spl discriminator crate (solana-labs#4556)

* spl discriminator

* fixed tlv impls for spec

* resolved some comments (naming conventions)

* remove TLV discrims

* new_with_hash_input fn

* HasDiscriminator

* added len function

* SplDiscriminates

* fix dependency issues

* merge fix lockfile

* bugfix on fat-finger in tlv libs

* update ArrayDiscriminator

* switch to SplDiscriminate

* drop len()

Cargo.toml

@@ -22,8 +22,9 @@ members = [
   "governance/tools",
   "governance/chat/program",
   "instruction-padding/program",
-  "libraries/math",
+  "libraries/discriminator",
   "libraries/concurrent-merkle-tree",
+  "libraries/math",
   "libraries/merkle-tree-reference",
   "libraries/program-error",
   "libraries/tlv-account-resolution",

libraries/discriminator/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "spl-discriminator"
+version = "0.1.0"
+description = "Solana Program Library 8-Byte Discriminator Management"
+authors = ["Solana Labs Maintainers <[email protected]>"]
+repository = "https://github.com/solana-labs/solana-program-library"
+license = "Apache-2.0"
+edition = "2021"
+
+[dependencies]
+bytemuck = { version = "1.13.1", features = ["derive"] }
+solana-program = "1.14.12"
+spl-discriminator-derive = { version = "0.1.0", path = "./derive" }
+
+[lib]
+crate-type = ["cdylib", "lib"]
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]

libraries/discriminator/README.md

@@ -0,0 +1,57 @@
+# SPL Discriminator
+
+This library allows for easy management of 8-byte discriminators.
+
+### The `ArrayDiscriminator` Struct
+
+With this crate, you can leverage the `ArrayDiscriminator` type to manage an 8-byte discriminator for generic purposes.
+
+```rust
+let my_discriminator = ArrayDiscriminator::new([8, 5, 1, 56, 10, 53, 9, 198]);
+```
+
+The `new(..)` function is also a **constant function**, so you can use `ArrayDiscriminator` in constants as well.
+
+```rust
+const MY_DISCRIMINATOR: ArrayDiscriminator = ArrayDiscriminator::new([8, 5, 1, 56, 10, 53, 9, 198]);
+```
+
+The `ArrayDiscriminator` struct also offers another constant function `as_slice(&self)`, so you can use `as_slice()` in constants as well.
+
+```rust
+const MY_DISCRIMINATOR_SLICE: &[u8] = MY_DISCRIMINATOR.as_slice();
+```
+
+### The `SplDiscriminate` Trait
+
+A trait, `SplDiscriminate` is also available, which will give you the `ArrayDiscriminator` constant type and also a slice representation of the discriminator. This can be particularly handy with match statements.
+
+```rust
+/// A trait for managing 8-byte discriminators in a slab of bytes
+pub trait SplDiscriminate {
+    /// The 8-byte discriminator as a `[u8; 8]`
+    const SPL_DISCRIMINATOR: ArrayDiscriminator;
+    /// The 8-byte discriminator as a slice (`&[u8]`)
+    const SPL_DISCRIMINATOR_SLICE: &'static [u8] = Self::SPL_DISCRIMINATOR.as_slice();
+}
+```
+
+### The `SplDiscriminate` Derive Macro
+
+The `SplDiscriminate` derive macro is a particularly useful tool for those who wish to derive their 8-byte discriminator from a particular string literal. Typically, you would have to run a hash function against the string literal, then copy the first 8 bytes, and then hard-code those bytes into a statement like the one above.
+
+Instead, you can simply annotate a struct or enum with `SplDiscriminate` and provide a **namespace** via the `discriminator_namespace` attribute, and the macro will automatically derive the 8-byte discriminator for you!
+
+```rust
+#[derive(SplDiscriminate)] // Implements `SplDiscriminate` for your struct/enum using your declared string literal namespace
+#[discriminator_namespace("some_discriminator_namespace")]
+pub struct MyInstruction1 {
+    arg1: String,
+    arg2: u8,
+}
+
+let my_discriminator: ArrayDiscriminator = MyInstruction1::SPL_DISCRIMINATOR;
+let my_discriminator_slice: &[u8] = MyInstruction1::SPL_DISCRIMINATOR_SLICE;
+```
+
+Note: the 8-byte discriminator derived using the macro is always the **first 8 bytes** of the resulting hashed bytes.

