TCP半开的几个测试,比较简单都在Erlang Shell中完成.立此存照,备忘.

gen_tcp提供了shutdown来实现这个功能,下面官方文档中提到了{exit_on_close,false}参数,如果要实现半开,无论是Read Write都要添加这个参数. 官网文档 Doc Ref

shutdown(Socket, How) -> ok | {error, Reason}

Types:

Socket = socket()
How = read | write | read_write
Reason = posix()
Immediately close a socket in one or two directions.

How == write means closing the socket for writing, reading from it is still possible.

To be able to handle that the peer has done a shutdown on the write side, the {exit_on_close, false} option is useful.

shutdown read

%% ServerEshell V5.9  (abort with ^G)
1>  {ok,S0}=gen_tcp:listen(5678,[]).
{ok,#Port<0.506>}
2> {ok,S2}=gen_tcp:accept(S0).
{ok,#Port<0.512>}
3> flush().
Shell got {tcp,#Port<0.512>,[104,105,44,121,111,117,32,104,97,118,101,32,110,101,119,32,109,115,103,32,0]}
ok
4> gen_tcp:shutdown(S2,read).
ok
5> flush().
Shell got {tcp_closed,#Port<0.512>}
ok
6> gen_tcp:send(S2,"are you alive?").
{error,closed}
7>%% ClientEshell V5.9  (abort with ^G)
1> {ok,S1}= gen_tcp:connect("localhost",5678,[]).
{ok,#Port<0.511>}
2> gen_tcp:send(S1,"hi,you have new msg \0").
ok
3> gen_tcp:send(S1,"hi,you have new msg \0").  %% 发送这条消息导致server端 接受到tcp_closed的消息
ok
4> gen_tcp:send(S1,"hi,you have new msg \0").  %% 服务器端宕掉之后再发送消息 Client也会出现{error,closed}错误
{error,closed}

Client添加一下选项 {exit_on_close, false} 试试

%% ServerEshell V5.9  (abort with ^G)
1>  {ok,S0}=gen_tcp:listen(5678,[]).
{ok,#Port<0.506>}
2>  {ok,S2}=gen_tcp:accept(S0).
{ok,#Port<0.512>}
3>  gen_tcp:send(S2,"are you alive?").
ok
4> flush().
Shell got {tcp,#Port<0.512>,[104,105,44,121,111,117,32,104,97,118,101,32,110,101,119,32,109,115,103,32,0]}
ok
5> gen_tcp:shutdown(S2,read).
ok
6>  inet:getstat(S2).  %%这时候检查一下Socket的状态
{ok,[{recv_oct,21},{recv_cnt,1},{recv_max,21},{recv_avg,21},{recv_dvi,0},{send_oct,14},{send_cnt,1},{send_max,14},{send_avg,14},{send_pend,0}]}
7>  gen_tcp:send(S2,"are you alive?====").  %% 由于server只关闭了read 所以发送消息还可以发送出去
ok
8> flush().                   %% Client尝试发送消息
Shell got {tcp_closed,#Port<0.512>}
ok
9>  inet:getstat(S2).
{error,einval}
10>%% ClientEshell V5.9  (abort with ^G)
1>  {ok,S1} = gen_tcp:connect("localhost",5678,[{exit_on_close, false} ]).
{ok,#Port<0.511>}
2> gen_tcp:send(S1,"hi,you have new msg \0").
ok
3> flush().
Shell got {tcp,#Port<0.511>,"are you alive?"}
ok
4> flush().                     %% 服务器端只关闭了read 还可以发送消息 这条消息还可以收到
Shell got {tcp,#Port<0.511>,"are you alive?===="}
ok
5> gen_tcp:send(S1,"hi,you have new msg \0").  %% Client向Server发送消息 会导致Server收到tcp_closed消息
ok
6> gen_tcp:send(S1,"hi,you have new msg \0").
{error,closed}
7>

shutdown write

下面的测试关注点是shutdown write,过程和上面类似:

%%ServerEshell V5.9  (abort with ^G)
1>  {ok,S0}=gen_tcp:listen(5678,[]).
{ok,#Port<0.506>}
2> {ok,S2}=gen_tcp:accept(S0).
{ok,#Port<0.512>}
3> flush().
Shell got {tcp,#Port<0.512>,[104,105,44,121,111,117,32,104,97,118,101,32,110,101,119,32,109,115,103,32,0]}
ok
4>  gen_tcp:send(S2,"are you alive?").
ok
5> gen_tcp:shutdown(S2,write). %% 执行完这一句 检查Socket已经是einval
ok
6>  inet:getstat(S2).
{error,einval}
7>%%ClientEshell V5.9  (abort with ^G)
1>  {ok,S1}= gen_tcp:connect("localhost",5678,[]).
{ok,#Port<0.511>}
2> gen_tcp:send(S1,"hi,you have new msg \0").
ok
3> flush().
Shell got {tcp,#Port<0.511>,"are you alive?"}
ok
4> gen_tcp:send(S1,"hi,you have new msg \0").
{error,closed}
5>

