Implement ErrorSink method

Changes

@@ -6,6 +6,9 @@ v1.2.5 (UNRELEASED)
   * Implement RFC7797. The value of the header field `b64` changes
     how the payload is treated in JWS
   * Implement detached payloads for JWS
+  * Implement (jwk.AutoRefresh).ErrorSink() to register a channel
+    where you can receive errors from fetches and parses that occur during
+    JWK(s) retrieval.
 
 v1.2.4 15 Jul 2021
 [Bug fixes]

jwk/interface.go

@@ -111,3 +111,8 @@ type HTTPClient interface {
 
 type DecodeCtx = json.DecodeCtx
 type KeyWithDecodeCtx = json.DecodeCtxContainer
+
+type AutoRefreshError struct {
+	Error error
+	URL   string
+}

jwk/refresh.go

@@ -26,9 +26,12 @@ import (
 // All JWKS objects that are retrieved via the auto-fetch mechanism should be
 // treated read-only, as they are shared among the consumers and this object.
 type AutoRefresh struct {
+	errDst       chan AutoRefreshError // user-specified error sink
+	errSink      chan AutoRefreshError // AutoRefresh's error sink
 	cache        map[string]Set
 	configureCh  chan struct{}
 	fetching     map[string]chan struct{}
+	muErrDst     sync.Mutex
 	muCache      sync.RWMutex
 	muFetching   sync.Mutex
 	muRegistry   sync.RWMutex
@@ -108,13 +111,15 @@ type resetTimerReq struct {
 // }
 func NewAutoRefresh(ctx context.Context) *AutoRefresh {
 	af := &AutoRefresh{
+		errSink:      make(chan AutoRefreshError, 1),
 		cache:        make(map[string]Set),
 		configureCh:  make(chan struct{}),
 		fetching:     make(map[string]chan struct{}),
 		registry:     make(map[string]*target),
 		resetTimerCh: make(chan *resetTimerReq),
 	}
 	go af.refreshLoop(ctx)
+	go af.drainErrSink(ctx)
 	return af
 }
 
@@ -445,30 +450,49 @@ func (af *AutoRefresh) doRefreshRequest(ctx context.Context, url string, enableB
 
 	res, err := fetch(ctx, url, options...)
 	if err == nil {
-		defer res.Body.Close()
-		keyset, parseErr := ParseReader(res.Body)
-		if parseErr == nil {
-			// Got a new key set. replace the keyset in the target
-			af.muCache.Lock()
-			af.cache[url] = keyset
-			af.muCache.Unlock()
-			nextInterval := calculateRefreshDuration(res, t.refreshInterval, t.minRefreshInterval)
-			rtr := &resetTimerReq{
-				t: t,
-				d: nextInterval,
-			}
-			select {
-			case <-ctx.Done():
-				return ctx.Err()
-			case af.resetTimerCh <- rtr:
+		if res.StatusCode != http.StatusOK {
+			// now, can there be a remote resource that responds with a status code
+			// other than 200 and still be valid...? naaaaaaahhhhhh....
+			err = errors.Errorf(`bad response status code (%d)`, res.StatusCode)
+		} else {
+			defer res.Body.Close()
+			keyset, parseErr := ParseReader(res.Body)
+			if parseErr == nil {
+				// Got a new key set. replace the keyset in the target
+				af.muCache.Lock()
+				af.cache[url] = keyset
+				af.muCache.Unlock()
+				nextInterval := calculateRefreshDuration(res, t.refreshInterval, t.minRefreshInterval)
+				rtr := &resetTimerReq{
+					t: t,
+					d: nextInterval,
+				}
+				select {
+				case <-ctx.Done():
+					return ctx.Err()
+				case af.resetTimerCh <- rtr:
+				}
+
+				now := time.Now()
+				t.lastRefresh = now.Local()
+				t.nextRefresh = now.Add(nextInterval).Local()
+				return nil
 			}
+			err = parseErr
+		}
+	}
 
-			now := time.Now()
-			t.lastRefresh = now.Local()
-			t.nextRefresh = now.Add(nextInterval).Local()
-			return nil
+	// At this point if err != nil, we know that there was something wrong
+	// in either the fetching or the parsing. Send this error to be processed,
+	// but take the extra mileage to not block regular processing by
+	// sending the error to a "proxy" sink, and not directly at the user-specified sink
+	// (see drainErrSink)
+	if err != nil && af.errSink != nil {
+		select {
+		case af.errSink <- AutoRefreshError{Error: err, URL: url}:
+		default:
+			panic("af.errSink is not draining")
 		}
-		err = parseErr
 	}
 
 	// We either failed to perform the HTTP GET, or we failed to parse the
@@ -479,7 +503,7 @@ func (af *AutoRefresh) doRefreshRequest(ctx context.Context, url string, enableB
 	// If we failed to get a single time, then queue another fetch in the future.
 	rtr := &resetTimerReq{
 		t: t,
-		d: t.minRefreshInterval,
+		d: calculateRefreshDuration(res, t.refreshInterval, t.minRefreshInterval),
 	}
 	select {
 	case <-ctx.Done():
@@ -490,38 +514,74 @@ func (af *AutoRefresh) doRefreshRequest(ctx context.Context, url string, enableB
 	return err
 }
 
