[MM-61077] Fix errcheck issues in server/channels/web/static.go (#29285)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/.golangci.yml

@@ -190,7 +190,6 @@ issues:
         channels/utils/license_test.go|\
         channels/web/oauth_test.go|\
         channels/web/saml.go|\
-        channels/web/static.go|\
         channels/web/web_test.go|\
         channels/web/webhook.go|\
         cmd/mattermost/commands/cmdtestlib.go|\

server/channels/web/static.go

@@ -64,7 +64,12 @@ func root(c *Context, w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Cache-Control", "no-store")
 		data := renderUnsupportedBrowser(c.AppContext, r)
 
-		c.App.Srv().TemplatesContainer().Render(w, "unsupported_browser", data)
+		err := c.App.Srv().TemplatesContainer().Render(w, "unsupported_browser", data)
+		if err != nil {
+			c.Logger.Error("Failed to render template", mlog.Err(err))
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
 		return
 	}
 
@@ -78,7 +83,10 @@ func root(c *Context, w http.ResponseWriter, r *http.Request) {
 	staticDir, _ := fileutils.FindDir(model.ClientDir)
 	contents, err := os.ReadFile(filepath.Join(staticDir, "root.html"))
 	if err != nil {
-		http.Error(w, err.Error(), http.StatusNotFound)
+		c.Logger.Warn("Failed to read content from file",
+			mlog.String("file_path", filepath.Join(staticDir, "root.html")),
+			mlog.Err(err))
+		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
 
@@ -90,7 +98,11 @@ func root(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Content-Type", "text/html")
-	w.Write(contents)
+	if _, err = w.Write(contents); err != nil {
+		c.Logger.Warn("Failed to write content to HTTP reply", mlog.Err(err))
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
 }
 
 func staticFilesHandler(handler http.Handler) http.Handler {
@@ -135,7 +147,11 @@ func robotsHandler(w http.ResponseWriter, r *http.Request) {
 		http.NotFound(w, r)
 		return
 	}
-	w.Write(robotsTxt)
+	if _, err := w.Write(robotsTxt); err != nil {
+		mlog.Warn("Failed to write robots.txt", mlog.Err(err))
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
 }
 
 func unsupportedBrowserScriptHandler(w http.ResponseWriter, r *http.Request) {