github.com/snowblossomcoin/go-ethereum@v1.9.25/rpc/doc.go (about)

     1  // Copyright 2015 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  /*
    18  
    19  Package rpc implements bi-directional JSON-RPC 2.0 on multiple transports.
    20  
    21  It provides access to the exported methods of an object across a network or other I/O
    22  connection. After creating a server or client instance, objects can be registered to make
    23  them visible as 'services'. Exported methods that follow specific conventions can be
    24  called remotely. It also has support for the publish/subscribe pattern.
    25  
    26  RPC Methods
    27  
    28  Methods that satisfy the following criteria are made available for remote access:
    29  
    30   - method must be exported
    31   - method returns 0, 1 (response or error) or 2 (response and error) values
    32  
    33  An example method:
    34  
    35   func (s *CalcService) Add(a, b int) (int, error)
    36  
    37  When the returned error isn't nil the returned integer is ignored and the error is sent
    38  back to the client. Otherwise the returned integer is sent back to the client.
    39  
    40  Optional arguments are supported by accepting pointer values as arguments. E.g. if we want
    41  to do the addition in an optional finite field we can accept a mod argument as pointer
    42  value.
    43  
    44   func (s *CalcService) Add(a, b int, mod *int) (int, error)
    45  
    46  This RPC method can be called with 2 integers and a null value as third argument. In that
    47  case the mod argument will be nil. Or it can be called with 3 integers, in that case mod
    48  will be pointing to the given third argument. Since the optional argument is the last
    49  argument the RPC package will also accept 2 integers as arguments. It will pass the mod
    50  argument as nil to the RPC method.
    51  
    52  The server offers the ServeCodec method which accepts a ServerCodec instance. It will read
    53  requests from the codec, process the request and sends the response back to the client
    54  using the codec. The server can execute requests concurrently. Responses can be sent back
    55  to the client out of order.
    56  
    57  An example server which uses the JSON codec:
    58  
    59   type CalculatorService struct {}
    60  
    61   func (s *CalculatorService) Add(a, b int) int {
    62  	return a + b
    63   }
    64  
    65   func (s *CalculatorService) Div(a, b int) (int, error) {
    66  	if b == 0 {
    67  		return 0, errors.New("divide by zero")
    68  	}
    69  	return a/b, nil
    70   }
    71  
    72   calculator := new(CalculatorService)
    73   server := NewServer()
    74   server.RegisterName("calculator", calculator)
    75   l, _ := net.ListenUnix("unix", &net.UnixAddr{Net: "unix", Name: "/tmp/calculator.sock"})
    76   server.ServeListener(l)
    77  
    78  Subscriptions
    79  
    80  The package also supports the publish subscribe pattern through the use of subscriptions.
    81  A method that is considered eligible for notifications must satisfy the following
    82  criteria:
    83  
    84   - method must be exported
    85   - first method argument type must be context.Context
    86   - method must have return types (rpc.Subscription, error)
    87  
    88  An example method:
    89  
    90   func (s *BlockChainService) NewBlocks(ctx context.Context) (rpc.Subscription, error) {
    91   	...
    92   }
    93  
    94  When the service containing the subscription method is registered to the server, for
    95  example under the "blockchain" namespace, a subscription is created by calling the
    96  "blockchain_subscribe" method.
    97  
    98  Subscriptions are deleted when the user sends an unsubscribe request or when the
    99  connection which was used to create the subscription is closed. This can be initiated by
   100  the client and server. The server will close the connection for any write error.
   101  
   102  For more information about subscriptions, see https://github.com/ethereum/go-ethereum/wiki/RPC-PUB-SUB.
   103  
   104  Reverse Calls
   105  
   106  In any method handler, an instance of rpc.Client can be accessed through the
   107  ClientFromContext method. Using this client instance, server-to-client method calls can be
   108  performed on the RPC connection.
   109  */
   110  package rpc