build: Remove async_generator as a dependency

Python 3.6+ can do this natively.

ssb/muxrpc.py

@@ -1,7 +1,5 @@
 from functools import wraps
 
-from async_generator import async_generator, yield_
-
 from ssb.packet_stream import PSMessageType
 
 
@@ -9,7 +7,7 @@ class MuxRPCAPIException(Exception):
     pass
 
 
-class MuxRPCHandler(object):
+class MuxRPCHandler:
     def check_message(self, msg):
         body = msg.body
         if isinstance(body, dict) and 'name' in body and body['name'] == 'Error':
@@ -30,14 +28,14 @@ class MuxRPCSourceHandler(MuxRPCHandler):
     def __init__(self, ps_handler):
         self.ps_handler = ps_handler
 
-    @async_generator
-    async def __aiter__(self):
-        async for msg in self.ps_handler:
-            try:
-                self.check_message(msg)
-                await yield_(msg)
-            except MuxRPCAPIException:
-                raise
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        msg = await self.ps_handler.__anext__()
+        self.check_message(msg)
+
+        return msg
 
 
 class MuxRPCSinkHandlerMixin(object):

ssb/packet_stream.py

@@ -6,7 +6,6 @@ from time import time
 from math import ceil
 
 import simplejson
-from async_generator import async_generator, yield_
 
 from secret_handshake import SHSClient, SHSServer
 
@@ -32,13 +31,16 @@ class PSStreamHandler(object):
     async def stop(self):
         await self.queue.put(None)
 
-    @async_generator
-    async def __aiter__(self):
-        while True:
-            elem = await self.queue.get()
-            if not elem:
-                return
-            await yield_(elem)
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        elem = await self.queue.get()
+
+        if not elem:
+            raise StopAsyncIteration()
+
+        return elem
 
 
 class PSRequestHandler(object):
@@ -113,15 +115,19 @@ class PacketStream(object):
     def is_connected(self):
         return self.connection.is_connected
 
-    @async_generator
-    async def __aiter__(self):
-        while True:
-            msg = await self.read()
-            if not msg:
-                return
-            # filter out replies
-            if msg.req >= 0:
-                await yield_(msg)
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        msg = await self.read()
+
+        if not msg:
+            raise StopAsyncIteration()
+
+        if msg.req >= 0:
+            return msg
+
+        return None
 
     async def __await__(self):
         async for data in self: