refactor(tvix/nix-compat): cleanup parse_{ca,hash} and fmt structs r/7045

These were used to format to and parse from strings.

Move this to the CAHash and NixHash structs directly, and be explicit in
the name about which encoding for digests is used.

For output path calculation, nix encodes the nixpaths in hex, but for
writing out NARInfos, it's using nixbase32.

Change-Id: Ia585a76a3811b2609e7ce259fda66a29403b7e07
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10079
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>

1 files changed, 28 insertions, 1 deletions

diff --git a/tvix/nix-compat/src/nixhash/mod.rs b/tvix/nix-compat/src/nixhash/mod.rs
index f699a4cd9524..a93d2b68da94 100644
--- a/tvix/nix-compat/src/nixhash/mod.rs
+++ b/tvix/nix-compat/src/nixhash/mod.rs
@@ -41,15 +41,42 @@ impl NixHash {
         }
     }
 
+    /// Constructs a [NixHash] from the Nix default hash format,
+    /// the inverse of [to_nix_hex_string].
+    pub fn from_nix_hex_str(s: &str) -> Option<Self> {
+        let (tag, digest) = s.split_once(':')?;
+
+        (match tag {
+            "md5" => nixbase32::decode_fixed(digest).map(NixHash::Md5),
+            "sha1" => nixbase32::decode_fixed(digest).map(NixHash::Sha1),
+            "sha256" => nixbase32::decode_fixed(digest).map(NixHash::Sha256),
+            "sha512" => nixbase32::decode_fixed(digest)
+                .map(Box::new)
+                .map(NixHash::Sha512),
+            _ => return None,
+        })
+        .ok()
+    }
+
     /// Formats a [NixHash] in the Nix default hash format,
     /// which is the algo, followed by a colon, then the lower hex encoded digest.
-    pub fn to_nix_hash_string(&self) -> String {
+    pub fn to_nix_hex_string(&self) -> String {
         format!(
             "{}:{}",
             self.algo(),
             HEXLOWER.encode(self.digest_as_bytes())
         )
     }
+
+    /// Formats a [NixHash] in the format that's used inside CAHash,
+    /// which is the algo, followed by a colon, then the nixbase32-encoded digest.
+    pub(crate) fn to_nix_nixbase32_string(&self) -> String {
+        format!(
+            "{}:{}",
+            self.algo(),
+            nixbase32::encode(self.digest_as_bytes())
+        )
+    }
 }
 
 impl TryFrom<(HashAlgo, &[u8])> for NixHash {