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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, "newHeads")
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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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