Updated when FIRE INIT is actually printed

The tracer will now keep the state of wheter the init has been sent or not and will emit it prior sending the very first block out.

eth/tracers/firehose.go

@@ -14,6 +14,7 @@ import (
 	"runtime/debug"
 	"strconv"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -56,6 +57,7 @@ func newFirehoseTracer() (core.BlockchainLogger, error) {
 type Firehose struct {
 	// Global state
 	outputBuffer *bytes.Buffer
+	initSent     *atomic.Bool
 
 	// Block state
 	block         *pbeth.Block
@@ -78,12 +80,10 @@ type Firehose struct {
 const FirehoseProtocolVersion = "3.0"
 
 func NewFirehoseLogger() *Firehose {
-	// FIXME: Where should we put our actual INIT line?
-	printToFirehose("INIT", FirehoseProtocolVersion, "geth", params.Version)
-
 	return &Firehose{
 		// Global state
 		outputBuffer: bytes.NewBuffer(make([]byte, 0, 100*1024*1024)),
+		initSent:     new(atomic.Bool),
 
 		// Block state
 		blockOrdinal:  &Ordinal{},
@@ -978,6 +978,10 @@ func (f *Firehose) panicNotInState(msg string) string {
 //
 // It flushes this through [flushToFirehose] to the `os.Stdout` writer.
 func (f *Firehose) printBlockToFirehose(block *pbeth.Block, finalityStatus *FinalityStatus) {
+	if wasNeverSent := f.initSent.CompareAndSwap(false, true); wasNeverSent {
+		printToFirehose("INIT", FirehoseProtocolVersion, "geth", params.Version)
+	}
+
 	marshalled, err := proto.Marshal(block)
 	if err != nil {
 		panic(fmt.Errorf("failed to marshal block: %w", err))