postcard_rpc/hash.rs
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//! URI and Schema Hashing
//!
//! We use `FNV1a` hashes with a digest size of 64 bits to represent dispatch keys.
//!
//! Unfortunately. using [core::hash::Hash] seems to not produce consistent results,
//! which [was noted] in the docs. To overcome this, we implement a custom method for
//! hashing the postcard [Schema].
//!
//! [was noted]: https://doc.rust-lang.org/stable/std/hash/trait.Hash.html#portability
use postcard_schema::{
schema::{DataModelType, NamedType, NamedValue, NamedVariant},
Schema,
};
/// A const compatible Fnv1a64 hasher
pub struct Fnv1a64Hasher {
state: u64,
}
impl Fnv1a64Hasher {
// source: https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
const BASIS: u64 = 0xcbf2_9ce4_8422_2325;
const PRIME: u64 = 0x0000_0100_0000_01b3;
/// Create a new hasher with the default basis as state contents
pub fn new() -> Self {
Self { state: Self::BASIS }
}
/// Calculate the hash for each of the given data bytes
pub fn update(&mut self, data: &[u8]) {
for b in data {
let ext = u64::from(*b);
self.state ^= ext;
self.state = self.state.wrapping_mul(Self::PRIME);
}
}
/// Extract the current state for finalizing the hash
pub fn digest(self) -> u64 {
self.state
}
/// Same as digest but as bytes
pub fn digest_bytes(self) -> [u8; 8] {
self.digest().to_le_bytes()
}
}
impl Default for Fnv1a64Hasher {
fn default() -> Self {
Self::new()
}
}
pub mod fnv1a64 {
//! Const and no-std helper methods and types for perfoming hash calculation
use postcard_schema::schema::DataModelVariant;
use super::*;
/// Calculate the Key hash for the given path and type T
pub const fn hash_ty_path<T: Schema + ?Sized>(path: &str) -> [u8; 8] {
let schema = T::SCHEMA;
let state = hash_update_str(Fnv1a64Hasher::BASIS, path);
hash_named_type(state, schema).to_le_bytes()
}
pub(crate) const fn hash_update(mut state: u64, bytes: &[u8]) -> u64 {
let mut idx = 0;
while idx < bytes.len() {
let ext = bytes[idx] as u64;
state ^= ext;
state = state.wrapping_mul(Fnv1a64Hasher::PRIME);
idx += 1;
}
state
}
pub(crate) const fn hash_update_str(state: u64, s: &str) -> u64 {
hash_update(state, s.as_bytes())
}
const fn hash_sdm_type(state: u64, sdmty: &'static DataModelType) -> u64 {
// The actual values we use here don't matter that much (as far as I know),
// as long as the values for each variant are unique. I am unsure of the
// implications of doing a TON of single byte calls to `update`, it may be
// worth doing some buffering, and only calling update every 4/8/16 bytes
// instead, if performance is a concern.
//
// As of initial implementation, I'm mostly concerned with "does it work",
// as hashing is typically only done on startup.
//
// Using all primes that fit into a single byte:
//
// all_primes = [
// 0x02, 0x03, 0x05, 0x07, 0x0B, 0x0D, 0x11, 0x13,
// 0x17, 0x1D, 0x1F, 0x25, 0x29, 0x2B, 0x2F, 0x35,
// 0x3B, 0x3D, 0x43, 0x47, 0x49, 0x4F, 0x53, 0x59,
// 0x61, 0x65, 0x67, 0x6B, 0x6D, 0x71, 0x7F, 0x83,
// 0x89, 0x8B, 0x95, 0x97, 0x9D, 0xA3, 0xA7, 0xAD,
// 0xB3, 0xB5, 0xBF, 0xC1, 0xC5, 0xC7, 0xD3, 0xDF,
// 0xE3, 0xE5, 0xE9, 0xEF, 0xF1, 0xFB,
// ];
// shuffled_primes = [
// 0x11, 0xC5, 0x3D, 0x95, 0x1D, 0x0D, 0x0B, 0x02,
// 0x83, 0xD3, 0x13, 0x8B, 0x6B, 0xAD, 0xEF, 0x71,
// 0xC1, 0x25, 0x65, 0x6D, 0x47, 0xBF, 0xB5, 0x9D,
// 0xDF, 0x03, 0xA7, 0x05, 0xC7, 0x4F, 0x7F, 0x67,
// 0xE9, 0xB3, 0xE5, 0x2B, 0x97, 0xFB, 0x61, 0x3B,
// 0x1F, 0xA3, 0x35, 0x43, 0x89, 0x49, 0xE3, 0x07,
// 0x53, 0xF1, 0x17, 0x2F, 0x29, 0x59,
// ];
match sdmty {
DataModelType::Bool => hash_update(state, &[0x11]),
DataModelType::I8 => hash_update(state, &[0xC5]),
DataModelType::U8 => hash_update(state, &[0x3D]),
DataModelType::I16 => hash_update(state, &[0x1D]),
DataModelType::I32 => hash_update(state, &[0x0D]),
DataModelType::I64 => hash_update(state, &[0x0B]),
DataModelType::I128 => hash_update(state, &[0x02]),
DataModelType::U16 => hash_update(state, &[0x83]),
DataModelType::U32 => hash_update(state, &[0xD3]),
