refactor: replace particular request not found errors with public err…

…or (#188)

graphsync.go

@@ -137,6 +137,13 @@ func (e RequestCancelledErr) Error() string {
 	return "Request Failed - Responder Cancelled"
 }
 
+// RequestNotFoundErr indicates that a request with a particular request ID was not found
+type RequestNotFoundErr struct{}
+
+func (e RequestNotFoundErr) Error() string {
+	return "request not found"
+}
+
 var (
 	// ErrExtensionAlreadyRegistered means a user extension can be registered only once
 	ErrExtensionAlreadyRegistered = errors.New("extension already registered")

requestmanager/requestmanager.go

@@ -449,7 +449,7 @@ func (crm *cancelRequestMessage) handle(rm *RequestManager) {
 	if !ok {
 		if crm.onTerminated != nil {
 			select {
-			case crm.onTerminated <- errors.New("request not found"):
+			case crm.onTerminated <- graphsync.RequestNotFoundErr{}:
 			case <-rm.ctx.Done():
 			}
 		}
@@ -659,7 +659,7 @@ func (rm *RequestManager) sendRequest(p peer.ID, request gsmsg.GraphSyncRequest)
 func (urm *unpauseRequestMessage) unpause(rm *RequestManager) error {
 	inProgressRequestStatus, ok := rm.inProgressRequestStatuses[urm.id]
 	if !ok {
-		return errors.New("request not found")
+		return graphsync.RequestNotFoundErr{}
 	}
 	if !inProgressRequestStatus.paused {
 		return errors.New("request is not paused")
@@ -685,7 +685,7 @@ func (urm *unpauseRequestMessage) handle(rm *RequestManager) {
 func (prm *pauseRequestMessage) pause(rm *RequestManager) error {
 	inProgressRequestStatus, ok := rm.inProgressRequestStatuses[prm.id]
 	if !ok {
-		return errors.New("request not found")
+		return graphsync.RequestNotFoundErr{}
 	}
 	if inProgressRequestStatus.paused {
 		return errors.New("request is already paused")