Question

我正在阅读“编程Erlang”一书，第253页有一个运行客户端/服务器连接的示例。下面的代码建议在两个独立的erlang控制台窗口中运行以下命令，我从中获得以下错误。

2> socket_examples:nano_client_eval("list_to_tuple([2+3*4,10+20])").
** exception error: no match of right hand side value {error,econnrefused}
     in function  socket_examples:nano_client_eval/1 (socket_examples.erl, line 28)

服务器端的命令： socket_examples:start_nano_server().

客户端的命令： socket_examples:nano_client_eval("list_to_tuple([2+3*4,10+20])").

我没有启用防火墙，但这不应该是一个问题，因为它不在线。

    %% ---
%%  Excerpted from "Programming Erlang",   
%%---
-module(socket_examples).
-compile(export_all).
-import(lists, [reverse/1]).


nano_get_url() ->
    nano_get_url("www.google.com").

nano_get_url(Host) ->
    {ok,Socket} = gen_tcp:connect(Host,80,[binary, {packet, 0}]), %% (1)
    ok = gen_tcp:send(Socket, "GET / HTTP/1.0\r\n\r\n"),  %% (2)
    receive_data(Socket, []).

receive_data(Socket, SoFar) ->
    receive
    {tcp,Socket,Bin} ->    %% (3)
        receive_data(Socket, [Bin|SoFar]);
    {tcp_closed,Socket} -> %% (4)
        list_to_binary(reverse(SoFar)) %% (5)
    end.



nano_client_eval(Str) ->
    {ok, Socket} = 
    gen_tcp:connect("localhost", 2345,
            [binary, {packet, 4}]),
    ok = gen_tcp:send(Socket, term_to_binary(Str)),
    receive
    {tcp,Socket,Bin} ->
        io:format("Client received binary = ~p~n",[Bin]),
        Val = binary_to_term(Bin),
        io:format("Client result = ~p~n",[Val]),
        gen_tcp:close(Socket)
    end.



start_nano_server() ->
    {ok, Listen} = gen_tcp:listen(2345, [binary, {packet, 4},  %% (6)
                     {reuseaddr, true},
                     {active, true}]),
    {ok, Socket} = gen_tcp:accept(Listen),  %% (7)
    gen_tcp:close(Listen),  %% (8)
    loop(Socket).

loop(Socket) ->
    receive
    {tcp, Socket, Bin} ->
        io:format("Server received binary = ~p~n",[Bin]),
        Str = binary_to_term(Bin),  %% (9)
        io:format("Server (unpacked)  ~p~n",[Str]),
        Reply = lib_misc:string2value(Str),  %% (10)
        io:format("Server replying = ~p~n",[Reply]),
        gen_tcp:send(Socket, term_to_binary(Reply)),  %% (11)
        loop(Socket);
    {tcp_closed, Socket} ->
        io:format("Server socket closed~n")
    end.



error_test() ->
    spawn(fun() -> error_test_server() end),
    lib_misc:sleep(2000),
    {ok,Socket} = gen_tcp:connect("localhost",4321,[binary, {packet, 2}]),
    io:format("connected to:~p~n",[Socket]),
    gen_tcp:send(Socket, <<"123">>),
    receive
    Any ->
        io:format("Any=~p~n",[Any])
    end.

error_test_server() ->
    {ok, Listen} = gen_tcp:listen(4321, [binary,{packet,2}]),
    {ok, Socket} = gen_tcp:accept(Listen),
    error_test_server_loop(Socket).

error_test_server_loop(Socket) ->
    receive
    {tcp, Socket, Data} ->
        io:format("received:~p~n",[Data]),
        atom_to_list(Data),
        error_test_server_loop(Socket)
    end.

Answer 1

您收到的消息（{error，econnrefused}）显示服务器已关闭。

正如Muzaaya所说，{packet，N}应该在系统中保持一致。如果不是服务器将在binary_to_term转换和崩溃中失败（我没有深入研究，但我想这与信息的传输方式有关）。

接下来的请求将获得连接被拒绝的消息。

根据Muzaaya建议的更改，服务器能够执行binary_to_term，并且一切正常，直到调用b_misc：string2value ...这不包含在帖子中。

我注意到奇怪的东西：

我使用spawn启动了服务器（socket_examples，start_nano_server，[]）。
服务器在调用未定义模块时崩溃 - ＆gt;正常行为。
但是shell挂起了，我无法输入任何新命令。

我无法理解发生了什么。

编辑：

感谢Muzaaya，我忘了查看客户端代码......

