c213fd1fd8
There is no need to depend on the old context package now that the minimum Go version is 1.7. The move to "context" eliminates our weird vendoring setup. Some vendored code still uses golang.org/x/net/context and it is now vendored in the normal way. This change triggered new vet checks around context.WithTimeout which didn't fire with golang.org/x/net/context.
89 lines
2.5 KiB
Go
89 lines
2.5 KiB
Go
// Copyright 2016 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package rpc_test
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import (
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"context"
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"fmt"
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"math/big"
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"time"
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"github.com/ethereum/go-ethereum/rpc"
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)
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// In this example, our client whishes to track the latest 'block number'
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// known to the server. The server supports two methods:
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//
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// eth_getBlockByNumber("latest", {})
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// returns the latest block object.
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//
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// eth_subscribe("newBlocks")
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// creates a subscription which fires block objects when new blocks arrive.
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type Block struct {
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Number *big.Int
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}
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func ExampleClientSubscription() {
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// Connect the client.
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client, _ := rpc.Dial("ws://127.0.0.1:8485")
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subch := make(chan Block)
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// Ensure that subch receives the latest block.
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go func() {
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for i := 0; ; i++ {
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if i > 0 {
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time.Sleep(2 * time.Second)
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}
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subscribeBlocks(client, subch)
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}
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}()
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// Print events from the subscription as they arrive.
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for block := range subch {
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fmt.Println("latest block:", block.Number)
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}
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}
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// subscribeBlocks runs in its own goroutine and maintains
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// a subscription for new blocks.
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func subscribeBlocks(client *rpc.Client, subch chan Block) {
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ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
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defer cancel()
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// Subscribe to new blocks.
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sub, err := client.EthSubscribe(ctx, subch, "newBlocks")
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if err != nil {
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fmt.Println("subscribe error:", err)
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return
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}
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// The connection is established now.
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// Update the channel with the current block.
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var lastBlock Block
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if err := client.CallContext(ctx, &lastBlock, "eth_getBlockByNumber", "latest"); err != nil {
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fmt.Println("can't get latest block:", err)
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return
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}
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subch <- lastBlock
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// The subscription will deliver events to the channel. Wait for the
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// subscription to end for any reason, then loop around to re-establish
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// the connection.
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fmt.Println("connection lost: ", <-sub.Err())
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}
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