libraries/discriminator/derive/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "spl-discriminator-derive"
+version = "0.1.0"
+description = "Derive macro library for the `spl-discriminator` library"
+authors = ["Solana Labs Maintainers <[email protected]>"]
+repository = "https://github.com/solana-labs/solana-program-library"
+license = "Apache-2.0"
+edition = "2021"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1.0"
+spl-discriminator-syn = { version = "0.1.0", path = "../syn" }
+syn = { version = "2.0", features = ["full"] }

libraries/discriminator/derive/src/lib.rs

@@ -0,0 +1,20 @@
+//! Derive macro library for the `spl-discriminator` library
+
+#![deny(missing_docs)]
+#![cfg_attr(not(test), forbid(unsafe_code))]
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+use quote::ToTokens;
+use spl_discriminator_syn::SplDiscriminateBuilder;
+use syn::parse_macro_input;
+
+/// Derive macro library to implement the `SplDiscriminate` trait
+/// on an enum or struct
+#[proc_macro_derive(SplDiscriminate, attributes(discriminator_hash_input))]
+pub fn spl_discriminator(input: TokenStream) -> TokenStream {
+    parse_macro_input!(input as SplDiscriminateBuilder)
+        .to_token_stream()
+        .into()
+}

libraries/discriminator/src/discriminator.rs

@@ -0,0 +1,68 @@
+//! The traits and types used to create a discriminator for a type
+
+use {
+    bytemuck::{Pod, Zeroable},
+    solana_program::{hash, program_error::ProgramError},
+};
+
+/// A trait for managing 8-byte discriminators in a slab of bytes
+pub trait SplDiscriminate {
+    /// The 8-byte discriminator as a `[u8; 8]`
+    const SPL_DISCRIMINATOR: ArrayDiscriminator;
+    /// The 8-byte discriminator as a slice (`&[u8]`)
+    const SPL_DISCRIMINATOR_SLICE: &'static [u8] = Self::SPL_DISCRIMINATOR.as_slice();
+}
+
+/// Array Discriminator type
+#[derive(Clone, Copy, Debug, Default, PartialEq, Pod, Zeroable)]
+#[repr(transparent)]
+pub struct ArrayDiscriminator([u8; ArrayDiscriminator::LENGTH]);
+impl ArrayDiscriminator {
+    /// Size for discriminator in account data
+    pub const LENGTH: usize = 8;
+    /// Uninitialized variant of a discriminator
+    pub const UNINITIALIZED: Self = Self::new([0; Self::LENGTH]);
+    /// Creates a discriminator from an array
+    pub const fn new(value: [u8; Self::LENGTH]) -> Self {
+        Self(value)
+    }
+    /// Get the array as a const slice
+    pub const fn as_slice(&self) -> &[u8] {
+        self.0.as_slice()
+    }
+    /// Creates a new `ArrayDiscriminator` from some hash input string literal
+    pub fn new_with_hash_input(hash_input: &str) -> Self {
+        let hash_bytes = hash::hashv(&[hash_input.as_bytes()]).to_bytes();
+        let mut discriminator_bytes = [0u8; 8];
+        discriminator_bytes.copy_from_slice(&hash_bytes[..8]);
+        Self(discriminator_bytes)
+    }
+}
+impl AsRef<[u8]> for ArrayDiscriminator {
+    fn as_ref(&self) -> &[u8] {
+        &self.0[..]
+    }
+}
+impl AsRef<[u8; ArrayDiscriminator::LENGTH]> for ArrayDiscriminator {
+    fn as_ref(&self) -> &[u8; ArrayDiscriminator::LENGTH] {
+        &self.0
+    }
+}
+impl From<u64> for ArrayDiscriminator {
+    fn from(from: u64) -> Self {
+        Self(from.to_le_bytes())
+    }
+}
+impl From<[u8; Self::LENGTH]> for ArrayDiscriminator {
+    fn from(from: [u8; Self::LENGTH]) -> Self {
+        Self(from)
+    }
+}
+impl TryFrom<&[u8]> for ArrayDiscriminator {
+    type Error = ProgramError;
+    fn try_from(a: &[u8]) -> Result<Self, Self::Error> {
+        <[u8; Self::LENGTH]>::try_from(a)
+            .map(Self::from)
+            .map_err(|_| ProgramError::InvalidAccountData)
+    }
+}

