fix: ensure delta metric values are never negative

go.sum

@@ -221,8 +221,6 @@ github.com/foxboron/go-tpm-keyfiles v0.0.0-20251226215517-609e4778396f/go.mod h1
 github.com/frankban/quicktest v1.14.6 h1:7Xjx+VpznH+oBnejlPUj8oUpdxnVs4f8XU8WnHkI4W8=
 github.com/frankban/quicktest v1.14.6/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
 github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbSClcnxKAGw=
-github.com/fsnotify/fsnotify v1.9.0 h1:2Ml+OJNzbYCTzsxtv8vKSFD9PbJjmhYF14k/jKC7S9k=
-github.com/fsnotify/fsnotify v1.9.0/go.mod h1:8jBTzvmWwFyi3Pb8djgCCO5IBqzKJ/Jwo8TRcHyHii0=
 github.com/fsnotify/fsnotify v1.10.1 h1:b0/UzAf9yR5rhf3RPm9gf3ehBPpf0oZKIjtpKrx59Ho=
 github.com/fsnotify/fsnotify v1.10.1/go.mod h1:TLheqan6HD6GBK6PrDWyDPBaEV8LspOxvPSjC+bVfgo=
 github.com/fxamacker/cbor/v2 v2.9.1 h1:2rWm8B193Ll4VdjsJY28jxs70IdDsHRWgQYAI80+rMQ=
@@ -1083,8 +1081,6 @@ golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
 golang.org/x/mod v0.15.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
 golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
-golang.org/x/mod v0.35.0 h1:Ww1D637e6Pg+Zb2KrWfHQUnH2dQRLBQyAtpr/haaJeM=
-golang.org/x/mod v0.35.0/go.mod h1:+GwiRhIInF8wPm+4AoT6L0FA1QWAad3OMdTRx4tFYlU=
 golang.org/x/mod v0.36.0 h1:JJjpVx6myfUsUdAzZuOSTTmRE0PfZeNWzzvKrP7amb4=
 golang.org/x/mod v0.36.0/go.mod h1:moc6ELqsWcOw5Ef3xVprK5ul/MvtVvkIXLziUOICjUQ=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=

internal/collector/metricsutil/util.go

@@ -0,0 +1,16 @@
+// Copyright (c) F5, Inc.
+//
+// This source code is licensed under the Apache License, Version 2.0 license found in the
+// LICENSE file in the root directory of this source tree.
+
+package metricsutil
+
+// Increase calculates the delta value (difference) from monotonically increasing counters.
+// If the current value is less than previous value, in the case of a reset, we take the current value.
+func Increase(current, previous int64) int64 {
+	if current >= previous {
+		return current - previous
+	}
+
+	return current
+}

internal/collector/metricsutil/util_test.go

@@ -0,0 +1,33 @@
+// Copyright (c) F5, Inc.
+//
+// This source code is licensed under the Apache License, Version 2.0 license found in the
+// LICENSE file in the root directory of this source tree.
+
+package metricsutil_test
+
+import (
+	"testing"
+
+	"github.com/nginx/agent/v3/internal/collector/metricsutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIncrease(t *testing.T) {
+	t.Parallel()
+
+	testcases := []struct {
+		current  int64
+		previous int64
+		expected int64
+	}{
+		{current: 10, previous: 5, expected: 5}, // normal increase
+		{current: 5, previous: 5, expected: 0},  // no change
+		{current: 0, previous: 4, expected: 0},  // reset
+		{current: 3, previous: 10, expected: 3}, // reset then non-zero
+	}
+
+	for _, tc := range testcases {
+		result := metricsutil.Increase(tc.current, tc.previous)
+		require.Equal(t, tc.expected, result)
+	}
+}

internal/collector/nginxplusreceiver/record/http_metrics.go

@@ -6,6 +6,7 @@
 package record
 
 import (
+	"github.com/nginx/agent/v3/internal/collector/metricsutil"
 	"github.com/nginx/agent/v3/internal/collector/nginxplusreceiver/internal/metadata"
 	plusapi "github.com/nginx/nginx-plus-go-client/v3/client"
 	"go.opentelemetry.io/collector/pdata/pcommon"
@@ -28,7 +29,7 @@ func (hm *HTTPMetrics) RecordHTTPMetrics(stats *plusapi.Stats, now pcommon.Times
 	hm.mb.RecordNginxHTTPRequestsDataPoint(now, int64(stats.HTTPRequests.Total), "", 0)
 
