fix: avoid HTTP healthcheck memory leak

state/prefix_health.go

@@ -2,6 +2,7 @@ package state
 
 import (
 	"fmt"
+	"io"
 	"log/slog"
 	"net"
 	"net/http"
@@ -196,24 +197,39 @@ func (h *HTTPPrefixHealth) Start(log *slog.Logger, t *RouterTunables) {
 	go func() {
 		ticker := time.NewTicker(*h.Delay)
 		defer ticker.Stop()
+		client := &http.Client{Timeout: *h.Delay}
 		for h.running.Load() { // TODO: add a way to interrupt this sleep, if ticker has a high delay
 			<-ticker.C
-			// HTTP probe logic would go here
-			startTime := time.Now()
-			resp, err := http.Get(h.URL)
-			if err != nil || resp.StatusCode != http.StatusOK {
-				// failed
-				h.lastMetric.Store(INF)
-				log.Debug("prefix healthcheck failed", "prefix", h.Prefix.String(), "url", h.URL, "error", err)
-			} else {
-				// success
-				rtt := time.Since(startTime)
-				h.lastMetric.Store(DurationToMetric(rtt))
-			}
+			h.checkHTTP(log, client)
 		}
 	}()
 }
 
+func (h *HTTPPrefixHealth) checkHTTP(log *slog.Logger, client *http.Client) {
+	startTime := time.Now()
+	resp, err := client.Get(h.URL)
+	if err != nil {
+		h.lastMetric.Store(INF)
+		log.Debug("prefix healthcheck failed", "prefix", h.Prefix.String(), "url", h.URL, "error", err)
+		return
+	}
+	_, drainErr := io.Copy(io.Discard, resp.Body)
+	closeErr := resp.Body.Close()
+	if drainErr != nil {
+		log.Debug("failed to drain prefix healthcheck response", "prefix", h.Prefix.String(), "url", h.URL, "error", drainErr)
+	}
+	if closeErr != nil {
+		log.Debug("failed to close prefix healthcheck response", "prefix", h.Prefix.String(), "url", h.URL, "error", closeErr)
+	}
+	if resp.StatusCode != http.StatusOK {
+		h.lastMetric.Store(INF)
+		log.Debug("prefix healthcheck failed", "prefix", h.Prefix.String(), "url", h.URL, "status", resp.StatusCode)
+		return
+	}
+	rtt := time.Since(startTime)
+	h.lastMetric.Store(DurationToMetric(rtt))
+}
+
 func (h *HTTPPrefixHealth) sameConfig(other PrefixHealth, tunables *RouterTunables) bool {
 	o, ok := other.(*HTTPPrefixHealth)
 	return ok &&

state/prefix_health_test.go

@@ -1,7 +1,11 @@
 package state
 
 import (
+	"io"
+	"log/slog"
+	"net/http"
 	"net/netip"
+	"strings"
 	"testing"
 	"time"
 
@@ -110,3 +114,46 @@ delay: 5s
 		})
 	}
 }
+
+type roundTripFunc func(*http.Request) (*http.Response, error)
+
+func (f roundTripFunc) RoundTrip(req *http.Request) (*http.Response, error) {
+	return f(req)
+}
+
+type closeTrackingBody struct {
+	*strings.Reader
+	closed bool
+}
+
+func (b *closeTrackingBody) Close() error {
+	b.closed = true
+	return nil
+}
+
+func TestHTTPPrefixHealthClosesResponseBody(t *testing.T) {
+	for _, statusCode := range []int{http.StatusOK, http.StatusServiceUnavailable} {
+		t.Run(http.StatusText(statusCode), func(t *testing.T) {
+			body := &closeTrackingBody{Reader: strings.NewReader("ok")}
+			client := &http.Client{
+				Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+					return &http.Response{
+						StatusCode: statusCode,
+						Body:       body,
+						Header:     make(http.Header),
+						Request:    req,
+					}, nil
+				}),
+			}
+			health := &HTTPPrefixHealth{
+				Prefix: netip.MustParsePrefix("172.16.0.0/16"),
+				URL:    "http://example.com/health",
+			}
+			logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+
+			health.checkHTTP(logger, client)
+
+			assert.True(t, body.closed)
+		})
+	}
+}