Can someone explain the transformation used to go from datamap to xor addresses to fetch from network

qi_ma · September 25, 2024, 12:58pm

Ah, it’s actually KeyBytes internally carry out transformation for distance calculation.

libp2p/rust-libp2p/blob/master/protocols/kad/src/kbucket/key.rs#L77


      
          /// Converts the key into its preimage.
          pub fn into_preimage(self) -> T {
              self.preimage
          }
          
          /// Computes the distance of the keys according to the XOR metric.
          pub fn distance<U>(&self, other: &U) -> Distance
          where
              U: AsRef<KeyBytes>,
          {
              self.bytes.distance(other)
          }
          
          /// Exposing the hashed bytes.
          pub fn hashed_bytes(&self) -> &[u8] {
              &self.bytes.0
          }
          
          /// Returns the uniquely determined key with the given distance to `self`.
          ///
          /// This implements the following equivalence:

github.com

libp2p/rust-libp2p/blob/master/protocols/kad/src/kbucket/key.rs#L158


      
          #[derive(PartialEq, Eq, Clone, Copy, Debug)]
          pub struct KeyBytes(GenericArray<u8, U32>);
          
          impl KeyBytes {
              /// Creates a new key in the DHT keyspace by running the given
              /// value through a random oracle.
              pub fn new<T>(value: T) -> Self
              where
                  T: Borrow<[u8]>,
              {
                  KeyBytes(Sha256::digest(value.borrow()))
              }
          
              /// Computes the distance of the keys according to the XOR metric.
              pub fn distance<U>(&self, other: &U) -> Distance
              where
                  U: AsRef<KeyBytes>,
              {
                  let a = U256::from(self.0.as_slice());
                  let b = U256::from(other.as_ref().0.as_slice());
                  Distance(a ^ b)

using Sha256::digest function, then trasnform to U256 for the ease of ^

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Can someone explain the transformation used to go from datamap to xor addresses to fetch from network

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