Add support for message perturbations to SMR

The SMR system can now be configured (using PerturbMessages)
to artificially introduce random delays and loss to all sent messages.

Signed-off-by: Matej Pavlovic <[email protected]>

pkg/systems/smr/system.go

@@ -4,18 +4,17 @@ import (
 	"github.com/libp2p/go-libp2p-core/host"
 	"github.com/pkg/errors"
 
-	"github.com/filecoin-project/mir/pkg/net"
-
-	"github.com/filecoin-project/mir/pkg/checkpoint"
-
 	"github.com/filecoin-project/mir/pkg/availability/batchdb/fakebatchdb"
 	"github.com/filecoin-project/mir/pkg/availability/multisigcollector"
 	"github.com/filecoin-project/mir/pkg/batchfetcher"
+	"github.com/filecoin-project/mir/pkg/checkpoint"
 	mircrypto "github.com/filecoin-project/mir/pkg/crypto"
+	"github.com/filecoin-project/mir/pkg/eventmangler"
 	"github.com/filecoin-project/mir/pkg/iss"
 	"github.com/filecoin-project/mir/pkg/logging"
 	"github.com/filecoin-project/mir/pkg/mempool/simplemempool"
 	"github.com/filecoin-project/mir/pkg/modules"
+	"github.com/filecoin-project/mir/pkg/net"
 	libp2pnet "github.com/filecoin-project/mir/pkg/net/libp2p"
 	t "github.com/filecoin-project/mir/pkg/types"
 )
@@ -50,6 +49,28 @@ func (sys *System) WithModule(moduleID t.ModuleID, module modules.Module) *Syste
 	return sys
 }
 
+// PerturbMessages configures the SMR system to randomly drop and delay some of the messages sent over the network.
+// Useful for debugging and stress-testing.
+// The params argument defines parameters of the perturbation, such as how many messages should be dropped
+// and how the remaining messages should be delayed.
+func (sys *System) PerturbMessages(params *eventmangler.ModuleParams) error {
+
+	// Create event mangler perturbing (dropping and delaying) events.
+	messageMangler, err := eventmangler.NewModule(
+		&eventmangler.ModuleConfig{Self: "net", Dest: "truenet", Timer: "timer"},
+		params,
+	)
+	if err != nil {
+		return err
+	}
+
+	// Intercept all events (in this case SendMessage events) directed to the "net" module by the mangler
+	// And change the actual transport module ID to "truenet", where the mangler forwards the surviving messages.
+	sys.modules[iss.DefaultModuleConfig().Net] = messageMangler
+	sys.modules["truenet"] = sys.transport
+	return nil
+}
+
 // Start starts the operation of the modules of the SMR system.
 // It starts the network transport and connects to the initial members of the system.
 func (sys *System) Start() error {