[exporter/signalfx] Add option to send histograms in OTLP format (open-telemetry#31197)

**Description:**
This PR introduces a new config `send_otlp_histograms` to the `signalfx`
exporter. When the option is enabled. the exporter will send histograms
in OTLP format to the Splunk Observability backend.

**Link to tracking Issue:**
[26298](open-telemetry#26298)

Author: jinja2

.chloggen/signalfx-exp-otlp.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: exporter/signalfx
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Send histograms in otlp format with new config `send_otlp_histograms` option
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [26298]
+
+# (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: [user]

.chloggen/signalfx-recv-otlp.yaml

@@ -10,7 +10,7 @@ component: receiver/signalfx
 note: Accept otlp protobuf requests when content-type is "application/x-protobuf;format=otlp"
 
 # Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
-issues: [31052]
+issues: [26298]
 
 # (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.

exporter/signalfxexporter/README.md

@@ -145,7 +145,8 @@ will be replaced with a `_`.
   api_tls:
       ca_file: "/etc/opt/certs/ca.pem"
   ```
-- `drop_histogram_buckets`:  (default = `false`) if set to true, histogram buckets will not be translated into datapoints with `_bucket` suffix but will be dropped instead, only datapoints with `_sum`, `_count`, `_min` (optional) and `_max` (optional) suffixes will be sent.
+- `drop_histogram_buckets`:  (default = `false`) if set to true, histogram buckets will not be translated into datapoints with `_bucket` suffix but will be dropped instead, only datapoints with `_sum`, `_count`, `_min` (optional) and `_max` (optional) suffixes will be sent. Please note that this option does not apply to histograms sent in OTLP format with `send_otlp_histograms` enabled.
+- `send_otlp_histograms`: (default: `false`) if set to true, any histogram metrics receiver by the exporter will be sent to Splunk Observability backend in OTLP format without conversion to SignalFx format. This can only be enabled if the Splunk Observability environment (realm) has the new Histograms feature rolled out. Please note that histograms sent in OTLP format do not apply to the exporter configurations `include_metrics` and `exclude_metrics`.
 In addition, this exporter offers queued retry which is enabled by default.
 Information about queued retry configuration parameters can be found
 [here](https://github.com/open-telemetry/opentelemetry-collector/blob/main/exporter/exporterhelper/README.md).

exporter/signalfxexporter/config.go

@@ -112,7 +112,7 @@ type Config struct {
 
 	// ExcludeMetrics defines dpfilter.MetricFilters that will determine metrics to be
 	// excluded from sending to SignalFx backend. If translations enabled with
-	// TranslationRules options, the exclusion will be applie on translated metrics.
+	// TranslationRules options, the exclusion will be applied on translated metrics.
 	ExcludeMetrics []dpfilters.MetricFilter `mapstructure:"exclude_metrics"`
 
 	// IncludeMetrics defines dpfilter.MetricFilters to override exclusion any of metric.
@@ -134,6 +134,10 @@ type Config struct {
 	// Whether to drop  histogram bucket metrics dispatched to Splunk Observability.
 	// Default value is set to false.
 	DropHistogramBuckets bool `mapstructure:"drop_histogram_buckets"`
+
+	// Whether to send histogram metrics in OTLP format to Splunk Observability.
+	// Default value is set to false.
+	SendOTLPHistograms bool `mapstructure:"send_otlp_histograms"`
 }
 
 type DimensionClientConfig struct {

exporter/signalfxexporter/config_test.go

