90 lines
2.6 KiB
Go
90 lines
2.6 KiB
Go
// Copyright 2016 The go-ethereum Authors
|
|
// This file is part of the go-ethereum library.
|
|
//
|
|
// The go-ethereum library is free software: you can redistribute it and/or modify
|
|
// it under the terms of the GNU Lesser General Public License as published by
|
|
// the Free Software Foundation, either version 3 of the License, or
|
|
// (at your option) any later version.
|
|
//
|
|
// The go-ethereum library is distributed in the hope that it will be useful,
|
|
// but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
// GNU Lesser General Public License for more details.
|
|
//
|
|
// You should have received a copy of the GNU Lesser General Public License
|
|
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
|
|
|
|
package rpc_test
|
|
|
|
import (
|
|
"context"
|
|
"fmt"
|
|
"time"
|
|
|
|
"github.com/ethereum/go-ethereum/common/hexutil"
|
|
"github.com/ethereum/go-ethereum/rpc"
|
|
)
|
|
|
|
// In this example, our client wishes to track the latest 'block number'
|
|
// known to the server. The server supports two methods:
|
|
//
|
|
// eth_getBlockByNumber("latest", {})
|
|
// returns the latest block object.
|
|
//
|
|
// eth_subscribe("newHeads")
|
|
// creates a subscription which fires block objects when new blocks arrive.
|
|
|
|
type Block struct {
|
|
Number *hexutil.Big
|
|
}
|
|
|
|
func ExampleClientSubscription() {
|
|
// Connect the client.
|
|
client, _ := rpc.Dial("ws://127.0.0.1:8545")
|
|
subch := make(chan Block)
|
|
|
|
// Ensure that subch receives the latest block.
|
|
go func() {
|
|
for i := 0; ; i++ {
|
|
if i > 0 {
|
|
time.Sleep(2 * time.Second)
|
|
}
|
|
subscribeBlocks(client, subch)
|
|
}
|
|
}()
|
|
|
|
// Print events from the subscription as they arrive.
|
|
for block := range subch {
|
|
fmt.Println("latest block:", block.Number)
|
|
}
|
|
}
|
|
|
|
// subscribeBlocks runs in its own goroutine and maintains
|
|
// a subscription for new blocks.
|
|
func subscribeBlocks(client *rpc.Client, subch chan Block) {
|
|
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
|
|
defer cancel()
|
|
|
|
// Subscribe to new blocks.
|
|
sub, err := client.EthSubscribe(ctx, subch, "newHeads")
|
|
if err != nil {
|
|
fmt.Println("subscribe error:", err)
|
|
return
|
|
}
|
|
|
|
// The connection is established now.
|
|
// Update the channel with the current block.
|
|
var lastBlock Block
|
|
err = client.CallContext(ctx, &lastBlock, "eth_getBlockByNumber", "latest", false)
|
|
if err != nil {
|
|
fmt.Println("can't get latest block:", err)
|
|
return
|
|
}
|
|
subch <- lastBlock
|
|
|
|
// The subscription will deliver events to the channel. Wait for the
|
|
// subscription to end for any reason, then loop around to re-establish
|
|
// the connection.
|
|
fmt.Println("connection lost: ", <-sub.Err())
|
|
}
|