 	// Request Count
-	requestsDiff := int64(stats.HTTPRequests.Total) - int64(hm.PreviousHTTPRequestsTotal)
+	requestsDiff := metricsutil.Increase(int64(stats.HTTPRequests.Total), int64(hm.PreviousHTTPRequestsTotal))
 	hm.mb.RecordNginxHTTPRequestCountDataPoint(now, requestsDiff, "", 0)
 	hm.PreviousHTTPRequestsTotal = stats.HTTPRequests.Total
 

internal/collector/nginxplusreceiver/record/location_zone_metrics.go

@@ -6,6 +6,7 @@
 package record
 
 import (
+	"github.com/nginx/agent/v3/internal/collector/metricsutil"
 	"github.com/nginx/agent/v3/internal/collector/nginxplusreceiver/internal/metadata"
 	plusapi "github.com/nginx/nginx-plus-go-client/v3/client"
 	"go.opentelemetry.io/collector/pdata/pcommon"
@@ -59,7 +60,7 @@ func (lzm *LocationZoneMetrics) RecordLocationZoneMetrics(stats *plusapi.Stats,
 		)
 
 		lzm.mb.RecordNginxHTTPRequestCountDataPoint(now,
-			lz.Requests-lzm.PreviousLocationZoneRequests[lzName],
+			metricsutil.Increase(lz.Requests, lzm.PreviousLocationZoneRequests[lzName]),
 			lzName,
 			metadata.AttributeNginxZoneTypeLOCATION,
 		)
@@ -110,32 +111,37 @@ func (lzm *LocationZoneMetrics) recordLocationZoneHTTPMetrics(lz plusapi.Locatio
 
 	// Requests
 	lzm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(lz.Responses.Responses1xx)-lzm.PreviousLocationZoneResponses[lzName].OneHundredStatusRange,
+		metricsutil.Increase(
+			int64(lz.Responses.Responses1xx), lzm.PreviousLocationZoneResponses[lzName].OneHundredStatusRange),
 		metadata.AttributeNginxStatusRange1xx,
 		lzName,
 		metadata.AttributeNginxZoneTypeLOCATION)
 
 	// Response Count Status
 	lzm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(lz.Responses.Responses2xx)-lzm.PreviousLocationZoneResponses[lzName].TwoHundredStatusRange,
+		metricsutil.Increase(
+			int64(lz.Responses.Responses2xx), lzm.PreviousLocationZoneResponses[lzName].TwoHundredStatusRange),
 		metadata.AttributeNginxStatusRange2xx,
 		lzName,
 		metadata.AttributeNginxZoneTypeLOCATION)
 
 	lzm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(lz.Responses.Responses3xx)-lzm.PreviousLocationZoneResponses[lzName].ThreeHundredStatusRange,
+		metricsutil.Increase(
+			int64(lz.Responses.Responses3xx), lzm.PreviousLocationZoneResponses[lzName].ThreeHundredStatusRange),
 		metadata.AttributeNginxStatusRange3xx,
 		lzName,
 		metadata.AttributeNginxZoneTypeLOCATION)
 
 	lzm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(lz.Responses.Responses4xx)-lzm.PreviousLocationZoneResponses[lzName].FourHundredStatusRange,
+		metricsutil.Increase(
+			int64(lz.Responses.Responses4xx), lzm.PreviousLocationZoneResponses[lzName].FourHundredStatusRange),
 		metadata.AttributeNginxStatusRange4xx,
 		lzName,
 		metadata.AttributeNginxZoneTypeLOCATION)
 
 	lzm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(lz.Responses.Responses5xx)-lzm.PreviousLocationZoneResponses[lzName].FiveHundredStatusRange,
+		metricsutil.Increase(
+			int64(lz.Responses.Responses5xx), lzm.PreviousLocationZoneResponses[lzName].FiveHundredStatusRange),
 		metadata.AttributeNginxStatusRange5xx,
 		lzName,
 		metadata.AttributeNginxZoneTypeLOCATION)

internal/collector/nginxplusreceiver/record/server_zone_metrics.go

@@ -6,6 +6,7 @@
 package record
 
 import (
+	"github.com/nginx/agent/v3/internal/collector/metricsutil"
 	"github.com/nginx/agent/v3/internal/collector/nginxplusreceiver/internal/metadata"
 	plusapi "github.com/nginx/nginx-plus-go-client/v3/client"
 	"go.opentelemetry.io/collector/pdata/pcommon"
@@ -45,7 +46,7 @@ func (szm *ServerZoneMetrics) RecordServerZoneMetrics(stats *plusapi.Stats, now
 		szm.mb.RecordNginxHTTPRequestsDataPoint(now, int64(sz.Requests), szName, metadata.AttributeNginxZoneTypeSERVER)
 
 		szm.mb.RecordNginxHTTPRequestCountDataPoint(now,
-			int64(sz.Requests)-szm.PreviousServerZoneRequests[szName],
+			metricsutil.Increase(int64(sz.Requests), szm.PreviousServerZoneRequests[szName]),
 			szName,
 			metadata.AttributeNginxZoneTypeSERVER,
 		)
@@ -98,31 +99,36 @@ func (szm *ServerZoneMetrics) recordServerZoneHTTPMetrics(sz plusapi.ServerZone,
 
