frontend: TrackerLogic interface returns modified context

HandleAnnounce and HandleScrape must return the modified context changed
by the hooks. These contexts are passed to AfterAnnounce and AfterScrape
for further use.

Closes #304

frontend/frontend.go

@@ -11,14 +11,20 @@ import (
 // after the response has been delivered to the client.
 type TrackerLogic interface {
 	// HandleAnnounce generates a response for an Announce.
-	HandleAnnounce(context.Context, *bittorrent.AnnounceRequest) (*bittorrent.AnnounceResponse, error)
+	//
+	// Returns the updated context, the generated AnnounceResponse and no error
+	// on success; nil and error on failure.
+	HandleAnnounce(context.Context, *bittorrent.AnnounceRequest) (context.Context, *bittorrent.AnnounceResponse, error)
 
 	// AfterAnnounce does something with the results of an Announce after it
 	// has been completed.
 	AfterAnnounce(context.Context, *bittorrent.AnnounceRequest, *bittorrent.AnnounceResponse)
 
 	// HandleScrape generates a response for a Scrape.
-	HandleScrape(context.Context, *bittorrent.ScrapeRequest) (*bittorrent.ScrapeResponse, error)
+	//
+	// Returns the updated context, the generated AnnounceResponse and no error
+	// on success; nil and error on failure.
+	HandleScrape(context.Context, *bittorrent.ScrapeRequest) (context.Context, *bittorrent.ScrapeResponse, error)
 
 	// AfterScrape does something with the results of a Scrape after it has been completed.
 	AfterScrape(context.Context, *bittorrent.ScrapeRequest, *bittorrent.ScrapeResponse)

frontend/http/frontend.go

@@ -191,7 +191,7 @@ func (f *Frontend) announceRoute(w http.ResponseWriter, r *http.Request, _ httpr
 	af = new(bittorrent.AddressFamily)
 	*af = req.IP.AddressFamily
 
-	resp, err := f.logic.HandleAnnounce(context.Background(), req)
+	ctx, resp, err := f.logic.HandleAnnounce(context.Background(), req)
 	if err != nil {
 		WriteError(w, err)
 		return
@@ -203,7 +203,7 @@ func (f *Frontend) announceRoute(w http.ResponseWriter, r *http.Request, _ httpr
 		return
 	}
 
-	go f.logic.AfterAnnounce(context.Background(), req, resp)
+	go f.logic.AfterAnnounce(ctx, req, resp)
 }
 
 // scrapeRoute parses and responds to a Scrape.
@@ -248,7 +248,7 @@ func (f *Frontend) scrapeRoute(w http.ResponseWriter, r *http.Request, _ httprou
 	af = new(bittorrent.AddressFamily)
 	*af = req.AddressFamily
 
-	resp, err := f.logic.HandleScrape(context.Background(), req)
+	ctx, resp, err := f.logic.HandleScrape(context.Background(), req)
 	if err != nil {
 		WriteError(w, err)
 		return
@@ -260,5 +260,5 @@ func (f *Frontend) scrapeRoute(w http.ResponseWriter, r *http.Request, _ httprou
 		return
 	}
 
-	go f.logic.AfterScrape(context.Background(), req, resp)
+	go f.logic.AfterScrape(ctx, req, resp)
 }

frontend/udp/frontend.go

@@ -286,8 +286,9 @@ func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string
 		af = new(bittorrent.AddressFamily)
 		*af = req.IP.AddressFamily
 
+		var ctx context.Context
 		var resp *bittorrent.AnnounceResponse
-		resp, err = t.logic.HandleAnnounce(context.Background(), req)
+		ctx, resp, err = t.logic.HandleAnnounce(context.Background(), req)
 		if err != nil {
 			WriteError(w, txID, err)
 			return
@@ -295,7 +296,7 @@ func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string
 
 		WriteAnnounce(w, txID, resp, actionID == announceV6ActionID)
 
-		go t.logic.AfterAnnounce(context.Background(), req, resp)
+		go t.logic.AfterAnnounce(ctx, req, resp)
 
 	case scrapeActionID:
 		actionName = "scrape"
@@ -319,8 +320,9 @@ func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string
 		af = new(bittorrent.AddressFamily)
 		*af = req.AddressFamily
 
+		var ctx context.Context
 		var resp *bittorrent.ScrapeResponse
-		resp, err = t.logic.HandleScrape(context.Background(), req)
+		ctx, resp, err = t.logic.HandleScrape(context.Background(), req)
 		if err != nil {
 			WriteError(w, txID, err)
 			return
@@ -328,7 +330,7 @@ func (t *Frontend) handleRequest(r Request, w ResponseWriter) (actionName string
 
 		WriteScrape(w, txID, resp)
 
-		go t.logic.AfterScrape(context.Background(), req, resp)
+		go t.logic.AfterScrape(ctx, req, resp)
 
 	default:
 		err = errUnknownAction

middleware/middleware.go

@@ -49,7 +49,7 @@ type Logic struct {
 }
 
 // HandleAnnounce generates a response for an Announce.
-func (l *Logic) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest) (resp *bittorrent.AnnounceResponse, err error) {
+func (l *Logic) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequest) (_ context.Context, resp *bittorrent.AnnounceResponse, err error) {
 	resp = &bittorrent.AnnounceResponse{
 		Interval:    l.announceInterval,
 		MinInterval: l.announceInterval,
@@ -57,12 +57,12 @@ func (l *Logic) HandleAnnounce(ctx context.Context, req *bittorrent.AnnounceRequ
 	}
 	for _, h := range l.preHooks {
 		if ctx, err = h.HandleAnnounce(ctx, req, resp); err != nil {
-			return nil, err
+			return nil, nil, err
 		}
 	}
 
 	log.WithFields(resp.LogFields()).Debug("generated announce response")
-	return resp, nil
+	return ctx, resp, nil
 }
 
 // AfterAnnounce does something with the results of an Announce after it has
@@ -78,18 +78,18 @@ func (l *Logic) AfterAnnounce(ctx context.Context, req *bittorrent.AnnounceReque
 }
 
 // HandleScrape generates a response for a Scrape.
-func (l *Logic) HandleScrape(ctx context.Context, req *bittorrent.ScrapeRequest) (resp *bittorrent.ScrapeResponse, err error) {
+func (l *Logic) HandleScrape(ctx context.Context, req *bittorrent.ScrapeRequest) (_ context.Context, resp *bittorrent.ScrapeResponse, err error) {
 	resp = &bittorrent.ScrapeResponse{
 		Files: make([]bittorrent.Scrape, 0, len(req.InfoHashes)),
 	}
 	for _, h := range l.preHooks {
 		if ctx, err = h.HandleScrape(ctx, req, resp); err != nil {
-			return nil, err
+			return nil, nil, err
 		}
 	}
 
 	log.WithFields(resp.LogFields()).Debug("generated scrape response")
-	return resp, nil
+	return ctx, resp, nil
 }
 
 // AfterScrape does something with the results of a Scrape after it has been