Implement stream_read_file for the Swift storage engine

Note that Swift doesn't seem to have a file-like interface, so we need to wrap the generator we get back from it.

Fixes #210

test/test_util.py

@@ -3,6 +3,49 @@ import unittest
 from itertools import islice
 
 from util.validation import generate_valid_usernames
+from util.generatorfile import GeneratorFile
+
+class TestGeneratorFile(unittest.TestCase):
+  def sample_generator(self):
+    yield 'this'
+    yield 'is'
+    yield 'a'
+    yield 'test'
+
+  def test_basic_generator(self):
+    with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals("thisisatest", f.read())
+
+  def test_same_lengths(self):
+    with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals("this", f.read(4))
+      self.assertEquals("is", f.read(2))
+      self.assertEquals("a", f.read(1))
+      self.assertEquals("test", f.read(4))
+
+  def test_indexed_lengths(self):
+    with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals("thisis", f.read(6))
+      self.assertEquals("atest", f.read(5))
+
+  def test_misindexed_lengths(self):
+    with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals("thisis", f.read(6))
+      self.assertEquals("ate", f.read(3))
+      self.assertEquals("st", f.read(2))
+      self.assertEquals("", f.read(2))
+
+  def test_misindexed_lengths_2(self):
+    with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals("thisisat", f.read(8))
+      self.assertEquals("e", f.read(1))
+      self.assertEquals("st", f.read(2))
+      self.assertEquals("", f.read(2))
+
+  def test_overly_long(self):
+    with GeneratorFile(self.sample_generator()) as f:
+      self.assertEquals("thisisatest", f.read(60))
+
 
 class TestUsernameGenerator(unittest.TestCase):
   def assert_generated_output(self, input_username, expected_output):
@@ -48,3 +91,8 @@ class TestUsernameGenerator(unittest.TestCase):
     self.assertEquals('a__0', generated_output[1])
     self.assertEquals('a__1', generated_output[2])
     self.assertEquals('a__2', generated_output[3])
+
+
+if __name__ == '__main__':
+  unittest.main()
+