fix(tvix/nix-compat): Make CAHash deserialize more formats r/7633

Currently CAHash only deserializes the hash in hex code while
the serializer outputs a nixbase32 hash. This means that you can't currently
deserialize what has been serialized.

This change makes deserialize support any digest format (so hex, nixbase32
and base64) as well as flattens the deserialize code and error handling.

It also implements serde methods of HashAlgo directly using Display and TryFrom
implementations because otherwise these would get serialized as eg. Sha256 instead
of sha256 which also broke CAHash serialize/deserialize.

Change-Id: I1941a72eaec741e4956292adaaf0115b97f260ba
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11082
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

2 files changed, 200 insertions, 67 deletions

diff --git a/tvix/nix-compat/src/nixhash/algos.rs b/tvix/nix-compat/src/nixhash/algos.rs
index f189eba09db6..ac8915314c83 100644
--- a/tvix/nix-compat/src/nixhash/algos.rs
+++ b/tvix/nix-compat/src/nixhash/algos.rs
@@ -5,7 +5,7 @@ use serde::{Deserialize, Serialize};
 use crate::nixhash::Error;
 
 /// This are the hash algorithms supported by cppnix.
-#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum HashAlgo {
     Md5,
     Sha1,
@@ -36,6 +36,25 @@ impl Display for HashAlgo {
     }
 }
 
+impl Serialize for HashAlgo {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        serializer.collect_str(&self)
+    }
+}
+
+impl<'de> Deserialize<'de> for HashAlgo {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let s: &str = Deserialize::deserialize(deserializer)?;
+        HashAlgo::try_from(s).map_err(serde::de::Error::custom)
+    }
+}
+
 /// TODO(Raito): this could be automated via macros, I suppose.
 /// But this may be more expensive than just doing it by hand
 /// and ensuring that is kept in sync.
diff --git a/tvix/nix-compat/src/nixhash/ca_hash.rs b/tvix/nix-compat/src/nixhash/ca_hash.rs
index d69d19ce68f3..1c2f61dc6c65 100644
--- a/tvix/nix-compat/src/nixhash/ca_hash.rs
+++ b/tvix/nix-compat/src/nixhash/ca_hash.rs
@@ -1,5 +1,5 @@
 use crate::nixbase32;
-use crate::nixhash::{self, HashAlgo, NixHash};
+use crate::nixhash::{HashAlgo, NixHash};
 use serde::de::Unexpected;
 use serde::ser::SerializeMap;
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
@@ -7,7 +7,7 @@ use serde_json::{Map, Value};
 use std::borrow::Cow;
 
 use super::algos::SUPPORTED_ALGOS;
-use super::from_algo_and_digest;
+use super::decode_digest;
 
 /// A Nix CAHash describes a content-addressed hash of a path.
 ///
@@ -99,73 +99,40 @@ impl CAHash {
             return Ok(None);
         }
 
-        let digest: Vec<u8> = {
-            if let Some(v) = map.get("hash") {
-                if let Some(s) = v.as_str() {
-                    data_encoding::HEXLOWER
-                        .decode(s.as_bytes())
-                        .map_err(|e| serde::de::Error::custom(e.to_string()))?
-                } else {
-                    return Err(serde::de::Error::invalid_type(
-                        Unexpected::Other(&v.to_string()),
-                        &"a string",
-                    ));
-                }
-            } else {
-                return Err(serde::de::Error::missing_field(
-                    "couldn't extract `hash` key but `hashAlgo` key present",
-                ));
-            }
+        let hash_algo_v = map.get("hashAlgo").ok_or_else(|| {
+            serde::de::Error::missing_field(
+                "couldn't extract `hashAlgo` key, but `hash` key present",
+            )
+        })?;
+        let hash_algo = hash_algo_v.as_str().ok_or_else(|| {
+            serde::de::Error::invalid_type(Unexpected::Other(&hash_algo_v.to_string()), &"a string")
+        })?;
+        let (mode_is_nar, hash_algo) = if let Some(s) = hash_algo.strip_prefix("r:") {
+            (true, s)
+        } else {
+            (false, hash_algo)
         };
+        let hash_algo = HashAlgo::try_from(hash_algo).map_err(|e| {
+            serde::de::Error::invalid_value(
+                Unexpected::Other(&e.to_string()),
+                &format!("one of {}", SUPPORTED_ALGOS.join(",")).as_str(),
+            )
+        })?;
 
