ACL should be set to Read Append only #16

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1. bourgeoa

   changed the title [-]ACL should be set to `Append` only[/-] [+]ACL should be set to `Read Append` only[/+] on Jan 10, 2026
2. melvincarvalho commented on Jan 11, 2026

   

   melvincarvalho

   on Jan 11, 2026

   Contributor

   More actions

   Deep Research Analysis: ACL Read Append

   Current State ✅

   The current solid-chat/app ACL setup is correct for public chats:

   # Public: Read + Append (can post, can't edit/delete others)
   <#public>
       a acl:Authorization ;
       acl:agentClass foaf:Agent ;
       acl:mode acl:Read, acl:Append .
   
   # Owner: Full control
   <#owner>
       a acl:Authorization ;
       acl:agent <owner-webid> ;
       acl:mode acl:Read, acl:Write, acl:Control .

   This aligns with the Solid Chat Specification.

   ---

   The Problem ⚠️

   Edit/Delete currently uses destructive SPARQL operations:

   // Edit - requires Write permission
   const updateQuery = `
     DELETE { <${msgUri}> sioc:content ?old }
     INSERT { <${msgUri}> sioc:content "new text" }
     WHERE { <${msgUri}> sioc:content ?old }
   `
   
   // Delete - requires Write permission  
   const deleteQuery = `DELETE DATA { ${triples} }`

   These operations won't work with Append-only ACLs because:

   • DELETE requires Write permission
   • Participants only have Append permission

   ---

   Solid Chat Spec Solution: Append-Only Patterns

   Use dct:replaces and schema:dateDeleted instead of destructive deletes:

   # Original message
   <#msg-123>
       a sioc:Post ;
       sioc:content "Hello" ;
       dct:created "2026-01-11T10:00:00Z" ;
       foaf:maker <https://alice.example/#me> .
   
   # "Delete" by appending (works with Append permission)
   <#msg-123-deleted>
       a sioc:Post ;
       dct:replaces <#msg-123> ;
       schema:dateDeleted "2026-01-11T12:00:00Z" ;
       foaf:maker <https://alice.example/#me> .
   
   # "Edit" by appending (works with Append permission)
   <#msg-123-edited>
       a sioc:Post ;
       dct:replaces <#msg-123> ;
       sioc:content "Hello (edited)" ;
       dct:created "2026-01-11T12:00:00Z" ;
       foaf:maker <https://alice.example/#me> .

   Benefits:

   • ✅ Works with Append-only ACLs
   • ✅ Maintains full audit trail
   • ✅ No destructive operations
   • ✅ Follows Solid Chat spec

   ---

   Security Comparison

   Permission	Post	Edit Own	Delete Own	Edit Others	Delete Others
   Read+Append	✅	✅ (append)	✅ (append)	❌	❌
   Read+Write	✅	✅	✅	⚠️ YES	⚠️ YES

   Security Risk: With Write permission, any authenticated user can delete/modify ANY message in the chat!

   ---

   Implementation Recommendations

   1. Refactor Delete to Append-Only

   // CURRENT (requires Write)
   async function deleteMessage(msgUri) {
     const deleteQuery = `DELETE DATA { ... }`
     await store.fetcher.webOperation('PATCH', doc, { body: deleteQuery })
   }
   
   // RECOMMENDED (works with Append)
   async function deleteMessage(msgUri, doc) {
     const deletionUri = `${doc.value}#deletion-${Date.now()}`
     const ins = [
       $rdf.st($rdf.sym(deletionUri), DCT('replaces'), $rdf.sym(msgUri), doc),
       $rdf.st($rdf.sym(deletionUri), SCHEMA('dateDeleted'), $rdf.lit(new Date().toISOString()), doc),
       $rdf.st($rdf.sym(deletionUri), FOAF('maker'), $rdf.sym(currentUser), doc)
     ]
     await store.updater.update([], ins)
   }

   2. Refactor Edit to Append-Only

   // RECOMMENDED (works with Append)
   async function editMessage(msgUri, newContent, doc) {
     const editUri = `${doc.value}#edit-${Date.now()}`
     const ins = [
       $rdf.st($rdf.sym(editUri), DCT('replaces'), $rdf.sym(msgUri), doc),
       $rdf.st($rdf.sym(editUri), SIOC('content'), $rdf.lit(newContent), doc),
       $rdf.st($rdf.sym(editUri), FOAF('maker'), $rdf.sym(currentUser), doc)
     ]
     await store.updater.update([], ins)
   }

   3. Update Message Rendering

   // When loading messages, check for replacements
   function isMessageDeleted(msgUri, store, doc) {
     const replacement = store.any(null, DCT('replaces'), msgUri, doc)
     if (replacement) {
       const deleted = store.any(replacement, SCHEMA('dateDeleted'), null, doc)
       return !!deleted
     }
     return false
   }
   
   function getLatestContent(msgUri, store, doc) {
     const replacement = store.any(null, DCT('replaces'), msgUri, doc)
     if (replacement) {
       const newContent = store.any(replacement, SIOC('content'), null, doc)
       if (newContent) return { content: newContent.value, edited: true }
     }
     return { content: store.any(msgUri, SIOC('content'))?.value, edited: false }
   }

   4. UI Indicators

   // Show edit/delete status
   if (isMessageDeleted(msgUri)) {
     messageEl.classList.add('deleted')
     messageEl.textContent = '(message deleted)'
   } else {
     const { content, edited } = getLatestContent(msgUri)
     messageEl.textContent = content
     if (edited) {
       messageEl.appendChild(createEditedBadge())  // Shows "(edited)"
     }
   }

   ---

   Summary

   Aspect	Current	Recommended
   ACL Setup	✅ Correct (Read+Append)	Keep as-is
   Edit Method	❌ SPARQL DELETE+INSERT	Use dct:replaces append
   Delete Method	❌ SPARQL DELETE	Use schema:dateDeleted append
   Audit Trail	❌ None (data destroyed)	✅ Full history preserved
   Security	⚠️ Relies on ACL	✅ Append-only by design

   ---

   References

   • Solid Chat Specification - Access Control
   • Solid Chat Specification - Modified Messages
   • WAC Specification - Append vs Write
   • Dublin Core Terms - replaces
   • Schema.org - dateDeleted