Properly handle empty job and label values

prometheus/push/push.go

@@ -37,6 +37,7 @@ package push
 import (
 	"bytes"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"net/http"
@@ -56,6 +57,8 @@ const (
 	base64Suffix = "@base64"
 )
 
+var errJobEmpty = errors.New("job name is empty")
+
 // HTTPDoer is an interface for the one method of http.Client that is used by Pusher
 type HTTPDoer interface {
 	Do(*http.Request) (*http.Response, error)
@@ -80,14 +83,17 @@ type Pusher struct {
 }
 
 // New creates a new Pusher to push to the provided URL with the provided job
-// name. You can use just host:port or ip:port as url, in which case “http://”
-// is added automatically. Alternatively, include the schema in the
-// URL. However, do not include the “/metrics/jobs/…” part.
+// name (which must not be empty). You can use just host:port or ip:port as url,
+// in which case “http://” is added automatically. Alternatively, include the
+// schema in the URL. However, do not include the “/metrics/jobs/…” part.
 func New(url, job string) *Pusher {
 	var (
 		reg = prometheus.NewRegistry()
 		err error
 	)
+	if job == "" {
+		err = errJobEmpty
+	}
 	if !strings.Contains(url, "://") {
 		url = "http://" + url
 	}
@@ -267,7 +273,7 @@ func (p *Pusher) push(method string) error {
 		return err
 	}
 	defer resp.Body.Close()
-	// Pushgateway 0.10+ responds with StatusOK, earlier versions with StatusAccepted.
+	// Depending on version and configuration of the PGW, StatusOK or StatusAccepted may be returned.
 	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusAccepted {
 		body, _ := ioutil.ReadAll(resp.Body) // Ignore any further error as this is for an error message only.
 		return fmt.Errorf("unexpected status code %d while pushing to %s: %s", resp.StatusCode, p.fullURL(), body)
@@ -278,9 +284,11 @@ func (p *Pusher) push(method string) error {
 // fullURL assembles the URL used to push/delete metrics and returns it as a
 // string. The job name and any grouping label values containing a '/' will
 // trigger a base64 encoding of the affected component and proper suffixing of
-// the preceding component. If the component does not contain a '/' but other
-// special character, the usual url.QueryEscape is used for compatibility with
-// older versions of the Pushgateway and for better readability.
+// the preceding component. Similarly, an empty grouping label value will be
+// encoded as base64 just with a single `=` padding character (to avoid an empty
+// path component). If the component does not contain a '/' but other special
+// characters, the usual url.QueryEscape is used for compatibility with older
+// versions of the Pushgateway and for better readability.
 func (p *Pusher) fullURL() string {
 	urlComponents := []string{}
 	if encodedJob, base64 := encodeComponent(p.job); base64 {
@@ -299,9 +307,12 @@ func (p *Pusher) fullURL() string {
 }
 
 // encodeComponent encodes the provided string with base64.RawURLEncoding in
-// case it contains '/'. If not, it uses url.QueryEscape instead. It returns
-// true in the former case.
+// case it contains '/' and as "=" in case it is empty. If neither is the case,
+// it uses url.QueryEscape instead. It returns true in the former two cases.
 func encodeComponent(s string) (string, bool) {
+	if s == "" {
+		return "=", true
+	}
 	if strings.Contains(s, "/") {
 		return base64.RawURLEncoding.EncodeToString([]byte(s)), true
 	}

prometheus/push/push_test.go

@@ -176,6 +176,36 @@ func TestPush(t *testing.T) {
 		t.Error("unexpected path:", lastPath)
 	}
 
+	// Empty label value triggers special base64 encoding.
+	if err := New(pgwOK.URL, "testjob").
+		Grouping("empty", "").
+		Collector(metric1).
+		Collector(metric2).
+		Push(); err != nil {
+		t.Fatal(err)
+	}
+	if lastMethod != http.MethodPut {
+		t.Errorf("got method %q for Push, want %q", lastMethod, http.MethodPut)
+	}
+	if !bytes.Equal(lastBody, wantBody) {
+		t.Errorf("got body %v, want %v", lastBody, wantBody)
+	}
+	if lastPath != "/metrics/job/testjob/empty@base64/=" {
+		t.Error("unexpected path:", lastPath)
+	}
+
+	// Empty job name results in error.
+	if err := New(pgwErr.URL, "").
+		Collector(metric1).
+		Collector(metric2).
+		Push(); err == nil {
+		t.Error("push with empty job succeded")
+	} else {
+		if got, want := err, errJobEmpty; got != want {
+			t.Errorf("got error %q, want %q", got, want)
+		}
+	}
+
 	// Push some Collectors with a broken PGW.
 	if err := New(pgwErr.URL, "testjob").
 		Collector(metric1).
@@ -251,5 +281,4 @@ func TestPush(t *testing.T) {
 	if lastPath != "/metrics/job/testjob/a/x/b/y" && lastPath != "/metrics/job/testjob/b/y/a/x" {
 		t.Error("unexpected path:", lastPath)
 	}
-
 }