1 files changed, 29 insertions, 0 deletions
diff --git a/tvix/eval/src/builtins/hash.rs b/tvix/eval/src/builtins/hash.rs
new file mode 100644
index 000000000000..d0145f1e7d75
--- /dev/null
+++ b/tvix/eval/src/builtins/hash.rs
@@ -0,0 +1,29 @@
+use bstr::ByteSlice;
+use data_encoding::HEXLOWER;
+use md5::Md5;
+use sha1::Sha1;
+use sha2::{digest::Output, Digest, Sha256, Sha512};
+
+use crate::ErrorKind;
+
+/// Reads through all data from the passed reader, and returns the resulting [Digest].
+/// The exact hash function used is left generic over all [Digest].
+fn hash<D: Digest + std::io::Write>(mut r: impl std::io::Read) -> Result<Output<D>, ErrorKind> {
+    let mut hasher = D::new();
+    std::io::copy(&mut r, &mut hasher)?;
+    Ok(hasher.finalize())
+}
+
+/// For a given algo "string" and reader for data, calculate the digest
+/// and return it as a hexlower encoded [String].
+pub fn hash_nix_string(algo: impl AsRef<[u8]>, s: impl std::io::Read) -> Result<String, ErrorKind> {
+    match algo.as_ref() {
+        b"md5" => Ok(HEXLOWER.encode(hash::<Md5>(s)?.as_bstr())),
+        b"sha1" => Ok(HEXLOWER.encode(hash::<Sha1>(s)?.as_bstr())),
+        b"sha256" => Ok(HEXLOWER.encode(hash::<Sha256>(s)?.as_bstr())),
+        b"sha512" => Ok(HEXLOWER.encode(hash::<Sha512>(s)?.as_bstr())),
+        _ => Err(ErrorKind::UnknownHashType(
+            algo.as_ref().as_bstr().to_string(),
+        )),
+    }
+}