[Platform] Add drain callback (#57)

nuclio_sdk/platform.py

@@ -35,6 +35,7 @@ def __init__(
 
         self._control_callback = on_control_callback
         self._termination_callback = None
+        self._drain_callback = None
 
     async def explicit_ack(self, qualified_offset):
         """
@@ -51,6 +52,16 @@ async def explicit_ack(self, qualified_offset):
                 "Cannot send explicit ack since control callback was not initialized"
             )
 
+    def set_drain_callback(self, callback):
+        """
+        Register a callback to be called when the platform is draining (rebalance happening in stream).
+        If already registered, the callback will be replaced.
+        When called, the callback will be called with zero arguments.
+
+        :param callback: the callback to call when terminating
+        """
+        self._drain_callback = callback
+
     def set_termination_callback(self, callback):
         """
         Register a callback to be called when the platform is terminating.
@@ -64,7 +75,6 @@ def set_termination_callback(self, callback):
     def call_function(
         self, function_name, event, node=None, timeout=None, service_name_override=None
     ):
-
         # get connection from provider
         connection = self._connection_provider(
             self._get_function_url(function_name, service_name_override),
@@ -106,7 +116,7 @@ def call_function(
         response_headers = {}
 
         # get response headers as lowercase
-        for (name, value) in response.getheaders():
+        for name, value in response.getheaders():
             response_headers[name.lower()] = value
 
         # if content type exists, use it
@@ -124,7 +134,6 @@ def call_function(
         )
 
     def _get_function_url(self, function_name, service_name_override=None):
-
         # local envs prefix namespace
         if self.kind == "local":
             service_name = service_name_override or "nuclio-{0}-{1}".format(
@@ -134,10 +143,14 @@ def _get_function_url(self, function_name, service_name_override=None):
             service_name = service_name_override or "nuclio-{0}".format(function_name)
         return "{0}:8080".format(service_name)
 
-    def _on_signal(self):
+    def _on_signal(self, callback_type="termination"):
         """
-        When a signal is received, call the termination callback as a hook before exiting
+        When a signal is received, call the termination/drain callback as a hook before exiting
         If not set, the callback will be a no-op
+
+        :arg callback_type:str - callback type, can be "termination" or "drain"
         """
-        if self._termination_callback:
+        if callback_type == "termination" and self._termination_callback:
             self._termination_callback()
+        elif callback_type == "drain" and self._drain_callback:
+            self._drain_callback()

setup.py

@@ -47,6 +47,8 @@ def get_version():
         version = f.read().strip()
     if version.startswith("v"):
         version = version[1:]
+    if version == "":
+        return "0.0.0-dev0"
     return version