Add an in memory implementation of cluster/client.Client (#2219)

What this PR does / why we need it:

This adds a small testing utility to back a cluster/client.Client with an in-memory kv.Store. We have the cluster/kv/mem implementation of kv.Store, but there's currently no way to back a cluster/client.Client with it. Construction of the kv.Store is tightly coupled with etcd in the current class; having a separate class seemed like a reasonable way to do this given the current code, but we could consider a more dependency injection style for that--let me know if you want to hash that out.

src/cluster/mem/mem.go

@@ -0,0 +1,142 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package memcluster
+
+import (
+	"errors"
+	"sync"
+
+	"github.com/m3db/m3/src/cluster/client"
+	"github.com/m3db/m3/src/cluster/kv"
+	"github.com/m3db/m3/src/cluster/kv/mem"
+	"github.com/m3db/m3/src/cluster/services"
+)
+
+const (
+	_kvPrefix = "_kv"
+)
+
+var (
+	// assert the interface matches.
+	_ client.Client = (*Client)(nil)
+)
+
+// Client provides a cluster/client.Client backed by kv/mem transaction store,
+// which stores data in memory instead of in etcd.
+type Client struct {
+	mu          sync.Mutex
+	serviceOpts kv.OverrideOptions
+	cache       map[cacheKey]kv.TxnStore
+}
+
+// New instantiates a client which defaults its stores to the given zone/env/namespace.
+func New(serviceOpts kv.OverrideOptions) *Client {
+	return &Client{
+		serviceOpts: serviceOpts,
+		cache:       make(map[cacheKey]kv.TxnStore),
+	}
+}
+
+// Services constructs a gateway to all cluster services, backed by a mem store.
+func (c *Client) Services(opts services.OverrideOptions) (services.Services, error) {
+	if opts == nil {
+		opts = services.NewOverrideOptions()
+	}
+
+	errUnsupported := errors.New("currently unsupported for inMemoryClusterClient")
+
+	kvGen := func(zone string) (kv.Store, error) {
+		return c.Store(kv.NewOverrideOptions().SetZone(zone))
+	}
+
+	heartbeatGen := func(sid services.ServiceID) (services.HeartbeatService, error) {
+		return nil, errUnsupported
+	}
+
+	leaderGen := func(sid services.ServiceID, opts services.ElectionOptions) (services.LeaderService, error) {
+		return nil, errUnsupported
+	}
+
+	return services.NewServices(
+		services.NewOptions().
+			SetKVGen(kvGen).
+			SetHeartbeatGen(heartbeatGen).
+			SetLeaderGen(leaderGen).
+			SetNamespaceOptions(opts.NamespaceOptions()),
+	)
+}
+
+// KV returns/constructs a mem backed kv.Store for the default zone/env/namespace.
+func (c *Client) KV() (kv.Store, error) {
+	return c.TxnStore(kv.NewOverrideOptions())
+}
+
+// Txn returns/constructs a mem backed kv.TxnStore for the default zone/env/namespace.
+func (c *Client) Txn() (kv.TxnStore, error) {
+	return c.TxnStore(kv.NewOverrideOptions())
+}
+
+// Store returns/constructs a mem backed kv.Store for the given env/zone/namespace.
+func (c *Client) Store(opts kv.OverrideOptions) (kv.Store, error) {
+	return c.TxnStore(opts)
+}
+
+// TxnStore returns/constructs a mem backed kv.TxnStore for the given env/zone/namespace.
+func (c *Client) TxnStore(opts kv.OverrideOptions) (kv.TxnStore, error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	opts = mergeOpts(c.serviceOpts, opts)
+	key := cacheKey{
+		Env:       opts.Environment(),
+		Zone:      opts.Zone(),
+		Namespace: opts.Namespace(),
+	}
+	if s, ok := c.cache[key]; ok {
+		return s, nil
+	}
+
+	store := mem.NewStore()
+	c.cache[key] = store
+	return store, nil
+}
+
+type cacheKey struct {
+	Env       string
+	Zone      string
+	Namespace string
+}
+
+func mergeOpts(defaults kv.OverrideOptions, opts kv.OverrideOptions) kv.OverrideOptions {
+	if opts.Zone() == "" {
+		opts = opts.SetZone(defaults.Zone())
+	}
+
+	if opts.Environment() == "" {
+		opts = opts.SetEnvironment(defaults.Environment())
+	}
+
+	if opts.Namespace() == "" {
+		opts = opts.SetNamespace(_kvPrefix)
+	}
+
+	return opts
+}

src/cluster/mem/mem_test.go

@@ -0,0 +1,94 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package memcluster
+
+import (
+	"testing"
+
+	"github.com/m3db/m3/src/cluster/kv"
+	"github.com/m3db/m3/src/cluster/placement"
+	"github.com/m3db/m3/src/cluster/services"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestReusesStores(t *testing.T) {
+	key := "my_key"
+
+	c := New(kv.NewOverrideOptions())
+	store, err := c.TxnStore(kv.NewOverrideOptions())
+	require.NoError(t, err)
+	version, err := store.Set(key, &dummyProtoMessage{"my_value"})
+	require.NoError(t, err)
+
+	// retrieve the same store
+	sameStore, err := c.TxnStore(kv.NewOverrideOptions())
+	require.NoError(t, err)
+
+	v, err := sameStore.Get(key)
+	require.NoError(t, err)
+	assert.Equal(t, version, v.Version())
+
+	// other store doesn't have the value.
+	otherZone, err := c.TxnStore(kv.NewOverrideOptions().SetZone("other"))
+	require.NoError(t, err)
+	_, err = otherZone.Get(key)
+	assert.EqualError(t, err, "key not found")
+}
+
+func TestServices_Placement(t *testing.T) {
+	c := New(kv.NewOverrideOptions())
+	svcs, err := c.Services(services.NewOverrideOptions())
+	require.NoError(t, err)
+
+	placementSvc, err := svcs.PlacementService(services.NewServiceID().SetName("test_svc"), placement.NewOptions())
+	require.NoError(t, err)
+
+	p := placement.NewPlacement().SetInstances([]placement.Instance{
+		placement.NewInstance().SetHostname("host").SetEndpoint("127.0.0.1"),
+	})
+
+	p, err = placementSvc.Set(p)
+	require.NoError(t, err)
+
+	retrieved, err := placementSvc.Placement()
+	require.NoError(t, err)
+
+	// n.b.: placements are hard to compare directly since they're interfaces and contain more pointers than
+	// they ought, and it's not worth writing the method here.
+	assert.Equal(t, p.Version(), retrieved.Version())
+}
+
+// dummyProtoMessage implements proto.Message and exists solely as a thing
+// to pass to a kv.Store.
+type dummyProtoMessage struct {
+	Val string
+}
+
+func (d *dummyProtoMessage) Reset() {
+}
+
+func (d *dummyProtoMessage) String() string {
+	return d.Val
+}
+
+func (d *dummyProtoMessage) ProtoMessage() {
+}