Cowboy Constrains¶

约束是应用于用户输入的验证和转换函数。

语法:

field
{field, Constraints}
{field, Constraints, Default}

实例:

PositiveFun = fun
    (_, V) when V > 0 ->
        {ok, V};
    (_, _) ->
        {error, not_positive}
end,
{my_value, [int, PositiveFun]}.

内置函数:

int
nonempty

自定义函数:

% forward
int(forward, Value) ->
  try
      {ok, binary_to_integer(Value)}
  catch _:_ ->
      {error, not_an_integer}
  end;

% reverse
int(reverse, Value) ->
  try
    {ok, integer_to_binary(Value)}
  catch _:_ ->
    {error, not_an_integer}
  end;

% format_error
int(format_error, {not_an_integer, Value}) ->
  io_lib:format("The value ~p is not an integer.", [Value]).