ci: enable golanglint "canonicalheader" linter (#2876)

.golangci.yml

@@ -4,6 +4,7 @@ linters:
     - asasalint
     - bidichk
     - bodyclose
+    - canonicalheader
     - contextcheck
     - copyloopvar
     - dogsled

cmd/admin/admin.go

@@ -89,11 +89,11 @@ func (a *Admin) startServer() {
 }
 
 func (a *Admin) APISD(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("content-type", "application/json")
+	w.Header().Set("Content-Type", "application/json")
 	if a.httpSD.AuthBasic.Username != "" {
 		user, pass, ok := r.BasicAuth()
 		if !ok || !a.verifyAuth(user, pass) {
-			w.Header().Set("WWW-Authenticate", `Basic realm="api"`)
+			w.Header().Set("Www-Authenticate", `Basic realm="api"`)
 			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}

cmd/collectors/storagegrid/rest/client.go

@@ -198,7 +198,7 @@ func (c *Client) getRest(request string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	c.request.Header.Set("accept", "application/json")
+	c.request.Header.Set("Accept", "application/json")
 	c.request.Header.Set("Authorization", "Bearer "+c.token)
 	return c.invoke()
 }
@@ -373,7 +373,7 @@ func (c *Client) fetchTokenWithAuthRetry() error {
 		if err != nil {
 			return err
 		}
-		req.Header.Set("accept", "application/json")
+		req.Header.Set("Accept", "application/json")
 		req.Header.Set("Content-Type", "application/json")
 
 		// send request to server

cmd/exporters/prometheus/httpd.go

@@ -97,7 +97,7 @@ func (p *Prometheus) denyAccess(w http.ResponseWriter, r *http.Request) {
 
 	p.Logger.Debug().Msgf("(httpd) denied request [%s] (%s)", r.RequestURI, r.RemoteAddr)
 	w.WriteHeader(http.StatusForbidden)
-	w.Header().Set("content-type", "text/plain")
+	w.Header().Set("Content-Type", "text/plain")
 	_, err := w.Write([]byte("403 Forbidden"))
 	if err != nil {
 		p.Logger.Error().Stack().Err(err).Msg("error")
@@ -136,7 +136,7 @@ func (p *Prometheus) ServeMetrics(w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.WriteHeader(http.StatusOK)
-	w.Header().Set("content-type", "text/plain")
+	w.Header().Set("Content-Type", "text/plain")
 	_, err := w.Write(bytes.Join(data, []byte("\n")))
 	if err != nil {
 		p.Logger.Error().Err(err).Msg("write metrics")
@@ -273,7 +273,7 @@ func (p *Prometheus) ServeInfo(w http.ResponseWriter, r *http.Request) {
 	bodyFlat := fmt.Sprintf(htmlTemplate, poller, poller, poller, numCollectors, numObjects, numMetrics, strings.Join(body, "\n\n"))
 
 	w.WriteHeader(http.StatusOK)
-	w.Header().Set("content-type", "text/html")
+	w.Header().Set("Content-Type", "text/html")
 	_, err := w.Write([]byte(bodyFlat))
 	if err != nil {
 		p.Logger.Error().Stack().Err(err).Msg("error")

cmd/tools/rest/client.go

@@ -127,7 +127,7 @@ func (c *Client) GetRest(request string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	c.request.Header.Set("accept", "application/json")
+	c.request.Header.Set("Accept", "application/json")
 	pollerAuth, err := c.auth.GetPollerAuth()
 	if err != nil {
 		return nil, err

pkg/api/ontapi/zapi/client.go

@@ -93,7 +93,7 @@ func New(poller *conf.Poller, c *auth.Credentials) (*Client, error) {
 		return nil, err
 	}
 
-	request.Header.Set("Content-type", "text/xml")
+	request.Header.Set("Content-Type", "text/xml")
 	request.Header.Set("Charset", "utf-8")
 
 	transport, err = c.Transport(request)