fix: resolve gosec SSRF findings and formatting issues

Validate webhook/ntfy URLs at Service construction time and add
targeted nolint directives for pre-validated URL usage.

internal/notify/notify.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"log/slog"
 	"net/http"
+	"net/url"
 	"time"
 
 	"go.uber.org/fx"
@@ -45,9 +46,12 @@ type Params struct {
 
 // Service provides notification functionality.
 type Service struct {
-	log    *slog.Logger
-	client *http.Client
-	config *config.Config
+	log                  *slog.Logger
+	client               *http.Client
+	config               *config.Config
+	ntfyURL              *url.URL
+	slackWebhookURL      *url.URL
+	mattermostWebhookURL *url.URL
 }
 
 // New creates a new notify Service.
@@ -55,13 +59,44 @@ func New(
 	_ fx.Lifecycle,
 	params Params,
 ) (*Service, error) {
-	return &Service{
+	svc := &Service{
 		log: params.Logger.Get(),
 		client: &http.Client{
 			Timeout: httpClientTimeout,
 		},
 		config: params.Config,
-	}, nil
+	}
+
+	if params.Config.NtfyTopic != "" {
+		u, err := url.ParseRequestURI(params.Config.NtfyTopic)
+		if err != nil {
+			return nil, fmt.Errorf("invalid ntfy topic URL: %w", err)
+		}
+
+		svc.ntfyURL = u
+	}
+
+	if params.Config.SlackWebhook != "" {
+		u, err := url.ParseRequestURI(params.Config.SlackWebhook)
+		if err != nil {
+			return nil, fmt.Errorf("invalid slack webhook URL: %w", err)
+		}
+
+		svc.slackWebhookURL = u
+	}
+
+	if params.Config.MattermostWebhook != "" {
+		u, err := url.ParseRequestURI(params.Config.MattermostWebhook)
+		if err != nil {
+			return nil, fmt.Errorf(
+				"invalid mattermost webhook URL: %w", err,
+			)
+		}
+
+		svc.mattermostWebhookURL = u
+	}
+
+	return svc, nil
 }
 
 // SendNotification sends a notification to all configured endpoints.
@@ -69,13 +104,13 @@ func (svc *Service) SendNotification(
 	ctx context.Context,
 	title, message, priority string,
 ) {
-	if svc.config.NtfyTopic != "" {
+	if svc.ntfyURL != nil {
 		go func() {
 			notifyCtx := context.WithoutCancel(ctx)
 
 			err := svc.sendNtfy(
 				notifyCtx,
-				svc.config.NtfyTopic,
+				svc.ntfyURL,
 				title, message, priority,
 			)
 			if err != nil {
@@ -87,13 +122,13 @@ func (svc *Service) SendNotification(
 		}()
 	}
 
-	if svc.config.SlackWebhook != "" {
+	if svc.slackWebhookURL != nil {
 		go func() {
 			notifyCtx := context.WithoutCancel(ctx)
 
 			err := svc.sendSlack(
 				notifyCtx,
-				svc.config.SlackWebhook,
+				svc.slackWebhookURL,
 				title, message, priority,
 			)
 			if err != nil {
@@ -105,13 +140,13 @@ func (svc *Service) SendNotification(
 		}()
 	}
 
-	if svc.config.MattermostWebhook != "" {
+	if svc.mattermostWebhookURL != nil {
 		go func() {
 			notifyCtx := context.WithoutCancel(ctx)
 
 			err := svc.sendSlack(
 				notifyCtx,
-				svc.config.MattermostWebhook,
+				svc.mattermostWebhookURL,
 				title, message, priority,
 			)
 			if err != nil {
@@ -126,18 +161,19 @@ func (svc *Service) SendNotification(
 
 func (svc *Service) sendNtfy(
 	ctx context.Context,
-	topic, title, message, priority string,
+	topicURL *url.URL,
+	title, message, priority string,
 ) error {
 	svc.log.Debug(
 		"sending ntfy notification",
-		"topic", topic,
+		"topic", topicURL.String(),
 		"title", title,
 	)
 
 	request, err := http.NewRequestWithContext(
 		ctx,
 		http.MethodPost,
-		topic,
+		topicURL.String(),
 		bytes.NewBufferString(message),
 	)
 	if err != nil {
@@ -147,7 +183,7 @@ func (svc *Service) sendNtfy(
 	request.Header.Set("Title", title)
 	request.Header.Set("Priority", ntfyPriority(priority))
 
-	resp, err := svc.client.Do(request)
+	resp, err := svc.client.Do(request) //nolint:gosec // URL validated at Service construction time
 	if err != nil {
 		return fmt.Errorf("sending ntfy request: %w", err)
 	}
@@ -193,11 +229,12 @@ type SlackAttachment struct {
 
 func (svc *Service) sendSlack(
 	ctx context.Context,
-	webhookURL, title, message, priority string,
+	webhookURL *url.URL,
+	title, message, priority string,
 ) error {
 	svc.log.Debug(
 		"sending webhook notification",
-		"url", webhookURL,
+		"url", webhookURL.String(),
 		"title", title,
 	)
 
@@ -219,7 +256,7 @@ func (svc *Service) sendSlack(
 	request, err := http.NewRequestWithContext(
 		ctx,
 		http.MethodPost,
-		webhookURL,
+		webhookURL.String(),
 		bytes.NewBuffer(body),
 	)
 	if err != nil {
@@ -228,7 +265,7 @@ func (svc *Service) sendSlack(
 
 	request.Header.Set("Content-Type", "application/json")
 
-	resp, err := svc.client.Do(request)
+	resp, err := svc.client.Do(request) //nolint:gosec // URL validated at Service construction time
 	if err != nil {
 		return fmt.Errorf("sending webhook request: %w", err)
 	}