@@ -104,6 +104,7 @@ func TestLoadConfig(t *testing.T) {
 					},
 				},
 				NonAlphanumericDimensionChars: "_-.",
+				SendOTLPHistograms:            false,
 			},
 		},
 		{
@@ -263,6 +264,7 @@ func TestLoadConfig(t *testing.T) {
 					},
 				},
 				NonAlphanumericDimensionChars: "_-.",
+				SendOTLPHistograms:            true,
 			},
 		},
 	}

exporter/signalfxexporter/dpclient.go

@@ -17,12 +17,20 @@ import (
 	sfxpb "github.com/signalfx/com_signalfx_metrics_protobuf/model"
 	"go.opentelemetry.io/collector/consumer/consumererror"
 	"go.opentelemetry.io/collector/pdata/pmetric"
+	"go.opentelemetry.io/collector/pdata/pmetric/pmetricotlp"
 	"go.uber.org/zap"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/exporter/signalfxexporter/internal/translation"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/exporter/signalfxexporter/internal/utils"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/splunk"
 )
 
+const (
+	contentEncodingHeader   = "Content-Encoding"
+	contentTypeHeader       = "Content-Type"
+	otlpProtobufContentType = "application/x-protobuf;format=otlp"
+)
+
 type sfxClientBase struct {
 	ingestURL *url.URL
 	headers   map[string]string
@@ -58,6 +66,7 @@ type sfxDPClient struct {
 	logger                 *zap.Logger
 	accessTokenPassthrough bool
 	converter              *translation.MetricsConverter
+	sendOTLPHistograms     bool
 }
 
 func (s *sfxDPClient) pushMetricsData(
@@ -81,48 +90,55 @@ func (s *sfxDPClient) pushMetricsData(
 	// All metrics in the pmetric.Metrics will have the same access token because of the BatchPerResourceMetrics.
 	metricToken := s.retrieveAccessToken(rms.At(0))
 
+	// export SFx format
 	sfxDataPoints := s.converter.MetricsToSignalFxV2(md)
-	if s.logDataPoints {
-		for _, dp := range sfxDataPoints {
-			s.logger.Debug("Dispatching SFx datapoint", zap.Stringer("dp", dp))
+	if len(sfxDataPoints) > 0 {
+		droppedCount, err := s.pushMetricsDataForToken(ctx, sfxDataPoints, metricToken)
+		if err != nil {
+			return droppedCount, err
 		}
 	}
-	return s.pushMetricsDataForToken(ctx, sfxDataPoints, metricToken)
-}
 
-func (s *sfxDPClient) pushMetricsDataForToken(ctx context.Context, sfxDataPoints []*sfxpb.DataPoint, accessToken string) (int, error) {
-	body, compressed, err := s.encodeBody(sfxDataPoints)
-	if err != nil {
-		return len(sfxDataPoints), consumererror.NewPermanent(err)
+	// export any histograms in otlp if sendOTLPHistograms is true
+	if s.sendOTLPHistograms {
+		histogramData, metricCount := utils.GetHistograms(md)
+		if metricCount > 0 {
+			droppedCount, err := s.pushOTLPMetricsDataForToken(ctx, histogramData, metricToken)
+			if err != nil {
+				return droppedCount, err
+			}
+		}
 	}
 
+	return 0, nil
+
+}
+
+func (s *sfxDPClient) postData(ctx context.Context, body io.Reader, headers map[string]string) error {
 	datapointURL := *s.ingestURL
 	if !strings.HasSuffix(datapointURL.Path, "v2/datapoint") {
 		datapointURL.Path = path.Join(datapointURL.Path, "v2/datapoint")
 	}
 	req, err := http.NewRequestWithContext(ctx, "POST", datapointURL.String(), body)
 	if err != nil {
-		return len(sfxDataPoints), consumererror.NewPermanent(err)
+		return consumererror.NewPermanent(err)
 	}
 
+	// Set the headers configured in sfxDPClient
 	for k, v := range s.headers {
 		req.Header.Set(k, v)
 	}
 
-	// Override access token in headers map if it's non empty.
-	if accessToken != "" {
-		req.Header.Set(splunk.SFxAccessTokenHeader, accessToken)
-	}
-
-	if compressed {
-		req.Header.Set("Content-Encoding", "gzip")
+	// Set any extra headers passed by the caller
+	for k, v := range headers {
+		req.Header.Set(k, v)
 	}
 
 	// TODO: Mark errors as partial errors wherever applicable when, partial
