feat(reporter/http): uses an interface for http client so users can p…

…lug other clients.

reporter/http/http.go

@@ -37,10 +37,15 @@ const (
 	defaultMaxBacklog    = 1000
 )
 
+// Client will do a request to the Zipkin HTTP Collector
+type Client interface {
+	Do(req *http.Request) (*http.Response, error)
+}
+
 // httpReporter will send spans to a Zipkin HTTP Collector using Zipkin V2 API.
 type httpReporter struct {
 	url           string
-	client        *http.Client
+	client        Client
 	logger        *log.Logger
 	batchInterval time.Duration
 	batchSize     int
@@ -200,7 +205,7 @@ func BatchInterval(d time.Duration) ReporterOption {
 }
 
 // Client sets a custom http client to use.
-func Client(client *http.Client) ReporterOption {
+func Client(client Client) ReporterOption {
 	return func(r *httpReporter) { r.client = client }
 }