DataModelType::U64 => hash_update(state, &[0x13]),
DataModelType::U128 => hash_update(state, &[0x8B]),
DataModelType::Usize => hash_update(state, &[0x6B]),
DataModelType::Isize => hash_update(state, &[0xAD]),
DataModelType::F32 => hash_update(state, &[0xEF]),
DataModelType::F64 => hash_update(state, &[0x71]),
DataModelType::Char => hash_update(state, &[0xC1]),
DataModelType::String => hash_update(state, &[0x25]),
DataModelType::ByteArray => hash_update(state, &[0x65]),
DataModelType::Option(nt) => {
let state = hash_update(state, &[0x6D]);
hash_named_type(state, nt)
}
DataModelType::Unit => hash_update(state, &[0x47]),
DataModelType::UnitStruct => hash_update(state, &[0xBF]),
DataModelType::NewtypeStruct(nt) => {
let state = hash_update(state, &[0x9D]);
hash_named_type(state, nt)
}
DataModelType::Seq(nt) => {
let state = hash_update(state, &[0x03]);
hash_named_type(state, nt)
}
DataModelType::Tuple(nts) => {
let mut state = hash_update(state, &[0xA7]);
let mut idx = 0;
while idx < nts.len() {
state = hash_named_type(state, nts[idx]);
idx += 1;
}
state
}
DataModelType::TupleStruct(nts) => {
let mut state = hash_update(state, &[0x05]);
let mut idx = 0;
while idx < nts.len() {
state = hash_named_type(state, nts[idx]);
idx += 1;
}
state
}
DataModelType::Map { key, val } => {
let state = hash_update(state, &[0x4F]);
let state = hash_named_type(state, key);
hash_named_type(state, val)
}
DataModelType::Struct(nvs) => {
let mut state = hash_update(state, &[0x7F]);
let mut idx = 0;
while idx < nvs.len() {
state = hash_named_value(state, nvs[idx]);
idx += 1;
}
state
}
DataModelType::Enum(nvs) => {
let mut state = hash_update(state, &[0xE9]);
let mut idx = 0;
while idx < nvs.len() {
state = hash_named_variant(state, nvs[idx]);
idx += 1;
}
state
}
DataModelType::Schema => hash_update(state, &[0xB3]),
}
}
const fn hash_named_type(state: u64, nt: &NamedType) -> u64 {
// NOTE: We do *not* hash the name of the type in hashv2. This
// is to allow "safe" type punning, e.g. treating `Vec<u8>` and
// `&[u8]` as compatible types, when talking between std and no-std
// targets
//
// let state = hash_update(state, nt.name.as_bytes());
hash_sdm_type(state, nt.ty)
}
const fn hash_named_variant(state: u64, nt: &NamedVariant) -> u64 {
let state = hash_update(state, nt.name.as_bytes());
match nt.ty {
DataModelVariant::UnitVariant => hash_update(state, &[0xB5]),
DataModelVariant::NewtypeVariant(nt) => {
let state = hash_update(state, &[0xDF]);
hash_named_type(state, nt)
}
DataModelVariant::TupleVariant(nts) => {
let mut state = hash_update(state, &[0xC7]);
let mut idx = 0;
while idx < nts.len() {
state = hash_named_type(state, nts[idx]);
idx += 1;
}
state
}
DataModelVariant::StructVariant(nvs) => {
let mut state = hash_update(state, &[0x67]);
let mut idx = 0;
while idx < nvs.len() {
state = hash_named_value(state, nvs[idx]);
idx += 1;
}
state
}
}
}
const fn hash_named_value(state: u64, nt: &NamedValue) -> u64 {
let state = hash_update(state, nt.name.as_bytes());
hash_named_type(state, nt.ty)
}
}
#[cfg(feature = "use-std")]
pub mod fnv1a64_owned {
//! Heapful helpers and versions of hashing for use on `std` targets
use postcard_schema::schema::owned::{
OwnedDataModelType, OwnedDataModelVariant, OwnedNamedType, OwnedNamedValue,
OwnedNamedVariant,
};
use super::fnv1a64::*;
use super::*;
/// Calculate the Key hash for the given path and OwnedNamedType
pub fn hash_ty_path_owned(path: &str, nt: &OwnedNamedType) -> [u8; 8] {
let state = hash_update_str(Fnv1a64Hasher::BASIS, path);
hash_named_type_owned(state, nt).to_le_bytes()
}
fn hash_sdm_type_owned(state: u64, sdmty: &OwnedDataModelType) -> u64 {
// The actual values we use here don't matter that much (as far as I know),
// as long as the values for each variant are unique. I am unsure of the
// implications of doing a TON of single byte calls to `update`, it may be
// worth doing some buffering, and only calling update every 4/8/16 bytes
// instead, if performance is a concern.
