bip32 0.5.3

BIP32 hierarchical key derivation implemented in a generic, no_std-friendly manner. Supports deriving keys using the pure Rust k256 crate or the C library-backed secp256k1 crate
Documentation 
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//! Derivation paths

use crate::{ChildNumber, Error, Result};
use alloc::vec::{self, Vec};
use core::{
    fmt::{self, Display},
    str::FromStr,
};

/// Prefix for all derivation paths.
const PREFIX: &str = "m";

/// Derivation paths within a hierarchical keyspace.
#[derive(Clone, Debug, Default, Eq, PartialEq)]
pub struct DerivationPath {
    path: Vec<ChildNumber>,
}

impl DerivationPath {
    /// Iterate over the [`ChildNumber`] values in this derivation path.
    pub fn iter(&self) -> impl Iterator<Item = ChildNumber> + '_ {
        self.path.iter().cloned()
    }

    /// Is this derivation path empty? (i.e. the root)
    pub fn is_empty(&self) -> bool {
        self.path.is_empty()
    }

    /// Get the count of [`ChildNumber`] values in this derivation path.
    pub fn len(&self) -> usize {
        self.path.len()
    }

    /// Get the parent [`DerivationPath`] for the current one.
    ///
    /// Returns `None` if this is already the root path.
    pub fn parent(&self) -> Option<Self> {
        self.path.len().checked_sub(1).map(|n| {
            let mut parent = self.clone();
            parent.path.truncate(n);
            parent
        })
    }

    /// Push a [`ChildNumber`] onto an existing derivation path.
    pub fn push(&mut self, child_number: ChildNumber) {
        self.path.push(child_number)
    }
}

impl AsRef<[ChildNumber]> for DerivationPath {
    fn as_ref(&self) -> &[ChildNumber] {
        &self.path
    }
}

impl Display for DerivationPath {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(PREFIX)?;

        for child_number in self.iter() {
            write!(f, "/{}", child_number)?;
        }

        Ok(())
    }
}

impl Extend<ChildNumber> for DerivationPath {
    fn extend<T>(&mut self, iter: T)
    where
        T: IntoIterator<Item = ChildNumber>,
    {
        self.path.extend(iter);
    }
}

impl FromStr for DerivationPath {
    type Err = Error;

    fn from_str(path: &str) -> Result<DerivationPath> {
        let mut path = path.split('/');

        if path.next() != Some(PREFIX) {
            return Err(Error::Decode);
        }

        Ok(DerivationPath {
            path: path.map(str::parse).collect::<Result<_>>()?,
        })
    }
}

impl IntoIterator for DerivationPath {
    type Item = ChildNumber;
    type IntoIter = vec::IntoIter<ChildNumber>;

    fn into_iter(self) -> vec::IntoIter<ChildNumber> {
        self.path.into_iter()
    }
}

#[cfg(test)]
mod tests {
    use super::DerivationPath;
    use alloc::string::ToString;

    /// BIP32 test vectors
    // TODO(tarcieri): consolidate test vectors
    #[test]
    fn round_trip() {
        let path_m = "m";
        assert_eq!(
            path_m.parse::<DerivationPath>().unwrap().to_string(),
            path_m
        );

        let path_m_0 = "m/0";
        assert_eq!(
            path_m_0.parse::<DerivationPath>().unwrap().to_string(),
            path_m_0
        );

        let path_m_0_2147483647h = "m/0/2147483647'";
        assert_eq!(
            path_m_0_2147483647h
                .parse::<DerivationPath>()
                .unwrap()
                .to_string(),
            path_m_0_2147483647h
        );

        let path_m_0_2147483647h_1 = "m/0/2147483647'/1";
        assert_eq!(
            path_m_0_2147483647h_1
                .parse::<DerivationPath>()
                .unwrap()
                .to_string(),
            path_m_0_2147483647h_1
        );

        let path_m_0_2147483647h_1_2147483646h = "m/0/2147483647'/1/2147483646'";
        assert_eq!(
            path_m_0_2147483647h_1_2147483646h
                .parse::<DerivationPath>()
                .unwrap()
                .to_string(),
            path_m_0_2147483647h_1_2147483646h
        );

        let path_m_0_2147483647h_1_2147483646h_2 = "m/0/2147483647'/1/2147483646'/2";
        assert_eq!(
            path_m_0_2147483647h_1_2147483646h_2
                .parse::<DerivationPath>()
                .unwrap()
                .to_string(),
            path_m_0_2147483647h_1_2147483646h_2
        );
    }

    #[test]
    fn parent() {
        let path_m_0_2147483647h = "m/0/2147483647'".parse::<DerivationPath>().unwrap();
        let path_m_0 = path_m_0_2147483647h.parent().unwrap();
        assert_eq!("m/0", path_m_0.to_string());

        let path_m = path_m_0.parent().unwrap();
        assert_eq!("m", path_m.to_string());
        assert_eq!(path_m.parent(), None);
    }
}