Enum NixHash

pub enum NixHash {
    Md5([u8; 16]),
    Sha1([u8; 20]),
    Sha256([u8; 32]),
    Sha512(Box<[u8; 64]>),
}

NixHash represents hashes known by Nix (md5/sha1/sha256/sha512).

Internally, these are represented as an enum of 4 kinds (the latter being boxed for size reasons, as we rarely use sha512, having a pointer there is fine).

There’s Self::algo and Self::digest_as_bytes accessors, as well as a Self::from_algo_and_digest constructor.

A few methods to parse (from_$format_$encoding) and emit (to_$format_$encoding) various formats and encodings Nix uses.

Formats

The following formats exist:

Nix Format

Lowercase algo, followed by a colon, then the digest.

SRI Format

Uses the lowercase algo, followed by a -, then the digest (base64-encoded). This is also used in the Display implementation.

Contrary to the SRI spec, Nix doesn’t have an understanding of passing multiple hashes (with different algos) in SRI hashes. It instead simply cuts everything off after the expected length for the specified algo, and tries to parse the rest in permissive base64 (allowing missing padding).

Digest only

It’s possible to not specify the algo at all. In that case, the expected NixHash algo MUST be provided externally.

Encodings

For “Nix” and “Digest only” formats, the following encodings are supported:

• lowerhex,
• nixbase32,
• base64 (StdEncoding)

Variants

Md5([u8; 16])

Sha1([u8; 20])

Sha256([u8; 32])

Sha512(Box<[u8; 64]>)

Implementations

impl NixHash

pub fn algo(&self) -> HashAlgo

returns the algo as HashAlgo.

pub fn digest_as_bytes(&self) -> &[u8]

returns the digest as variable-length byte slice.

pub fn from_algo_and_digest( algo: HashAlgo, digest: &[u8], ) -> Result<NixHash, Error>

Constructs a new NixHash by specifying HashAlgo and digest. It can fail if the passed digest length doesn’t match what’s expected for the passed algo.

pub fn from_nix_nixbase32(s: &str) -> Option<Self>

Constructs a new NixHash from the Nix default hash format, the inverse of Self::to_nix_nixbase32.

pub fn to_nix_nixbase32(&self) -> String

Formats a NixHash in the Nix nixbase32 format.

pub fn from_sri(s: &str) -> Result<NixHash, Error>

Parses a Nix SRI string to a NixHash. (See caveats in Self on the deviations from the SRI spec)

pub fn write_sri_str(&self, w: &mut impl Write) -> Result<(), Error>

Writes a NixHash in SRI format to a std::fmt::Write.

pub fn to_sri_string(&self) -> String

Formats a NixHash to an SRI string.

pub fn to_nix_lowerhex_string(&self) -> String

Formats a NixHash in the Nix lowerhex format.

pub fn from_str(s: &str, want_algo: Option<HashAlgo>) -> Result<NixHash, Error>

This parses all known output formats for NixHash. See NixHash for a list. An optional algo needs to be provided, which is mandatory to be specified if the “digest only” format is used. In other cases, consistency of an optionally externally configured algo with the one parsed is ensured.

Trait Implementations

impl Clone for NixHash

fn clone(&self) -> NixHash

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for NixHash

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for NixHash

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for NixHash

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Ord for NixHash

Same order as sorting the corresponding nixbase32 strings.

This order is used in the ATerm serialization of a derivation and thus affects the calculated output hash.

fn cmp(&self, other: &NixHash) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for NixHash

fn eq(&self, other: &NixHash) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for NixHash

fn partial_cmp(&self, other: &NixHash) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Serialize for NixHash

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.

impl Eq for NixHash

impl StructuralPartialEq for NixHash