Interpret triplecount-exactness in ExternalHdtDatasource

Author: rubensworks

config/config-composite.json

@@ -7,7 +7,7 @@
       "type": "CompositeDatasource",
       "description": "A test composite datasource",
       "settings": {
-        "references": [ "hdt", "ttl", "jsonld" ]
+        "references": [ "hdt", "ttl", "jsonld", "hdtext" ]
       }
     },
     "hdt": {
@@ -30,6 +30,13 @@
       "type": "JsonLdDatasource",
       "description": "A test jsonld datasource",
       "settings": { "file": "test/assets/test.jsonld" }
+    },
+    "hdtext": {
+      "hide": true,
+      "title": "HDT-EXT",
+      "type": "ExternalHdtDatasource",
+      "description": "A blank test HDT datasource",
+      "settings": { "file": "test/assets/test-blank.hdt" }
     }
   }
 }

lib/datasources/ExternalHdtDatasource.js

@@ -43,7 +43,7 @@ ExternalHdtDatasource.prototype._executeQuery = function (query, tripleStream, m
                                '--', hdtFile], { stdio: ['ignore', 'pipe', 'ignore'] });
   // Parse the result triples
   hdt.stdout.setEncoding('utf8');
-  var parser = new N3Parser(), tripleCount = 0, estimatedTotalCount = 0;
+  var parser = new N3Parser(), tripleCount = 0, estimatedTotalCount = 0, exactCount = true;
   parser.parse(hdt.stdout, function (error, triple) {
     if (error)
       tripleStream.emit('error', new Error('Invalid query result: ' + error.message));
@@ -53,7 +53,7 @@ ExternalHdtDatasource.prototype._executeQuery = function (query, tripleStream, m
       // Ensure the estimated total count is as least as large as the number of triples
       if (tripleCount && estimatedTotalCount < offset + tripleCount)
         estimatedTotalCount = offset + (tripleCount < query.limit ? tripleCount : 2 * tripleCount);
-      metadataCallback({ totalCount: estimatedTotalCount, exactCount: false });
+      metadataCallback({ totalCount: estimatedTotalCount, exactCount: exactCount });
       tripleStream.push(null);
     }
   });
@@ -62,6 +62,7 @@ ExternalHdtDatasource.prototype._executeQuery = function (query, tripleStream, m
   // Extract the estimated number of total matches from the first (comment) line
   hdt.stdout.once('data', function (header) {
     estimatedTotalCount = parseInt(header.match(/\d+/), 10) || 0;
+    exactCount = header.indexOf("Exact") > -1;
   });
 
   // Report query errors