feat(tvix/eval): implement `builtins.hashFile` r/7625

The primary addition is the `builtin_hashFile` function which attempts
value-path coercion and on success reads the file to a nix_string.
Similar to the `builtins_hashString` implementation, the hash is then
derived using the `hash_nix_string` function in the introduced hash
module which has extracted hashing functionality initially specified in
cl/11005.

Change-Id: I5e3ef0317223af99488ebb79efc2fb49b4cbc1b6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11007
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

1 files changed, 25 insertions, 0 deletions

diff --git a/tvix/eval/src/builtins/hash.rs b/tvix/eval/src/builtins/hash.rs
new file mode 100644
index 0000000000..6d07fc9b2d
--- /dev/null
+++ b/tvix/eval/src/builtins/hash.rs
@@ -0,0 +1,25 @@
+use bstr::ByteSlice;
+use data_encoding::HEXLOWER;
+use md5::Md5;
+use sha1::Sha1;
+use sha2::{digest::Output, Digest, Sha256, Sha512};
+
+use crate::ErrorKind;
+
+fn hash<D: Digest>(b: &[u8]) -> Output<D> {
+    let mut hasher = D::new();
+    hasher.update(b);
+    hasher.finalize()
+}
+
+pub fn hash_nix_string(algo: impl AsRef<[u8]>, s: impl AsRef<[u8]>) -> Result<String, ErrorKind> {
+    match algo.as_ref() {
+        b"md5" => Ok(HEXLOWER.encode(hash::<Md5>(s.as_ref()).as_bstr())),
+        b"sha1" => Ok(HEXLOWER.encode(hash::<Sha1>(s.as_ref()).as_bstr())),
+        b"sha256" => Ok(HEXLOWER.encode(hash::<Sha256>(s.as_ref()).as_bstr())),
+        b"sha512" => Ok(HEXLOWER.encode(hash::<Sha512>(s.as_ref()).as_bstr())),
+        _ => Err(ErrorKind::UnknownHashType(
+            algo.as_ref().as_bstr().to_string(),
+        )),
+    }
+}