Merge pull request #21011 from overleaf/ls-serve-static-wrapper

add a wrapper for serve static to handle premature close error

GitOrigin-RevId: 8128702d9340a893624061d07bf0da15ea457f43

services/web/app/src/infrastructure/ServeStaticWrapper.mjs

@@ -0,0 +1,34 @@
+import express from 'express'
+import { plainTextResponse } from './Response.js'
+
+/*
+    This wrapper is implemented specifically to handle "Premature Close" errors.
+    These errors occur when the client cancels a request while static assets are being loaded.
+    This issue is beyond our control, it can result in unnecessary log noise.
+    Therefore, this wrapper is added to handle such errors.
+*/
+function serveStaticWrapper(root, options) {
+  const serveStatic = express.static(root, options)
+  return (req, res, next) => {
+    serveStatic(req, res, error => {
+      if (!error) {
+        return next()
+      }
+
+      if (error.code !== 'ERR_STREAM_PREMATURE_CLOSE') {
+        return next(error)
+      }
+
+      req.logger.addFields({ err: error })
+      req.logger.setLevel('debug')
+      if (res.headersSent) {
+        res.end()
+      } else {
+        res.status(400)
+        plainTextResponse(res, 'Premature close')
+      }
+    })
+  }
+}
+
+export default serveStaticWrapper

services/web/app/src/infrastructure/Server.mjs

@@ -37,6 +37,7 @@ import noCache from 'nocache'
 import os from 'os'
 import http from 'http'
 import { fileURLToPath } from 'url'
+import serveStaticWrapper from './ServeStaticWrapper.mjs'
 
 const sessionsRedisClient = UserSessionsRedis.client()
 
@@ -120,10 +121,13 @@ if (Settings.exposeHostname) {
 }
 
 webRouter.use(
-  express.static(fileURLToPath(new URL('../../../public', import.meta.url)), {
+  serveStaticWrapper(
+    fileURLToPath(new URL('../../../public', import.meta.url)),
+    {
       maxAge: STATIC_CACHE_AGE,
       setHeaders: csp.removeCSPHeaders,
-  })
+    }
+  )
 )
 
 app.set('views', fileURLToPath(new URL('../../views', import.meta.url)))

services/web/test/unit/src/infrastructure/ServeStaticWrapperTests.mjs

@@ -0,0 +1,62 @@
+import { strict as esmock } from 'esmock'
+import { expect } from 'chai'
+import Path from 'node:path'
+import { fileURLToPath } from 'node:url'
+import sinon from 'sinon'
+import MockResponse from '../helpers/MockResponse.js'
+import MockRequest from '../helpers/MockRequest.js'
+
+const __dirname = fileURLToPath(new URL('.', import.meta.url))
+const modulePath = Path.join(
+  __dirname,
+  '../../../../app/src/infrastructure/ServeStaticWrapper'
+)
+
+describe('ServeStaticWrapperTests', function () {
+  let error = null
+
+  beforeEach(async function () {
+    this.req = new MockRequest()
+    this.res = new MockResponse()
+    this.express = {
+      static: () => (req, res, next) => {
+        if (error) {
+          next(error)
+        } else {
+          next()
+        }
+      },
+    }
+    this.serveStaticWrapper = await esmock(modulePath, {
+      express: this.express,
+    })
+  })
+
+  this.afterEach(() => {
+    error = null
+  })
+
+  it('Premature close error thrown', async function () {
+    error = new Error()
+    error.code = 'ERR_STREAM_PREMATURE_CLOSE'
+    const middleware = this.serveStaticWrapper('test_folder', {})
+    const next = sinon.stub()
+    middleware(this.req, this.res, next)
+    expect(next.called).to.be.false
+  })
+
+  it('No error thrown', async function () {
+    const middleware = this.serveStaticWrapper('test_folder', {})
+    const next = sinon.stub()
+    middleware(this.req, this.res, next)
+    expect(next).to.be.calledWith()
+  })
+
+  it('Other error thrown', async function () {
+    error = new Error()
+    const middleware = this.serveStaticWrapper('test_folder', {})
+    const next = sinon.stub()
+    middleware(this.req, this.res, next)
+    expect(next).to.be.calledWith(error)
+  })
+})