fix: add Last-Modified header to GET and HEAD responses

Only sent when access is granted (200 path), using the resource's
mtime from fs.stat, as required by the Solid protocol.

Fixes #1793

Author: AlyNotMe

lib/handlers/get.mjs

@@ -76,19 +76,22 @@ export default async function handler (req, res, next) {
   let container
   let contentRange
   let chunksize
+  let mtime
 
   if (ret) {
     stream = ret.stream
     contentType = ret.contentType
     container = ret.container
     contentRange = ret.contentRange
     chunksize = ret.chunksize
+    mtime = ret.mtime
   }
 
   // Till here it must exist
   if (!includeBody) {
     debug('HEAD only')
     res.setHeader('Content-Type', ret.contentType)
+    if (mtime) res.setHeader('Last-Modified', mtime.toUTCString())
     return res.status(200).send('OK')
   }
 
@@ -118,7 +121,8 @@ export default async function handler (req, res, next) {
   // If request accepts the content-type we found
   if (stream && negotiator.mediaType([contentType])) {
     let headers = {
-      'Content-Type': contentType
+      'Content-Type': contentType,
+      ...(mtime && { 'Last-Modified': mtime.toUTCString() })
     }
 
     if (contentRange) {
@@ -160,6 +164,9 @@ export default async function handler (req, res, next) {
       headers
     })) return
     res.setHeader('Content-Type', possibleRDFType)
+    if (mtime) {
+      res.setHeader('Last-Modified', mtime.toUTCString())
+    }
     res.send(data)
     return next()
   } catch (err) {

lib/ldp.mjs

@@ -451,7 +451,7 @@ class LDP {
     }
 
     if (!options.includeBody) {
-      return { stream: stats, contentType, container: stats.isDirectory() }
+      return { stream: stats, contentType, container: stats.isDirectory(), mtime: stats.mtime }
     }
 
     if (stats.isDirectory()) {
@@ -465,7 +465,7 @@ class LDP {
         throw err
       }
       const stream = stringToStream(data)
-      return { stream, contentType, container: true }
+      return { stream, contentType, container: true, mtime: stats.mtime }
     } else {
       let chunksize, contentRange, start, end
       if (options.range) {
@@ -487,7 +487,7 @@ class LDP {
           })
           .on('open', function () {
             debug.handlers(`GET -- Reading ${pathLocal}`)
-            return resolve({ stream, contentType, container: false, contentRange, chunksize })
+            return resolve({ stream, contentType, container: false, contentRange, chunksize, mtime: stats.mtime })
           })
       }))
     }

test/integration/header-test.mjs

@@ -68,6 +68,23 @@ describe('Header handler', () => {
     })
   })
 
+  describe('Last-Modified', () => {
+    describeHeaderTest('read/append for the public', {
+      resource: '/public-ra',
+      headers: {
+        'Last-Modified': /^\w{3}, \d{2} \w{3} \d{4} \d{2}:\d{2}:\d{2} GMT$/
+      }
+    })
+
+    describe('on a HEAD request', () => {
+      it('has a Last-Modified header', async () => {
+        const { headers } = await request.head('/public-ra')
+        expect(headers).to.have.property('last-modified')
+        expect(headers['last-modified']).to.match(/^\w{3}, \d{2} \w{3} \d{4} \d{2}:\d{2}:\d{2} GMT$/)
+      })
+    })
+  })
+
   function describeHeaderTest (label, { resource, headers }) {
     describe(`a resource that is ${label}`, () => {
       // Retrieve the response headers