From 9f01ea12b95521a7ec35b2c930a04a71183d560b Mon Sep 17 00:00:00 2001
From: Arthur Silva Sens <arthursens2005@gmail.com>
Date: Fri, 10 Jan 2025 15:47:08 -0300
Subject: [PATCH] Add default Fallback Scrape Config

Signed-off-by: Arthur Silva Sens <arthursens2005@gmail.com>
---
 receiver/prometheusreceiver/factory.go         |  9 +++++++++
 receiver/prometheusreceiver/factory_test.go    | 18 ++++++++++++++++++
 .../config_fallback_scrape_protocol.yaml       |  8 ++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 receiver/prometheusreceiver/testdata/config_fallback_scrape_protocol.yaml

diff --git a/receiver/prometheusreceiver/factory.go b/receiver/prometheusreceiver/factory.go
index 247ffb428cdd..bbb82a9442e9 100644
--- a/receiver/prometheusreceiver/factory.go
+++ b/receiver/prometheusreceiver/factory.go
@@ -63,6 +63,7 @@ func createMetricsReceiver(
 	nextConsumer consumer.Metrics,
 ) (receiver.Metrics, error) {
 	configWarnings(set.Logger, cfg.(*Config))
+	addDefaultFallbackScrapeProtocol(cfg.(*Config))
 	return newPrometheusReceiver(set, cfg.(*Config), nextConsumer), nil
 }
 
@@ -75,3 +76,11 @@ func configWarnings(logger *zap.Logger, cfg *Config) {
 		}
 	}
 }
+
+func addDefaultFallbackScrapeProtocol(cfg *Config) {
+	for _, sc := range cfg.PrometheusConfig.ScrapeConfigs {
+		if sc.ScrapeFallbackProtocol == "" {
+			sc.ScrapeFallbackProtocol = promconfig.PrometheusText1_0_0
+		}
+	}
+}
diff --git a/receiver/prometheusreceiver/factory_test.go b/receiver/prometheusreceiver/factory_test.go
index 2fe0592f7d2d..9f52e9310d20 100644
--- a/receiver/prometheusreceiver/factory_test.go
+++ b/receiver/prometheusreceiver/factory_test.go
@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"testing"
 
+	promconfig "github.com/prometheus/prometheus/config"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/collector/component"
@@ -62,3 +63,20 @@ func TestMultipleCreate(t *testing.T) {
 	require.NoError(t, secondRcvr.Start(context.Background(), host))
 	require.NoError(t, secondRcvr.Shutdown(context.Background()))
 }
+
+func TestDefaultFallbackScrapeProtocol(t *testing.T) {
+	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "config_fallback_scrape_protocol.yaml"))
+	require.NoError(t, err)
+	factory := NewFactory()
+	cfg := factory.CreateDefaultConfig()
+
+	sub, err := cm.Sub(component.NewIDWithName(metadata.Type, "").String())
+	require.NoError(t, err)
+	assert.NoError(t, sub.Unmarshal(cfg))
+
+	factory.CreateMetrics(context.Background(), receivertest.NewNopSettings(), cfg, consumertest.NewNop())
+	
+	// During receiver creation, scrapeconfig without fallback scrape protocol set, should be set to 'PrometheusText1.0.0'.
+	assert.Equal(t, promconfig.PrometheusText1_0_0, cfg.(*Config).PrometheusConfig.ScrapeConfigs[0].ScrapeFallbackProtocol)
+	assert.Equal(t, promconfig.OpenMetricsText1_0_0, cfg.(*Config).PrometheusConfig.ScrapeConfigs[1].ScrapeFallbackProtocol)
+}
diff --git a/receiver/prometheusreceiver/testdata/config_fallback_scrape_protocol.yaml b/receiver/prometheusreceiver/testdata/config_fallback_scrape_protocol.yaml
new file mode 100644
index 000000000000..1fd77527bc05
--- /dev/null
+++ b/receiver/prometheusreceiver/testdata/config_fallback_scrape_protocol.yaml
@@ -0,0 +1,8 @@
+prometheus:
+  config:
+    scrape_configs:
+      - job_name: test1
+        scrape_interval: 5s
+      - job_name: test2
+        scrape_interval: 5s
+        fallback_scrape_protocol: OpenMetricsText1.0.0