topcoat_runtime/

signal.rs

use std::{iter::empty, ops::Deref};

use serde::{Deserialize, Serialize, de::DeserializeOwned};
use topcoat_core::context::Cx;
use topcoat_view::{NodeViewParts, PartsWriter};
use uuid::Uuid;

use crate::{Surrogate, Surrogated};

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(transparent)]
pub struct SignalId(Uuid);

impl SignalId {
    #[inline]
    #[must_use]
    pub fn new() -> Self {
        Self(Uuid::new_v4())
    }
}

impl Default for SignalId {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

impl std::fmt::Display for SignalId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}

#[derive(Debug)]
pub struct Signal<T> {
    id: SignalId,
    value: T,
}

impl<T> Signal<T> {
    #[inline]
    pub fn new(value: T) -> Self {
        Self {
            id: SignalId::new(),
            value,
        }
    }

    pub(crate) fn id(&self) -> SignalId {
        self.id
    }

    pub(crate) fn read(&self) -> &T {
        &self.value
    }
}

impl<T> Signal<T>
where
    T: Clone,
{
    pub(crate) fn get(&self) -> T {
        self.value.clone()
    }
}

pub struct SignalDeclaration<'a, T>(&'a Signal<T>);

impl<'a, T> SignalDeclaration<'a, T> {
    #[inline]
    pub fn new(signal: &'a Signal<T>) -> Self {
        Self(signal)
    }
}

impl<T> NodeViewParts for SignalDeclaration<'_, T>
where
    for<'a> &'a T: Surrogated,
    for<'a> <&'a T as Surrogated>::Surrogate: Serialize,
{
    fn into_view_parts(self, _cx: &Cx, parts: &mut PartsWriter<'_>) {
        #[derive(Serialize)]
        struct SignalDeclarationPayload<'a, V>
        where
            V: ?Sized,
        {
            t: &'static str,
            id: std::string::String,
            v: &'a V,
        }

        let value = (&self.0.value).into_surrogate();
        let payload = SignalDeclarationPayload {
            t: "signal",
            id: self.0.id().to_string(),
            v: &value,
        };
        let json = serde_json::to_string(&payload)
            .expect("failed to serialize signal declaration payload");

        parts.push_comment(|comment| {
            // `json` is untrusted application data and must be escaped to prevent XSS attacks.
            comment
                .push_str_unescaped("::topcoat::signal(")
                .push_str(json)
                .push_str_unescaped(")");
        });
    }
}

#[derive(Debug, Clone)]
pub struct ReadSignal<T> {
    id: SignalId,
    value: T,
}

impl<T> ReadSignal<T> {
    pub fn new(signal: &Signal<T>) -> Self
    where
        T: Clone,
    {
        Self {
            id: signal.id,
            value: signal.value.clone(),
        }
    }

    pub fn id(&self) -> SignalId {
        self.id
    }
}

impl<T> Deref for ReadSignal<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.value
    }
}

impl<'de, T> Deserialize<'de> for ReadSignal<T>
where
    T: Surrogated,
    T::Surrogate: Deserialize<'de>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        #[derive(Deserialize)]
        #[serde(deny_unknown_fields)]
        struct EncodedReadSignal<S> {
            id: SignalId,
            value: S,
        }

        let encoded = EncodedReadSignal::<T::Surrogate>::deserialize(deserializer)?;
        Ok(Self {
            id: encoded.id,
            value: encoded.value.into_real(),
        })
    }
}

pub trait Signals: Sized {
    fn ids(&self) -> impl Iterator<Item = SignalId>;
    fn decode(encoded_signals: EncodedSignals) -> Self;
}

impl Signals for () {
    fn ids(&self) -> impl Iterator<Item = SignalId> {
        empty()
    }

    fn decode(_encoded_signals: EncodedSignals) -> Self {}
}

macro_rules! impl_signals_for_tuple {
    ($($n:tt $t:ident),+) => {
        impl<$($t),+> Signals for ($(ReadSignal<$t>,)+)
        where
            $(
                $t: Surrogated,
                <$t as Surrogated>::Surrogate: DeserializeOwned,
            )+
        {
            fn ids(&self) -> impl Iterator<Item = SignalId> {
                [$(self.$n.id),+].into_iter()
            }

            fn decode(encoded_signals: EncodedSignals) -> Self {
                serde_json::from_str(&encoded_signals.0).unwrap()
            }
        }
    };
}

impl_signals_for_tuple!(0 T0);
impl_signals_for_tuple!(0 T0, 1 T1);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5, 6 T6);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5, 6 T6, 7 T7);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5, 6 T6, 7 T7, 8 T8);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5, 6 T6, 7 T7, 8 T8, 9 T9);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5, 6 T6, 7 T7, 8 T8, 9 T9, 10 T10);
impl_signals_for_tuple!(0 T0, 1 T1, 2 T2, 3 T3, 4 T4, 5 T5, 6 T6, 7 T7, 8 T8, 9 T9, 10 T10, 11 T11);

pub struct EncodedSignals(String);

impl EncodedSignals {
    pub fn new(inner: impl Into<String>) -> Self {
        Self(inner.into())
    }
}

#[cfg(test)]
mod tests {
    use topcoat_view::{HtmlContext, PartsWriter, View, ViewParts};

    use super::*;

    #[test]
    fn payload_cannot_terminate_the_comment() {
        // A value carrying `-->`, a quote, and an ampersand: the characters
        // that could break out of the comment or corrupt its JSON payload.
        let signal = Signal::new(String::from("a-->b\"c&d"));

        let cx = Cx::default();
        let mut parts = ViewParts::new();
        SignalDeclaration::new(&signal)
            .into_view_parts(&cx, &mut PartsWriter::new(&mut parts, HtmlContext::Text));
        let html = View::new(parts).render(&cx);

        // The comment context escaped `>`, so the only `-->` left is the
        // marker's own terminator; the payload cannot end the comment early.
        assert_eq!(html.matches("-->").count(), 1);
        assert!(html.ends_with(") -->"));
        assert!(html.contains("--&gt;"));
        // The JSON's own quotes round-trip as entities the client decodes.
        assert!(html.contains("&quot;"));
    }
}