Merge pull request #700 from stephenplusplus/spp--storage-tail-bytes

storage: support tail bytes

lib/storage/file.js

@@ -396,13 +396,25 @@ File.prototype.move = function(destination, callback) {
  *   })
  *   .pipe(fs.createWriteStream('/Users/stephen/logfile.txt'))
  *   .on('error', function(err) {});
+ *
+ * //-
+ * // To read a tail byte range, specify only `options.end` as a negative
+ * // number.
+ * //-
+ * var logFile = myBucket.file('access_log');
+ * logFile.createReadStream({
+ *     end: -100
+ *   })
+ *   .pipe(fs.createWriteStream('/Users/stephen/logfile.txt'))
+ *   .on('error', function(err) {});
  */
 File.prototype.createReadStream = function(options) {
   options = options || {};
 
   var that = this;
   var rangeRequest =
     util.is(options.start, 'number') || util.is(options.end, 'number');
+  var tailRequest = options.end < 0;
   var throughStream = streamEvents(through());
 
   var requestStream;
@@ -477,6 +489,12 @@ File.prototype.createReadStream = function(options) {
       };
     }
 
+    if (tailRequest) {
+      reqOpts.headers = {
+        Range: 'bytes=' + options.end
+      };
+    }
+
     that.bucket.storage.makeAuthorizedRequest_(reqOpts, {
       onAuthorized: function(err, authorizedReqOpts) {
         if (err) {

test/storage/file.js

@@ -801,6 +801,22 @@ describe('File', function() {
         readStream.destroy = done;
       });
     });
+
+    describe('tail requests', function() {
+      it('should make a request for the tail bytes', function(done) {
+        var endOffset = -10;
+
+        request_Override = function(opts) {
+          setImmediate(function () {
+            assert.equal(opts.headers.Range, 'bytes=' + endOffset);
+            done();
+          });
+          return duplexify();
+        };
+
+        file.createReadStream({ end: endOffset });
+      });
+    });
   });
 
   describe('createWriteStream', function() {