//
// As of initial implementation, I'm mostly concerned with "does it work",
// as hashing is typically only done on startup.
//
// Using all primes that fit into a single byte:
//
// all_primes = [
// 0x02, 0x03, 0x05, 0x07, 0x0B, 0x0D, 0x11, 0x13,
// 0x17, 0x1D, 0x1F, 0x25, 0x29, 0x2B, 0x2F, 0x35,
// 0x3B, 0x3D, 0x43, 0x47, 0x49, 0x4F, 0x53, 0x59,
// 0x61, 0x65, 0x67, 0x6B, 0x6D, 0x71, 0x7F, 0x83,
// 0x89, 0x8B, 0x95, 0x97, 0x9D, 0xA3, 0xA7, 0xAD,
// 0xB3, 0xB5, 0xBF, 0xC1, 0xC5, 0xC7, 0xD3, 0xDF,
// 0xE3, 0xE5, 0xE9, 0xEF, 0xF1, 0xFB,
// ];
// shuffled_primes = [
// 0x11, 0xC5, 0x3D, 0x95, 0x1D, 0x0D, 0x0B, 0x02,
// 0x83, 0xD3, 0x13, 0x8B, 0x6B, 0xAD, 0xEF, 0x71,
// 0xC1, 0x25, 0x65, 0x6D, 0x47, 0xBF, 0xB5, 0x9D,
// 0xDF, 0x03, 0xA7, 0x05, 0xC7, 0x4F, 0x7F, 0x67,
// 0xE9, 0xB3, 0xE5, 0x2B, 0x97, 0xFB, 0x61, 0x3B,
// 0x1F, 0xA3, 0x35, 0x43, 0x89, 0x49, 0xE3, 0x07,
// 0x53, 0xF1, 0x17, 0x2F, 0x29, 0x59,
// ];
match sdmty {
OwnedDataModelType::Bool => hash_update(state, &[0x11]),
OwnedDataModelType::I8 => hash_update(state, &[0xC5]),
OwnedDataModelType::U8 => hash_update(state, &[0x3D]),
OwnedDataModelType::I16 => hash_update(state, &[0x1D]),
OwnedDataModelType::I32 => hash_update(state, &[0x0D]),
OwnedDataModelType::I64 => hash_update(state, &[0x0B]),
OwnedDataModelType::I128 => hash_update(state, &[0x02]),
OwnedDataModelType::U16 => hash_update(state, &[0x83]),
OwnedDataModelType::U32 => hash_update(state, &[0xD3]),
OwnedDataModelType::U64 => hash_update(state, &[0x13]),
OwnedDataModelType::U128 => hash_update(state, &[0x8B]),
OwnedDataModelType::Usize => hash_update(state, &[0x6B]),
OwnedDataModelType::Isize => hash_update(state, &[0xAD]),
OwnedDataModelType::F32 => hash_update(state, &[0xEF]),
OwnedDataModelType::F64 => hash_update(state, &[0x71]),
OwnedDataModelType::Char => hash_update(state, &[0xC1]),
OwnedDataModelType::String => hash_update(state, &[0x25]),
OwnedDataModelType::ByteArray => hash_update(state, &[0x65]),
OwnedDataModelType::Option(nt) => {
let state = hash_update(state, &[0x6D]);
hash_named_type_owned(state, nt)
}
OwnedDataModelType::Unit => hash_update(state, &[0x47]),
OwnedDataModelType::UnitStruct => hash_update(state, &[0xBF]),
OwnedDataModelType::NewtypeStruct(nt) => {
let state = hash_update(state, &[0x9D]);
hash_named_type_owned(state, nt)
}
OwnedDataModelType::Seq(nt) => {
let state = hash_update(state, &[0x03]);
hash_named_type_owned(state, nt)
}
OwnedDataModelType::Tuple(nts) => {
let mut state = hash_update(state, &[0xA7]);
let mut idx = 0;
while idx < nts.len() {
state = hash_named_type_owned(state, &nts[idx]);
idx += 1;
}
state
}
OwnedDataModelType::TupleStruct(nts) => {
let mut state = hash_update(state, &[0x05]);
let mut idx = 0;
while idx < nts.len() {
state = hash_named_type_owned(state, &nts[idx]);
idx += 1;
}
