From 90e832c861df33e17b7240ddf1d57441860953dd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Giedrius=20Statkevi=C4=8Dius?=
 <giedrius.statkevicius@vinted.com>
Date: Mon, 2 Dec 2024 16:08:37 +0200
Subject: [PATCH 1/3] scrape: fix nil panic after scrape loop reload
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Don't forget to set `metrics` field as otherwise scraping will lead to a
nil panic in case the body size limit is reached.

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
---
 scrape/scrape.go      |  1 +
 scrape/scrape_test.go | 55 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/scrape/scrape.go b/scrape/scrape.go
index eeab208d6..47ed73c05 100644
--- a/scrape/scrape.go
+++ b/scrape/scrape.go
@@ -359,6 +359,7 @@ func (sp *scrapePool) restartLoops(reuseCache bool) {
 				bodySizeLimit:        bodySizeLimit,
 				acceptHeader:         acceptHeader(sp.config.ScrapeProtocols, validationScheme),
 				acceptEncodingHeader: acceptEncodingHeader(enableCompression),
+				metrics:              sp.metrics,
 			}
 			newLoop = sp.newLoop(scrapeLoopOptions{
 				target:                   t,
diff --git a/scrape/scrape_test.go b/scrape/scrape_test.go
index ce1686fec..e8494e2db 100644
--- a/scrape/scrape_test.go
+++ b/scrape/scrape_test.go
@@ -4794,3 +4794,58 @@ func newScrapableServer(scrapeText string) (s *httptest.Server, scrapedTwice cha
 		}
 	})), scrapedTwice
 }
+
+type srvSameResp struct {
+	resp []byte
+}
+
+func (s *srvSameResp) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	w.Write(s.resp)
+}
+
+func TestTargetScraperSegfault(t *testing.T) {
+	emptySrv := &srvSameResp{
+		resp: []byte{0x42, 0x42},
+	}
+	h := httptest.NewServer(emptySrv)
+	t.Cleanup(h.Close)
+
+	cfg := &config.ScrapeConfig{
+		BodySizeLimit:     1,
+		JobName:           "test",
+		Scheme:            "http",
+		ScrapeInterval:    model.Duration(100 * time.Millisecond),
+		ScrapeTimeout:     model.Duration(100 * time.Millisecond),
+		EnableCompression: false,
+		ServiceDiscoveryConfigs: discovery.Configs{
+			&discovery.StaticConfig{
+				{
+					Targets: []model.LabelSet{{model.AddressLabel: model.LabelValue(h.URL)}},
+				},
+			},
+		},
+	}
+
+	p, err := newScrapePool(
+		cfg,
+		&nopAppendable{},
+		0,
+		nil,
+		pool.New(1e3, 100e6, 3, func(sz int) interface{} { return make([]byte, 0, sz) }),
+		&Options{},
+		newTestScrapeMetrics(t),
+	)
+	require.NoError(t, err)
+	t.Cleanup(p.stop)
+
+	p.Sync([]*targetgroup.Group{
+		{
+			Targets: []model.LabelSet{{model.AddressLabel: model.LabelValue(strings.TrimPrefix(h.URL, "http://"))}},
+			Source:  "test",
+		},
+	})
+
+	require.NoError(t, p.reload(cfg))
+
+	<-time.After(1 * time.Second)
+}

From 5479fb3cfd92f5f34e71b465c5caed5439ca7bc3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Giedrius=20Statkevi=C4=8Dius?=
 <giedrius.statkevicius@vinted.com>
Date: Mon, 9 Dec 2024 08:17:32 +0200
Subject: [PATCH 2/3] scrape: update test after review
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
---
 scrape/scrape_test.go | 29 +++++++----------------------
 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/scrape/scrape_test.go b/scrape/scrape_test.go
index e8494e2db..9e1bd81d6 100644
--- a/scrape/scrape_test.go
+++ b/scrape/scrape_test.go
@@ -4795,19 +4795,12 @@ func newScrapableServer(scrapeText string) (s *httptest.Server, scrapedTwice cha
 	})), scrapedTwice
 }
 
-type srvSameResp struct {
-	resp []byte
-}
-
-func (s *srvSameResp) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	w.Write(s.resp)
-}
-
-func TestTargetScraperSegfault(t *testing.T) {
-	emptySrv := &srvSameResp{
-		resp: []byte{0x42, 0x42},
-	}
-	h := httptest.NewServer(emptySrv)
+func TestTargetScraperSetsMetricsField(t *testing.T) {
+	h := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			w.Write([]byte{0x42, 0x42})
+		},
+	))
 	t.Cleanup(h.Close)
 
 	cfg := &config.ScrapeConfig{
@@ -4826,15 +4819,7 @@ func TestTargetScraperSegfault(t *testing.T) {
 		},
 	}
 
-	p, err := newScrapePool(
-		cfg,
-		&nopAppendable{},
-		0,
-		nil,
-		pool.New(1e3, 100e6, 3, func(sz int) interface{} { return make([]byte, 0, sz) }),
-		&Options{},
-		newTestScrapeMetrics(t),
-	)
+	p, err := newScrapePool(cfg, &nopAppendable{}, 0, nil, nil, &Options{}, newTestScrapeMetrics(t))
 	require.NoError(t, err)
 	t.Cleanup(p.stop)
 

From 5d76510bd6194fdf0a027749d2fa40ba46e541fc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Giedrius=20Statkevi=C4=8Dius?=
 <giedrius.statkevicius@vinted.com>
Date: Mon, 9 Dec 2024 17:36:36 +0200
Subject: [PATCH 3/3] scrape: update test name
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
---
 scrape/scrape_test.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scrape/scrape_test.go b/scrape/scrape_test.go
index 9e1bd81d6..b4a1ab7b9 100644
--- a/scrape/scrape_test.go
+++ b/scrape/scrape_test.go
@@ -4795,7 +4795,8 @@ func newScrapableServer(scrapeText string) (s *httptest.Server, scrapedTwice cha
 	})), scrapedTwice
 }
 
-func TestTargetScraperSetsMetricsField(t *testing.T) {
+// Regression test for the panic fixed in https://github.com/prometheus/prometheus/pull/15523.
+func TestScrapePoolScrapeAfterReload(t *testing.T) {
 	h := httptest.NewServer(http.HandlerFunc(
 		func(w http.ResponseWriter, r *http.Request) {
 			w.Write([]byte{0x42, 0x42})