API connection status notifications

CHANGELOG.md

@@ -6,6 +6,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 - [#1240](https://github.com/plotly/dash/pull/1240) Adds `callback_context` to clientside callbacks (e.g. `dash_clientside.callback_context.triggered`). Supports `triggered`, `inputs`, `inputs_list`, `states`, and `states_list`, all of which closely resemble their serverside cousins.
 
+### Changed
+- [#1237](https://github.com/plotly/dash/pull/1237) Closes [#920](https://github.com/plotly/dash/issues/920): Converts hot reload fetch failures into a server status indicator showing whether the latest fetch succeeded or failed. Callback fetch failures still appear as errors but have a clearer message.
+
 ## [1.12.0] - 2020-05-05
 ### Added
 - [#1228](https://github.com/plotly/dash/pull/1228) Adds control over firing callbacks on page (or layout chunk) load. Individual callbacks can have their initial calls disabled in their definition `@app.callback(..., prevent_initial_call=True)` and similar for `app.clientside_callback`. The app-wide default can also be changed with `app=Dash(prevent_initial_callbacks=True)`, then individual callbacks may disable this behavior.

dash-renderer/src/actions/api.js

@@ -30,43 +30,61 @@ const request = {GET, POST};
 
 export default function apiThunk(endpoint, method, store, id, body) {
     return (dispatch, getState) => {
-        const config = getState().config;
+        const {config} = getState();
         const url = `${urlBase(config)}${endpoint}`;
 
+        function setConnectionStatus(connected) {
+            if (getState().error.backEndConnected !== connected) {
+                dispatch({
+                    type: 'SET_CONNECTION_STATUS',
+                    payload: connected,
+                });
+            }
+        }
+
         dispatch({
             type: store,
             payload: {id, status: 'loading'},
         });
         return request[method](url, config.fetch, body)
-            .then(res => {
-                const contentType = res.headers.get('content-type');
-                if (
-                    contentType &&
-                    contentType.indexOf('application/json') !== -1
-                ) {
-                    return res.json().then(json => {
-                        dispatch({
-                            type: store,
-                            payload: {
-                                status: res.status,
-                                content: json,
-                                id,
-                            },
+            .then(
+                res => {
+                    setConnectionStatus(true);
+                    const contentType = res.headers.get('content-type');
+                    if (
+                        contentType &&
+                        contentType.indexOf('application/json') !== -1
+                    ) {
+                        return res.json().then(json => {
+                            dispatch({
+                                type: store,
+                                payload: {
+                                    status: res.status,
+                                    content: json,
+                                    id,
+                                },
+                            });
+                            return json;
                         });
-                        return json;
+                    }
+                    logWarningOnce(
+                        'Response is missing header: content-type: application/json'
+                    );
+                    return dispatch({
+                        type: store,
+                        payload: {
+                            id,
+                            status: res.status,
+                        },
                     });
+                },
+                () => {
+                    // fetch rejection - this means the request didn't return,
+                    // we don't get here from 400/500 errors, only network
+                    // errors or unresponsive servers.
+                    setConnectionStatus(false);
                 }
-                logWarningOnce(
-                    'Response is missing header: content-type: application/json'
-                );
-                return dispatch({
-                    type: store,
-                    payload: {
-                        id,
-                        status: res.status,
-                    },
-                });
-            })
+            )
             .catch(err => {
                 const message = 'Error from API call: ' + endpoint;
                 handleAsyncError(err, message, dispatch);

dash-renderer/src/actions/index.js

@@ -495,29 +495,37 @@ function handleServerside(config, payload, hooks) {
             headers: getCSRFHeader(),
             body: JSON.stringify(payload),
         })
-    ).then(res => {
-        const {status} = res;
-        if (status === STATUS.OK) {
-            return res.json().then(data => {
-                const {multi, response} = data;
-                if (hooks.request_post !== null) {
-                    hooks.request_post(payload, response);
-                }
+    ).then(
+        res => {
+            const {status} = res;
+            if (status === STATUS.OK) {
+                return res.json().then(data => {
+                    const {multi, response} = data;
+                    if (hooks.request_post !== null) {
+                        hooks.request_post(payload, response);
+                    }
 
-                if (multi) {
-                    return response;
-                }
+                    if (multi) {
+                        return response;
+                    }
 
