Handle Prom/OpenMetrics upgrade

Signed-off-by: Martin Baillie <[email protected]>

github/path_metrics.go

@@ -10,8 +10,8 @@ import (
 	"github.com/hashicorp/vault/sdk/logical"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/collectors"
+	"github.com/prometheus/client_golang/prometheus/collectors/version"
 	"github.com/prometheus/common/expfmt"
-	"github.com/prometheus/common/version"
 )
 
 const prefixMetrics = "vault_github_token"
@@ -96,17 +96,18 @@ func (b *backend) pathMetricsRead(
 	buf := new(bytes.Buffer)
 	defer buf.Reset()
 
+	text := expfmt.NewFormat(expfmt.TypeTextPlain)
 	// Write metrics as Prometheus exposition format.
 	for _, mf := range metricsFamilies {
-		if err = expfmt.NewEncoder(buf, expfmt.FmtText).Encode(mf); err != nil {
+		if err = expfmt.NewEncoder(buf, text).Encode(mf); err != nil {
 			res.Data[logical.HTTPRawBody] = fmt.Sprintf("%s: %s", errFailedMetricsEncoding, err)
 
 			return res, fmt.Errorf("%s: %w", errFailedMetricsEncoding, err)
 		}
 	}
 
 	res.Data[logical.HTTPStatusCode] = http.StatusOK
-	res.Data[logical.HTTPContentType] = string(expfmt.FmtText)
+	res.Data[logical.HTTPContentType] = string(text)
 	res.Data[logical.HTTPRawBody] = buf.Bytes()
 
 	return res, nil

github/path_metrics_test.go

@@ -26,7 +26,7 @@ func TestBackend_PathMetricsRead(t *testing.T) {
 
 		assert.NilError(t, err)
 		assert.Assert(t, statusCode(res.Data[logical.HTTPStatusCode].(int)).Successful())
-		assert.Equal(t, res.Data[logical.HTTPContentType], string(expfmt.FmtText))
+		assert.Equal(t, res.Data[logical.HTTPContentType], string(expfmt.NewFormat(expfmt.TypeTextPlain)))
 		assert.Assert(t, strings.Contains(
 			string(res.Data[logical.HTTPRawBody].([]byte)),
 			fmt.Sprintf("%s_build_info", prefixMetrics)),