将C回调API转换为流

如何解决将C回调API转换为流

Playground link

我可以通过异步C api访问Pulseaudio。

pub fn get_sink_info_by_index<F>(
    &self,index: u32,callback: F
) -> Operation<dyn FnMut(ListResult<&SinkInfo>)> where
    F: FnMut(ListResult<&SinkInfo>) + 'static,

来源：https://docs.rs/libpulse-binding/2.16.1/libpulse_binding/context/introspect/struct.Introspector.html#method.get_sink_info_by_index

我已经实现了一个辅助函数（可以很好地编译），该函数生成一个回调以传递给C函数和输出流。

pub fn callbackStream<T:Sized + Clone>() -> (Box<dyn FnMut(ListResult<&'static T>)>,Box<dyn Stream<Item=T>>) {
    let (sender,recv) = channel(1024); // TODO channel size?
    let cb  = {|c: ListResult<&'static T>| match c {
        Item(it) => match sender.try_send(it.clone()) {
            Ok(_) => (),Err(err) => () // TODO
        },End => (),Error => () // TODO
    }};
    (Box::new(cb),Box::new(recv))
}

但是，当尝试使用它时，我却无法使用：

    fn stream_sink_info_by_index(
        &self,index: u32
    ) -> Box<dyn Stream<Item=SinkInfo>> {
        let (callback,stream): (Box<dyn FnMut(ListResult<&SinkInfo>) + 'static>,Box<dyn Stream<Item=SinkInfo>>) = callbackStream();
        self.get_sink_info_by_index(index,callback);
        stream
    }

给我

error[E0308]: mismatched types
  --> src/futuristicPulse.rs:31:117
   |
31 |         let (callback,Box<dyn Stream<Item=SinkInfo>>) = callbackStream();
   |                                 ---------------------------------------------------------------------------------   ^^^^^^^^^^^^^^^^ expected concrete lifetime,found bound lifetime parameter
   |                                 |
   |                                 expected due to this
   |
   = note: expected tuple `(std::boxed::Box<(dyn for<'r,'s> std::ops::FnMut(pulse::callbacks::ListResult<&'r pulse::context::introspect::SinkInfo<'s>>) + 'static)>,std::boxed::Box<dyn futures_core::stream::Stream<Item = pulse::context::introspect::SinkInfo<'_>>>)`
              found tuple `(std::boxed::Box<(dyn std::ops::FnMut(pulse::callbacks::ListResult<&'static _>) + 'static)>,std::boxed::Box<(dyn futures_core::stream::Stream<Item = _> + 'static)>)`

error: aborting due to previous error; 10 warnings emitted

如果我将(callback,stream)上的类型批注调整为类型检查器找到的内容，我会将错误转发给对get_sink_info_by_index的调用：

error[E0271]: type mismatch resolving `for<'r,'s> <std::boxed::Box<dyn std::ops::FnMut(pulse::callbacks::ListResult<&'static pulse::context::introspect::SinkInfo<'_>>)> as std::ops::FnOnce<(pulse::callbacks::ListResult<&'r pulse::context::introspect::SinkInfo<'s>>,)>>::Output == ()`
  --> src/futuristicPulse.rs:32:14
   |
32 |         self.get_sink_info_by_index(index,callback);
   |              ^^^^^^^^^^^^^^^^^^^^^^ expected bound lifetime parameter,found concrete lifetime

error: aborting due to previous error; 10 warnings emitted

解决方法

非常粗略的答案-问题确实出在it.clone()上。它没有正确转移所有权，因为它是SinkInfo<'r>而不是SinkInfo。我写了SinkInfo<'r> -> SinkInfo<'static>，现在一切正常。