pdk-serde-fixint 1.9.2

// Copyright (c) 2026, Salesforce, Inc.,
// All rights reserved.
// For full license text, see the LICENSE.txt file

//! Size-computing pass for the fixint format.
//!
//! Mirrors the legacy crate's strategy: before encoding, walk the value once
//! with a serializer that only accumulates the exact output length (integer
//! adds, no memory writes). [`crate::ser::to_vec`] then allocates the output
//! `Vec` with that exact capacity, so the real encode pass never reallocates.
//! The extra walk is far cheaper than the repeated grow+memcpy a `Vec::new()`
//! encode incurs on any compound value.

use crate::error::{Error, Result};
use serde::{ser, Serialize};
use std::mem::size_of;

/// Compute the exact number of bytes `value` will occupy in the fixint format.
pub(crate) fn serialized_size<T: Serialize + ?Sized>(value: &T) -> Result<usize> {
    let mut checker = SizeChecker { total: 0 };
    value.serialize(&mut checker)?;
    Ok(checker.total)
}

/// A serializer that writes nothing and only sums the output length.
struct SizeChecker {
    total: usize,
}

impl SizeChecker {
    #[inline]
    fn add(&mut self, n: usize) {
        self.total += n;
    }

    /// A collection length is encoded as a `u64`.
    #[inline]
    fn add_len(&mut self) {
        self.total += size_of::<u64>();
    }
}

impl ser::Serializer for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    type SerializeSeq = Self;
    type SerializeTuple = Self;
    type SerializeTupleStruct = Self;
    type SerializeTupleVariant = Self;
    type SerializeMap = Self;
    type SerializeStruct = Self;
    type SerializeStructVariant = Self;

    #[inline]
    fn serialize_bool(self, _v: bool) -> Result<()> {
        self.add(1);
        Ok(())
    }

    #[inline]
    fn serialize_i8(self, _v: i8) -> Result<()> {
        self.add(size_of::<i8>());
        Ok(())
    }

    #[inline]
    fn serialize_i16(self, _v: i16) -> Result<()> {
        self.add(size_of::<i16>());
        Ok(())
    }

    #[inline]
    fn serialize_i32(self, _v: i32) -> Result<()> {
        self.add(size_of::<i32>());
        Ok(())
    }

    #[inline]
    fn serialize_i64(self, _v: i64) -> Result<()> {
        self.add(size_of::<i64>());
        Ok(())
    }

    #[inline]
    fn serialize_i128(self, _v: i128) -> Result<()> {
        self.add(size_of::<i128>());
        Ok(())
    }

    #[inline]
    fn serialize_u8(self, _v: u8) -> Result<()> {
        self.add(size_of::<u8>());
        Ok(())
    }

    #[inline]
    fn serialize_u16(self, _v: u16) -> Result<()> {
        self.add(size_of::<u16>());
        Ok(())
    }

    #[inline]
    fn serialize_u32(self, _v: u32) -> Result<()> {
        self.add(size_of::<u32>());
        Ok(())
    }

    #[inline]
    fn serialize_u64(self, _v: u64) -> Result<()> {
        self.add(size_of::<u64>());
        Ok(())
    }

    #[inline]
    fn serialize_u128(self, _v: u128) -> Result<()> {
        self.add(size_of::<u128>());
        Ok(())
    }

    #[inline]
    fn serialize_f32(self, _v: f32) -> Result<()> {
        self.add(size_of::<f32>());
        Ok(())
    }

    #[inline]
    fn serialize_f64(self, _v: f64) -> Result<()> {
        self.add(size_of::<f64>());
        Ok(())
    }

    #[inline]
    fn serialize_char(self, v: char) -> Result<()> {
        self.add(v.len_utf8());
        Ok(())
    }

    #[inline]
    fn serialize_str(self, v: &str) -> Result<()> {
        self.add_len();
        self.add(v.len());
        Ok(())
    }

    #[inline]
    fn serialize_bytes(self, v: &[u8]) -> Result<()> {
        self.add_len();
        self.add(v.len());
        Ok(())
    }

    #[inline]
    fn serialize_none(self) -> Result<()> {
        self.add(1);
        Ok(())
    }

    #[inline]
    fn serialize_some<T: Serialize + ?Sized>(self, value: &T) -> Result<()> {
        self.add(1);
        value.serialize(self)
    }

    #[inline]
    fn serialize_unit(self) -> Result<()> {
        Ok(())
    }

    #[inline]
    fn serialize_unit_struct(self, _name: &'static str) -> Result<()> {
        Ok(())
    }

    #[inline]
    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
    ) -> Result<()> {
        self.add(size_of::<u32>());
        Ok(())
    }

    #[inline]
    fn serialize_newtype_struct<T: Serialize + ?Sized>(
        self,
        _name: &'static str,
        value: &T,
    ) -> Result<()> {
        value.serialize(self)
    }

    #[inline]
    fn serialize_newtype_variant<T: Serialize + ?Sized>(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        value: &T,
    ) -> Result<()> {
        self.add(size_of::<u32>());
        value.serialize(self)
    }

    #[inline]
    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
        len.ok_or_else(|| Error::Message("sequence length must be known".into()))?;
        self.add_len();
        Ok(self)
    }

    #[inline]
    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
        Ok(self)
    }

    #[inline]
    fn serialize_tuple_struct(
        self,
        _name: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeTupleStruct> {
        Ok(self)
    }

    #[inline]
    fn serialize_tuple_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeTupleVariant> {
        self.add(size_of::<u32>());
        Ok(self)
    }

    #[inline]
    fn serialize_map(self, len: Option<usize>) -> Result<Self::SerializeMap> {
        len.ok_or_else(|| Error::Message("map length must be known".into()))?;
        self.add_len();
        Ok(self)
    }

    #[inline]
    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
        Ok(self)
    }

    #[inline]
    fn serialize_struct_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeStructVariant> {
        self.add(size_of::<u32>());
        Ok(self)
    }
}

impl ser::SerializeSeq for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_element<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}

impl ser::SerializeTuple for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_element<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}

impl ser::SerializeTupleStruct for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_field<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}

impl ser::SerializeTupleVariant for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_field<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}

impl ser::SerializeMap for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_key<T: Serialize + ?Sized>(&mut self, key: &T) -> Result<()> {
        key.serialize(&mut **self)
    }

    #[inline]
    fn serialize_value<T: Serialize + ?Sized>(&mut self, value: &T) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}

impl ser::SerializeStruct for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_field<T: Serialize + ?Sized>(
        &mut self,
        _key: &'static str,
        value: &T,
    ) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}

impl ser::SerializeStructVariant for &mut SizeChecker {
    type Ok = ();
    type Error = Error;

    #[inline]
    fn serialize_field<T: Serialize + ?Sized>(
        &mut self,
        _key: &'static str,
        value: &T,
    ) -> Result<()> {
        value.serialize(&mut **self)
    }

    #[inline]
    fn end(self) -> Result<()> {
        Ok(())
    }
}