 	// error for metrics is available.
 	resp, err := s.client.Do(req)
 	if err != nil {
-		return len(sfxDataPoints), err
+		return err
 	}
 
 	defer func() {
@@ -132,7 +148,39 @@ func (s *sfxDPClient) pushMetricsDataForToken(ctx context.Context, sfxDataPoints
 
 	err = splunk.HandleHTTPCode(resp)
 	if err != nil {
-		return len(sfxDataPoints), err
+		return err
+	}
+	return nil
+}
+
+func (s *sfxDPClient) pushMetricsDataForToken(ctx context.Context, sfxDataPoints []*sfxpb.DataPoint, accessToken string) (int, error) {
+
+	if s.logDataPoints {
+		for _, dp := range sfxDataPoints {
+			s.logger.Debug("Dispatching SFx datapoint", zap.Stringer("dp", dp))
+		}
+	}
+
+	body, compressed, err := s.encodeBody(sfxDataPoints)
+	dataPointCount := len(sfxDataPoints)
+	if err != nil {
+		return dataPointCount, consumererror.NewPermanent(err)
+	}
+
+	headers := make(map[string]string)
+
+	// Override access token in headers map if it's non empty.
+	if accessToken != "" {
+		headers[splunk.SFxAccessTokenHeader] = accessToken
+	}
+
+	if compressed {
+		headers[contentEncodingHeader] = "gzip"
+	}
+
+	err = s.postData(ctx, body, headers)
+	if err != nil {
+		return dataPointCount, err
 	}
 	return 0, nil
 }
@@ -160,3 +208,61 @@ func (s *sfxDPClient) retrieveAccessToken(md pmetric.ResourceMetrics) string {
 	}
 	return ""
 }
+
+func (s *sfxDPClient) pushOTLPMetricsDataForToken(ctx context.Context, mh pmetric.Metrics, accessToken string) (int, error) {
+
+	dataPointCount := mh.DataPointCount()
+	if s.logDataPoints {
+		s.logger.Debug("Count of metrics to send in OTLP format",
+			zap.Int("resource metrics", mh.ResourceMetrics().Len()),
+			zap.Int("metrics", mh.MetricCount()),
+			zap.Int("data points", dataPointCount))
+		buf, err := metricsMarshaler.MarshalMetrics(mh)
+		if err != nil {
+			s.logger.Error("Failed to marshal metrics for logging otlp histograms", zap.Error(err))
+		} else {
+			s.logger.Debug("Dispatching OTLP metrics", zap.String("pmetrics", string(buf)))
+		}
+	}
+
+	body, compressed, err := s.encodeOTLPBody(mh)
+	if err != nil {
+		return dataPointCount, consumererror.NewPermanent(err)
+	}
+
+	headers := make(map[string]string)
+
+	// Set otlp content-type header
+	headers[contentTypeHeader] = otlpProtobufContentType
+
+	// Override access token in headers map if it's non-empty.
+	if accessToken != "" {
+		headers[splunk.SFxAccessTokenHeader] = accessToken
+	}
+
+	if compressed {
+		headers[contentEncodingHeader] = "gzip"
+	}
+
+	s.logger.Debug("Sending metrics in OTLP format")
+
+	err = s.postData(ctx, body, headers)
+
+	if err != nil {
+		return dataPointCount, consumererror.NewMetrics(err, mh)
+	}
+
+	return 0, nil
+}
+
+func (s *sfxDPClient) encodeOTLPBody(md pmetric.Metrics) (bodyReader io.Reader, compressed bool, err error) {
+
+	tr := pmetricotlp.NewExportRequestFromMetrics(md)
+
+	body, err := tr.MarshalProto()
+
+	if err != nil {
+		return nil, false, err
+	}
+	return s.getReader(body)
+}

exporter/signalfxexporter/exporter.go

@@ -84,6 +84,7 @@ func newSignalFxExporter(
 		config.IncludeMetrics,
 		config.NonAlphanumericDimensionChars,
 		config.DropHistogramBuckets,
+		!config.SendOTLPHistograms, // if SendOTLPHistograms is true, do not process histograms when converting to SFx
 	)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create metric converter: %w", err)
@@ -121,6 +122,7 @@ func (se *signalfxExporter) start(ctx context.Context, host component.Host) (err
 		logger:                 se.logger,
 		accessTokenPassthrough: se.config.AccessTokenPassthrough,
 		converter:              se.converter,
+		sendOTLPHistograms:     se.config.SendOTLPHistograms,
 	}
 
 	apiTLSCfg, err := se.config.APITLSSettings.LoadTLSConfig()