pdk-serde-fixint 1.9.2

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

//! Serializer for the fixint format: little-endian, fixed-width integers,
//! `u64` length prefixes, and `u32` enum variant tags. Byte-compatible with
//! the legacy serialization crate's default configuration.

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

/// Serialize a value into a `Vec<u8>` using the fixint format.
///
/// Walks the value once to compute the exact output size, then encodes into a
/// `Vec` pre-allocated to that capacity so the encode pass never reallocates.
/// The size pass is cheaper than the repeated grow+memcpy an unsized `Vec`
/// would incur on any compound value.
pub fn to_vec<T: Serialize + ?Sized>(value: &T) -> Result<Vec<u8>> {
    let size = crate::size::serialized_size(value)?;
    let mut serializer = Serializer {
        output: Vec::with_capacity(size),
    };
    value.serialize(&mut serializer)?;
    Ok(serializer.output)
}

/// Byte sink for the fixint encoding.
pub struct Serializer {
    output: Vec<u8>,
}

impl ser::Serializer for &mut Serializer {
    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.output.push(v as u8);
        Ok(())
    }

    #[inline]
    fn serialize_i8(self, v: i8) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_i16(self, v: i16) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_i32(self, v: i32) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_i64(self, v: i64) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_i128(self, v: i128) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_u8(self, v: u8) -> Result<()> {
        self.output.push(v);
        Ok(())
    }

    #[inline]
    fn serialize_u16(self, v: u16) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_u32(self, v: u32) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_u64(self, v: u64) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_u128(self, v: u128) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_f32(self, v: f32) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_f64(self, v: f64) -> Result<()> {
        self.output.extend_from_slice(&v.to_le_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_char(self, v: char) -> Result<()> {
        // bincode encodes a char as its UTF-8 bytes (1..=4 bytes), no length.
        let mut buf = [0u8; 4];
        let encoded = v.encode_utf8(&mut buf);
        self.output.extend_from_slice(encoded.as_bytes());
        Ok(())
    }

    #[inline]
    fn serialize_str(self, v: &str) -> Result<()> {
        self.serialize_bytes(v.as_bytes())
    }

    #[inline]
    fn serialize_bytes(self, v: &[u8]) -> Result<()> {
        // Length prefix is a u64 in the default config.
        self.serialize_len(v.len())?;
        self.output.extend_from_slice(v);
        Ok(())
    }

    #[inline]
    fn serialize_none(self) -> Result<()> {
        self.output.push(0);
        Ok(())
    }

    #[inline]
    fn serialize_some<T: Serialize + ?Sized>(self, value: &T) -> Result<()> {
        self.output.push(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<()> {
        // Variant tag is a u32.
        self.serialize_u32(variant_index)
    }

    #[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.serialize_u32(variant_index)?;
        value.serialize(self)
    }

    #[inline]
    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
        // Sequences of unknown length still carry a u64 length prefix; serde
        // requires the length to be known here for bincode.
        let len = _len.ok_or_else(|| Error::Message("sequence length must be known".into()))?;
        self.serialize_len(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.serialize_u32(variant_index)?;
        Ok(self)
    }

    #[inline]
    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
        let len = _len.ok_or_else(|| Error::Message("map length must be known".into()))?;
        self.serialize_len(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.serialize_u32(variant_index)?;
        Ok(self)
    }
}

impl Serializer {
    /// Write a collection length as a little-endian `u64`, matching the
    /// bincode default config.
    #[inline]
    fn serialize_len(&mut self, len: usize) -> Result<()> {
        self.output.extend_from_slice(&(len as u64).to_le_bytes());
        Ok(())
    }
}

impl ser::SerializeSeq for &mut Serializer {
    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 Serializer {
    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 Serializer {
    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 Serializer {
    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 Serializer {
    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 Serializer {
    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 Serializer {
    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(())
    }
}