Dev/19: ServiceInstanceListSupplierBuilder design basic implementation

pyproject.toml

@@ -12,6 +12,7 @@ python = "^3.7"
 pre-commit = "^2.7.1"
 pytest = "^6.1.2"
 pytest-cov = "^2.10.1"
+pytest-mock = "^3.3.1"
 
 [build-system]
 requires = ["poetry>=0.12"]

spring_cloud/commons/client/loadbalancer/supplier/__init__.py

@@ -0,0 +1,3 @@
+# -*- coding: utf-8 -*-
+from .base import *
+from .decorator import *

spring_cloud/commons/client/loadbalancer/supplier/base.py

@@ -0,0 +1,85 @@
+# -*- coding: utf-8 -*-
+"""
+Since the load-balancer is responsible for choosing one instance
+per service request from a list of instances. We need a ServiceInstanceListSupplier for
+each service to decouple the source of the instances from load-balancers.
+"""
+# standard library
+from abc import ABC, abstractmethod
+from typing import List
+
+# scip plugin
+from spring_cloud.commons.client import ServiceInstance
+from spring_cloud.commons.client.discovery import DiscoveryClient
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+
+class ServiceInstanceListSupplier(ABC):
+    """
+    Non-Reactive version of ServiceInstanceListSupplier.
+    (Spring Cloud implement the supplier in the reactive way, means that
+    its supplier returns an Observable which broadcasts the instances on every change.)
+
+    We may consider to adopt reactive programming in the future.
+    """
+
+    @property
+    @abstractmethod
+    def service_id(self) -> str:
+        """
+        :return: (str) the service's id
+        """
+        pass
+
+    @abstractmethod
+    def get(self, request=None) -> List[ServiceInstance]:
+        """
+        :param request (opt) TODO not sure will we need this,
+                        this extension was designed by spring-cloud.
+        :return: (*ServiceInstance) a list of instances
+        """
+        pass
+
+
+class FixedServiceInstanceListSupplier(ServiceInstanceListSupplier):
+    """
+    A supplier that is initialized with fixed instances. (i.e. they won't be changed)
+    """
+
+    def __init__(self, service_id: str, instances: List[ServiceInstance]):
+        """
+        :param service_id: (str)
+        :param instances: (*ServiceInstance)
+        """
+        self._service_id = service_id
+        self._instances = instances
+
+    def get(self, request=None) -> List[ServiceInstance]:
+        return self._instances
+
+    @property
+    def service_id(self) -> str:
+        return self._service_id
+
+
+class DiscoveryClientServiceInstanceListSupplier(ServiceInstanceListSupplier):
+    """
+    The adapter delegating to discovery client for querying instances
+    """
+
+    def __init__(self, service_id: str, discovery_client: DiscoveryClient):
+        """
+        :param service_id: (str)
+        :param discovery_client: (DiscoveryClient)
+        """
+        self.__service_id = service_id
+        self.__delegate = discovery_client
+
+    @property
+    def service_id(self) -> str:
+        return self.__service_id
+
+    def get(self, request=None) -> List[ServiceInstance]:
+        return self.__delegate.get_instances(self.service_id)

spring_cloud/commons/client/loadbalancer/supplier/decorator.py

@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+# standard library
+from typing import List
+
+# scip plugin
+from spring_cloud.commons.client import ServiceInstance
+from spring_cloud.commons.exceptions import NoneTypeError
+from spring_cloud.commons.utils import validate
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+# standard library
+from abc import ABC
+
+# scip plugin
+from spring_cloud.commons.helpers import CacheManager
+
+from .base import ServiceInstanceListSupplier
+
+
+class DelegatingServiceInstanceListSupplier(ServiceInstanceListSupplier, ABC):
+    """
+    An application of decorator pattern that adds behaviors to ServiceInstanceListSupplier.
+    The decorators should inherit this class.
+    """
+
+    def __init__(self, delegate: ServiceInstanceListSupplier):
+        self.delegate = validate.not_none(delegate)
+
+    @property
+    def service_id(self) -> str:
+        return self.delegate.service_id
+
+
+class CachingServiceInstanceListSupplier(DelegatingServiceInstanceListSupplier):
+    CACHE_NAME = "CacheKey"
+
+    def __init__(self, cache_manager: CacheManager, delegate: ServiceInstanceListSupplier):
+        super().__init__(delegate)
+        self.__cache_manager = cache_manager
+
+    def get(self, request=None) -> List[ServiceInstance]:
+        return self.__cache_manager.get(self.CACHE_NAME).on_cache_miss(self.delegate.get)

spring_cloud/commons/client/service_instance.py

@@ -3,7 +3,6 @@
 __author__ = "Waterball ([email protected])"
 __license__ = "Apache 2.0"
 
-
 # standard library
 from abc import ABC, abstractmethod
 from urllib.parse import urlparse
@@ -95,3 +94,17 @@ def uri(self) -> str:
     @property
     def scheme(self) -> str:
         return self._scheme
+
+    def __eq__(self, o: object) -> bool:
+        if isinstance(o, ServiceInstance):
+            return (
+                self.uri == o.uri
+                and self.service_id == o.service_id
+                and self.instance_id == o.instance_id
+                and self.host == o.host
+                and self.port == o.port
+                and self.secure == o.secure
+                and self.scheme == o.scheme
+            )
+
+        return False