我在这里发布了修改过的代码，除了数据包定义外，我在服务器和客户端做了一些更改。我必须说我没有深入了解文档，但似乎原始代码中有一些问题，包括打开，关闭和接受。我不确定这里的代码是否正确，我知道它错过了正确关闭套接字的东西，最重要的是这个代码并没有并行提供多个请求。

 -module(socket_examples).
-compile(export_all).
-import(lists, [reverse/1]).


nano_get_url() ->
    nano_get_url("www.google.com").

nano_get_url(Host) ->
    {ok,Socket} = gen_tcp:connect(Host,80,[binary, {packet, 0}]), %% (1)
    ok = gen_tcp:send(Socket, "GET / HTTP/1.0\r\n\r\n"),  %% (2)
    receive_data(Socket, []).

receive_data(Socket, SoFar) ->
    receive
    {tcp,Socket,Bin} ->    %% (3)
        receive_data(Socket, [Bin|SoFar]);
    {tcp_closed,Socket} -> %% (4)
        list_to_binary(reverse(SoFar)) %% (5)
    end.



nano_client_eval(Str) ->
    {ok, Socket} = 
    gen_tcp:connect("localhost", 2345,
            [binary, {packet, 0}]),
    ok = gen_tcp:send(Socket, term_to_binary(Str)),
    R = receive
        {tcp,Socket,Bin} ->
            io:format("Client received binary = ~p~n",[Bin]),
            Val = binary_to_term(Bin),
            io:format("Client result = ~p~n",[Val]),
            {ok,Val}
        after 5000 ->
            io:format("nano_client_eval got not answer to ~p~n",[Str]),
            {error,timeout}
    end,
%   gen_tcp:close(Socket),
    R.



start_nano_server() ->
    {ok, Listen} = gen_tcp:listen(2345, [binary, {packet, 0},  %% (6)
                     {reuseaddr, true},
                     {active, true}]),
 %   {ok, Socket} = gen_tcp:accept(Listen),  %% (7)
 %   gen_tcp:close(Listen),  %% (8)
%    loop(Socket).
    loop(Listen).

% loop(Socket) ->
loop(Listen) ->
    {ok, Socket} = gen_tcp:accept(Listen),
    receive
    {tcp, Socket, Bin} ->
        io:format("Server received binary = ~p~n",[Bin]),
        Str = binary_to_term(Bin),  %% (9)
        io:format("Server (unpacked)  ~p~n",[Str]),
%        Reply = lib_misc:string2value(Str),  %% (10)
        Reply = string:to_upper(Str),  %% (10)
        io:format("Server replying = ~p~n",[Reply]),
        gen_tcp:send(Socket, term_to_binary(Reply)),  %% (11)
%        loop(Socket);
        loop(Listen);
    {tcp_closed, Socket} ->
        io:format("Server socket closed~n")
    end.



error_test() ->
    spawn(fun() -> error_test_server() end),
    lib_misc:sleep(2000),
    {ok,Socket} = gen_tcp:connect("localhost",4321,[binary, {packet, 0}]),
    io:format("connected to:~p~n",[Socket]),
    gen_tcp:send(Socket, <<"123">>),
    receive
    Any ->
        io:format("Any=~p~n",[Any])
    end.

error_test_server() ->
    {ok, Listen} = gen_tcp:listen(4321, [binary,{packet,0}]),
    {ok, Socket} = gen_tcp:accept(Listen),
    error_test_server_loop(Socket).

error_test_server_loop(Socket) ->
    receive
    {tcp, Socket, Data} ->
        io:format("received:~p~n",[Data]),
        atom_to_list(Data),
        error_test_server_loop(Socket)
    end.

Erlang客户端 - 服务器错误

1 个答案: