ic-backup 0.25.1

Host-side snapshot backup and same-release recovery for Internet Computer canisters
Documentation 
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//! Bounded persisted-record sequences without allocating from untrusted hints.

use serde::{Deserialize, Deserializer, de};
use std::{fmt, marker::PhantomData};

pub(super) fn deserialize<'de, D, T, const LIMIT: usize>(
    deserializer: D,
    expected: impl fmt::Display,
    overflow: impl fmt::Display,
) -> Result<Vec<T>, D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de>,
{
    deserialize_with::<D, T, _, _, LIMIT, false>(deserializer, expected, overflow)
}

/// IC wire values reject excessive hints and decode the one excess value by type.
pub(crate) fn deserialize_wire<'de, D, T, const LIMIT: usize>(
    deserializer: D,
    expected: impl fmt::Display,
    overflow: impl fmt::Display,
) -> Result<Vec<T>, D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de>,
{
    deserialize_with::<D, T, _, _, LIMIT, true>(deserializer, expected, overflow)
}

fn deserialize_with<'de, D, T, X, E, const LIMIT: usize, const WIRE: bool>(
    deserializer: D,
    expected: X,
    overflow: E,
) -> Result<Vec<T>, D::Error>
where
    D: Deserializer<'de>,
    T: Deserialize<'de>,
    X: fmt::Display,
    E: fmt::Display,
{
    struct Visitor<T, X, E, const LIMIT: usize, const WIRE: bool> {
        expected: X,
        overflow: E,
        item: PhantomData<T>,
    }
    impl<
        'de,
        T: Deserialize<'de>,
        X: fmt::Display,
        E: fmt::Display,
        const LIMIT: usize,
        const WIRE: bool,
    > de::Visitor<'de> for Visitor<T, X, E, LIMIT, WIRE>
    {
        type Value = Vec<T>;

        fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(formatter, "{}", self.expected)
        }

        fn visit_seq<A: de::SeqAccess<'de>>(
            self,
            mut sequence: A,
        ) -> Result<Self::Value, A::Error> {
            if WIRE && sequence.size_hint().is_some_and(|size| size > LIMIT) {
                return Err(de::Error::custom(self.overflow));
            }
            let mut entries = Vec::new();
            while entries.len() < LIMIT {
                match sequence.next_element()? {
                    Some(entry) => entries.push(entry),
                    None => return Ok(entries),
                }
            }
            let excess = if WIRE {
                sequence.next_element::<T>()?.is_some()
            } else {
                sequence.next_element::<de::IgnoredAny>()?.is_some()
            };
            if excess {
                return Err(de::Error::custom(self.overflow));
            }
            Ok(entries)
        }
    }
    deserializer.deserialize_seq(Visitor::<T, _, _, LIMIT, WIRE> {
        expected,
        overflow,
        item: PhantomData,
    })
}