server: Allow --debug mode to reload the browser window

To ease debugging, allow the landing page to be loaded multiple times.

Normally, to catch mistakes and bugs, we do not permit this since we
would have anywhere to report on a second or third run of test results
from the same clientId, since we will have closed that stream and
finished the report on that client already.

Author: Krinkle

src/server.js

@@ -463,21 +463,25 @@ class ControlServer {
     if (!filePath.startsWith(this.root)) {
       // Disallow outside directory traversal
       this.logger.debug('respond_static_deny', url.pathname);
-      return this.serveError(resp, 403, 'Forbidden');
+      return this.serveError(resp, 403, 'HTTP 403: QTap respond_static_deny');
     }
 
     const clientId = url.searchParams.get('qtap_clientId');
     if (clientId !== null) {
       // Serve the testfile from any URL path, as chosen by launchBrowser()
       const browser = this.browsers.get(clientId);
-      if (!browser) {
-        this.logger.debug('browser_connected_unknown', clientId);
-        return this.serveError(resp, 403, 'Forbidden');
+      if (browser) {
+        browser.logger.debug('browser_connected', `${browser.getDisplayName()} connected! Serving test file.`);
+        this.eventbus.emit('online', { clientId });
+      } else if (this.debugMode) {
+        // Allow users to reload the page when in --debug mode.
+        // Note that do not handle more TAP results after a given test run has finished.
+        this.logger.debug('browser_reload_debug', clientId);
+      } else {
+        this.logger.debug('browser_unknown_clientId', clientId);
+        return this.serveError(resp, 403, 'HTTP 403: QTap browser_unknown_clientId.\n\nThis clientId was likely already served and cannot be repeated. Run qtap with --debug to bypass this restriction.');
       }
 
-      browser.logger.debug('browser_connected', `${browser.getDisplayName()} connected! Serving test file.`);
-      this.eventbus.emit('online', { clientId });
-
       const testFileResp = await this.getTestFile(clientId);
       for (const [name, value] of testFileResp.headers) {
         resp.setHeader(name, value);
@@ -490,13 +494,15 @@ class ControlServer {
       resp.end();
 
       // Count proxying the test file toward connectTimeout, not idleTimeout.
-      browser.clientIdleActive = performance.now();
+      if (browser) {
+        browser.clientIdleActive = performance.now();
+      }
       return;
     }
 
     if (!fs.existsSync(filePath)) {
       this.logger.debug('respond_static_notfound', filePath);
-      return this.serveError(resp, 404, 'Not Found');
+      return this.serveError(resp, 404, 'HTTP 404: QTap respond_static_notfound');
     }
 
     this.logger.debug('respond_static_pipe', filePath);