accept bert and json content-type

shovel plugin does not support bert encoding.
If only bert is accepted it fails with error 406.
Now if bert is enabled, bert is preferred but json is also accepted.

shovel support  kbudde#121

decoder.go

@@ -32,9 +32,9 @@ type RabbitReply interface {
 }
 
 // MakeReply instantiates the apropriate reply parser for a given
-// reply and the current configuration.
-func MakeReply(config rabbitExporterConfig, body []byte) (RabbitReply, error) {
-	if isCapEnabled(config, rabbitCapBert) {
+// reply and the content-type header
+func MakeReply(contentType string, body []byte) (RabbitReply, error) {
+	if contentType == "application/bert" {
 		return makeBERTReply(body)
 	}
 	return makeJSONReply(body)

exporter_overview.go

@@ -70,12 +70,12 @@ func (e exporterOverview) NodeInfo() NodeInfo {
 }
 
 func (e *exporterOverview) Collect(ctx context.Context, ch chan<- prometheus.Metric) error {
-	body, err := apiRequest(config, "overview")
+	body, contentType, err := apiRequest(config, "overview")
 	if err != nil {
 		return err
 	}
 
-	reply, err := MakeReply(config, body)
+	reply, err := MakeReply(contentType, body)
 	if err != nil {
 		return err
 	}

rabbitClient.go

@@ -38,7 +38,7 @@ func initClient() {
 
 }
 
-func apiRequest(config rabbitExporterConfig, endpoint string) ([]byte, error) {
+func apiRequest(config rabbitExporterConfig, endpoint string) ([]byte, string, error) {
 	var args string
 	enabled, exists := config.RabbitCapabilities[rabbitCapNoSort]
 	if enabled && exists {
@@ -48,7 +48,7 @@ func apiRequest(config rabbitExporterConfig, endpoint string) ([]byte, error) {
 	req, err := http.NewRequest("GET", config.RabbitURL+"/api/"+endpoint+args, nil)
 	if err != nil {
 		log.WithFields(log.Fields{"error": err, "host": config.RabbitURL}).Error("Error while constructing rabbitHost request")
-		return nil, errors.New("Error while constructing rabbitHost request")
+		return nil, "", errors.New("Error while constructing rabbitHost request")
 	}
 
 	req.SetBasicAuth(config.RabbitUsername, config.RabbitPassword)
@@ -62,25 +62,26 @@ func apiRequest(config rabbitExporterConfig, endpoint string) ([]byte, error) {
 			status = resp.StatusCode
 		}
 		log.WithFields(log.Fields{"error": err, "host": config.RabbitURL, "statusCode": status}).Error("Error while retrieving data from rabbitHost")
-		return nil, errors.New("Error while retrieving data from rabbitHost")
+		return nil, "", errors.New("Error while retrieving data from rabbitHost")
 	}
 
 	body, err := ioutil.ReadAll(resp.Body)
 	resp.Body.Close()
+	content := resp.Header.Get("Content-type")
 	if err != nil {
-		return nil, err
+		return nil, "", err
 	}
 	log.WithFields(log.Fields{"body": string(body), "endpoint": endpoint}).Debug("Metrics loaded")
 
-	return body, nil
+	return body, content, nil
 }
 
 func loadMetrics(config rabbitExporterConfig, endpoint string) (RabbitReply, error) {
-	body, err := apiRequest(config, endpoint)
+	body, content, err := apiRequest(config, endpoint)
 	if err != nil {
 		return nil, err
 	}
-	return MakeReply(config, body)
+	return MakeReply(content, body)
 }
 
 func getStatsInfo(config rabbitExporterConfig, apiEndpoint string, labels []string) ([]StatsInfo, error) {
@@ -99,12 +100,12 @@ func getStatsInfo(config rabbitExporterConfig, apiEndpoint string, labels []stri
 func getMetricMap(config rabbitExporterConfig, apiEndpoint string) (MetricMap, error) {
 	var overview MetricMap
 
-	body, err := apiRequest(config, apiEndpoint)
+	body, content, err := apiRequest(config, apiEndpoint)
 	if err != nil {
 		return overview, err
 	}
 
-	reply, err := MakeReply(config, body)
+	reply, err := MakeReply(content, body)
 	if err != nil {
 		return overview, err
 	}
@@ -114,7 +115,7 @@ func getMetricMap(config rabbitExporterConfig, apiEndpoint string) (MetricMap, e
 
 func acceptContentType(config rabbitExporterConfig) string {
 	if isCapEnabled(config, rabbitCapBert) {
-		return "application/bert"
+		return "application/bert, application/json;q=0.1"
 	}
 	return "application/json"
 }