusy = errors.New("port is busy")
+
+var (
+	regexPortBusy = regexp.MustCompile(`^port \d+ is busy\. `)
+	regexNumber   = regexp.MustCompile(`\d+`)
+)
+
 func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr, data piaPortForwardData) (err error) {
 	// Define a timeout since the default client has a large timeout and we don't
 	// want to wait too long.
@@ -431,7 +453,9 @@ func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr,
 	}
 	defer response.Body.Close()
 
-	if response.StatusCode != http.StatusOK {
+	switch response.StatusCode {
+	case http.StatusOK, http.StatusConflict:
+	default:
 		return makeNOKStatusError(response, errSubstitutions)
 	}
 
@@ -444,11 +468,24 @@ func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr,
 		return fmt.Errorf("decoding response: from %s: %w", bindPortURL.String(), err)
 	}
 
-	if responseData.Status != "OK" {
-		return fmt.Errorf("bad response received with status %q and message %q", responseData.Status, responseData.Message)
+	switch response.StatusCode {
+	case http.StatusOK:
+		if responseData.Status != "OK" {
+			return fmt.Errorf("bad response received with status %q and message %q", responseData.Status, responseData.Message)
+		}
+		return nil
+	case http.StatusConflict:
+		portIsBusy := regexPortBusy.FindString(responseData.Message)
+		if portIsBusy == "" {
+			return fmt.Errorf("port busy response received with unexpected message %q not matching regex %q",
+				responseData.Message, regexPortBusy.String())
+		}
+		portStr := regexNumber.FindString(portIsBusy)
+		rest := strings.TrimPrefix(responseData.Message, portIsBusy)
+		return fmt.Errorf("%w: %s - %s", errPortBusy, portStr, rest)
+	default:
+		panic("unreachable code")
 	}
-
-	return nil
 }
 
 // replaceInErr is used to remove sensitive information from errors.