Support configurable HTTP user agent per exchange

exchanges/request/request.go

@@ -25,6 +25,7 @@ type Requester struct {
 	UnauthLimit   *RateLimit
 	AuthLimit     *RateLimit
 	Name          string
+	UserAgent     string
 	Cycle         time.Time
 	m             sync.Mutex
 	Jobs          chan Job
@@ -230,6 +231,10 @@ func (r *Requester) checkRequest(method, path string, body io.Reader, headers ma
 		req.Header.Add(k, v)
 	}
 
+	if r.UserAgent != "" && req.Header.Get("User-Agent") == "" {
+		req.Header.Add("User-Agent", r.UserAgent)
+	}
+
 	return req, nil
 }
 
@@ -245,7 +250,6 @@ func (r *Requester) DoRequest(req *http.Request, method, path string, headers ma
 		if r.RequiresRateLimiter() {
 			r.DecrementRequests(authRequest)
 		}
-
 		return err
 	}
 	if resp == nil {