add tx observability example

examples/tx-observability/README.md

@@ -0,0 +1,38 @@
+# tx observability
+
+Opt into a standardized set of events ([TBD](https://github.com/flashbots/suave-std/pull/85)) to enable interoperability with other SUAPPS, block-builders, L2 networks, etc.
+
+Events are defined in an abstract contract (ideally in suave-std):
+
+```solidity
+abstract contract ObservableOrderflow {
+    event SentTransaction(bytes32 txHash);
+}
+```
+
+Then SUAPP developers import and emit those events in their own callbacks:
+
+```solidity
+contract Suapp is ObservableOrderflow {
+    event MySuappEvent(uint256 x);
+
+    modifier confidential() {
+        require(Suave.isConfidential(), "must be called confidentially");
+        _;
+    }
+
+    function didSomething(bytes32[] memory txHashes, uint256 x) public confidential {
+        emit MySuappEvent(x);
+        emit SentTransactions(txHashes);
+    }
+
+    function doSomething() public confidential returns (bytes memory) {
+        // pretend these are tx hashes that we're handling in our SUAPP
+        bytes32[] memory txHashes = new bytes32[](3);
+        for (uint256 i = 0; i < txHashes.length; i++) {
+            txHashes[i] = keccak256(abi.encode("tx", i));
+        }
+        return abi.encodeWithSelector(this.didSomethingWithTxs.selector, txHashes, 9001);
+    }
+}
+```

examples/tx-observability/main.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"log"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/flashbots/suapp-examples/framework"
+)
+
+// SentTransactionsEvent is emitted by SUAPPs to indicate that the SUAPP sent some transactions to L1.
+type SentTransactionsEvent struct {
+	TxHashes []common.Hash `abi:"txHashes"`
+}
+
+func main() {
+	fr := framework.New(framework.WithL1())
+	suappContract := fr.Suave.DeployContract("observability.sol/Suapp.json")
+
+	res := suappContract.SendConfidentialRequest("doSomethingWithTxs", nil, nil)
+	if res.Status != 1 {
+		log.Fatal("confidential request failed")
+	}
+
+	var event SentTransactionsEvent
+	err := suappContract.Abi.UnpackIntoInterface(&event, "SentTransactions", res.Logs[0].Data)
+	if err != nil {
+		log.Fatalf("Failed to unpack log data: %v", err)
+	}
+	log.Printf("logged tx hashes: %v", event.TxHashes)
+}

examples/tx-observability/observability.sol

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.19;
+
+import "suave-std/suavelib/Suave.sol";
+
+// This could be added to suave-std so that all SUAPPs can use it.
+abstract contract TxSender {
+    event SentTransactions(bytes32[] txHashes);
+}
+
+contract Suapp is TxSender {
+    modifier confidential() {
+        require(Suave.isConfidential(), "must be called confidentially");
+        _;
+    }
+
+    function didSomethingWithTxs(bytes32[] memory txHashes) public confidential {
+        emit SentTransactions(txHashes);
+    }
+
+    function doSomethingWithTxs() public confidential returns (bytes memory) {
+        // pretend these are tx hashes that we're handling in our SUAPP
+        bytes32[] memory txHashes = new bytes32[](3);
+        for (uint256 i = 0; i < txHashes.length; i++) {
+            txHashes[i] = keccak256(abi.encode("tx", i));
+        }
+        return abi.encodeWithSelector(this.didSomethingWithTxs.selector, txHashes);
+    }
+}

framework/framework.go

@@ -163,8 +163,6 @@ func (c *Contract) SendConfidentialRequest(method string, args []interface{}, co
 		panic(err)
 	}
 
-	log.Printf("transaction hash: %s", txnResult.Hash().Hex())
-
 	receipt, err := txnResult.Wait()
 	if err != nil {
 		panic(err)