HTTP Client: Outgoing tracing middleware (#34466)

Following #33439 this adds support for outgoing tracing middleware 
in HTTP client provider.

Fixes #24004

pkg/infra/httpclient/httpclientprovider/tracing_middleware.go

@@ -0,0 +1,62 @@
+package httpclientprovider
+
+import (
+	"net/http"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend/httpclient"
+	"github.com/grafana/grafana/pkg/infra/log"
+	"github.com/opentracing/opentracing-go"
+	"github.com/opentracing/opentracing-go/ext"
+)
+
+const (
+	TracingMiddlewareName   = "tracing"
+	httpContentLengthTagKey = "http.content_length"
+)
+
+func TracingMiddleware(logger log.Logger) httpclient.Middleware {
+	return httpclient.NamedMiddlewareFunc(TracingMiddlewareName, func(opts httpclient.Options, next http.RoundTripper) http.RoundTripper {
+		return httpclient.RoundTripperFunc(func(req *http.Request) (*http.Response, error) {
+			span, ctx := opentracing.StartSpanFromContext(req.Context(), "HTTP Outgoing Request")
+			defer span.Finish()
+
+			req = req.WithContext(ctx)
+			for k, v := range opts.Labels {
+				span.SetTag(k, v)
+			}
+
+			if err := opentracing.GlobalTracer().Inject(
+				span.Context(),
+				opentracing.HTTPHeaders,
+				opentracing.HTTPHeadersCarrier(req.Header)); err != nil {
+				logger.Error("Failed to inject span context instance", "err", err)
+			}
+
+			res, err := next.RoundTrip(req)
+
+			ext.HTTPUrl.Set(span, req.URL.String())
+			ext.HTTPMethod.Set(span, req.Method)
+			ext.SpanKind.Set(span, ext.SpanKindRPCClientEnum)
+
+			if err != nil {
+				ext.Error.Set(span, true)
+				return res, err
+			}
+
+			if res != nil {
+				// we avoid measuring contentlength less than zero because it indicates
+				// that the content size is unknown. https://godoc.org/github.com/badu/http#Response
+				if res.ContentLength > 0 {
+					span.SetTag(httpContentLengthTagKey, res.ContentLength)
+				}
+
+				ext.HTTPStatusCode.Set(span, uint16(res.StatusCode))
+				if res.StatusCode >= 400 {
+					ext.Error.Set(span, true)
+				}
+			}
+
+			return res, err
+		})
+	})
+}