request: provide observability over HTTP request latency (#848)

exchanges/request/options.go

@@ -20,3 +20,10 @@ func WithRetryPolicy(p RetryPolicy) RequesterOption {
 		r.retryPolicy = p
 	}
 }
+
+// WithReporter configures the reporter for a Requester.
+func WithReporter(rep Reporter) RequesterOption {
+	return func(r *Requester) {
+		r.reporter = rep
+	}
+}

exchanges/request/report.go

@@ -0,0 +1,17 @@
+package request
+
+import (
+	"time"
+)
+
+// Reporter interface groups observability functionality over
+// HTTP request latency.
+type Reporter interface {
+	Latency(name, method, path string, t time.Duration)
+}
+
+// SetupGlobalReporter sets a reporter interface to be used
+// for all exchange requests
+func SetupGlobalReporter(r Reporter) {
+	globalReporter = r
+}

exchanges/request/request.go

@@ -39,6 +39,7 @@ func New(name string, httpRequester *http.Client, opts ...RequesterOption) *Requ
 		retryPolicy: DefaultRetryPolicy,
 		maxRetries:  MaxRetryAttempts,
 		timedLock:   timedmutex.NewTimedMutex(DefaultMutexLockTimeout),
+		reporter:    globalReporter,
 	}
 
 	for _, o := range opts {
@@ -150,7 +151,14 @@ func (r *Requester) doRequest(ctx context.Context, endpoint EndpointLimit, newRe
 			}
 		}
 
+		start := time.Now()
+
 		resp, err := r.HTTPClient.Do(req)
+
+		if r.reporter != nil {
+			r.reporter.Latency(r.Name, p.Method, p.Path, time.Since(start))
+		}
+
 		if retry, checkErr := r.retryPolicy(resp, err); checkErr != nil {
 			return checkErr
 		} else if retry {

exchanges/request/request_types.go

@@ -23,12 +23,14 @@ const (
 var (
 	MaxRequestJobs   = DefaultMaxRequestJobs
 	MaxRetryAttempts = DefaultMaxRetryAttempts
+	globalReporter   Reporter
 )
 
 // Requester struct for the request client
 type Requester struct {
 	HTTPClient         *http.Client
 	limiter            Limiter
+	reporter           Reporter
 	Name               string
 	UserAgent          string
 	maxRetries         int