Guarantee all WebApp handler functions run in a Fiber.

https://github.com/VeliovGroup/Meteor-Files/issues/538

packages/webapp/connect.js

@@ -0,0 +1,40 @@
+import npmConnect from "connect";
+
+export function connect(...connectArgs) {
+  const handlers = npmConnect.apply(this, connectArgs);
+  const originalUse = handlers.use;
+
+  // Wrap the handlers.use method so that any provided handler functions
+  // alway run in a Fiber.
+  handlers.use = function use(...useArgs) {
+    const { stack } = this;
+    const originalLength = stack.length;
+    const result = originalUse.apply(this, useArgs);
+
+    // If we just added anything to the stack, wrap each new entry.handle
+    // with a function that calls Promise.asyncApply to ensure the
+    // original handler runs in a Fiber.
+    for (let i = originalLength; i < stack.length; ++i) {
+      const entry = stack[i];
+      const originalHandle = entry.handle;
+
+      if (originalHandle.length >= 4) {
+        // If the original handle had four (or more) parameters, the
+        // wrapper must also have four parameters, since connect uses
+        // handle.length to dermine whether to pass the error as the first
+        // argument to the handle function.
+        entry.handle = function handle(err, req, res, next) {
+          return Promise.asyncApply(originalHandle, this, arguments);
+        };
+      } else {
+        entry.handle = function handle(req, res, next) {
+          return Promise.asyncApply(originalHandle, this, arguments);
+        };
+      }
+    }
+
+    return result;
+  };
+
+  return handlers;
+}

packages/webapp/webapp_server.js

@@ -7,7 +7,7 @@ import {
 } from "path";
 import { parse as parseUrl } from "url";
 import { createHash } from "crypto";
-import connect from "connect";
+import { connect } from "./connect.js";
 import compress from "compression";
 import cookieParser from "cookie-parser";
 import query from "qs-middleware";
@@ -687,9 +687,7 @@ function runWebAppServer() {
   // Serve static files from the manifest.
   // This is inspired by the 'static' middleware.
   app.use(function (req, res, next) {
-    Promise.resolve().then(() => {
-      WebAppInternals.staticFilesMiddleware(staticFiles, req, res, next);
-    });
+    WebAppInternals.staticFilesMiddleware(staticFiles, req, res, next);
   });
 
   // Core Meteor packages like dynamic-import can add handlers before
@@ -715,11 +713,10 @@ function runWebAppServer() {
   });
 
   app.use(function (req, res, next) {
-    Promise.resolve().then(() => {
-      if (! appUrl(req.url)) {
-        return next();
-      }
+    if (! appUrl(req.url)) {
+      return next();
 
+    } else {
       var headers = {
         'Content-Type': 'text/html; charset=utf-8'
       };
@@ -803,7 +800,7 @@ function runWebAppServer() {
         res.writeHead(500, headers);
         res.end();
       });
-    });
+    }
   });
 
   // Return 404 by default, if no other handlers serve this URL.