spring_cloud/commons/exceptions/__init__.py

@@ -0,0 +1,3 @@
+# -*- coding: utf-8 -*-
+
+from .primitive import *

spring_cloud/commons/exceptions/primitive.py

@@ -0,0 +1,17 @@
+# -*- coding: utf-8 -*-
+"""
+All primitive exceptions are included here
+"""
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+
+class NoneTypeError(Exception):
+    @staticmethod
+    def raise_if_none(obj):
+        if obj is None:
+            raise NoneTypeError
+
+    def __init__(self, message):
+        self.message = message

spring_cloud/commons/helpers/__init__.py

@@ -0,0 +1,2 @@
+# -*- coding: utf-8 -*-
+from .cache import *

spring_cloud/commons/helpers/cache/__init__.py

@@ -0,0 +1,3 @@
+# -*- coding: utf-8 -*-
+
+from .cache_manager import *

spring_cloud/commons/helpers/cache/cache_manager.py

@@ -0,0 +1,69 @@
+# -*- coding: utf-8 -*-
+
+"""
+A cache manager wrapper that supports some syntax sugar.
+
+Usage:
+    value = cache_manager.get(cache_key) \
+                .on_cache_miss(lambda: retrieve_value(key))
+"""
+
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+# standard library
+from abc import ABC, abstractmethod
+
+
+class OnCacheMiss:
+    def __init__(self, cache_manager, key, value):
+        self.__cache_manager = cache_manager
+        self.__key = key
+        self.__value = value
+
+    @abstractmethod
+    def on_cache_miss(self, cache_miss_func):
+        """
+        :param cache_miss_func: (lambda ()->value)
+        """
+        if not self.__value:
+            value = cache_miss_func()
+            self.__cache_manager.put(self.__key, value)
+            return value
+        return self.__value
+
+
+class CacheManager(ABC):
+    """
+    Service Provider Interface (SPI) for basic caching.
+    We might want to extend this class with many features in the future.
+    (e.g. timeout, evict-and-replacement)
+    """
+
+    def get(self, key) -> OnCacheMiss:
+        value = self.retrieve_value(key)
+        return OnCacheMiss(self, key, value)
+
+    @abstractmethod
+    def retrieve_value(self, key):
+        pass
+
+    @abstractmethod
+    def put(self, key, value):
+        pass
+
+
+class NaiveCacheManager(CacheManager):
+    """
+    A very simple cache implementation.
+    """
+
+    def __init__(self):
+        self.cache_dict = {}
+
+    def retrieve_value(self, key):
+        return self.cache_dict.get(key, None)
+
+    def put(self, key, value):
+        self.cache_dict[key] = value

spring_cloud/commons/utils/validate.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+# scip plugin
+from spring_cloud.commons.exceptions.primitive import NoneTypeError
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+
+def not_none(obj):
+    if obj:
+        return obj
+    raise NoneTypeError
+
+
+def is_instance_of(obj, the_type):
+    if isinstance(obj, the_type):
+        return obj
+    raise TypeError()

tests/commons/client/loadbalancer/supplier/decorator_test.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+# standard library
+from unittest.mock import Mock
+
+# scip plugin
+from spring_cloud.commons.client.loadbalancer.supplier.decorator import CachingServiceInstanceListSupplier
+from spring_cloud.commons.helpers.cache.cache_manager import NaiveCacheManager
+from tests.commons.client.loadbalancer.supplier.stubs import INSTANCES
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+
+class TestCachingServiceInstanceListSupplier:
+    def setup_class(self):
+        self.delegate = Mock()
+        self.delegate.get = Mock(return_value=INSTANCES)
+        self.supplier = CachingServiceInstanceListSupplier(NaiveCacheManager(), self.delegate)
+
+    def test_Given_cache_When_10_invocations_Then_only_1_cache_miss_and_delegate(self):
+        for i in range(1, 10):
+            self.supplier.get()
+        assert self.delegate.get.call_count == 1

tests/commons/client/loadbalancer/supplier/service_instance_list_supplier_test.py

@@ -0,0 +1,37 @@
+# -*- coding: utf-8 -*-
+# standard library
+from unittest.mock import Mock
+
+# scip plugin
+from spring_cloud.commons.client.loadbalancer.supplier import (
+    DiscoveryClientServiceInstanceListSupplier,
+    FixedServiceInstanceListSupplier,
+)
+from tests.commons.client.loadbalancer.supplier.stubs import INSTANCES, SERVICE_ID
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+
+class TestFixedServiceInstanceListSupplier:
+    def setup_class(self):
+        self.supplier = FixedServiceInstanceListSupplier(SERVICE_ID, INSTANCES)
+
+    def test_get_service_id(self):
+        assert SERVICE_ID == self.supplier.service_id
+
+    def test_get_instances(self):
+        assert INSTANCES == self.supplier.get()
+
+
+class TestDiscoveryClientServiceInstanceListSupplier:
+    def setup_class(self):
+        self.discovery_client = Mock()
+        self.discovery_client.get_instances = Mock(return_value=INSTANCES)
+        self.supplier = DiscoveryClientServiceInstanceListSupplier(SERVICE_ID, self.discovery_client)
+
+    def test_get_service_id(self):
+        assert SERVICE_ID == self.supplier.service_id
+
+    def test_get_instances(self):
+        assert INSTANCES == self.supplier.get()

tests/commons/client/loadbalancer/supplier/stubs.py

@@ -0,0 +1,10 @@
+# -*- coding: utf-8 -*-
+# scip plugin
+from spring_cloud.commons.client import StaticServiceInstance
+
+__author__ = "Waterball ([email protected])"
+__license__ = "Apache 2.0"
+
+
+SERVICE_ID = "serviceId"
+INSTANCES = [StaticServiceInstance("uri", SERVICE_ID, instance_id) for instance_id in ["1", "2", "3"]]