pool: add a connection even on connection error

From a user's perspective, it is useful to add all target instances
to the pool, even some that are not currently unavailable. This way
the user don’t have to keep track of the list of actually added
instances.

The patch make it possible.

Closes #372

Author: oleg-jukovec

CHANGELOG.md

@@ -52,8 +52,8 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
   connection objects (#136). This function now does not attempt to reconnect 
   and tries to establish a connection only once. Function might be canceled 
   via context. Context accepted as first argument.
-  `pool.Connect` and `pool.Add` now accept context as first argument, which 
-  user may cancel in process. If `pool.Connect` is canceled in progress, an 
+  `pool.Connect` now accept context as first argument, which user may cancel
+  in process. If `pool.Connect` is canceled in progress, an
   error will be returned. All created connections will be closed.
 - `iproto.Feature` type now used instead of `ProtocolFeature` (#337)
 - `iproto.IPROTO_FEATURE_` constants now used instead of local `Feature` 
@@ -95,6 +95,8 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 - Renamed `StrangerResponse` to `MockResponse` (#237)
 - `pool.Connect`, `pool.ConnetcWithOpts` and `pool.Add` use a new type
   `pool.Instance` to determinate connection options (#356)
+- `pool.Connect`, `pool.ConnectWithOpts` and `pool.Add` add connections to
+  the pool even it is unable to connect to it (#372)
 
 ### Deprecated
 

README.md

@@ -199,9 +199,10 @@ The subpackage has been deleted. You could use `pool` instead.
   the second argument instead of a list of addresses. Each instance is
   associated with a unique string name, `Dialer` and connection options which
   allows instances to be independently configured.
-* `pool.Add` now accepts context as the first argument, which user may cancel
-  in process.
-* `pool.Add` now accepts `pool.Instance` as the second argument instead of
+* `pool.Connect`, `pool.ConnectWithOpts` and `pool.Add` add instances into
+  the pool even it is unable to connect to it. The pool will try to connect to
+  the instance later.
+* `pool.Add` now accepts `pool.Instance` as the first argument instead of
   an address, it allows to configure a new instance more flexible.
 * `pool.GetPoolInfo` has been renamed to `pool.GetInfo`. Return type has been
   changed to `map[string]ConnectionInfo`.

pool/connection_pool.go

@@ -24,9 +24,7 @@ import (
 )
 
 var (
-	ErrEmptyInstances    = errors.New("instances (second argument) should not be empty")
 	ErrWrongCheckTimeout = errors.New("wrong check timeout, must be greater than 0")
-	ErrNoConnection      = errors.New("no active connections")
 	ErrTooManyArgs       = errors.New("too many arguments")
 	ErrIncorrectResponse = errors.New("incorrect response format")
 	ErrIncorrectStatus   = errors.New("incorrect instance status: status should be `running`")
@@ -155,9 +153,6 @@ func newEndpoint(name string, dialer tarantool.Dialer, opts tarantool.Opts) *end
 // opts. Instances must have unique names.
 func ConnectWithOpts(ctx context.Context, instances []Instance,
 	opts Opts) (*ConnectionPool, error) {
-	if len(instances) == 0 {
-		return nil, ErrEmptyInstances
-	}
 	unique := make(map[string]bool)
 	for _, instance := range instances {
 		if _, ok := unique[instance.Name]; ok {
@@ -185,13 +180,10 @@ func ConnectWithOpts(ctx context.Context, instances []Instance,
 		anyPool: anyPool,
 	}
 
-	somebodyAlive, ctxCanceled := connPool.fillPools(ctx, instances)
-	if !somebodyAlive {
+	canceled := connPool.fillPools(ctx, instances)
+	if canceled {
 		connPool.state.set(closedState)
-		if ctxCanceled {
-			return nil, ErrContextCanceled
-		}
-		return nil, ErrNoConnection
+		return nil, ErrContextCanceled
 	}
 
 	connPool.state.set(connectedState)
@@ -252,9 +244,9 @@ func (p *ConnectionPool) ConfiguredTimeout(mode Mode) (time.Duration, error) {
 	return conn.ConfiguredTimeout(), nil
 }
 
-// Add adds a new instance into the pool. This function adds the instance
-// only after successful connection.
-func (p *ConnectionPool) Add(ctx context.Context, instance Instance) error {
+// Add adds a new instance into the pool. The pool will try to connect to the
+// instance later if it is unable to establish a connection.
+func (p *ConnectionPool) Add(instance Instance) error {
 	e := newEndpoint(instance.Name, instance.Dialer, instance.Opts)
 
 	p.endsMutex.Lock()
@@ -274,14 +266,9 @@ func (p *ConnectionPool) Add(ctx context.Context, instance Instance) error {
 	p.ends[instance.Name] = e
 	p.endsMutex.Unlock()
 
