feat: PREP Notifications

Implements Per Resource Events notifications in Node Solid Server.

Implementation Notes:
+ Uses `--experimental-require-module` to load esm packages natively. Requires node > 22.0.0. Start scripts and test invocations have been appropriately modified.
+ NSS converts strings into an older streaming format which was not being detected by Express-PREP. Express-PREP was modified to ask the user if the body provided is a stream, thus circumventing this issue.
+ Notifications are triggered from a common middleware, which is invoked after the response has been succesfully sent.
+ Uses Express PREP supplied default template for notifications.

Author: CxRes

bin/solid

@@ -1,3 +1,3 @@
-#!/usr/bin/env node
+#!/usr/bin/env -S node --experimental-require-module
 const startCli = require('./lib/cli')
 startCli()

bin/solid.js

@@ -1,3 +1,3 @@
-#!/usr/bin/env node
+#!/usr/bin/env -S node --experimental-require-module
 const startCli = require('./lib/cli')
 startCli()

lib/create-app.js

@@ -28,6 +28,11 @@ const ResourceMapper = require('./resource-mapper')
 const aclCheck = require('@solid/acl-check')
 const { version } = require('../package.json')
 
+const acceptEvents = require('express-accept-events').default
+const events = require('express-negotiate-events').default
+const eventID = require('express-prep/event-id').default
+const prep = require('express-prep').default
+
 const corsSettings = cors({
   methods: [
     'OPTIONS', 'HEAD', 'GET', 'PATCH', 'POST', 'PUT', 'DELETE'
@@ -61,6 +66,9 @@ function createApp (argv = {}) {
 
   const app = express()
 
+  // Add PREP support
+  app.use(acceptEvents, events, eventID, prep)
+
   initAppLocals(app, argv, ldp)
   initHeaders(app)
   initViews(app, configPath)

lib/handlers/get.js

@@ -17,6 +17,7 @@ const translate = require('../utils.js').translate
 const error = require('../http-error')
 
 const RDFs = require('../ldp').mimeTypesAsArray()
+const isRdf = require('../ldp').mimeTypeIsRdf
 
 async function handler (req, res, next) {
   const ldp = req.app.locals.ldp
@@ -110,15 +111,39 @@ async function handler (req, res, next) {
   }
 
   // If request accepts the content-type we found
+  // if (stream && negotiator.mediaType([contentType])) {
+  //   res.setHeader('Content-Type', contentType)
+  //   if (contentRange) {
+  //     const headers = { 'Content-Range': contentRange, 'Accept-Ranges': 'bytes', 'Content-Length': chunksize }
+  //     res.writeHead(206, headers)
+  //     return stream.pipe(res)
+  //   } else {
+  //     return stream.pipe(res)
+  //   }
+  // }
+
   if (stream && negotiator.mediaType([contentType])) {
-    res.setHeader('Content-Type', contentType)
+    let headers = {
+      'Content-Type': contentType
+    }
     if (contentRange) {
-      const headers = { 'Content-Range': contentRange, 'Accept-Ranges': 'bytes', 'Content-Length': chunksize }
-      res.writeHead(206, headers)
-      return stream.pipe(res)
-    } else {
-      return stream.pipe(res)
+      headers = {
+        ...headers,
+        'Content-Range': contentRange,
+        'Accept-Ranges': 'bytes',
+        'Content-Length': chunksize
+      }
+      res.statusCode = 206
     }
+
+    if (isRdf(contentType) && !res.sendEvents({
+      config: { prep: '' },
+      body: stream,
+      isBodyStream: true,
+      headers
+    })) return
+    res.set(headers)
+    return stream.pipe(res)
   }
 
   // If it is not in our RDFs we can't even translate,
@@ -130,6 +155,14 @@ async function handler (req, res, next) {
     // Translate from the contentType found to the possibleRDFType desired
     const data = await translate(stream, baseUri, contentType, possibleRDFType)
     debug(req.originalUrl + ' translating ' + contentType + ' -> ' + possibleRDFType)
+    const headers = {
+      'Content-Type': possibleRDFType
+    }
+    if (isRdf(contentType) && !res.sendEvents({
+      config: { prep: '' },
+      body: data,
+      headers
+    })) return
     res.setHeader('Content-Type', possibleRDFType)
     res.send(data)
     return next()

lib/handlers/notify.js

@@ -0,0 +1,12 @@
+module.exports = handler
+
+function handler (req, res, next) {
+  res.events.prep.trigger({
+    generateNotifications () {
+      return res.events.prep.defaultNotification({
+        ...(res.method === 'POST') && { location: res.getHeader('Content-Location') }
+      })
+    }
+  })
+  next()
+}

lib/ldp-middleware.js

@@ -10,6 +10,7 @@ const del = require('./handlers/delete')
 const patch = require('./handlers/patch')
 const index = require('./handlers/index')
 const copy = require('./handlers/copy')
+const notify = require('./handlers/notify')
 
 function LdpMiddleware (corsSettings) {
   const router = express.Router('/')
@@ -24,9 +25,9 @@ function LdpMiddleware (corsSettings) {
   router.copy('/*', allow('Write'), copy)
   router.get('/*', index, allow('Read'), header.addPermissions, get)
   router.post('/*', allow('Append'), post)
-  router.patch('/*', allow('Append'), patch)
+  router.patch('/*', allow('Append'), patch, notify)
   router.put('/*', allow('Append'), put)
-  router.delete('/*', allow('Write'), del)
+  router.delete('/*', allow('Write'), del, notify)
 
   return router
 }