ci: add PR checks and harden outputs

.dockerignore

@@ -0,0 +1,12 @@
+.git
+.github
+.idea
+.vscode
+
+.env
+.env.*
+
+data/
+*.csv
+
+*.log

.github/workflows/ci.yml

@@ -0,0 +1,44 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  go:
+    name: Go vet/test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+
+      - name: Check gofmt
+        run: |
+          test -z "$(gofmt -l .)"
+
+      - name: Run go vet
+        run: |
+          go vet ./...
+
+      - name: Run go test
+        run: |
+          go test ./...
+
+  docker:
+    name: Docker build (no push)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: false

README.md

@@ -1,4 +1,34 @@
 # transaction-latency
 
+Measures transaction inclusion latency against two RPC endpoints (e.g. Base + Flashblocks) and writes results to CSV.
+
+## Requirements
+
+- Docker
+- A funded EOA private key for the target network
+
+## Setup
+
+1. Copy the env template and fill values:
+
+```bash
+cp .env.example .env
+```
+
+2. Create an output directory (CSV files are written to `./data`):
+
+```bash
+mkdir -p data
+```
+
+## Run
+
+```bash
 docker build -t transaction-latency .
-docker run -v $(pwd)/data:/app/data --env-file .env --rm -it  transaction-latency
+docker run --rm -it -v "$(pwd)/data:/app/data" --env-file .env transaction-latency
+```
+
+## Outputs
+
+- `data/flashblocks-<REGION>.csv`
+- `data/base-<REGION>.csv` (if `RUN_STANDARD_TRANSACTION_SENDING` is not set to `false`)

main.go

@@ -5,14 +5,17 @@ import (
 	"crypto/ecdsa"
 	"encoding/csv"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"log"
 	"math/big"
 	"math/rand"
 	"os"
+	"path/filepath"
 	"strconv"
 	"time"
 
+	"github.com/ethereum/go-ethereum"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto"
@@ -60,9 +63,13 @@ func main() {
 		log.Fatal("TO_ADDRESS environment variable not set")
 	}
 
+	if !common.IsHexAddress(toAddressRaw) {
+		log.Fatal("TO_ADDRESS environment variable is not a valid hex address")
+	}
+
 	toAddress := common.HexToAddress(toAddressRaw)
 	if toAddress == (common.Address{}) {
-		log.Fatal("TO_ADDRESS environment variable not set")
+		log.Fatal("TO_ADDRESS environment variable cannot be the zero address")
 	}
 
 	flashblocksUrl := os.Getenv("FLASHBLOCKS_URL")
@@ -203,9 +210,16 @@ func main() {
 }
 
 func writeToFile(filename string, data []stats) error {
+	dir := filepath.Dir(filename)
+	if dir != "." {
+		if err := os.MkdirAll(dir, 0o755); err != nil {
+			return fmt.Errorf("failed to create output directory %s: %w", dir, err)
+		}
+	}
+
 	file, err := os.Create(filename)
 	if err != nil {
-		log.Fatalf("Failed to create file: %v", err)
+		return fmt.Errorf("failed to create file %s: %w", filename, err)
 	}
 	defer file.Close()
 
@@ -214,7 +228,7 @@ func writeToFile(filename string, data []stats) error {
 
 	header := []string{"sent_at", "txn_hash", "included_in_block", "inclusion_delay_ms"}
 	if err := writer.Write(header); err != nil {
-		log.Fatalf("Failed to write to file: %v", err)
+		return fmt.Errorf("failed to write CSV header: %w", err)
 	}
 
 	for _, d := range data {
@@ -225,7 +239,7 @@ func writeToFile(filename string, data []stats) error {
 			strconv.FormatInt(d.InclusionDelay.Milliseconds(), 10),
 		}
 		if err := writer.Write(row); err != nil {
-			log.Fatalf("Failed to write to file: %v", err)
+			return fmt.Errorf("failed to write CSV row: %w", err)
 		}
 	}
 
@@ -324,7 +338,12 @@ func sendTransactionAsync(client *ethclient.Client, signedTx *types.Transaction,
 	for i := 0; i < 1000; i++ {
 		receipt, err := client.TransactionReceipt(context.Background(), signedTx.Hash())
 		if err != nil {
-			time.Sleep(time.Duration(pollingIntervalMs) * time.Millisecond)
+			if errors.Is(err, ethereum.NotFound) {
+				time.Sleep(time.Duration(pollingIntervalMs) * time.Millisecond)
+				continue
+			}
+
+			return stats{}, fmt.Errorf("failed to fetch receipt: %w", err)
 		} else {
 			now := time.Now()
 			return stats{