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111 lines
4.2 KiB
Go
111 lines
4.2 KiB
Go
// Copyright 2015 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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/*
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Package rpc implements bi-directional JSON-RPC 2.0 on multiple transports.
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It provides access to the exported methods of an object across a network or other I/O
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connection. After creating a server or client instance, objects can be registered to make
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them visible as 'services'. Exported methods that follow specific conventions can be
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called remotely. It also has support for the publish/subscribe pattern.
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RPC Methods
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Methods that satisfy the following criteria are made available for remote access:
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- method must be exported
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- method returns 0, 1 (response or error) or 2 (response and error) values
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An example method:
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func (s *CalcService) Add(a, b int) (int, error)
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When the returned error isn't nil the returned integer is ignored and the error is sent
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back to the client. Otherwise the returned integer is sent back to the client.
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Optional arguments are supported by accepting pointer values as arguments. E.g. if we want
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to do the addition in an optional finite field we can accept a mod argument as pointer
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value.
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func (s *CalcService) Add(a, b int, mod *int) (int, error)
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This RPC method can be called with 2 integers and a null value as third argument. In that
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case the mod argument will be nil. Or it can be called with 3 integers, in that case mod
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will be pointing to the given third argument. Since the optional argument is the last
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argument the RPC package will also accept 2 integers as arguments. It will pass the mod
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argument as nil to the RPC method.
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The server offers the ServeCodec method which accepts a ServerCodec instance. It will read
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requests from the codec, process the request and sends the response back to the client
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using the codec. The server can execute requests concurrently. Responses can be sent back
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to the client out of order.
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An example server which uses the JSON codec:
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type CalculatorService struct {}
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func (s *CalculatorService) Add(a, b int) int {
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return a + b
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}
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func (s *CalculatorService) Div(a, b int) (int, error) {
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if b == 0 {
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return 0, errors.New("divide by zero")
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}
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return a/b, nil
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}
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calculator := new(CalculatorService)
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server := NewServer()
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server.RegisterName("calculator", calculator)
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l, _ := net.ListenUnix("unix", &net.UnixAddr{Net: "unix", Name: "/tmp/calculator.sock"})
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server.ServeListener(l)
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Subscriptions
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The package also supports the publish subscribe pattern through the use of subscriptions.
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A method that is considered eligible for notifications must satisfy the following
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criteria:
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- method must be exported
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- first method argument type must be context.Context
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- method must have return types (rpc.Subscription, error)
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An example method:
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func (s *BlockChainService) NewBlocks(ctx context.Context) (rpc.Subscription, error) {
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...
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}
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When the service containing the subscription method is registered to the server, for
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example under the "blockchain" namespace, a subscription is created by calling the
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"blockchain_subscribe" method.
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Subscriptions are deleted when the user sends an unsubscribe request or when the
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connection which was used to create the subscription is closed. This can be initiated by
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the client and server. The server will close the connection for any write error.
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For more information about subscriptions, see https://github.com/ledgerwatch/erigon/wiki/RPC-PUB-SUB.
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Reverse Calls
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In any method handler, an instance of rpc.Client can be accessed through the
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ClientFromContext method. Using this client instance, server-to-client method calls can be
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performed on the RPC connection.
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*/
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package rpc
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