Add leaked logs example (#43)

* Add leaked logs example

* Update suave-std

Makefile

@@ -33,4 +33,5 @@ run-integration:
 	go run examples/mevm-is-confidential/main.go 
 	go run examples/onchain-callback/main.go 
 	go run examples/onchain-state/main.go
+	go run examples/offchain-logs/main.go
 	go run examples/mevm-context/main.go

examples/offchain-logs/README.md

@@ -0,0 +1,35 @@
+# Example Suapp with Offchain logs
+
+This example shows how Suapps can emit logs during the confidential execution that are leaked during the onchain callback. To do so, the Suapp has to import the `suave-std/Suapp.sol` contract and use the `emitOffchainLogs` modifier in the onchain callback function. Then, logs emitted during the confidential execution which triggers the onchain computation will be emitted on the Suave chain.
+
+The Suapp will look like this:
+
+```
+import "suave-std/Suapp.sol";
+
+contract ExampleSuapp is Suapp {
+    function onchainCallback() public emitOffchainLogs {
+    }
+
+    event OffchainLog();
+
+    function offchain() public {
+        emit OffchainLog();
+        return abi.encodeWithSelector(this.onchainCallback.selector);
+    }
+}
+```
+
+## How to use
+
+Run `Suave` in development mode:
+
+```
+$ suave --suave.dev
+```
+
+Execute the deployment script:
+
+```
+$ go run main.go
+```

examples/offchain-logs/main.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"log"
+
+	"github.com/flashbots/suapp-examples/framework"
+)
+
+func main() {
+	fr := framework.New()
+	contract := fr.Suave.DeployContract("offchain-logs.sol/OffchainLogs.json")
+
+	receipt := contract.SendTransaction("example", nil, nil)
+	if len(receipt.Logs) != 2 {
+		log.Fatal("two logs expected")
+	}
+
+	// emit the CCR but DO NOT leak the logs
+	receipt = contract.SendTransaction("exampleNoLogs", nil, nil)
+	if len(receipt.Logs) != 1 {
+		log.Fatal("only one log expected")
+	}
+}

examples/offchain-logs/offchain-logs.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.8;
+
+import "suave-std/Suapp.sol";
+
+contract OffchainLogs is Suapp {
+    event OnchainEvent(uint256 num);
+    event OffchainEvent(uint256 num);
+
+    function emitCallbackWithLogs(uint256 num) public emitOffchainLogs {
+        emit OnchainEvent(num);
+    }
+
+    function example() external returns (bytes memory) {
+        emit OffchainEvent(101);
+
+        return bytes.concat(this.emitCallbackWithLogs.selector, abi.encode(101));
+    }
+
+    /* This function pair do not leak the events in the onchain transaction */
+
+    function emitCallbackWithoutLogs(uint256 num) public {
+        // this callback **does not** emit logs
+        emit OnchainEvent(num);
+    }
+
+    function exampleNoLogs() external returns (bytes memory) {
+        emit OffchainEvent(101);
+
+        return bytes.concat(this.emitCallbackWithoutLogs.selector, abi.encode(101));
+    }
+}

examples/onchain-callback/onchain-callback.sol

@@ -6,16 +6,11 @@ import "suave-std/suavelib/Suave.sol";
 contract OnChainCallback {
     event CallbackEvent(uint256 num);
 
-    event NilEvent();
-
     function emitCallback(uint256 num) public {
         emit CallbackEvent(num);
     }
 
     function example() external returns (bytes memory) {
-        // event emitted in the off-chain confidential context, no effect.
-        emit NilEvent();
-
         return bytes.concat(this.emitCallback.selector, abi.encode(1));
     }
 }