2016-08-15 09:00:18 +02:00
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/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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2016-08-18 23:50:50 +02:00
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package cmd
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2016-08-15 09:00:18 +02:00
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import (
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2016-08-27 12:16:52 +02:00
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"errors"
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"net/rpc"
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"sync"
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)
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// RPCClient is a wrapper type for rpc.Client which provides reconnect on first failure.
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type RPCClient struct {
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mu sync.Mutex
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rpcPrivate *rpc.Client
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node string
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rpcPath string
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}
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// newClient constructs a RPCClient object with node and rpcPath initialized.
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// It _doesn't_ connect to the remote endpoint. See Call method to see when the
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// connect happens.
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func newClient(node, rpcPath string) *RPCClient {
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return &RPCClient{
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node: node,
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rpcPath: rpcPath,
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}
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}
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2016-08-27 12:16:52 +02:00
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// clearRPCClient clears the pointer to the rpc.Client object in a safe manner
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func (rpcClient *RPCClient) clearRPCClient() {
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rpcClient.mu.Lock()
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rpcClient.rpcPrivate = nil
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rpcClient.mu.Unlock()
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}
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// getRPCClient gets the pointer to the rpc.Client object in a safe manner
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func (rpcClient *RPCClient) getRPCClient() *rpc.Client {
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rpcClient.mu.Lock()
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rpcLocalStack := rpcClient.rpcPrivate
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rpcClient.mu.Unlock()
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return rpcLocalStack
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}
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// dialRPCClient tries to establish a connection to the server in a safe manner
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func (rpcClient *RPCClient) dialRPCClient() (*rpc.Client, error) {
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rpcClient.mu.Lock()
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defer rpcClient.mu.Unlock()
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// After acquiring lock, check whether another thread may not have already dialed and established connection
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if rpcClient.rpcPrivate != nil {
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return rpcClient.rpcPrivate, nil
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}
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rpc, err := rpc.DialHTTPPath("tcp", rpcClient.node, rpcClient.rpcPath)
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if err != nil {
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return nil, err
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} else if rpc == nil {
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return nil, errors.New("No valid RPC Client created after dial")
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}
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rpcClient.rpcPrivate = rpc
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return rpcClient.rpcPrivate, nil
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}
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// Call makes a RPC call to the remote endpoint using the default codec, namely encoding/gob.
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func (rpcClient *RPCClient) Call(serviceMethod string, args interface{}, reply interface{}) error {
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// Make a copy below so that we can safely (continue to) work with the rpc.Client.
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// Even in the case the two threads would simultaneously find that the connection is not initialised,
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// they would both attempt to dial and only one of them would succeed in doing so.
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rpcLocalStack := rpcClient.getRPCClient()
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// If the rpc.Client is nil, we attempt to (re)connect with the remote endpoint.
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if rpcLocalStack == nil {
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var err error
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rpcLocalStack, err = rpcClient.dialRPCClient()
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if err != nil {
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return err
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}
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}
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// If the RPC fails due to a network-related error, then we reset
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// rpc.Client for a subsequent reconnect.
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err := rpcLocalStack.Call(serviceMethod, args, reply)
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if err != nil {
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if err.Error() == rpc.ErrShutdown.Error() {
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// Reset rpcClient.rpc to nil to trigger a reconnect in future
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// and close the underlying connection.
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rpcClient.clearRPCClient()
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// Close the underlying connection.
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rpcLocalStack.Close()
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// Set rpc error as rpc.ErrShutdown type.
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err = rpc.ErrShutdown
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}
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}
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return err
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}
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// Close closes the underlying socket file descriptor.
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func (rpcClient *RPCClient) Close() error {
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// See comment above for making a copy on local stack
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rpcLocalStack := rpcClient.getRPCClient()
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// If rpc client has not connected yet there is nothing to close.
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if rpcLocalStack == nil {
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return nil
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}
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// Reset rpcClient.rpc to allow for subsequent calls to use a new
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// (socket) connection.
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rpcClient.clearRPCClient()
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return rpcLocalStack.Close()
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}
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