Add preliminary N3 patch support.

Author: RubenVerborgh

lib/handlers/patch.js

@@ -14,7 +14,8 @@ const DEFAULT_TARGET_TYPE = 'text/turtle'
 
 // Patch handlers by request body content type
 const PATCHERS = {
-  'application/sparql-update': require('./patch/sparql-update-patcher.js')
+  'application/sparql-update': require('./patch/sparql-update-patcher.js'),
+  'text/n3': require('./patch/n3-patcher.js')
 }
 
 // Handles a PATCH request

lib/handlers/patch/n3-patcher.js

@@ -0,0 +1,72 @@
+// Performs a text/n3 patch on a graph
+
+module.exports = patch
+
+const $rdf = require('rdflib')
+const debug = require('../../debug').handlers
+const error = require('../../http-error')
+
+const PATCH_NS = 'http://example.org/patch#'
+const PREFIXES = `PREFIX p: <${PATCH_NS}>\n`
+
+// Patches the given graph
+function patch (targetKB, targetURI, 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))
+}
+
+// Parses the given N3 patch document
+function parsePatchDocument (targetURI, patchURI, patchText, patchKB) {
+  debug('PATCH -- Parsing patch...')
+
+  // Parse the N3 document into triples
+  return new Promise((resolve, reject) => {
+    const patchGraph = $rdf.graph()
+    $rdf.parse(patchText, patchGraph, patchURI, 'text/n3')
+    resolve(patchGraph)
+  })
+  // Query the N3 document for insertions and deletions
+  .then(patchGraph => queryForFirstResult(patchGraph, `${PREFIXES}
+    SELECT ?insert ?delete WHERE {
+      ?patch p:patches <${targetURI}>.
+      OPTIONAL { ?patch p:insert ?insert. }
+      OPTIONAL { ?patch p:delete ?delete. }
+    }`)
+  )
+  // Return the insertions and deletions as an rdflib patch document
+  .then(result => {
+    return {
+      insert: result['?insert'],
+      delete: result['?delete']
+    }
+  })
+}
+
+// Applies the patch to the target graph
+function applyPatch (patchObject, target, targetKB) {
+  return new Promise((resolve, reject) =>
+    targetKB.applyPatch(patchObject, target, (err) => {
+      if (err) {
+        const message = err.message || err // returns string at the moment
+        debug('PATCH FAILED. Returning 409. Message: \'' + message + '\'')
+        return reject(error(409, 'Error when applying the patch'))
+      }
+      resolve(targetKB)
+    })
+  )
+}
+
+// Queries the store with the given SPARQL query and returns the first result
+function queryForFirstResult (store, sparql) {
+  return new Promise((resolve, reject) => {
+    const query = $rdf.SPARQLToQuery(sparql, false, store)
+    store.query(query, resolve)
+  })
+}