[prometheusreceiver] Enable proto negotiation (open-telemetry#27030)

Exposes the protobuf negotiation flag for the scrape manager.
open-telemetry#27027

---------

Co-authored-by: David Ashpole <[email protected]>

.chloggen/prometheus-receiver-proto-negotiation-option.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusreceiver
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: add a new flag, enable_protobuf_negotiation, which enables protobuf negotiation when scraping prometheus clients
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [27027]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/prometheusreceiver/config.go

@@ -52,6 +52,10 @@ type Config struct {
  // that requires that all keys present in the config actually exist on the
  // structure, ie.: it will error if an unknown key is present.
  ConfigPlaceholder interface{} `mapstructure:"config"`
+
+ // EnableProtobufNegotiation allows the collector to set the scraper option for
+ // protobuf negotiation when conferring with a prometheus client.
+ EnableProtobufNegotiation bool `mapstructure:"enable_protobuf_negotiation"`
 }
 
 type targetAllocator struct {

receiver/prometheusreceiver/config_test.go

@@ -41,6 +41,7 @@ func TestLoadConfig(t *testing.T) {
  assert.Equal(t, time.Duration(r1.PrometheusConfig.ScrapeConfigs[0].ScrapeInterval), 5*time.Second)
  assert.Equal(t, r1.UseStartTimeMetric, true)
  assert.Equal(t, r1.TrimMetricSuffixes, true)
+ assert.Equal(t, r1.EnableProtobufNegotiation, true)
  assert.Equal(t, r1.StartTimeMetricRegex, "^(.+_)*process_start_time_seconds$")
  assert.True(t, r1.ReportExtraScrapeMetrics)
 

receiver/prometheusreceiver/metrics_receiver.go

@@ -267,8 +267,9 @@ func (r *pReceiver) initPrometheusComponents(ctx context.Context, host component
  }
 
  r.scrapeManager = scrape.NewManager(&scrape.Options{
- PassMetadataInContext: true,
- ExtraMetrics: r.cfg.ReportExtraScrapeMetrics,
+ PassMetadataInContext: true,
+ EnableProtobufNegotiation: r.cfg.EnableProtobufNegotiation,
+ ExtraMetrics: r.cfg.ReportExtraScrapeMetrics,
  HTTPClientOptions: []commonconfig.HTTPClientOption{
  commonconfig.WithUserAgent(r.settings.BuildInfo.Command + "/" + r.settings.BuildInfo.Version),
  },

receiver/prometheusreceiver/testdata/config.yaml

@@ -4,6 +4,7 @@ prometheus/customname:
  use_start_time_metric: true
  start_time_metric_regex: '^(.+_)*process_start_time_seconds$'
  report_extra_scrape_metrics: true
+ enable_protobuf_negotiation: true
  target_allocator:
  endpoint: http:https://my-targetallocator-service
  interval: 30s