From b20cf0bede4b543d720231b5de7c97c0955e3fe2 Mon Sep 17 00:00:00 2001
From: Bora Tanrikulu <me@bora.sh>
Date: Tue, 27 Jan 2026 18:29:34 +0300
Subject: [PATCH] [SC-23705] fix(sematext): prevent field name corruption on
 re-processing
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The fallback in Rename.Process() was using ChangeNames(key) where key
included the measurement prefix. This caused field names to accumulate
prefixes when metrics were re-processed:

  BEFORE: measurement="etcd", field="slow_requests" → "etcd.slow.requests"
  AFTER:  measurement="etcd", field="slow_requests" → "slow.requests"

For mapped fields (apache, nginx, etc.) there is no change - they use
fieldReplaces mappings. The fix ensures idempotency: processing a metric
multiple times no longer corrupts field names.
---
 plugins/outputs/sematext/processors/rename.go |  4 +++-
 .../sematext/processors/rename_test.go        | 24 ++++++++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/plugins/outputs/sematext/processors/rename.go b/plugins/outputs/sematext/processors/rename.go
index aa7dbbdcbd272..6e0b5fbaaa36c 100644
--- a/plugins/outputs/sematext/processors/rename.go
+++ b/plugins/outputs/sematext/processors/rename.go
@@ -229,7 +229,9 @@ func (r *Rename) Process(points []telegraf.Metric) []telegraf.Metric {
 
 			replace, ok := fieldReplaces[key]
 			if !ok {
-				replace = ChangeNames(key)
+				// Use field.Key directly to avoid prepending measurement name.
+				// This prevents corruption on re-processing and ensures idempotency.
+				replace = ChangeNames(field.Key)
 			}
 			// we can't remove the fields
 			// while iterating because it
diff --git a/plugins/outputs/sematext/processors/rename_test.go b/plugins/outputs/sematext/processors/rename_test.go
index 8f8e335f5ca10..3a729d4fd7630 100644
--- a/plugins/outputs/sematext/processors/rename_test.go
+++ b/plugins/outputs/sematext/processors/rename_test.go
@@ -25,7 +25,7 @@ func TestRename(t *testing.T) {
 	assert.Equal(t, "apache", results[0].Name())
 	assert.Equal(t, "php", results[1].Name())
 	assert.Equal(t, "workers.dns", results[2].FieldList()[0].Key)
-	assert.Equal(t, "etcd.slow.requests", results[3].FieldList()[0].Key)
+	assert.Equal(t, "slow.requests", results[3].FieldList()[0].Key)
 	assert.Equal(t, "fpm.requests.slow", results[4].FieldList()[0].Key)
 	assert.Equal(t, "mongo", results[5].Name())
 	assert.Equal(t, "mongodb_col_stats.ok", results[5].FieldList()[0].Key)
@@ -34,6 +34,28 @@ func TestRename(t *testing.T) {
 	assert.Equal(t, "mongodb_shard_stats.in_use", results[8].FieldList()[0].Key)
 }
 
+func TestRenameIdempotent(t *testing.T) {
+	r := Rename{}
+
+	// Process a metric multiple times - field names should remain stable
+	m := newMetric("apache", nil, map[string]interface{}{"scboard_dnslookup": 120})
+
+	// First pass
+	results := r.Process([]telegraf.Metric{m})
+	assert.Equal(t, "apache", results[0].Name())
+	assert.Equal(t, "workers.dns", results[0].FieldList()[0].Key)
+
+	// Second pass - should NOT corrupt field names
+	results = r.Process(results)
+	assert.Equal(t, "apache", results[0].Name())
+	assert.Equal(t, "workers.dns", results[0].FieldList()[0].Key, "Field should remain 'workers.dns', not 'apache.workers.dns'")
+
+	// Third pass - still stable
+	results = r.Process(results)
+	assert.Equal(t, "apache", results[0].Name())
+	assert.Equal(t, "workers.dns", results[0].FieldList()[0].Key, "Field should remain 'workers.dns' after multiple passes")
+}
+
 func newMetric(name string, tags map[string]string, fields map[string]interface{}) telegraf.Metric {
 	if tags == nil {
 		tags = map[string]string{}