rpc: add new client, use it everywhere

The new client implementation supports concurrent requests,
subscriptions and replaces the various ad hoc RPC clients
throughout go-ethereum.

rpc/client_example_test.go

@@ -0,0 +1,83 @@
+// 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 (
+	"fmt"
+	"math/big"
+	"time"
+
+	"github.com/ethereum/go-ethereum/rpc"
+)
+
+// In this example, our client whishes 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("newBlocks")
+//    creates a subscription which fires block objects when new blocks arrive.
+
+type Block struct {
+	Number *big.Int
+}
+
+func ExampleClientSubscription() {
+	// Connect the client.
+	client, _ := rpc.Dial("ws://127.0.0.1:8485")
+	subch := make(chan Block)
+	go 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) {
+	for i := 0; ; i++ {
+		if i > 0 {
+			time.Sleep(2 * time.Second)
+		}
+
+		// Subscribe to new blocks.
+		sub, err := client.EthSubscribe(subch, "newBlocks")
+		if err == rpc.ErrClientQuit {
+			return // Stop reconnecting if the client was closed.
+		} else if err != nil {
+			fmt.Println("subscribe error:", err)
+			continue
+		}
+
+		// The connection is established now.
+		// Update the channel with the current block.
+		var lastBlock Block
+		if err := client.Call(&lastBlock, "eth_getBlockByNumber", "latest"); err != nil {
+			fmt.Println("can't get latest block:", err)
+			continue
+		}
+		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())
+	}
+}