minio/cmd/net-rpc-client.go

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/*
* Minio Cloud Storage, (C) 2016 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cmd
import (
"errors"
"net/rpc"
"sync"
)
// RPCClient is a wrapper type for rpc.Client which provides reconnect on first failure.
type RPCClient struct {
mu sync.Mutex
rpcPrivate *rpc.Client
node string
rpcPath string
}
// newClient constructs a RPCClient object with node and rpcPath initialized.
// It _doesn't_ connect to the remote endpoint. See Call method to see when the
// connect happens.
func newClient(node, rpcPath string) *RPCClient {
return &RPCClient{
node: node,
rpcPath: rpcPath,
}
}
// clearRPCClient clears the pointer to the rpc.Client object in a safe manner
func (rpcClient *RPCClient) clearRPCClient() {
rpcClient.mu.Lock()
rpcClient.rpcPrivate = nil
rpcClient.mu.Unlock()
}
// getRPCClient gets the pointer to the rpc.Client object in a safe manner
func (rpcClient *RPCClient) getRPCClient() *rpc.Client {
rpcClient.mu.Lock()
rpcLocalStack := rpcClient.rpcPrivate
rpcClient.mu.Unlock()
return rpcLocalStack
}
// dialRPCClient tries to establish a connection to the server in a safe manner
func (rpcClient *RPCClient) dialRPCClient() (*rpc.Client, error) {
rpcClient.mu.Lock()
defer rpcClient.mu.Unlock()
// After acquiring lock, check whether another thread may not have already dialed and established connection
if rpcClient.rpcPrivate != nil {
return rpcClient.rpcPrivate, nil
}
rpc, err := rpc.DialHTTPPath("tcp", rpcClient.node, rpcClient.rpcPath)
if err != nil {
return nil, err
} else if rpc == nil {
return nil, errors.New("No valid RPC Client created after dial")
}
rpcClient.rpcPrivate = rpc
return rpcClient.rpcPrivate, nil
}
// Call makes a RPC call to the remote endpoint using the default codec, namely encoding/gob.
func (rpcClient *RPCClient) Call(serviceMethod string, args interface{}, reply interface{}) error {
// Make a copy below so that we can safely (continue to) work with the rpc.Client.
// Even in the case the two threads would simultaneously find that the connection is not initialised,
// they would both attempt to dial and only one of them would succeed in doing so.
rpcLocalStack := rpcClient.getRPCClient()
// If the rpc.Client is nil, we attempt to (re)connect with the remote endpoint.
if rpcLocalStack == nil {
var err error
rpcLocalStack, err = rpcClient.dialRPCClient()
if err != nil {
return err
}
}
// If the RPC fails due to a network-related error, then we reset
// rpc.Client for a subsequent reconnect.
err := rpcLocalStack.Call(serviceMethod, args, reply)
if err != nil {
if err.Error() == rpc.ErrShutdown.Error() {
// Reset rpcClient.rpc to nil to trigger a reconnect in future
// and close the underlying connection.
rpcClient.clearRPCClient()
// Close the underlying connection.
rpcLocalStack.Close()
// Set rpc error as rpc.ErrShutdown type.
err = rpc.ErrShutdown
}
}
return err
}
// Close closes the underlying socket file descriptor.
func (rpcClient *RPCClient) Close() error {
// See comment above for making a copy on local stack
rpcLocalStack := rpcClient.getRPCClient()
// If rpc client has not connected yet there is nothing to close.
if rpcLocalStack == nil {
return nil
}
// Reset rpcClient.rpc to allow for subsequent calls to use a new
// (socket) connection.
rpcClient.clearRPCClient()
return rpcLocalStack.Close()
}
// Node returns the node (network address) of the connection
func (rpcClient *RPCClient) Node() string {
return rpcClient.node
}
// RPCPath returns the RPC path of the connection
func (rpcClient *RPCClient) RPCPath() string {
return rpcClient.rpcPath
}