Add AllowInBandSync handler option

env.go

@@ -36,21 +36,11 @@ func DevServerURL() string {
 	return devServerURL
 }
 
-func allowInBandSync() bool {
-	val := os.Getenv(envKeyAllowInBandSync)
-	if val == "" {
-		// TODO: Default to true once in-band syncing is stable
-		return false
-	}
-
-	return isTruthy(val)
-}
-
-func isTruthy(val string) bool {
+func isTrue(val string) bool {
 	val = strings.ToLower(val)
-	if val == "false" || val == "0" || val == "" {
-		return false
+	if val == "true" || val == "1" {
+		return true
 	}
 
-	return true
+	return false
 }

handler.go

@@ -95,6 +95,10 @@ type HandlerOpts struct {
 	// UseStreaming enables streaming - continued writes to the HTTP writer.  This
 	// differs from true streaming in that we don't support server-sent events.
 	UseStreaming bool
+
+	// AllowInBandSync allows in-band syncs to occur. If nil, in-band syncs are
+	// disallowed.
+	AllowInBandSync *bool
 }
 
 // GetSigningKey returns the signing key defined within HandlerOpts, or the default
@@ -142,6 +146,19 @@ func (h HandlerOpts) GetRegisterURL() string {
 	return *h.RegisterURL
 }
 
+func (h HandlerOpts) IsInBandSyncAllowed() bool {
+	if h.AllowInBandSync != nil {
+		return *h.AllowInBandSync
+	}
+
+	// TODO: Default to true once in-band syncing is stable
+	if isTrue(os.Getenv(envKeyAllowInBandSync)) {
+		return true
+	}
+
+	return false
+}
+
 // Handler represents a handler which serves the Inngest API via HTTP.  This provides
 // function registration to Inngest, plus the invocation of registered functions via
 // an HTTP POST.
@@ -274,7 +291,7 @@ func (h *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 // by incoming events or schedules.
 func (h *handler) register(w http.ResponseWriter, r *http.Request) error {
 	var err error
-	if r.Header.Get(HeaderKeySyncKind) == SyncKindInBand && allowInBandSync() {
+	if r.Header.Get(HeaderKeySyncKind) == SyncKindInBand && h.IsInBandSyncAllowed() {
 		err = h.inBandSync(w, r)
 	} else {
 		err = h.outOfBandSync(w, r)

handler_test.go

@@ -555,9 +555,6 @@ func TestIntrospection(t *testing.T) {
 }
 
 func TestInBandSync(t *testing.T) {
-	os.Setenv(envKeyAllowInBandSync, "1")
-	defer os.Unsetenv(envKeyAllowInBandSync)
-
 	appID := "test-in-band-sync"
 
 	fn := CreateFunction(
@@ -568,7 +565,8 @@ func TestInBandSync(t *testing.T) {
 		},
 	)
 	h := NewHandler(appID, HandlerOpts{
-		Env: toPtr("my-env"),
+		AllowInBandSync: toPtr(true),
+		Env:             toPtr("my-env"),
 	})
 	h.Register(fn)
 	server := httptest.NewServer(h)