-	if err := p.tryConnect(ctx, e); err != nil {
-		p.endsMutex.Lock()
-		delete(p.ends, instance.Name)
-		p.endsMutex.Unlock()
-		e.cancel()
-		close(e.closed)
-		return err
-	}
+	// The result does not matter, but we should try to connect to the instance
+	// as fast as possible.
+	_ = p.tryConnect(endpointCtx, e)
 
 	go p.controller(endpointCtx, e)
 	return nil
@@ -1146,34 +1133,29 @@ func (p *ConnectionPool) deactivateConnections() {
 }
 
 func (p *ConnectionPool) processConnection(conn *tarantool.Connection,
-	name string, end *endpoint) bool {
+	name string, end *endpoint) {
 	role, err := p.getConnectionRole(conn)
 	if err != nil {
 		conn.Close()
 		log.Printf("tarantool: storing connection to %s failed: %s\n", name, err)
-		return false
+		return
 	}
 
 	if !p.handlerDiscovered(name, conn, role) {
 		conn.Close()
-		return false
+		return
 	}
 	if p.addConnection(name, conn, role) != nil {
 		conn.Close()
 		p.handlerDeactivated(name, conn, role)
-		return false
+		return
 	}
 
 	end.conn = conn
 	end.role = role
-	return true
 }
 
-func (p *ConnectionPool) fillPools(ctx context.Context,
-	instances []Instance) (bool, bool) {
-	somebodyAlive := false
-	ctxCanceled := false
-
+func (p *ConnectionPool) fillPools(ctx context.Context, instances []Instance) bool {
 	// It is called before controller() goroutines, so we don't expect
 	// concurrency issues here.
 	for _, instance := range instances {
@@ -1187,22 +1169,20 @@ func (p *ConnectionPool) fillPools(ctx context.Context,
 				instance.Name, err)
 			select {
 			case <-ctx.Done():
-				ctxCanceled = true
-
 				p.ends[instance.Name] = nil
 				log.Printf("tarantool: operation was canceled")
 
 				p.deactivateConnections()
 
-				return false, ctxCanceled
+				return true
 			default:
 			}
-		} else if p.processConnection(conn, instance.Name, end) {
-			somebodyAlive = true
+		} else {
+			p.processConnection(conn, instance.Name, end)
 		}
 	}
 
-	return somebodyAlive, ctxCanceled
+	return false
 }
 
 func (p *ConnectionPool) updateConnection(e *endpoint) {

pool/connection_pool_test.go

@@ -86,22 +86,6 @@ var defaultTimeoutRetry = 500 * time.Millisecond
 
 var helpInstances []test_helpers.TarantoolInstance
 
-func TestConnect_error_empty_instances(t *testing.T) {
-	ctx, cancel := test_helpers.GetPoolConnectContext()
-	connPool, err := pool.Connect(ctx, []pool.Instance{})
-	cancel()
-	require.Nilf(t, connPool, "conn is not nil with incorrect param")
-	require.ErrorIs(t, err, pool.ErrEmptyInstances)
-}
-
-func TestConnect_error_unavailable(t *testing.T) {
-	ctx, cancel := test_helpers.GetPoolConnectContext()
-	connPool, err := pool.Connect(ctx, makeInstances([]string{"err1", "err2"}, connOpts))
-	cancel()
-	require.Nilf(t, connPool, "conn is not nil with incorrect param")
-	require.ErrorIs(t, err, pool.ErrNoConnection)
-}
-
 func TestConnect_error_duplicate(t *testing.T) {
 	ctx, cancel := test_helpers.GetPoolConnectContext()
 	connPool, err := pool.Connect(ctx, makeInstances([]string{"foo", "foo"}, connOpts))
@@ -145,6 +129,48 @@ func TestConnSuccessfully(t *testing.T) {
 	require.Nil(t, err)
 }
 
+func TestConnect_empty(t *testing.T) {
+	cases := []struct {
+		Name      string
+		Instances []pool.Instance
+	}{
+		{"nil", nil},
+		{"empty", []pool.Instance{}},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.Name, func(t *testing.T) {
+			ctx, cancel := test_helpers.GetPoolConnectContext()
+			defer cancel()
+			connPool, err := pool.Connect(ctx, tc.Instances)
+			if connPool != nil {
+				defer connPool.Close()
+			}
+			require.NoError(t, err, "failed to create a pool")
+			require.NotNilf(t, connPool, "pool is nil after Connect")
+			require.Lenf(t, connPool.GetInfo(), 0, "empty pool expected")
+		})
+	}
+}
+
+func TestConnect_unavailable(t *testing.T) {
+	servers := []string{"err1", "err2"}
+	ctx, cancel := test_helpers.GetPoolConnectContext()
+	connPool, err := pool.Connect(ctx, makeInstances([]string{"err1", "err2"}, connOpts))
+	cancel()
+
+	if connPool != nil {
+		defer connPool.Close()
+	}
+
+	require.NoError(t, err, "failed to create a pool")
+	require.NotNilf(t, connPool, "pool is nil after Connect")
+	require.Equal(t, map[string]pool.ConnectionInfo{
+		servers[0]: pool.ConnectionInfo{ConnectedNow: false, ConnRole: pool.UnknownRole},
+		servers[1]: pool.ConnectionInfo{ConnectedNow: false, ConnRole: pool.UnknownRole},
+	}, connPool.GetInfo())
+}
+
 func TestConnErrorAfterCtxCancel(t *testing.T) {
 	var connLongReconnectOpts = tarantool.Opts{
 		Timeout:       5 * time.Second,
@@ -410,16 +436,14 @@ func TestDisconnectAll(t *testing.T) {
 func TestAdd(t *testing.T) {
 	ctx, cancel := test_helpers.GetPoolConnectContext()
 	defer cancel()
-	connPool, err := pool.Connect(ctx, makeInstances(servers[:1], connOpts))
+	connPool, err := pool.Connect(ctx, []pool.Instance{})
 	require.Nilf(t, err, "failed to connect")
 	require.NotNilf(t, connPool, "conn is nil after Connect")
 
