From 15fcfe60a95b2f7b05d115029f6237405ec4634e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luis=20Rasc=C3=A3o?= <luis.rascao@gmail.com>
Date: Fri, 17 Dec 2021 00:39:34 +0000
Subject: [PATCH] request: provide observability over HTTP request latency
 (#848)

---
 exchanges/request/options.go       |  7 +++++++
 exchanges/request/report.go        | 17 +++++++++++++++++
 exchanges/request/request.go       |  8 ++++++++
 exchanges/request/request_types.go |  2 ++
 4 files changed, 34 insertions(+)
 create mode 100644 exchanges/request/report.go

diff --git a/exchanges/request/options.go b/exchanges/request/options.go
index 7a86727e..51f16735 100644
--- a/exchanges/request/options.go
+++ b/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
+	}
+}
diff --git a/exchanges/request/report.go b/exchanges/request/report.go
new file mode 100644
index 00000000..8288c1a4
--- /dev/null
+++ b/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
+}
diff --git a/exchanges/request/request.go b/exchanges/request/request.go
index 6cccfae1..15c77938 100644
--- a/exchanges/request/request.go
+++ b/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 {
diff --git a/exchanges/request/request_types.go b/exchanges/request/request_types.go
index 166fa6c0..6279d8fc 100644
--- a/exchanges/request/request_types.go
+++ b/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