nickva commented on PR #4729:
URL: https://github.com/apache/couchdb/pull/4729#issuecomment-1689241307
A bit more of a cleaned up connection script version which should work on
macos, linux and freebsd:
```erlang
#!/usr/bin/env escript
is_closed(Sock) ->
OsType = os:type(),
case tcp_info_opt(OsType) of
{raw, _, _, _} = TcpInfoOpt ->
case inet:getopts(Sock, [TcpInfoOpt]) of
{ok, [{raw, _, _, <<State:8/native, _/binary>>}]} ->
tcp_fsm_state(State, OsType);
{ok, []} ->
false;
{error, einval} ->
% Already cleaned up
true;
{error, _} ->
false
end;
undefined ->
false
end.
% All OS-es have the tcpi_state (uint8) as first member of tcp_info struct
tcp_info_opt({unix, linux}) ->
%% include/netinet/in.h
%% IPPROTO_TCP = 6
%%
%% include/netinet/tcp.h
%% #define TCP_INFO 11
%%
{raw, 6, 11, 1};
tcp_info_opt({unix, darwin}) ->
%% include/netinet/in.h
%% #define IPPROTO_TCP 6
%%
%% netinet/tcp.h
%% #define TCP_CONNECTION_INFO 0x106
%%
{raw, 6, 16#106, 1};
tcp_info_opt({unix, freebsd}) ->
%% sys/netinet/in.h
%% #define IPPROTO_TCP 6 /* tcp */
%%
%% sys/netinet/tcp.h
%% #define TCP_INFO 32 /* retrieve tcp_info structure */
%%
{raw, 6, 32, 1};
tcp_info_opt({_, _}) ->
undefined.
tcp_fsm_state(State, {unix, linux}) ->
%% netinet/tcp.h
%% enum
%% {
%% TCP_ESTABLISHED = 1,
%% TCP_SYN_SENT,
%% TCP_SYN_RECV,
%% TCP_FIN_WAIT1,
%% TCP_FIN_WAIT2,
%% TCP_TIME_WAIT,
%% TCP_CLOSE,
%% TCP_CLOSE_WAIT,
%% TCP_LAST_ACK,
%% TCP_LISTEN,
%% TCP_CLOSING
%% }
%%
lists:member(State, [4, 5, 6, 7, 8, 9, 10]);
tcp_fsm_state(State, {unix, darwin}) ->
%% netinet/tcp_fsm.h
%% #define TCPS_CLOSED 0 /* closed */
%% #define TCPS_LISTEN 1 /* listening for connection
*/
%% #define TCPS_SYN_SENT 2 /* active, have sent syn */
%% #define TCPS_SYN_RECEIVED 3 /* have send and received
syn */
%% #define TCPS_ESTABLISHED 4 /* established */
%% #define TCPS_CLOSE_WAIT 5 /* rcvd fin, waiting for
close */
%% #define TCPS_FIN_WAIT_1 6 /* have closed, sent fin */
%% #define TCPS_CLOSING 7 /* closed xchd FIN; await
FIN ACK */
%% #define TCPS_LAST_ACK 8 /* had fin and close; await
FIN ACK */
%% #define TCPS_FIN_WAIT_2 9 /* have closed, fin is
acked */
%% #define TCPS_TIME_WAIT 10 /* in 2*msl quiet wait
after close */
%%
lists:member(State, [0, 5, 6, 7, 8, 9, 10]);
tcp_fsm_state(State, {unix, freebsd}) ->
%% netinet/tcp_fsm.h
%% #define TCPS_CLOSED 0 /* closed */
%% #define TCPS_LISTEN 1 /* listening for connection */
%% #define TCPS_SYN_SENT 2 /* active, have sent syn */
%% #define TCPS_SYN_RECEIVED 3 /* have sent and received syn */
%% #define TCPS_ESTABLISHED 4 /* established */
%% #define TCPS_CLOSE_WAIT 5 /* rcvd fin, waiting for close */
%% #define TCPS_FIN_WAIT_1 6 /* have closed, sent fin */
%% #define TCPS_CLOSING 7/* closed xchd FIN; await FIN ACK */
%% #define TCPS_LAST_ACK 8/* had fin and close; await FIN ACK */
%% #define TCPS_FIN_WAIT_2 9/* have closed, fin is acked */
%% #define TCPS_TIME_WAIT 10 /* in 2*msl quiet wait after close */
%%
lists:member(State, [0, 5, 6, 7, 8, 9, 10]).
monitor_loop(Sock) ->
timer:sleep(1000),
io:format("[mon] is_closed: ~p~n", [is_closed(Sock)]),
monitor_loop(Sock).
client(Port) ->
timer:sleep(1000),
io:format("[client] connecting on ~p~n", [Port]),
{ok, ClientSock} = gen_tcp:connect("127.0.0.1", Port, [{active, false},
binary]),
io:format("[client] connected ~p sleeping for 5 seconds and exiting~n",
[ClientSock]),
timer:sleep(5000),
io:format("[client] exiting ~n", []),
ok.
main(_) ->
{ok, ListenSocket} = gen_tcp:listen(0, [binary, {active, false}]),
{ok, Port} = inet:port(ListenSocket),
io:format("[srv] spawning client to connect to port ~p~n", [Port]),
spawn_link(fun() -> client(Port) end),
{ok, ClientSocket} = gen_tcp:accept(ListenSocket),
io:format("[srv] accepted a connection ~p, sleeping for 10 seconds then
exiting ~n", [ClientSocket]),
spawn_link(fun() -> monitor_loop(ClientSocket) end),
timer:sleep(10000).
```
```
./tcp_server_erlang.escript
[srv] spawning client to connect to port 59121
[client] connecting on 59121
[srv] accepted a connection #Port<0.8>, sleeping for 10 seconds then exiting
[client] connected #Port<0.7> sleeping for 5 seconds and exiting
[mon] is_closed: false
[mon] is_closed: false
[mon] is_closed: false
[mon] is_closed: false
[client] exiting
[mon] is_closed: true
[mon] is_closed: true
[mon] is_closed: true
[mon] is_closed: true
[mon] is_closed: true
```
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