feat: expose Live message size limit to frontend (#100169)

Developers using Grafana Live need to know whether a message is too
big to be sent over the Grafana Live websocket. Since this limit
is configurable, it is useful to expose it to the frontend.

This commit adds a new field to the frontend settings,
`liveMessageSizeLimit`, which the frontend can use to access the
limit configured in the backend.

Relates to #99770.

packages/grafana-data/src/types/config.ts

@@ -199,6 +199,7 @@ export interface GrafanaConfig {
   trustedTypesDefaultPolicyEnabled: boolean;
   cspReportOnlyEnabled: boolean;
   liveEnabled: boolean;
+  liveMessageSizeLimit: number;
   /** @deprecated Use `theme2` instead. */
   theme: GrafanaTheme;
   theme2: GrafanaTheme2;

packages/grafana-runtime/src/config.ts

@@ -107,6 +107,7 @@ export class GrafanaBootConfig implements GrafanaConfig {
   trustedTypesDefaultPolicyEnabled = false;
   cspReportOnlyEnabled = false;
   liveEnabled = true;
+  liveMessageSizeLimit = 65536;
   /** @deprecated Use `theme2` instead. */
   theme: GrafanaTheme;
   theme2: GrafanaTheme2;

pkg/api/dtos/frontend_settings.go

@@ -167,6 +167,7 @@ type FrontendSettingsDTO struct {
 	JwtHeaderName        string                           `json:"jwtHeaderName"`
 	JwtUrlLogin          bool                             `json:"jwtUrlLogin"`
 	LiveEnabled          bool                             `json:"liveEnabled"`
+	LiveMessageSizeLimit int                              `json:"liveMessageSizeLimit"`
 	AutoAssignOrg        bool                             `json:"autoAssignOrg"`
 
 	VerifyEmailEnabled  bool `json:"verifyEmailEnabled"`

pkg/api/frontendsettings.go

@@ -194,6 +194,7 @@ func (hs *HTTPServer) getFrontendSettings(c *contextmodel.ReqContext) (*dtos.Fro
 		JwtHeaderName:                       hs.Cfg.JWTAuth.HeaderName,
 		JwtUrlLogin:                         hs.Cfg.JWTAuth.URLLogin,
 		LiveEnabled:                         hs.Cfg.LiveMaxConnections != 0,
+		LiveMessageSizeLimit:                hs.Cfg.LiveMessageSizeLimit,
 		AutoAssignOrg:                       hs.Cfg.AutoAssignOrg,
 		VerifyEmailEnabled:                  hs.Cfg.VerifyEmailEnabled,
 		SigV4AuthEnabled:                    hs.Cfg.SigV4AuthEnabled,