调整实验添加exit_on_close选项

%%ServerEshell V5.9  (abort with ^G)
1> {ok,S0}=gen_tcp:listen(5678,[]).
{ok,#Port<0.506>}
2>  {ok,S2}=gen_tcp:accept(S0).
{ok,#Port<0.512>}
3> flush().
Shell got {tcp,#Port<0.512>,[104,105,44,121,111,117,32,104,97,118,101,32,110,101,119,32,109,115,103,32,0]}
ok
4>  gen_tcp:send(S2,"are you alive?").
ok
5> gen_tcp:shutdown(S2,write).
ok
6>   inet:getstat(S2).  %% 对比上面的测试结果 这里是正常的状态
{ok,[{recv_oct,21},{recv_cnt,1},{recv_max,21},{recv_avg,21},{recv_dvi,0},{send_oct,14},{send_cnt,1},{send_max,14},{send_avg,14},{send_pend,0}]}
7> flush().                %% 由于只关闭了写,读还是正常的,接受到的消息
Shell got {tcp,#Port<0.512>,[104,105,44,121,111,117,32,104,97,118,101,32,110,101,119,32,109,115,103,32,50,32,0]}
ok
8>  gen_tcp:send(S2,"are you alive?").  %% 关闭了写  这里的调用就会报错了
{error,closed}
9>   inet:getstat(S2).
{error,einval}
10>%% ClientEshell V5.9  (abort with ^G)
1>  {ok,S1} = gen_tcp:connect("localhost",5678,[{exit_on_close, false} ]).
{ok,#Port<0.511>}
2>  gen_tcp:send(S1,"hi,you have new msg \0").
ok
3> flush().
Shell got {tcp,#Port<0.511>,"are you alive?"}
ok
4>  gen_tcp:send(S1,"hi,you have new msg 2 \0").
ok
5>

gen_tcp shutdown

看看gen_tcp 的shutdown的逻辑:

shutdown(S, How) when is_port(S) ->case inet_db:lookup_socket(S) of{ok, Mod} ->Mod:shutdown(S, How);Error ->Errorend.

inet_db:lookup_socket(S) 的结果是什么?在Shell里面测试一下:

Eshell V5.9  (abort with ^G)
1>  {ok,S0}=gen_tcp:listen(5678,[]).
{ok,#Port<0.506>}
2> inet_db:lookup_socket(S0).
{ok,inet_tcp}
3>

|--> inet_tcp

%%
%% Shutdown one end of a socket
%%
shutdown(Socket, How) ->prim_inet:shutdown(Socket, How).

|--> prim_inet.erl

shutdown(S, read) when is_port(S) ->shutdown_2(S, 0);
shutdown(S, write) when is_port(S) ->shutdown_1(S, 1);
shutdown(S, read_write) when is_port(S) ->shutdown_1(S, 2).shutdown_1(S, How) ->case subscribe(S, [subs_empty_out_q]) of{ok,[{subs_empty_out_q,N}]} when N > 0 ->shutdown_pend_loop(S, N);   %% wait for pending output to be sent_Other -> okend,shutdown_2(S, How).shutdown_2(S, How) ->case ctl_cmd(S, ?TCP_REQ_SHUTDOWN, [How]) of{ok, []} -> ok;{error,_}=Error -> Errorend.shutdown_pend_loop(S, N0) ->receive{empty_out_q,S} -> okafter ?INET_CLOSE_TIMEOUT ->case getstat(S, [send_pend]) of{ok,[{send_pend,N0}]} -> ok;{ok,[{send_pend,N}]} -> shutdown_pend_loop(S, N);_ -> okendend.

上面处理考虑的相当周全,如果shutdown的时候有消息还没有发送完成,就会先完成暂存数据的发送,霸爷有一篇很详细的分析: gen_tcp调用进程收到{empty_out_q, Port}消息奇怪行为分析

最后小图一张 Natalie Portman :

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[Erlang 0097] TCP半开的几个小测试

shutdown read

shutdown write

gen_tcp shutdown

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