Append the globalPrefix only after sourceRegex alterations to the mea…

lib/librato.js

@@ -241,24 +241,26 @@ var flushStats = function libratoFlush(ts, metrics) {
   var addMeasure = function addMeasure(mType, measure, countStat) {
     countStat = typeof countStat !== 'undefined' ? countStat : true;
     var match;
-    var measureName = globalPrefix + measure.name;
+    var measureName = measure.name;
     measure.tags = {};
     measureName = parseAndSetTags(measureName, measure);
     // Use first capturing group as source name.
     // NOTE: Only legacy users will a) have a source and b) have a source set by regex
     if (sourceRegex && (match = measureName.match(sourceRegex)) && match[1]) {
       measure.source = sanitizeName(match[1]);
-      // Remove entire matching string from the measure name & add global prefix.
-      measure.name = sanitizeName(measureName.slice(0, match.index) + measureName.slice(match.index + match[0].length));
+      // Remove entire matching string from the measure name, add global prefix and sanitize the final measure name.
+      measure.name = sanitizeName(globalPrefix + measureName.slice(0, match.index) + measureName.slice(match.index + match[0].length));
       // Create a measurement-level tag named source
       measure.tags.source = measure.source;
     } else {
-      measure.name = sanitizeName(measureName);
+      // add global prefix and sanitize the final measure name.
+      measure.name = sanitizeName(globalPrefix + measureName);
       // Use the global config sourceName as a source tag, if it exists.
       if (sourceName !== null) {
         measure.tags.source = sourceName;
       }
     }
+
     if (brokenMetrics[measure.name]) {
       return;
     }

test/librato_tests.js

@@ -409,4 +409,31 @@ module.exports.legacy = {
 
     this.emitter.emit('flush', 123, metrics);
   },
+
+  testGlobalPrefix: function(test) {
+    config.librato.sourceRegex = /^(.*?)--/;
+    config.librato.globalPrefix = 'global.prefix';
+    librato.init(null, config, this.emitter);
+
+    test.expect(6);
+    let metrics = {gauges: {'rails-application--my_gauge': 1}};
+    this.apiServer.post('/v1/measurements')
+                  .reply(200, (uri, requestBody) => {
+                    let measurement = requestBody.measurements[0];
+                    test.ok(requestBody);
+                    test.equal(measurement.name.startsWith('global.prefix'), true);
+                    test.deepEqual(measurement.tags, {source: 'rails-application'});
+                  });
+
+    this.apiServer.post('/v1/metrics')
+                  .reply(200, (uri, requestBody) => {
+                    let gauge = requestBody.gauges[0];
+                    test.ok(requestBody);
+                    test.equal(gauge.name.startsWith('global.prefix'), true);
+                    test.equal(gauge.source, 'rails-application');
+                    test.done();
+                  });
+
+    this.emitter.emit('flush', 123, metrics);
+  },
 };