Construct the patch URI through a hash of its contents.

Author: RubenVerborgh

lib/handlers/patch.js

@@ -9,6 +9,7 @@ const debug = require('../debug').handlers
 const utils = require('../utils.js')
 const error = require('../http-error')
 const $rdf = require('rdflib')
+const crypto = require('crypto')
 
 const DEFAULT_TARGET_TYPE = 'text/turtle'
 
@@ -23,31 +24,32 @@ function patchHandler (req, res, next) {
   debug('PATCH -- ' + req.originalUrl)
   res.header('MS-Author-Via', 'SPARQL')
 
-  // Obtain details of the patch document
-  const patch = {
-    text: req.body ? req.body.toString() : '',
-    contentType: (req.get('content-type') || '').match(/^[^;\s]*/)[0]
-  }
-  const patchGraph = PATCHERS[patch.contentType]
-  if (!patchGraph) {
-    return next(error(415, 'Unknown patch content type: ' + patch.contentType))
-  }
-  debug('PATCH -- Received patch (%d bytes, %s)', patch.text.length, patch.contentType)
-
   // Obtain details of the target resource
   const ldp = req.app.locals.ldp
   const root = !ldp.idp ? ldp.root : ldp.root + req.hostname + '/'
-  const target = {
-    file: utils.uriToFilename(req.path, root),
-    uri: utils.uriAbs(req) + req.originalUrl
-  }
+  const target = {}
+  target.file = utils.uriToFilename(req.path, root)
+  target.uri = utils.uriAbs(req) + req.originalUrl
   target.contentType = mime.lookup(target.file) || DEFAULT_TARGET_TYPE
   debug('PATCH -- Target <%s> (%s)', target.uri, target.contentType)
 
+  // Obtain details of the patch document
+  const patch = {}
+  patch.text = req.body ? req.body.toString() : ''
+  patch.uri = `${target.uri}#patch-${hash(patch.text)}`
+  patch.contentType = (req.get('content-type') || '').match(/^[^;\s]*/)[0]
+  debug('PATCH -- Received patch (%d bytes, %s)', patch.text.length, patch.contentType)
+
+  // Find the appropriate patcher for the given content type
+  const patchGraph = PATCHERS[patch.contentType]
+  if (!patchGraph) {
+    return next(error(415, 'Unknown patch content type: ' + patch.contentType))
+  }
+
   // Read the RDF graph to be patched from the file
   readGraph(target)
   // Patch the graph and write it back to the file
-  .then(graph => patchGraph(graph, target.uri, patch.text))
+  .then(graph => patchGraph(graph, target.uri, patch.uri, patch.text))
   .then(graph => writeGraph(graph, target))
   // Send the result to the client
   .then(result => { res.send(result) })
@@ -108,3 +110,8 @@ function writeGraph (graph, resource) {
     })
   })
 }
+
+// Creates a hash of the given text
+function hash (text) {
+  return crypto.createHash('md5').update(text).digest('hex')
+}

lib/handlers/patch/n3-patcher.js

@@ -10,14 +10,10 @@ const PATCH_NS = 'http://example.org/patch#'
 const PREFIXES = `PREFIX p: <${PATCH_NS}>\n`
 
 // Patches the given graph
-function patch (targetKB, targetURI, patchText) {
+function patch (targetKB, targetURI, patchURI, patchText) {
   const patchKB = $rdf.graph()
   const target = patchKB.sym(targetURI)
 
-  // Must parse relative to document's base address but patch doc should get diff URI
-  // @@@ beware the triples from the patch ending up in the same place
-  const patchURI = targetURI + '#patch'
-
   return parsePatchDocument(targetURI, patchURI, patchText, patchKB)
          .then(patchObject => applyPatch(patchObject, target, targetKB))
 }

lib/handlers/patch/sparql-update-patcher.js

@@ -7,14 +7,10 @@ const debug = require('../../debug').handlers
 const error = require('../../http-error')
 
 // Patches the given graph
-function patch (targetKB, targetURI, patchText) {
+function patch (targetKB, targetURI, patchURI, patchText) {
   const patchKB = $rdf.graph()
   const target = patchKB.sym(targetURI)
 
-  // Must parse relative to document's base address but patch doc should get diff URI
-  // @@@ beware the triples from the patch ending up in the same place
-  const patchURI = targetURI
-
   return parsePatchDocument(patchURI, patchText, patchKB)
          .then(patchObject => applyPatch(patchObject, target, targetKB))
 }
@@ -23,8 +19,9 @@ function patch (targetKB, targetURI, patchText) {
 function parsePatchDocument (patchURI, patchText, patchKB) {
   debug('PATCH -- Parsing patch...')
   return new Promise((resolve, reject) => {
+    const baseURI = patchURI.replace(/#.*/, '')
     try {
-      resolve($rdf.sparqlUpdateParser(patchText, patchKB, patchURI))
+      resolve($rdf.sparqlUpdateParser(patchText, patchKB, baseURI))
     } catch (err) {
       reject(error(400, 'Patch format syntax error:\n' + err + '\n'))
     }