Allow storage write streams to start at an offset

lib/storage/bucket.js

@@ -964,6 +964,8 @@ Bucket.prototype.makePublic = function(options, callback) {
  *     `options.predefinedAcl = 'publicRead'`)
  * @param {boolean} options.resumable - Force a resumable upload. (default:
  *     true for files larger than 5 MB).
+ * @param {string} options.offset - The starting byte of the upload stream, for
+ *     resuming an interrupted upload. Defaults to 0.
  * @param {function} callback - The callback function.
  * @param {?error} callback.err - An error returned while making this request
  * @param {module:storage/file} callback.file - The uploaded File.

lib/storage/file.js

@@ -747,6 +747,8 @@ File.prototype.createResumableUpload = function(options, callback) {
  *     `options.predefinedAcl = 'private'`)
  * @param {boolean} options.public - Make the uploaded file public. (Alias for
  *     `options.predefinedAcl = 'publicRead'`)
+ * @param {string} options.offset - The starting byte of the upload stream, for
+ *     resuming an interrupted upload. Defaults to 0.
  * @param {string|boolean} options.validation - Possible values: `"md5"`,
  *     `"crc32c"`, or `false`. By default, data integrity is validated with an
  *     MD5 checksum for maximum reliability. CRC32c will provide better
@@ -1536,7 +1538,8 @@ File.prototype.startResumableUpload_ = function(dup, options) {
     metadata: options.metadata,
     predefinedAcl: options.predefinedAcl,
     private: options.private,
-    public: options.public
+    public: options.public,
+    offset: options.offset
   });
 
   uploadStream

test/storage/file.js

@@ -1073,6 +1073,21 @@ describe('File', function() {
       writable.end('data');
     });
 
+    it('should pass through a provided offset', function(done) {
+          var options = {
+            offset: 1234
+          };
+
+          var writable = file.createWriteStream(options);
+
+          file.startResumableUpload_ = function(stream, options_) {
+            assert.deepEqual(options_.offset, options.offset);
+            done();
+          };
+
+          writable.write('data');
+        });
+
     describe('validation', function() {
       var data = 'test';