Add user agent header to outgoing prometheus remote write exporter ht…

…tp request (#2000)

Added User-Agent header to Prometheus Remote Write Exporter's outgoing http request. This allows endpoints to identify whether an incoming metric has come from an OTel Collector instance.

**Testing:**
Unit tests added conforming with existing tests to check headers.

**Documentation:**
No documentation has been added as it is for internal usage rather than customer usage.

Note: I am assuming here that the `VERSION` variable in the makefile will be set when we reach GA, as currently it is not and the version in the version package is just the default value of "latest"

exporter/prometheusremotewriteexporter/exporter.go

@@ -33,6 +33,7 @@ import (
 	"go.opentelemetry.io/collector/component/componenterror"
 	"go.opentelemetry.io/collector/consumer/pdata"
 	otlp "go.opentelemetry.io/collector/internal/data/opentelemetry-proto-gen/metrics/v1"
+	"go.opentelemetry.io/collector/internal/version"
 )
 
 // PrwExporter converts OTLP metrics to Prometheus remote write TimeSeries and sends them to a remote endpoint
@@ -233,6 +234,7 @@ func (prwe *PrwExporter) export(ctx context.Context, tsMap map[string]*prompb.Ti
 	httpReq.Header.Add("Content-Encoding", "snappy")
 	httpReq.Header.Set("Content-Type", "application/x-protobuf")
 	httpReq.Header.Set("X-Prometheus-Remote-Write-Version", "0.1.0")
+	httpReq.Header.Set("User-Agent", "OpenTelemetry-Collector/"+version.Version)
 
 	httpResp, err := prwe.client.Do(httpReq)
 	if err != nil {

exporter/prometheusremotewriteexporter/exporter_test.go

@@ -35,6 +35,7 @@ import (
 	"go.opentelemetry.io/collector/exporter/exporterhelper"
 	otlp "go.opentelemetry.io/collector/internal/data/opentelemetry-proto-gen/metrics/v1"
 	"go.opentelemetry.io/collector/internal/data/testdata"
+	"go.opentelemetry.io/collector/internal/version"
 )
 
 // Test_ NewPrwExporter checks that a new exporter instance with non-nil fields is initialized
@@ -143,6 +144,7 @@ func Test_export(t *testing.T) {
 		// Receives the http requests and unzip, unmarshals, and extracts TimeSeries
 		assert.Equal(t, "0.1.0", r.Header.Get("X-Prometheus-Remote-Write-Version"))
 		assert.Equal(t, "snappy", r.Header.Get("Content-Encoding"))
+		assert.Equal(t, "OpenTelemetry-Collector/"+version.Version, r.Header.Get("User-Agent"))
 		writeReq := &prompb.WriteRequest{}
 		unzipped := []byte{}
 
@@ -437,6 +439,7 @@ func Test_PushMetrics(t *testing.T) {
 		dest, err := snappy.Decode(buf, body)
 		assert.Equal(t, "0.1.0", r.Header.Get("x-prometheus-remote-write-version"))
 		assert.Equal(t, "snappy", r.Header.Get("content-encoding"))
+		assert.Equal(t, "OpenTelemetry-Collector/"+version.Version, r.Header.Get("user-agent"))
 		assert.NotNil(t, r.Header.Get("tenant-id"))
 		require.NoError(t, err)
 		wr := &prompb.WriteRequest{}