Fix issues with hanging transcoding processes

When a connection that is consuming a generated response is closed,
Flask closes the generator making it raise the special `GeneratorExit`
exception when the program tries to yield from it again. Because the
`transcode` function was called (returning a generator) before being
passed into `set_generated`, the exception was being handled in the
wrong order.

By passing the `transcode` function to `set_generated` and letting
`set_transcode` call it to return a generator while generating the
response for the client, the exception properly bubbles up through
`transcode` into `set_generated`. This allows both of them to handle it
properly by stopping the subproceses and not caching the incomplete
response data respectively.

supysonic/api/media.py

@@ -127,7 +127,7 @@ def stream_media():
                 if dec_proc != None:
                     dec_proc.wait()
                 proc.wait()
-            resp_content = cache.set_generated(cache_key, transcode())
+            resp_content = cache.set_generated(cache_key, transcode)
 
             logger.info('Transcoding track {0.id} for user {1.id}. Source: {2} at {0.bitrate}kbps. Dest: {3} at {4}kbps'.format(res, request.user, src_suffix, dst_suffix, dst_bitrate))
             response = Response(resp_content, mimetype=dst_mimetype)

supysonic/cache.py

@@ -161,17 +161,19 @@ class Cache(object):
             f.write(value)
         return self._filepath(key)
 
-    def set_generated(self, key, gen):
+    def set_generated(self, key, gen_function):
-        """Pass the generated values through and set the end result in the cache
+        """Pass the values yielded from the generator function through and set
+        the end result in the cache.
 
-        The contents will be set into the cache when the generator completes.
+        The contents will be set into the cache only if and when the generator
+        completes.
 
         Ex:
-        >>> for x in cache.set_generated(key, some_generator()):
+        >>> for x in cache.set_generated(key, generator_function):
         ...     print(x)
         """
         with self.set_fileobj(key) as f:
-            for data in gen:
+            for data in gen_function():
                 f.write(data)
                 yield data
 

tests/base/test_cache.py

@@ -76,7 +76,7 @@ class CacheTestCase(unittest.TestCase):
                 yield b
 
         t = []
-        for x in cache.set_generated("key", gen()):
+        for x in cache.set_generated("key", gen):
             t.append(x)
             self.assertEqual(cache.size, 0)
             self.assertFalse(cache.has("key"))
@@ -103,7 +103,7 @@ class CacheTestCase(unittest.TestCase):
         self.assertEqual(cache.get_value("key"), val)
 
         with cache.get_fileobj("key") as f:
-            self.assertEquals(f.read(), val)
+            self.assertEqual(f.read(), val)
 
         with open(cache.get("key"), 'rb') as f:
             self.assertEqual(f.read(), val)
@@ -162,7 +162,7 @@ class CacheTestCase(unittest.TestCase):
                 yield b
 
         with self.assertRaises(TypeError):
-            for x in cache.set_generated("key", gen()):
+            for x in cache.set_generated("key", gen):
                 pass
 
         # Make sure no partial files are left after the error
@@ -174,8 +174,8 @@ class CacheTestCase(unittest.TestCase):
             for b in [b'0', b'12', b'345', b'6789']:
                 yield b
 
-        g1 = cache.set_generated("key", gen())
+        g1 = cache.set_generated("key", gen)
-        g2 = cache.set_generated("key", gen())
+        g2 = cache.set_generated("key", gen)
 
         next(g1)
         files = os.listdir(self.__dir)