Fast Account IDs

src/fast_account_id.rs

@@ -0,0 +1,181 @@
+//! A fast alternative to `near_sdk::AccountId` that is faster to use, and has a
+//! smaller Borsh serialization footprint.
+
+use std::{ops::Deref, sync::Arc};
+
+use near_sdk::borsh::{BorshDeserialize, BorshSerialize};
+
+/// An alternative to `near_sdk::AccountId` that is faster to use, and has a
+/// smaller Borsh serialization footprint.
+///
+/// Limitations:
+///  - Does not implement `serde` serialization traits.
+///  - No parsing/validation logic. This is basically just a string wrapper
+///     with NEAR-account-ID-specific serialization logic.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct FastAccountId(Arc<str>);
+
+impl std::fmt::Display for FastAccountId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", &self.0)
+    }
+}
+
+impl Deref for FastAccountId {
+    type Target = str;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl AsRef<str> for FastAccountId {
+    fn as_ref(&self) -> &str {
+        &self.0
+    }
+}
+
+impl From<near_sdk::AccountId> for FastAccountId {
+    fn from(account_id: near_sdk::AccountId) -> Self {
+        Self(Arc::from(account_id.as_str()))
+    }
+}
+
+impl From<&str> for FastAccountId {
+    fn from(account_id: &str) -> Self {
+        Self(Arc::from(account_id))
+    }
+}
+
+impl BorshSerialize for FastAccountId {
+    fn serialize<W: std::io::Write>(&self, writer: &mut W) -> std::io::Result<()> {
+        let len: u8 = self.0.len() as u8;
+        writer.write_all(&[len])?;
+        let compressed = compress_account_id(&self.0).unwrap();
+        writer.write_all(&compressed)?;
+        Ok(())
+    }
+}
+
+impl BorshDeserialize for FastAccountId {
+    fn deserialize(buf: &mut &[u8]) -> std::io::Result<Self> {
+        let len = buf[0] as usize;
+        let compressed = &buf[1..];
+        let account_id = decompress_account_id(compressed, len);
+        *buf = &buf[1 + compressed_size(len)..];
+        Ok(Self(Arc::from(account_id)))
+    }
+}
+
+static ALPHABET: &[u8; 39] = b".abcdefghijklmnopqrstuvwxyz0123456789-_";
+
+fn char_index(c: u8) -> Option<usize> {
+    ALPHABET.iter().position(|&x| x == c)
+}
+
+fn append_sub_byte(v: &mut [u8], start_bit: usize, sub_byte: u8, num_bits: usize) {
+    assert!(num_bits <= 8);
+
+    let sub_bits = sub_byte & (0b1111_1111 >> (8 - num_bits));
+
+    let bit_offset = start_bit % 8;
+    let keep_mask = !(0b1111_1111 << bit_offset)
+        | !(0b1111_1111 >> (8usize.saturating_sub(num_bits + bit_offset)));
+    let first_byte = (v[start_bit / 8] & keep_mask) | (sub_bits << bit_offset);
+
+    v[start_bit / 8] = first_byte;
+
+    if bit_offset + num_bits > 8 {
+        let second_byte = sub_bits >> (8 - bit_offset);
+        v[start_bit / 8 + 1] = second_byte;
+    }
+}
+
+fn read_sub_byte(v: &[u8], start_bit: usize, num_bits: usize) -> u8 {
+    assert!(num_bits <= 8);
+
+    let bit_offset = start_bit % 8;
+    let keep_mask = (0b1111_1111 << bit_offset)
+        & (0b1111_1111 >> (8usize.saturating_sub(num_bits + bit_offset)));
+    let first_byte = v[start_bit / 8] & keep_mask;
+
+    let mut sub_byte = first_byte >> bit_offset;
+
+    if bit_offset + num_bits > 8 {
+        let num_bits_second = bit_offset + num_bits - 8;
+        let second_byte = v[start_bit / 8 + 1];
+        let keep_mask = 0b1111_1111 >> (8 - num_bits_second);
+        sub_byte |= (second_byte & keep_mask) << (8 - bit_offset);
+    }
+
+    sub_byte
+}
+
+fn decompress_account_id(compressed: &[u8], len: usize) -> String {
+    let mut s = String::with_capacity(len);
+    for i in 0..len {
+        let sub_byte = read_sub_byte(compressed, i * 6, 6);
+        let c = ALPHABET[sub_byte as usize] as char;
+        s.push(c);
+    }
+    s
+}
+
+fn compressed_size(len: usize) -> usize {
+    len * 3 / 4 + (len * 3 % 4 > 0) as usize
+}
+
+fn compress_account_id(account_id: &str) -> Option<Vec<u8>> {
+    let mut v = vec![0u8; compressed_size(account_id.len())];
+
+    let mut i = 0;
+    for c in account_id.as_bytes() {
+        let index = char_index(*c).unwrap() as u8;
+        append_sub_byte(&mut v, i, index, 6);
+        i += 6;
+    }
+
+    Some(v)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_append_sub_byte() {
+        let mut v = vec![0u8; 2];
+        append_sub_byte(&mut v, 0, 0b111, 3);
+        append_sub_byte(&mut v, 3, 0b010, 3);
+        append_sub_byte(&mut v, 6, 0b110, 3);
+        append_sub_byte(&mut v, 9, 0b1110101, 7);
+
+        assert_eq!(v, vec![0b10010111, 0b11101011]);
+    }
+
+    #[test]
+    fn test_read_sub_byte() {
+        let v = vec![0b10010111, 0b11101011];
+        assert_eq!(read_sub_byte(&v, 0, 3), 0b111);
+        assert_eq!(read_sub_byte(&v, 3, 3), 0b010);
+        assert_eq!(read_sub_byte(&v, 6, 3), 0b110);
+        assert_eq!(read_sub_byte(&v, 9, 7), 0b1110101);
+    }
+
+    #[test]
+    fn test() {
+        let account_id = "test.near";
+        let compressed = compress_account_id(account_id).unwrap();
+        let decompressed = decompress_account_id(&compressed, account_id.len());
+        assert_eq!(account_id, decompressed);
+    }
+
+    #[test]
+    fn test_account_id_borsh() {
+        let account_id = "0".repeat(64);
+        let account_id = FastAccountId(Arc::from(account_id));
+        let serialized = account_id.try_to_vec().unwrap();
+        let deserializalized = FastAccountId::try_from_slice(&serialized).unwrap();
+        assert_eq!(account_id, deserializalized);
+    }
+}

src/lib.rs

@@ -30,6 +30,7 @@ impl IntoStorageKey for DefaultStorageKey {
 pub mod standard;
 
 pub mod approval;
+pub mod fast_account_id;
 pub mod migrate;
 pub mod owner;
 pub mod pause;