Implement Clients with throttling and metrics

client.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"net/http"
+	"time"
+)
+
+// Client is an http.Client with rate limiting and time series instrumentation.
+type Client struct {
+	cli      http.Client
+	qps      uint
+	codes    []uint64
+	timings  []time.Duration
+	bytesOut []int64
+	bytesIn  []int64
+}
+
+func NewClient(qps uint) *Client {
+	return &Client{
+		cli:      http.Client{},
+		qps:      qps,
+		codes:    []uint64{},
+		timings:  []time.Duration{},
+		bytesOut: []int64{},
+		bytesIn:  []int64{},
+	}
+}
+
+// Drill loops over the passed reqs channel and executes each request.
+// It is throttled to the qps specified in the initializer
+func (c *Client) Drill(reqs chan *http.Request) {
+	throttle := time.Tick(time.Duration(1e9 / c.qps))
+	for req := range reqs {
+		<-throttle
+		go c.Do(req)
+	}
+}
+
+// Do executes the passed http.Request and saves some metrics
+// (timings, bytesIn, bytesOut, codes)
+func (c *Client) Do(req *http.Request) (*http.Response, error) {
+	began := time.Now()
+	resp, err := c.cli.Do(req)
+	c.timings = append(c.timings, time.Since(began))
+	c.bytesOut = append(c.bytesOut, req.ContentLength)
+	c.bytesIn = append(c.bytesIn, resp.ContentLength)
+	c.codes[resp.StatusCode]++
+	return resp, err
+}