use std::{convert::TryInto, fmt}; use crate::{ObjectId, SIZE_OF_SHA1_DIGEST}; /// A borrowed reference to a hash identifying objects. /// /// # Future Proofing /// /// In case we wish to support multiple hashes with the same length we cannot discriminate /// using the slice length anymore. To make that work, we will use the high bits of the /// internal `bytes` slice length (a fat pointer, pointing to data and its length in bytes) /// to encode additinoal information. Before accessing or returning the bytes, a new adjusted /// slice will be constructed, while the high bits will be used to help resolving the /// hash `[`kind()`][oid::kind()]`. /// We expect to have quite a few bits available for such 'conflict resolution' as most hashes aren't longer /// than 64 bytes. #[derive(PartialEq, Eq, Hash, Ord, PartialOrd)] #[repr(transparent)] #[allow(non_camel_case_types)] #[cfg_attr(feature = "serde1", derive(serde::Serialize))] pub struct oid { bytes: [u8], } impl std::fmt::Debug for oid { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { match self.kind() { crate::Kind::Sha1 => f.write_str("Sha1(")?, } for b in self.as_bytes() { write!(f, "{:02x}", b)?; } f.write_str(")") } } use quick_error::quick_error; quick_error! { #[derive(Debug)] pub enum Error { InvalidByteSliceLength(length: usize) { display("Cannot instantiate git hash from a digest of length {}", length) } } } /// Conversion impl oid { /// Try to create a shared object id from a slice of bytes representing a hash `digest` pub fn try_from(digest: &[u8]) -> Result<&Self, Error> { match digest.len() { 20 => Ok( #[allow(unsafe_code)] unsafe { &*(digest as *const [u8] as *const oid) }, ), len => Err(Error::InvalidByteSliceLength(len)), } } /// Only from code that statically assures correct sizes using array conversions fn from(value: &[u8]) -> &Self { #[allow(unsafe_code)] unsafe { &*(value as *const [u8] as *const oid) } } } /// Access impl oid { /// The kind of hash used for this Digest pub fn kind(&self) -> crate::Kind { match self.bytes.len() { 20 => crate::Kind::Sha1, _ => unreachable!("creating this instance is checked and fails on unknown lengths"), } } /// The first byte of the hash, commonly used to partition a set of `Id`s pub fn first_byte(&self) -> u8 { self.bytes[0] } #[inline] /// Interpret this object id as raw byte slice. pub fn as_bytes(&self) -> &[u8] { &self.bytes } } /// Sha1 specific methods impl oid { /// Returns an array with a hexadecimal encoded version of the Sha1 hash this `Id` represents. /// /// **Panics** if this is not a Sha1 hash, as identifiable by [`ObjectId::kind()`]. pub fn to_sha1_hex(&self) -> [u8; SIZE_OF_SHA1_DIGEST * 2] { let mut buf = [0u8; SIZE_OF_SHA1_DIGEST * 2]; hex::encode_to_slice(&self.bytes, &mut buf).expect("to count correctly"); buf } /// Returns the bytes making up the Sha1. /// /// **Panics** if this is not a Sha1 hash, as identifiable by [`ObjectId::kind()`]. pub fn sha1(&self) -> &[u8; SIZE_OF_SHA1_DIGEST] { self.bytes.try_into().expect("correctly sized slice") } /// Returns a Sha1 digest with all bytes being initialized to zero. pub fn null_sha1() -> &'static Self { oid::from([0u8; SIZE_OF_SHA1_DIGEST].as_ref()) } } impl AsRef for &oid { fn as_ref(&self) -> &oid { self } } impl ToOwned for oid { type Owned = crate::ObjectId; fn to_owned(&self) -> Self::Owned { match self.kind() { crate::Kind::Sha1 => crate::ObjectId::Sha1(self.bytes.try_into().expect("no bug in hash detection")), } } } impl<'a> From<&'a [u8; SIZE_OF_SHA1_DIGEST]> for &'a oid { fn from(v: &'a [u8; SIZE_OF_SHA1_DIGEST]) -> Self { oid::from(v.as_ref()) } } impl fmt::Display for &oid { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { for b in self.as_bytes() { write!(f, "{:02x}", b)?; } Ok(()) } } impl PartialEq for &oid { fn eq(&self, other: &ObjectId) -> bool { *self == other.as_ref() } } /// Manually created from a version that uses a slice, and we forcefully try to convert it into a borrowed array of the desired size /// Could be improved by fitting this into serde /// Unfortunately the serde::Deserialize derive wouldn't work for borrowed arrays. #[cfg(feature = "serde1")] impl<'de: 'a, 'a> serde::Deserialize<'de> for &'a oid { fn deserialize(deserializer: D) -> Result>::Error> where D: serde::Deserializer<'de>, { struct __Visitor<'de: 'a, 'a> { marker: std::marker::PhantomData<&'a oid>, lifetime: std::marker::PhantomData<&'de ()>, } impl<'de: 'a, 'a> serde::de::Visitor<'de> for __Visitor<'de, 'a> { type Value = &'a oid; fn expecting(&self, __formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { std::fmt::Formatter::write_str(__formatter, "tuple struct Digest") } #[inline] fn visit_newtype_struct<__E>(self, __e: __E) -> std::result::Result where __E: serde::Deserializer<'de>, { let __field0: &'a [u8] = match <&'a [u8] as serde::Deserialize>::deserialize(__e) { Ok(__val) => __val, Err(__err) => { return Err(__err); } }; Ok(oid::try_from(__field0).expect("exactly 20 bytes")) } #[inline] fn visit_seq<__A>(self, mut __seq: __A) -> std::result::Result where __A: serde::de::SeqAccess<'de>, { let __field0 = match match serde::de::SeqAccess::next_element::<&'a [u8]>(&mut __seq) { Ok(__val) => __val, Err(__err) => { return Err(__err); } } { Some(__value) => __value, None => { return Err(serde::de::Error::invalid_length( 0usize, &"tuple struct Digest with 1 element", )); } }; Ok(oid::try_from(__field0).expect("exactly 20 bytes")) } } serde::Deserializer::deserialize_newtype_struct( deserializer, "Digest", __Visitor { marker: std::marker::PhantomData::<&'a oid>, lifetime: std::marker::PhantomData, }, ) } }