Refactor SPARQL update patcher with promises.

This improves reuse for future parsers.

Author: RubenVerborgh

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

@@ -8,29 +8,39 @@ const error = require('../../http-error')
 
 // 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
+
+  return parsePatchDocument(patchURI, patchText, patchKB)
+         .then(patchObject => applyPatch(patchObject, target, targetKB))
+}
+
+// Parses the given SPARQL UPDATE document
+function parsePatchDocument (patchURI, patchText, patchKB) {
+  debug('PATCH -- Parsing patch...')
   return new Promise((resolve, reject) => {
-    // Parse the patch document
-    debug('PATCH -- Parsing patch...')
-    const patchURI = targetURI // @@@ beware the triples from the patch ending up in the same place
-    const patchKB = $rdf.graph()
-    var patchObject
     try {
-      // Must parse relative to document's base address but patch doc should get diff URI
-      patchObject = $rdf.sparqlUpdateParser(patchText, patchKB, patchURI)
-    } catch (e) {
-      return reject(error(400, 'Patch format syntax error:\n' + e + '\n'))
+      resolve($rdf.sparqlUpdateParser(patchText, patchKB, patchURI))
+    } catch (err) {
+      reject(error(400, 'Patch format syntax error:\n' + err + '\n'))
     }
-    debug('PATCH -- reading target file ...')
+  })
+}
 
-    // Apply the patch to the target graph
-    var target = patchKB.sym(targetURI)
-    targetKB.applyPatch(patchObject, target, function (err) {
+// Applies the patch to the target graph
+function applyPatch (patchObject, target, targetKB) {
+  return new Promise((resolve, reject) =>
+    targetKB.applyPatch(patchObject, target, (err) => {
       if (err) {
-        var message = err.message || err // returns string at the moment
+        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)
     })
-  })
+  )
 }