health: Add comments

health/check_block.go

@@ -5,6 +5,7 @@ import (
 	"math/big"
 )
 
+// checkBlockNumber confirms this node is aware of a specific block.
 func checkBlockNumber(ec ethClient, blockNumber *big.Int) error {
 	_, err := ec.BlockByNumber(context.TODO(), blockNumber)
 	if err != nil {

health/check_peers.go

@@ -10,6 +10,7 @@ var (
 	errNotEnoughPeers = errors.New("not enough peers")
 )
 
+// checkMinPeers returns 'errNotEnoughPeers' if the current peer count its lower than 'minPeerCount'
 func checkMinPeers(ec ethClient, minPeerCount uint) error {
 	peerCount, err := ec.PeerCount(context.TODO())
 	if err != nil {

health/check_synced.go

@@ -12,6 +12,7 @@ var (
 	errNotSynced = errors.New("not synced")
 )
 
+// checkSynced returns 'errNotSynced' if the node is in the syncing state.
 func checkSynced(ec ethClient, r *http.Request) error {
 	i, err := ec.SyncProgress(context.TODO())
 	if err != nil {

health/check_time.go

@@ -11,18 +11,19 @@ var (
 	errTimestampTooOld = errors.New("timestamp too old")
 )
 
+// checkTime fetches the timestamp of the most recent block and returns an error if it is earlier than 'minTimestamp'.
 func checkTime(
 	ec ethClient,
 	r *http.Request,
-	seconds int,
+	minTimestamp int,
 ) error {
 	i, err := ec.BlockByNumber(context.TODO(), nil)
 	if err != nil {
 		return err
 	}
 	timestamp := i.Time()
-	if timestamp < uint64(seconds) {
-		return fmt.Errorf("%w: got ts: %d, need: %d", errTimestampTooOld, timestamp, seconds)
+	if timestamp < uint64(minTimestamp) {
+		return fmt.Errorf("%w: got ts: %d, need: %d", errTimestampTooOld, timestamp, minTimestamp)
 	}
 
 	return nil

health/health.go

@@ -35,6 +35,7 @@ type requestBody struct {
 	MaxSecondsBehind *int    `json:"max_seconds_behind"`
 }
 
+// processFromHeaders handles requests when 'X-GETH-HEALTHCHECK' header labels are present.
 func processFromHeaders(ec ethClient, headers []string, w http.ResponseWriter, r *http.Request) {
 	var (
 		errCheckSynced  = errCheckDisabled
@@ -82,6 +83,7 @@ func processFromHeaders(ec ethClient, headers []string, w http.ResponseWriter, r
 	reportHealth(nil, errCheckSynced, errCheckPeer, errCheckBlock, errCheckSeconds, w)
 }
 
+// processFromBody handles requests when 'X-GETH-HEALTHCHECK' headers are not present.
 func processFromBody(ec ethClient, w http.ResponseWriter, r *http.Request) {
 	body, errParse := parseHealthCheckBody(r.Body)
 	defer r.Body.Close()
@@ -125,6 +127,7 @@ func processFromBody(ec ethClient, w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// reportHealth builds the response body, sets the status code and calls for it to be written.
 func reportHealth(errParse, errCheckSynced, errCheckPeer, errCheckBlock, errCheckSeconds error, w http.ResponseWriter) error {
 	statusCode := http.StatusOK
 	errs := make(map[string]string)
@@ -157,6 +160,7 @@ func reportHealth(errParse, errCheckSynced, errCheckPeer, errCheckBlock, errChec
 	return writeResponse(w, errs, statusCode)
 }
 
+// parseHealthCheckBody parses and type checks the request body when 'X-GETH-HEALTHCHECK' headers are not present.
 func parseHealthCheckBody(reader io.Reader) (requestBody, error) {
 	var body requestBody
 
@@ -173,6 +177,7 @@ func parseHealthCheckBody(reader io.Reader) (requestBody, error) {
 	return body, nil
 }
 
+// writeResponse delivers the status and body to the response writer.
 func writeResponse(w http.ResponseWriter, errs map[string]string, statusCode int) error {
 	w.WriteHeader(statusCode)
 
@@ -189,10 +194,12 @@ func writeResponse(w http.ResponseWriter, errs map[string]string, statusCode int
 	return nil
 }
 
+// shouldChangeStatusCode returns 'true' if an error exists and is not 'errCheckDisabled'.
 func shouldChangeStatusCode(err error) bool {
 	return err != nil && !errors.Is(err, errCheckDisabled)
 }
 
+// errorStringOrOK returns "OK", "DISABLED" or the error message based on the output of the check.
 func errorStringOrOK(err error) string {
 	if err == nil {
 		return "OK"

health/service.go

@@ -11,6 +11,7 @@ type handler struct {
 	ec *ethclient.Client
 }
 
+// ServeHTTP implements the http.Handler interface.
 func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	headers := r.Header.Values(healthHeader)
 	if len(headers) != 0 {