Add HTTP client request histogram function (#43)

http/client/client.go

@@ -0,0 +1,30 @@
+package client
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"strconv"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/weaveworks/common/instrument"
+	oldcontext "golang.org/x/net/context"
+)
+
+// TimeRequestHistogram performs an HTTP client request and records the duration in a histogram
+func TimeRequestHistogram(ctx context.Context, operation string, metric *prometheus.HistogramVec, client *http.Client, request *http.Request) (*http.Response, error) {
+	var response *http.Response
+	doRequest := func(_ oldcontext.Context) error {
+		var err error
+		response, err = client.Do(request)
+		return err
+	}
+	toStatusCode := func(err error) string {
+		if err == nil {
+			return strconv.Itoa(response.StatusCode)
+		}
+		return "error"
+	}
+	err := instrument.TimeRequestHistogramStatus(ctx, fmt.Sprintf("%s %s", request.Method, operation), metric, toStatusCode, doRequest)
+	return response, err
+}