Attach <boolean> to <sparql> instead of <result>.

Fixes XML output of ASK queries.

Author: RubenVerborgh

lib/writers/SparqlXMLResultWriter.js

@@ -12,20 +12,35 @@ function SparqlXMLResultWriter(sparqlIterator) {
 SparqlResultWriter.subclass(SparqlXMLResultWriter);
 
 SparqlXMLResultWriter.prototype._writeHead = function (variableNames) {
-  var root = this._root = xml.element({ _attr: { xlmns: 'http://www.w3.org/2005/sparql-results#' } }),
-      results = this._results = xml.element({}), self = this;
+  // Write root element
+  var self = this,
+      root = this._root = xml.element({
+        _attr: { xlmns: 'http://www.w3.org/2005/sparql-results#' },
+      });
   xml({ sparql: root }, { stream: true, indent: '  ', declaration: true })
      .on('data', function (chunk) { self._push(chunk + '\n'); });
-  if (variableNames.length)
-    root.push({ head: variableNames.map(function (v) { return { variable: { _attr: { name: v } } }; }) });
-  root.push({ results: results });
+
+  // Write head element
+  if (variableNames.length) {
+    root.push({
+      head: variableNames.map(function (v) {
+        return { variable: { _attr: { name: v } } };
+      }),
+    });
+  }
 };
 
 SparqlXMLResultWriter.prototype._writeBindings = function (result) {
+  // With the first result, write the results element
+  if (!this._results)
+    this._root.push({ results: this._results = xml.element({}) });
+
   // Unbound variables cannot be part of XML
   result = _.omit(result, function (value) {
     return value === undefined || value === null;
   });
+
+  // Write the result element
   this._results.push({
     result: _.map(result, function (value, variable) {
       var xmlValue, lang, type;
@@ -48,7 +63,12 @@ SparqlXMLResultWriter.prototype._writeBoolean = function (result) {
 };
 
 SparqlXMLResultWriter.prototype._flush = function (done) {
-  this._results.close();
+  // If there were no matches, the results element hasn't been created yet
+  if (this._empty)
+    this._root.push({ results: this._results = xml.element({}) });
+  // There's no results element for ASK queries
+  if (this._results)
+    this._results.close();
   this._root.close();
   done();
 };