-                const {output} = payload;
-                const id = output.substr(0, output.lastIndexOf('.'));
-                return {[id]: response.props};
-            });
-        }
-        if (status === STATUS.PREVENT_UPDATE) {
-            return {};
+                    const {output} = payload;
+                    const id = output.substr(0, output.lastIndexOf('.'));
+                    return {[id]: response.props};
+                });
+            }
+            if (status === STATUS.PREVENT_UPDATE) {
+                return {};
+            }
+            throw res;
+        },
+        () => {
+            // fetch rejection - this means the request didn't return,
+            // we don't get here from 400/500 errors, only network
+            // errors or unresponsive servers.
+            throw new Error('Callback failed: the server did not respond.');
         }
-        throw res;
-    });
+    );
 }
 
 const getVals = input =>

dash-renderer/src/components/error/FrontEnd/FrontEndErrorContainer.react.js

@@ -9,15 +9,16 @@ class FrontEndErrorContainer extends Component {
     }
 
     render() {
-        const errorsLength = this.props.errors.length;
+        const {errors, connected} = this.props;
+        const errorsLength = errors.length;
         if (errorsLength === 0) {
             return null;
         }
 
         const inAlertsTray = this.props.inAlertsTray;
         let cardClasses = 'dash-error-card dash-error-card--container';
 
-        const errorElements = this.props.errors.map((error, i) => {
+        const errorElements = errors.map((error, i) => {
             return <FrontEndError e={error} isListItem={true} key={i} />;
         });
         if (inAlertsTray) {
@@ -31,7 +32,7 @@ class FrontEndErrorContainer extends Component {
                         <strong className="test-devtools-error-count">
                             {errorsLength}
                         </strong>
-                        )
+                        ){connected ? null : '\u00a0 🚫 Server Unavailable'}
                     </div>
                 </div>
                 <div className="dash-error-card__list">{errorElements}</div>
@@ -42,6 +43,7 @@ class FrontEndErrorContainer extends Component {
 
 FrontEndErrorContainer.propTypes = {
     errors: PropTypes.array,
+    connected: PropTypes.bool,
     inAlertsTray: PropTypes.any,
 };
 

dash-renderer/src/components/error/GlobalErrorContainer.react.js

@@ -10,10 +10,14 @@ class UnconnectedGlobalErrorContainer extends Component {
     }
 
     render() {
-        const {error, graphs, children} = this.props;
+        const {config, error, graphs, children} = this.props;
         return (
             <div id="_dash-global-error-container">
-                <DebugMenu error={error} graphs={graphs}>
+                <DebugMenu
+                    error={error}
+                    graphs={graphs}
+                    hotReload={Boolean(config.hot_reload)}
+                >
                     <div id="_dash-app-content">{children}</div>
                 </DebugMenu>
             </div>
@@ -23,11 +27,13 @@ class UnconnectedGlobalErrorContainer extends Component {
 
 UnconnectedGlobalErrorContainer.propTypes = {
     children: PropTypes.object,
+    config: PropTypes.object,
     error: PropTypes.object,
     graphs: PropTypes.object,
 };
 
 const GlobalErrorContainer = connect(state => ({
+    config: state.config,
     error: state.error,
     graphs: state.graphs,
 }))(Radium(UnconnectedGlobalErrorContainer));

dash-renderer/src/components/error/GlobalErrorOverlay.react.js

@@ -11,13 +11,18 @@ export default class GlobalErrorOverlay extends Component {
     }
 
     render() {
-        const {visible, error, toastsEnabled} = this.props;
+        const {visible, error, errorsOpened} = this.props;
 
         let frontEndErrors;
-        if (toastsEnabled) {
+        if (errorsOpened) {
             const errors = concat(error.frontEnd, error.backEnd);
 
-            frontEndErrors = <FrontEndErrorContainer errors={errors} />;
+            frontEndErrors = (
+                <FrontEndErrorContainer
+                    errors={errors}
+                    connected={error.backEndConnected}
+                />
+            );
         }
         return (
             <div>
@@ -36,5 +41,5 @@ GlobalErrorOverlay.propTypes = {
     children: PropTypes.object,
     visible: PropTypes.bool,
     error: PropTypes.object,
-    toastsEnabled: PropTypes.any,
+    errorsOpened: PropTypes.any,
 };