push.go: add ability to cancel periodic push via passed context

push.go

@@ -2,6 +2,8 @@ package metrics
 
 import (
 	"bytes"
+	"context"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -32,6 +34,8 @@ type PushOptions struct {
 
 // InitPushWithOptions sets up periodic push for globally registered metrics to the given pushURL with the given interval.
 //
+// The periodic push is stopped when ctx is canceled.
+//
 // If pushProcessMetrics is set to true, then 'process_*' and `go_*` metrics are also pushed to pushURL.
 //
 // opts may contain additional configuration options if non-nil.
@@ -44,11 +48,11 @@ type PushOptions struct {
 //
 // It is OK calling InitPushWithOptions multiple times with different pushURL -
 // in this case metrics are pushed to all the provided pushURL urls.
-func InitPushWithOptions(pushURL string, interval time.Duration, pushProcessMetrics bool, opts *PushOptions) error {
+func InitPushWithOptions(ctx context.Context, pushURL string, interval time.Duration, pushProcessMetrics bool, opts *PushOptions) error {
 	writeMetrics := func(w io.Writer) {
 		WritePrometheus(w, pushProcessMetrics)
 	}
-	return initPushWithOptions(pushURL, interval, writeMetrics, opts)
+	return initPushWithOptions(ctx, pushURL, interval, writeMetrics, opts)
 }
 
 // InitPushProcessMetrics sets up periodic push for 'process_*' metrics to the given pushURL with the given interval.
@@ -95,6 +99,8 @@ func InitPush(pushURL string, interval time.Duration, extraLabels string, pushPr
 
 // InitPushWithOptions sets up periodic push for metrics from s to the given pushURL with the given interval.
 //
+// The periodic push is stopped when the ctx is canceled.
+//
 // opts may contain additional configuration options if non-nil.
 //
 // The metrics are pushed to pushURL in Prometheus text exposition format.
@@ -105,11 +111,11 @@ func InitPush(pushURL string, interval time.Duration, extraLabels string, pushPr
 //
 // It is OK calling InitPushWithOptions multiple times with different pushURL -
 // in this case metrics are pushed to all the provided pushURL urls.
-func (s *Set) InitPushWithOptions(pushURL string, interval time.Duration, opts *PushOptions) error {
+func (s *Set) InitPushWithOptions(ctx context.Context, pushURL string, interval time.Duration, opts *PushOptions) error {
 	writeMetrics := func(w io.Writer) {
 		s.WritePrometheus(w)
 	}
-	return initPushWithOptions(pushURL, interval, writeMetrics, opts)
+	return initPushWithOptions(ctx, pushURL, interval, writeMetrics, opts)
 }
 
 // InitPush sets up periodic push for metrics from s to the given pushURL with the given interval.
@@ -152,10 +158,10 @@ func InitPushExt(pushURL string, interval time.Duration, extraLabels string, wri
 	opts := &PushOptions{
 		ExtraLabels: extraLabels,
 	}
-	return initPushWithOptions(pushURL, interval, writeMetrics, opts)
+	return initPushWithOptions(context.Background(), pushURL, interval, writeMetrics, opts)
 }
 
-func initPushWithOptions(pushURL string, interval time.Duration, writeMetrics func(w io.Writer), opts *PushOptions) error {
+func initPushWithOptions(ctx context.Context, pushURL string, interval time.Duration, writeMetrics func(w io.Writer), opts *PushOptions) error {
 	// validate pushURL
 	pu, err := url.Parse(pushURL)
 	if err != nil {
@@ -183,7 +189,7 @@ func initPushWithOptions(pushURL string, interval time.Duration, writeMetrics fu
 	}
 
 	// validate Headers
-	var headers http.Header
+	headers := make(http.Header)
 	if opts != nil {
 		for _, h := range opts.Headers {
 			n := strings.IndexByte(h, ':')
@@ -219,7 +225,14 @@ func initPushWithOptions(pushURL string, interval time.Duration, writeMetrics fu
 		var bb bytes.Buffer
 		var tmpBuf []byte
 		zw := gzip.NewWriter(&bb)
-		for range ticker.C {
+		stopCh := ctx.Done()
+		for {
+			select {
+			case <-ticker.C:
+			case <-stopCh:
+				return
+			}
+
 			bb.Reset()
 			writeMetrics(&bb)
 			if len(extraLabels) > 0 {
@@ -244,7 +257,7 @@ func initPushWithOptions(pushURL string, interval time.Duration, writeMetrics fu
 			blockLen := bb.Len()
 			bytesPushedTotal.Add(blockLen)
 			pushBlockSize.Update(float64(blockLen))
-			req, err := http.NewRequest("GET", pushURL, &bb)
+			req, err := http.NewRequestWithContext(ctx, "GET", pushURL, &bb)
 			if err != nil {
 				panic(fmt.Errorf("BUG: metrics.push: cannot initialize request for metrics push to %q: %w", pushURLRedacted, err))
 			}
@@ -266,8 +279,10 @@ func initPushWithOptions(pushURL string, interval time.Duration, writeMetrics fu
 			resp, err := c.Do(req)
 			pushDuration.UpdateDuration(startTime)
 			if err != nil {
-				log.Printf("ERROR: metrics.push: cannot push metrics to %q: %s", pushURLRedacted, err)
+				if !errors.Is(err, context.Canceled) {
-				pushErrorsTotal.Inc()
+					log.Printf("ERROR: metrics.push: cannot push metrics to %q: %s", pushURLRedacted, err)
+					pushErrorsTotal.Inc()
+				}
 				continue
 			}
 			if resp.StatusCode/100 != 2 {