+// drainErrSink is used proxy the errors that were sent to the main
+// error sink (af.errSink) to the user specified error sink
+func (af *AutoRefresh) drainErrSink(ctx context.Context) {
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case err := <-af.errSink:
+			af.muErrDst.Lock()
+			dst := af.errDst
+			af.muErrDst.Unlock()
+			if dst != nil {
+				// This will block if the user isn't properly draining the channel.
+				// It is the user's responsibility to drain it once they
+				// requested the errors to be streamed
+				dst <- err
+			}
+		}
+	}
+}
+
+// ErrorSink sets a channel to receive JWK fetch errors, if any.
+// Only the errors that occurred *after* the channel was set  will be sent.
+//
+// The user is responsible for properly draining the channel. If the channel
+// is not drained, the fetch operation will block on repeated errors.
+//
+// To disable, set a nil channel.
+func (af *AutoRefresh) ErrorSink(ch chan AutoRefreshError) {
+	af.muErrDst.Lock()
+	af.errDst = ch
+	af.muErrDst.Unlock()
+}
+
 func calculateRefreshDuration(res *http.Response, refreshInterval *time.Duration, minRefreshInterval time.Duration) time.Duration {
 	// This always has precedence
 	if refreshInterval != nil {
 		return *refreshInterval
 	}
 
-	if v := res.Header.Get(`Cache-Control`); v != "" {
-		dir, err := httpcc.ParseResponse(v)
-		if err == nil {
-			maxAge, ok := dir.MaxAge()
-			if ok {
-				resDuration := time.Duration(maxAge) * time.Second
-				if resDuration > minRefreshInterval {
-					return resDuration
+	if res != nil {
+		if v := res.Header.Get(`Cache-Control`); v != "" {
+			dir, err := httpcc.ParseResponse(v)
+			if err == nil {
+				maxAge, ok := dir.MaxAge()
+				if ok {
+					resDuration := time.Duration(maxAge) * time.Second
+					if resDuration > minRefreshInterval {
+						return resDuration
+					}
+					return minRefreshInterval
 				}
-				return minRefreshInterval
+				// fallthrough
 			}
 			// fallthrough
 		}
-		// fallthrough
-	}
 
-	if v := res.Header.Get(`Expires`); v != "" {
-		expires, err := http.ParseTime(v)
-		if err == nil {
-			resDuration := time.Until(expires)
-			if resDuration > minRefreshInterval {
-				return resDuration
+		if v := res.Header.Get(`Expires`); v != "" {
+			expires, err := http.ParseTime(v)
+			if err == nil {
+				resDuration := time.Until(expires)
+				if resDuration > minRefreshInterval {
+					return resDuration
+				}
+				return minRefreshInterval
 			}
-			return minRefreshInterval
+			// fallthrough
 		}
-		// fallthrough
 	}
 
 	// Previous fallthroughs are a little redandunt, but hey, it's all good.

jwk/refresh_test.go

@@ -281,3 +281,63 @@ func TestRefreshSnapshot(t *testing.T) {
 		t.Logf("%s last refreshed at %s, next refresh at %s", target.URL, target.LastRefresh, target.NextRefresh)
 	}
 }
+
+func TestErrorSink(t *testing.T) {
+	t.Parallel()
+
+	testcases := []struct {
+		Name    string
+		Handler http.Handler
+	}{
+		{
+			Name: "non-200 response",
+			Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusForbidden)
+			}),
+		},
+		{
+			Name: "invalid JWK",
+			Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusOK)
+				w.Write([]byte(`{"empty": "nonthingness"}`))
+			}),
+		},
+	}
+
+	for _, tc := range testcases {
+		tc := tc
+		t.Run(tc.Name, func(t *testing.T) {
+			t.Parallel()
+			ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
+			defer cancel()
+			srv := httptest.NewServer(tc.Handler)
+			defer srv.Close()
+
+			ar := jwk.NewAutoRefresh(ctx)
+			ar.Configure(srv.URL, jwk.WithRefreshInterval(500*time.Millisecond))
+			ch := make(chan jwk.AutoRefreshError, 256) // big buffer
+			ar.ErrorSink(ch)
+			ar.Fetch(ctx, srv.URL)
+
+			timer := time.NewTimer(3 * time.Second)
+
+			select {
+			case <-ctx.Done():
+				t.Errorf(`ctx.Done before timer`)
+			case <-timer.C:
+			}
+
+			cancel() // forcefully end context, and thus the AutoRefresh
+
+			// timing issues can cause this to be non-deterministic...
+			// we'll say it's okay as long as we're in +/- 1 range
+			l := len(ch)
+			if !assert.True(t, l <= 7, "number of errors shold be less than or equal to 7 (%d)", l) {
+				return
+			}
+			if !assert.True(t, l >= 5, "number of errors shold be greather than or equal to 5 (%d)", l) {
+				return
+			}
+		})
+	}
+}