【发布时间】：2019-07-10 00:16:53
【问题描述】：
模块调用gen_server 来处理流，该流使用记录作为状态。
handle_call 使用来自State 的函数处理流，该函数将完成的数据和尾部分开，
现在下一次，在模块发送更多数据之前，应先馈送尾部但更新State。
handle_call({stream, Data}, _From, State = #mystate{myfun=Fun}) ->
case Fun(Data) of
{completed piece,tail} ->
dosomethingwithpieace,
NewState = State##mystate{myfun=resetfun()};
% How do i call this again to feed Tail first with new state?
{stillstreaming, Currentstate} ->
NewState = State##mystate{myfun=CurrentState};
我无法致电gen_server:call(self(),{stream, Tail})，因为需要先更新State。
而且我无法回复新的State，因为模块会发送更多数据并且尾部会消失。
有没有办法用更新的State 再次调用它而不用尾部回复并从模块反馈尾部？？
更新，代码：
% caller module
case gen_tcp:recv(Socket, 0) of % cannot set Length as it will block untill it is done reading Length number of bytes
{ok, Data} ->
Response = gen_server:call(Pid, {handle_init,Socket,Data}),
case Response of
{ok, continue} ->
pre_loop(Socket, Pid);
{ok, logged_in} ->
{UserId, UserName} = get_user_data(), % ignore it for now.
receiver_loop(UserId, UserName, Socket, Pid);
{stop, Reason} ->
io:format("Error at pre_loop: ~p~n", [Reason]);
_ ->
io:format("Unknown response from call in pre-loop: ~p~n", [Response])
end;
{error, closed} -> % done here as no data was stored in mnesia yet.
gen_server:stop(Pid),
io:format("Client died in pre_loop~n")
end.
和 gen_server 模块：
% gen_server module
handle_call({handle_init, _Socket, Data}, _From, State = #server_state{data_fun = {incomplete, Fun}}) ->
case catch Fun(Data) of
{incomplete, F} ->
NewState = State#server_state{data_fun = {incomplete, F}},
{reply, {ok, continue}, NewState};
{with_tail, Term, Tail} ->
% handle Term login/register only
case handle_input_init(Term, Tail) of
{incomplete, Fn, logged_in} ->
NewState = State#server_state{data_fun = {incomplete, Fn}},
{reply, {ok, logged_in}, NewState};
{incomplete, Fn} ->
NewState = State#server_state{data_fun = {incomplete, Fn}},
{reply, {ok, continue}, NewState};
{stop, malformed_data} ->
{reply, {stop, malformed_data}, State}
end;
_ ->
{reply, {stop, malformed_data}, State}
end;
handle_call(_Message, _From, State = #server_state{}) ->
{reply, {stop , unknown_call}, State}.
handle_input_init(Term, Tail) ->
case handle_term_init(Term) of
{ok, login_passed} ->
io:format("send user a login pass msg"),
handle_tail_init(Tail, logged_in);
{error, login_failed} ->
io:format("send user a login failed error~n"),
handle_tail_init(Tail);
{ok, registration_passed} ->
io:format("send user a registeration passed msg"),
handle_tail_init(Tail);
{error, registration_failed} ->
io:format("send user a registeration failed error"),
handle_tail_init(Tail);
{error, invalidreq} ->
io:format("send user an invalid requst error~n"),
handle_tail_init(Tail)
end.
handle_tail_init(Tail) ->
case catch jsx:decode(Tail, [stream, return_tail, return_maps]) of
{incomplete, F} ->
{incomplete, F};
{with_tail, Term, Tail2} ->
handle_input_init(Term, Tail2);
_ ->
{stop, malformed_data}
end.
handle_tail_init(Tail, logged_in) -> % because it was logged in already, any further requests should be ignored
case catch jsx:decode(Tail, [stream, return_tail, return_maps]) of
{incomplete, F} ->
{incomplete, F, logged_in};
{with_tail, _Term, Tail2} ->
io:format("send user an invalid requst error~n"),
handle_tail_init(Tail2, logged_in);
_ ->
{stop, malformed_data}
end.
handle_term_init(Term) ->
case Term of
#{<<"Login">> := [UserName,Password]} ->
login_user(UserName,Password);
#{<<"Register">> := [UserName,Password]} ->
register_user(UserName,Password);
_ ->
{error, invalidreq}
end.
它按预期工作，但这是我的第一个 Erlang 代码，我很肯定它可以简化为单个 recursive handle_call，保持 OTP 风格，这是我选择 Erlang 的原因.
【问题讨论】：
-
在写任何东西时都不要使用代词——谁知道
it和this指的是什么。好吧，你知道——但你是唯一的一个。你可以在 State 中保存你想要的任何东西：如果需要，将它扩展为一个 1,000 个元素的元组，其中一个元素是你的记录，然后你可以使用其他 999 个插槽来存储你想要的任何东西——包括你消失的尾巴。另外，我认为您的问题与流没有任何关系，因此请创建一个简单的示例来演示您的问题而不使用流，例如handle_call({go, Data}, _From, Func) -> case Func(Data) of {X, Y} -
它不是我的尾巴 xD，是的，我知道我可以，但这并不能解决问题，我可以使用数千个元组或编写多个函数来解决它，但它会产生更多问题，即如果尾部包含完整的数据还是完整的数据本身？除了编写复杂的代码之外，我还必须在任何地方处理已完成的部分。
标签： erlang erlang-otp gen-server