1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165

use std::{
    any::{Any, TypeId},
    future::Future,
    marker::PhantomData,
    pin::Pin,
};

use crate::{AsyncMakeService, MakeService, Service};

pub struct BoxedService<Request, Response, E> {
    svc: *const (),
    type_id: TypeId,
    vtable: ServiceVtable<Request, Response, E>,
}

impl<Request, Response, E> BoxedService<Request, Response, E> {
    pub fn new<S>(s: S) -> Self
    where
        S: Service<Request, Response = Response, Error = E> + 'static,
        Request: 'static,
    {
        let type_id = s.type_id();
        let svc = Box::into_raw(Box::new(s)) as *const ();
        BoxedService {
            svc,
            type_id,
            vtable: ServiceVtable {
                call: call::<Request, S>,
                drop: drop::<S>,
            },
        }
    }

    pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
        let t = TypeId::of::<T>();
        if self.type_id == t {
            Some(unsafe { self.downcast_ref_unchecked() })
        } else {
            None
        }
    }

    /// # Safety
    /// If you are sure the inner type is T, you can downcast it.
    pub unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T {
        &*(self.svc as *const T)
    }
}

impl<Request, Response, E> Drop for BoxedService<Request, Response, E> {
    #[inline]
    fn drop(&mut self) {
        unsafe { (self.vtable.drop)(self.svc) };
    }
}

impl<Request, Response, E> Service<Request> for BoxedService<Request, Response, E> {
    type Response = Response;
    type Error = E;

    #[inline]
    fn call(&self, req: Request) -> impl Future<Output = Result<Self::Response, Self::Error>> {
        unsafe { (self.vtable.call)(self.svc, req) }
    }
}

pub trait BoxService<Request, Response, E> {
    fn into_boxed(self) -> BoxedService<Request, Response, E>;
}

impl<T, Request, Response, E> BoxService<Request, Response, E> for T
where
    T: Service<Request, Response = Response, Error = E> + 'static,
    Request: 'static,
{
    fn into_boxed(self) -> BoxedService<Request, Response, E> {
        BoxedService::new(self)
    }
}

type LocalStaticBoxedFuture<T, E> = Pin<Box<dyn Future<Output = Result<T, E>> + 'static>>;

struct ServiceVtable<T, U, E> {
    call: unsafe fn(raw: *const (), req: T) -> LocalStaticBoxedFuture<U, E>,
    drop: unsafe fn(raw: *const ()),
}

unsafe fn call<R, S>(svc: *const (), req: R) -> LocalStaticBoxedFuture<S::Response, S::Error>
where
    R: 'static,
    S: Service<R> + 'static,
{
    let svc = &*svc.cast::<S>();
    let fut = S::call(svc, req);
    Box::pin(fut)
}

unsafe fn drop<S>(raw: *const ()) {
    std::ptr::drop_in_place(raw as *mut S);
}

pub struct BoxServiceFactory<F, Req> {
    pub inner: F,
    _marker: PhantomData<Req>,
}

unsafe impl<F: Send, Req> Send for BoxServiceFactory<F, Req> {}

unsafe impl<F: Sync, Req> Sync for BoxServiceFactory<F, Req> {}

impl<F, Req> BoxServiceFactory<F, Req> {
    pub fn new(inner: F) -> Self {
        BoxServiceFactory {
            inner,
            _marker: PhantomData,
        }
    }
}

impl<F, Req> MakeService for BoxServiceFactory<F, Req>
where
    F: MakeService,
    F::Service: Service<Req> + 'static,
    Req: 'static,
{
    type Service = BoxedService<
        Req,
        <F::Service as Service<Req>>::Response,
        <F::Service as Service<Req>>::Error,
    >;
    type Error = F::Error;

    fn make_via_ref(&self, old: Option<&Self::Service>) -> Result<Self::Service, Self::Error> {
        let svc = match old {
            Some(inner) => self.inner.make_via_ref(inner.downcast_ref())?,
            None => self.inner.make()?,
        };
        Ok(svc.into_boxed())
    }
}

impl<F, Req> AsyncMakeService for BoxServiceFactory<F, Req>
where
    F: AsyncMakeService,
    F::Service: Service<Req> + 'static,
    Req: 'static,
{
    type Service = BoxedService<
        Req,
        <F::Service as Service<Req>>::Response,
        <F::Service as Service<Req>>::Error,
    >;
    type Error = F::Error;

    async fn make_via_ref(
        &self,
        old: Option<&Self::Service>,
    ) -> Result<Self::Service, Self::Error> {
        let svc = match old {
            Some(inner) => self.inner.make_via_ref(inner.downcast_ref()).await?,
            None => self.inner.make().await?,
        };
        Ok(svc.into_boxed())
    }
}