libraries/discriminator/src/lib.rs

@@ -0,0 +1,69 @@
+//! Crate defining a discriminator type, which creates a set of bytes
+//! meant to be unique for instructions or struct types
+
+#![deny(missing_docs)]
+#![cfg_attr(not(test), forbid(unsafe_code))]
+
+extern crate self as spl_discriminator;
+
+/// Exports the discriminator module
+pub mod discriminator;
+
+// Export for downstream
+pub use {
+    discriminator::{ArrayDiscriminator, SplDiscriminate},
+    spl_discriminator_derive::SplDiscriminate,
+};
+
+#[cfg(test)]
+mod tests {
+    use {super::*, crate::discriminator::ArrayDiscriminator};
+
+    #[allow(dead_code)]
+    #[derive(SplDiscriminate)]
+    #[discriminator_hash_input("some_discriminator_hash_input")]
+    pub struct MyInstruction1 {
+        arg1: String,
+        arg2: u8,
+    }
+
+    #[allow(dead_code)]
+    #[derive(SplDiscriminate)]
+    #[discriminator_hash_input("yet_another_discriminator_hash_input")]
+    pub struct MyInstruction2 {
+        arg1: u64,
+    }
+
+    #[allow(dead_code)]
+    #[derive(SplDiscriminate)]
+    #[discriminator_hash_input("global:my_instruction_3")]
+    pub enum MyInstruction3 {
+        One,
+        Two,
+        Three,
+    }
+
+    fn assert_discriminator<T: spl_discriminator::discriminator::SplDiscriminate>(
+        hash_input: &str,
+    ) {
+        let discriminator = build_discriminator(hash_input);
+        assert_eq!(T::SPL_DISCRIMINATOR, discriminator);
+        assert_eq!(T::SPL_DISCRIMINATOR_SLICE, discriminator.as_slice());
+    }
+
+    fn build_discriminator(hash_input: &str) -> ArrayDiscriminator {
+        let preimage = solana_program::hash::hashv(&[hash_input.as_bytes()]);
+        let mut bytes = [0u8; 8];
+        bytes.copy_from_slice(&preimage.to_bytes()[..8]);
+        ArrayDiscriminator::new(bytes)
+    }
+
+    #[test]
+    fn test_discrminators() {
+        assert_discriminator::<MyInstruction1>("some_discriminator_hash_input");
+        assert_discriminator::<MyInstruction2>("yet_another_discriminator_hash_input");
+        assert_discriminator::<MyInstruction3>("global:my_instruction_3");
+        let runtime_discrim = ArrayDiscriminator::new_with_hash_input("my_new_hash_input");
+        assert_eq!(runtime_discrim, build_discriminator("my_new_hash_input"),);
+    }
+}

libraries/discriminator/syn/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "spl-discriminator-syn"
+version = "0.1.0"
+description = "Token parsing and generating library for the `spl-discriminator` library"
+authors = ["Solana Labs Maintainers <[email protected]>"]
+repository = "https://github.com/solana-labs/solana-program-library"
+license = "Apache-2.0"
+edition = "2021"
+
+[dependencies]
+proc-macro2 = "1.0"
+quote = "1.0"
+solana-program = "1.14.12"
+syn = { version = "2.0", features = ["full"] }
+thiserror = "1.0"

libraries/discriminator/syn/src/error.rs

@@ -0,0 +1,12 @@
+//! Error types for the `hash_input` parser
+
+/// Error types for the `hash_input` parser
+#[derive(Clone, Debug, Eq, thiserror::Error, PartialEq)]
+pub enum SplDiscriminateError {
+    /// Discriminator hash_input attribute not provided
+    #[error("Discriminator `hash_input` attribute not provided")]
+    HashInputAttributeNotProvided,
+    /// Error parsing discriminator hash_input attribute
+    #[error("Error parsing discriminator `hash_input` attribute")]
+    HashInputAttributeParseError,
+}