state
}
OwnedDataModelType::Map { key, val } => {
let state = hash_update(state, &[0x4F]);
let state = hash_named_type_owned(state, key);
hash_named_type_owned(state, val)
}
OwnedDataModelType::Struct(nvs) => {
let mut state = hash_update(state, &[0x7F]);
let mut idx = 0;
while idx < nvs.len() {
state = hash_named_value_owned(state, &nvs[idx]);
idx += 1;
}
state
}
OwnedDataModelType::Enum(nvs) => {
let mut state = hash_update(state, &[0xE9]);
let mut idx = 0;
while idx < nvs.len() {
state = hash_named_variant_owned(state, &nvs[idx]);
idx += 1;
}
state
}
OwnedDataModelType::Schema => hash_update(state, &[0xB3]),
}
}
fn hash_named_type_owned(state: u64, nt: &OwnedNamedType) -> u64 {
// NOTE: We do *not* hash the name of the type in hashv2. This
// is to allow "safe" type punning, e.g. treating `Vec<u8>` and
// `&[u8]` as compatible types, when talking between std and no-std
// targets
//
// let state = hash_update(state, nt.name.as_bytes());
hash_sdm_type_owned(state, &nt.ty)
}
fn hash_named_variant_owned(state: u64, nt: &OwnedNamedVariant) -> u64 {
let state = hash_update(state, nt.name.as_bytes());
match &nt.ty {
OwnedDataModelVariant::UnitVariant => hash_update(state, &[0xB5]),
OwnedDataModelVariant::NewtypeVariant(nt) => {
let state = hash_update(state, &[0xDF]);
hash_named_type_owned(state, nt)
}
OwnedDataModelVariant::TupleVariant(nts) => {
let mut state = hash_update(state, &[0xC7]);
let mut idx = 0;
while idx < nts.len() {
state = hash_named_type_owned(state, &nts[idx]);
idx += 1;
}
state
}
OwnedDataModelVariant::StructVariant(nvs) => {
let mut state = hash_update(state, &[0x67]);
let mut idx = 0;
while idx < nvs.len() {
state = hash_named_value_owned(state, &nvs[idx]);
idx += 1;
}
state
}
}
}
fn hash_named_value_owned(state: u64, nt: &OwnedNamedValue) -> u64 {
let state = hash_update(state, nt.name.as_bytes());
hash_named_type_owned(state, &nt.ty)
}
}
#[cfg(test)]
mod test {
use super::fnv1a64::hash_ty_path;
use super::*;
#[test]
fn type_punning_good() {
let hash_1 = hash_ty_path::<Vec<u8>>("test_path");
let hash_2 = hash_ty_path::<&[u8]>("test_path");
let hash_3 = hash_ty_path::<Vec<u16>>("test_path");
let hash_4 = hash_ty_path::<&[u16]>("test_path");
let hash_5 = hash_ty_path::<Vec<u8>>("test_patt");
let hash_6 = hash_ty_path::<&[u8]>("test_patt");
assert_eq!(hash_1, hash_2);
assert_eq!(hash_3, hash_4);
assert_ne!(hash_1, hash_3);
assert_ne!(hash_2, hash_4);
assert_ne!(hash_1, hash_5);
assert_ne!(hash_2, hash_6);
}
// TODO: It is questionable if I like this outcome
#[test]
fn type_punning_questionable() {
#[derive(Schema)]
#[allow(unused)]
struct Wrapper1(u8);
#[derive(Schema)]
#[allow(unused)]
struct Wrapper2(u8);
let hash_1 = hash_ty_path::<Wrapper1>("test_path");
let hash_2 = hash_ty_path::<Wrapper2>("test_path");
assert_eq!(hash_1, hash_2);
}
}