 	// Response Count Status
 	szm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(sz.Responses.Responses1xx)-szm.PreviousServerZoneResponses[szName].OneHundredStatusRange,
+		metricsutil.Increase(
+			int64(sz.Responses.Responses1xx), szm.PreviousServerZoneResponses[szName].OneHundredStatusRange),
 		metadata.AttributeNginxStatusRange1xx,
 		szName,
 		metadata.AttributeNginxZoneTypeSERVER)
 
 	szm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(sz.Responses.Responses2xx)-szm.PreviousServerZoneResponses[szName].TwoHundredStatusRange,
+		metricsutil.Increase(
+			int64(sz.Responses.Responses2xx), szm.PreviousServerZoneResponses[szName].TwoHundredStatusRange),
 		metadata.AttributeNginxStatusRange2xx,
 		szName,
 		metadata.AttributeNginxZoneTypeSERVER)
 
 	szm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(sz.Responses.Responses3xx)-szm.PreviousServerZoneResponses[szName].ThreeHundredStatusRange,
+		metricsutil.Increase(
+			int64(sz.Responses.Responses3xx), szm.PreviousServerZoneResponses[szName].ThreeHundredStatusRange),
 		metadata.AttributeNginxStatusRange3xx,
 		szName,
 		metadata.AttributeNginxZoneTypeSERVER)
 
 	szm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(sz.Responses.Responses4xx)-szm.PreviousServerZoneResponses[szName].FourHundredStatusRange,
+		metricsutil.Increase(
+			int64(sz.Responses.Responses4xx), szm.PreviousServerZoneResponses[szName].FourHundredStatusRange),
 		metadata.AttributeNginxStatusRange4xx,
 		szName,
 		metadata.AttributeNginxZoneTypeSERVER)
 
 	szm.mb.RecordNginxHTTPResponseCountDataPoint(now,
-		int64(sz.Responses.Responses5xx)-szm.PreviousServerZoneResponses[szName].FiveHundredStatusRange,
+		metricsutil.Increase(
+			int64(sz.Responses.Responses5xx), szm.PreviousServerZoneResponses[szName].FiveHundredStatusRange),
 		metadata.AttributeNginxStatusRange5xx,
 		szName,
 		metadata.AttributeNginxZoneTypeSERVER)

internal/collector/nginxreceiver/internal/scraper/stubstatus/stub_status_scraper.go

@@ -23,6 +23,7 @@ import (
 	"go.opentelemetry.io/collector/receiver"
 	"go.uber.org/zap"
 
+	"github.com/nginx/agent/v3/internal/collector/metricsutil"
 	"github.com/nginx/agent/v3/internal/collector/nginxreceiver/internal/config"
 	"github.com/nginx/agent/v3/internal/collector/nginxreceiver/internal/metadata"
 )
@@ -36,7 +37,7 @@ type NginxStubStatusScraper struct {
 	rb               *metadata.ResourceBuilder
 	settings         receiver.Settings
 	init             sync.Once
-	previousRequests int
+	previousRequests int64
 }
 
 func NewScraper(
@@ -124,7 +125,7 @@ func (s *NginxStubStatusScraper) Scrape(context.Context) (pmetric.Metrics, error
 			return
 		}
 
-		s.previousRequests = int(stats.Requests)
+		s.previousRequests = stats.Requests
 	})
 
 	// Init client in scrape method in case there are transient errors in the constructor.
@@ -146,8 +147,8 @@ func (s *NginxStubStatusScraper) Scrape(context.Context) (pmetric.Metrics, error
 
 	s.mb.RecordNginxHTTPRequestsDataPoint(now, stats.Requests)
 
-	s.mb.RecordNginxHTTPRequestCountDataPoint(now, int64(int(stats.Requests)-s.previousRequests))
-	s.previousRequests = int(stats.Requests)
+	s.mb.RecordNginxHTTPRequestCountDataPoint(now, metricsutil.Increase(stats.Requests, s.previousRequests))
+	s.previousRequests = stats.Requests
 
 	s.mb.RecordNginxHTTPConnectionsDataPoint(
 		now,