emit a basepath event on first run

src/api/dev.ts

@@ -6,7 +6,6 @@ import * as ports from 'port-authority';
 import mkdirp from 'mkdirp';
 import rimraf from 'rimraf';
 import format_messages from 'webpack-format-messages';
-import prettyMs from 'pretty-ms';
 import { locations } from '../config';
 import { EventEmitter } from 'events';
 import { create_routes, create_main_manifests, create_compilers, create_serviceworker_manifest } from '../core';
@@ -172,6 +171,14 @@ class Watcher extends EventEmitter {
 						}, process.env),
 						stdio: ['ipc']
 					});
+
+					this.proc.on('message', message => {
+						if (message.__sapper__ && message.event === 'basepath') {
+							this.emit('basepath', {
+								basepath: message.basepath
+							});
+						}
+					});
 				});
 			}
 		});

src/api/export.ts

@@ -66,7 +66,7 @@ async function execute(emitter: EventEmitter, {
 	const saved = new Set();
 
 	proc.on('message', message => {
-		if (!message.__sapper__) return;
+		if (!message.__sapper__ || message.event !== 'file') return;
 
 		let file = new URL(message.url, origin).pathname.slice(1);
 		let { body } = message;

src/middleware.ts

@@ -58,6 +58,8 @@ export default function middleware({ App, routes, store }: {
 
 	const client_assets = JSON.parse(fs.readFileSync(path.join(output, 'client_assets.json'), 'utf-8'));
 
+	let emitted_basepath = false;
+
 	const middleware = compose_handlers([
 		(req: Req, res: ServerResponse, next: () => void) => {
 			if (req.baseUrl === undefined) {
@@ -66,6 +68,16 @@ export default function middleware({ App, routes, store }: {
 					: '';
 			}
 
+			if (!emitted_basepath && process.send) {
+				process.send({
+					__sapper__: true,
+					event: 'basepath',
+					basepath: req.baseUrl
+				});
+
+				emitted_basepath = true;
+			}
+
 			if (req.path === undefined) {
 				req.path = req.url.replace(/\?.*/, '');
 			}
@@ -276,6 +288,7 @@ function get_route_handler(chunks: Record<string, string>, App: Component, route
 						if (process.send) {
 							process.send({
 								__sapper__: true,
+								event: 'file',
 								url: req.url,
 								method: req.method,
 								status: 200,
@@ -315,6 +328,7 @@ function get_route_handler(chunks: Record<string, string>, App: Component, route
 
 								process.send({
 									__sapper__: true,
+									event: 'file',
 									url: req.url,
 									method: req.method,
 									status: res.statusCode,