push_test.go

@@ -1,6 +1,12 @@
 package metrics
 
 import (
+	"bytes"
+	"compress/gzip"
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 )
@@ -59,3 +65,88 @@ func TestInitPushFailure(t *testing.T) {
 	f("http://foobar", time.Second, `{foo="bar"}`)
 	f("http://foobar", time.Second, `a{foo="bar"}`)
 }
+
+func TestInitPushWithOptions(t *testing.T) {
+	f := func(s *Set, opts *PushOptions, expectedHeaders, expectedData string) {
+		t.Helper()
+
+		var reqHeaders []byte
+		var reqData []byte
+		var reqErr error
+		doneCh := make(chan struct{})
+		firstRequest := true
+		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if firstRequest {
+				var bb bytes.Buffer
+				r.Header.WriteSubset(&bb, map[string]bool{
+					"Accept-Encoding": true,
+					"Content-Length":  true,
+					"User-Agent":      true,
+				})
+				reqHeaders = bb.Bytes()
+				reqData, reqErr = io.ReadAll(r.Body)
+				close(doneCh)
+				firstRequest = false
+			}
+		}))
+		ctx, cancel := context.WithCancel(context.Background())
+		if err := s.InitPushWithOptions(ctx, srv.URL, time.Millisecond, opts); err != nil {
+			t.Fatalf("unexpected error: %s", err)
+		}
+		select {
+		case <-time.After(5 * time.Second):
+			t.Fatalf("timeout!")
+		case <-doneCh:
+			// stop the periodic pusher
+			cancel()
+		}
+		if reqErr != nil {
+			t.Fatalf("unexpected error: %s", reqErr)
+		}
+		if opts == nil || !opts.DisableCompression {
+			zr, err := gzip.NewReader(bytes.NewBuffer(reqData))
+			if err != nil {
+				t.Fatalf("cannot initialize gzip reader: %s", err)
+			}
+			data, err := io.ReadAll(zr)
+			if err != nil {
+				t.Fatalf("cannot read data from gzip reader: %s", err)
+			}
+			if err := zr.Close(); err != nil {
+				t.Fatalf("unexpected error when closing gzip reader: %s", err)
+			}
+			reqData = data
+		}
+		if string(reqHeaders) != expectedHeaders {
+			t.Fatalf("unexpected request headers; got\n%s\nwant\n%s", reqHeaders, expectedHeaders)
+		}
+		if string(reqData) != expectedData {
+			t.Fatalf("unexpected data; got\n%s\nwant\n%s", reqData, expectedData)
+		}
+	}
+
+	s := NewSet()
+	c := s.NewCounter("foo")
+	c.Set(1234)
+	_ = s.NewGauge("bar", func() float64 {
+		return 42.12
+	})
+
+	// nil PushOptions
+	f(s, nil, "Content-Encoding: gzip\r\nContent-Type: text/plain\r\n", "bar 42.12\nfoo 1234\n")
+
+	// Disable compression on the pushed request body
+	f(s, &PushOptions{
+		DisableCompression: true,
+	}, "Content-Type: text/plain\r\n", "bar 42.12\nfoo 1234\n")
+
+	// Add extra labels
+	f(s, &PushOptions{
+		ExtraLabels: `label1="value1",label2="value2"`,
+	}, "Content-Encoding: gzip\r\nContent-Type: text/plain\r\n", `bar{label1="value1",label2="value2"} 42.12`+"\n"+`foo{label1="value1",label2="value2"} 1234`+"\n")
+
+	// Add extra headers
+	f(s, &PushOptions{
+		Headers: []string{"Foo: Bar", "baz:aaaa-bbb"},
+	}, "Baz: aaaa-bbb\r\nContent-Encoding: gzip\r\nContent-Type: text/plain\r\nFoo: Bar\r\n", "bar 42.12\nfoo 1234\n")
+}