 	defer connPool.Close()
 
-	for _, server := range servers[1:] {
-		ctx, cancel := test_helpers.GetConnectContext()
-		err = connPool.Add(ctx, makeInstance(server, connOpts))
-		cancel()
+	for _, server := range servers {
+		err = connPool.Add(makeInstance(server, connOpts))
 		require.Nil(t, err)
 	}
 
@@ -452,9 +476,7 @@ func TestAdd_exist(t *testing.T) {
 
 	defer connPool.Close()
 
-	ctx, cancel = test_helpers.GetConnectContext()
-	err = connPool.Add(ctx, makeInstance(server, connOpts))
-	cancel()
+	err = connPool.Add(makeInstance(server, connOpts))
 	require.Equal(t, pool.ErrExists, err)
 
 	args := test_helpers.CheckStatusesArgs{
@@ -484,25 +506,23 @@ func TestAdd_unreachable(t *testing.T) {
 	defer connPool.Close()
 
 	unhealthyServ := "127.0.0.2:6667"
-	ctx, cancel = test_helpers.GetConnectContext()
-	err = connPool.Add(ctx, pool.Instance{
+	err = connPool.Add(pool.Instance{
 		Name: unhealthyServ,
 		Dialer: tarantool.NetDialer{
 			Address: unhealthyServ,
 		},
 		Opts: connOpts,
 	})
-	cancel()
-	// The OS-dependent error so we just check for existence.
-	require.NotNil(t, err)
+	require.NoError(t, err)
 
 	args := test_helpers.CheckStatusesArgs{
 		ConnPool:           connPool,
 		Mode:               pool.ANY,
 		Servers:            servers,
 		ExpectedPoolStatus: true,
 		ExpectedStatuses: map[string]bool{
-			server: true,
+			server:        true,
+			unhealthyServ: false,
 		},
 	}
 
@@ -520,9 +540,7 @@ func TestAdd_afterClose(t *testing.T) {
 	require.NotNilf(t, connPool, "conn is nil after Connect")
 
 	connPool.Close()
-	ctx, cancel = test_helpers.GetConnectContext()
-	err = connPool.Add(ctx, makeInstance(server, connOpts))
-	cancel()
+	err = connPool.Add(makeInstance(server, connOpts))
 	assert.Equal(t, err, pool.ErrClosed)
 }
 
@@ -541,9 +559,7 @@ func TestAdd_Close_concurrent(t *testing.T) {
 	go func() {
 		defer wg.Done()
 
-		ctx, cancel := test_helpers.GetConnectContext()
-		err = connPool.Add(ctx, makeInstance(serv1, connOpts))
-		cancel()
+		err = connPool.Add(makeInstance(serv1, connOpts))
 		if err != nil {
 			assert.Equal(t, pool.ErrClosed, err)
 		}
@@ -569,9 +585,7 @@ func TestAdd_CloseGraceful_concurrent(t *testing.T) {
 	go func() {
 		defer wg.Done()
 
-		ctx, cancel := test_helpers.GetConnectContext()
-		err = connPool.Add(ctx, makeInstance(serv1, connOpts))
-		cancel()
+		err = connPool.Add(makeInstance(serv1, connOpts))
 		if err != nil {
 			assert.Equal(t, pool.ErrClosed, err)
 		}
@@ -1028,8 +1042,17 @@ func TestConnectionHandlerOpenError(t *testing.T) {
 	if err == nil {
 		defer connPool.Close()
 	}
-	require.NotNilf(t, err, "success to connect")
-	require.Equalf(t, 2, h.discovered, "unexpected discovered count")
+	require.NoError(t, err, "failed to connect")
+	require.NotNil(t, connPool, "pool expected")
+	require.Equal(t, map[string]pool.ConnectionInfo{
+		servers[0]: pool.ConnectionInfo{ConnectedNow: false, ConnRole: pool.UnknownRole},
+		servers[1]: pool.ConnectionInfo{ConnectedNow: false, ConnRole: pool.UnknownRole},
+	}, connPool.GetInfo())
+	connPool.Close()
+
+	// It could happen additional reconnect attempts in the background, but
+	// at least 2 connects on start.
+	require.GreaterOrEqualf(t, h.discovered, 2, "unexpected discovered count")
 	require.Equalf(t, 0, h.deactivated, "unexpected deactivated count")
 }