-        if let Some(v) = map.get("hashAlgo") {
-            if let Some(s) = v.as_str() {
-                match s.strip_prefix("r:") {
-                    Some(rest) => Ok(Some(Self::Nar(
-                        from_algo_and_digest(
-                            HashAlgo::try_from(rest).map_err(|e| {
-                                serde::de::Error::invalid_value(
-                                    Unexpected::Other(&e.to_string()),
-                                    &format!("one of {}", SUPPORTED_ALGOS.join(",")).as_str(),
-                                )
-                            })?,
-                            &digest,
-                        )
-                        .map_err(|e: nixhash::Error| {
-                            serde::de::Error::invalid_value(
-                                Unexpected::Other(&e.to_string()),
-                                &"a digest with right length",
-                            )
-                        })?,
-                    ))),
-                    None => Ok(Some(Self::Flat(
-                        from_algo_and_digest(
-                            HashAlgo::try_from(s).map_err(|e| {
-                                serde::de::Error::invalid_value(
-                                    Unexpected::Other(&e.to_string()),
-                                    &format!("one of {}", SUPPORTED_ALGOS.join(",")).as_str(),
-                                )
-                            })?,
-                            &digest,
-                        )
-                        .map_err(|e: nixhash::Error| {
-                            serde::de::Error::invalid_value(
-                                Unexpected::Other(&e.to_string()),
-                                &"a digest with right length",
-                            )
-                        })?,
-                    ))),
-                }
-            } else {
-                Err(serde::de::Error::invalid_type(
-                    Unexpected::Other(&v.to_string()),
-                    &"a string",
-                ))
-            }
+        let hash_v = map.get("hash").ok_or_else(|| {
+            serde::de::Error::missing_field(
+                "couldn't extract `hash` key but `hashAlgo` key present",
+            )
+        })?;
+        let hash = hash_v.as_str().ok_or_else(|| {
+            serde::de::Error::invalid_type(Unexpected::Other(&hash_v.to_string()), &"a string")
+        })?;
+        let hash = decode_digest(hash.as_bytes(), hash_algo)
+            .map_err(|e| serde::de::Error::custom(e.to_string()))?;
+        if mode_is_nar {
+            Ok(Some(Self::Nar(hash)))
         } else {
-            Err(serde::de::Error::missing_field(
-                "couldn't extract `hashAlgo` key, but `hash` key present",
-            ))
+            Ok(Some(Self::Flat(hash)))
         }
     }
 }
@@ -211,3 +178,150 @@ impl<'de> Deserialize<'de> for CAHash {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{derivation::CAHash, nixhash};
+
+    #[test]
+    fn serialize_flat() {
+        let json_bytes = r#"{
+  "hash": "1fnf2m46ya7r7afkcb8ba2j0sc4a85m749sh9jz64g4hx6z3r088",
+  "hashAlgo": "sha256"
+}"#;
+        let hash = CAHash::Flat(
+            nixhash::from_nix_str(
+                "sha256:08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba",
+            )
+            .unwrap(),
+        );
+        let serialized = serde_json::to_string_pretty(&hash).unwrap();
+        assert_eq!(serialized, json_bytes);
+    }
+
+    #[test]
+    fn serialize_nar() {
+        let json_bytes = r#"{
+  "hash": "1fnf2m46ya7r7afkcb8ba2j0sc4a85m749sh9jz64g4hx6z3r088",
+  "hashAlgo": "r:sha256"
+}"#;
+        let hash = CAHash::Nar(
+            nixhash::from_nix_str(
+                "sha256:08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba",
+            )
+            .unwrap(),
+        );
+        let serialized = serde_json::to_string_pretty(&hash).unwrap();
+        assert_eq!(serialized, json_bytes);
+    }
+
+    #[test]
+    fn deserialize_flat() {
+        let json_bytes = r#"
+        {
+            "hash": "08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba",
+            "hashAlgo": "sha256"
+        }"#;
+        let hash: CAHash = serde_json::from_str(json_bytes).expect("must parse");
+
+        assert_eq!(
+            hash,
+            CAHash::Flat(
+                nixhash::from_nix_str(
+                    "sha256:08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba"
+                )
+                .unwrap()
+            )
+        );
+    }
+
+    #[test]
+    fn deserialize_hex() {
+        let json_bytes = r#"
+        {
+            "hash": "08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba",
+            "hashAlgo": "r:sha256"
+        }"#;
+        let hash: CAHash = serde_json::from_str(json_bytes).expect("must parse");
+
+        assert_eq!(
+            hash,
+            CAHash::Nar(
+                nixhash::from_nix_str(
+                    "sha256:08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba"
+                )
+                .unwrap()
+            )
+        );
+    }
+
+    #[test]
+    fn deserialize_nixbase32() {
+        let json_bytes = r#"
+        {
+            "hash": "1fnf2m46ya7r7afkcb8ba2j0sc4a85m749sh9jz64g4hx6z3r088",
+            "hashAlgo": "r:sha256"
+        }"#;
+        let hash: CAHash = serde_json::from_str(json_bytes).expect("must parse");
+
+        assert_eq!(
+            hash,
+            CAHash::Nar(
+                nixhash::from_nix_str(
+                    "sha256:08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba"
+                )
+                .unwrap()
+            )
+        );
+    }
+
+    #[test]
+    fn deserialize_base64() {
+        let json_bytes = r#"
+        {
+            "hash": "CIE8vumQPGK+TFAncmpBijANpFALLTadOvkob0gVzro=",
+            "hashAlgo": "r:sha256"
+        }"#;
+        let hash: CAHash = serde_json::from_str(json_bytes).expect("must parse");
+
+        assert_eq!(
+            hash,
+            CAHash::Nar(
+                nixhash::from_nix_str(
+                    "sha256:08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba"
+                )
+                .unwrap()
+            )
+        );
+    }
+
+    #[test]
+    fn serialize_deserialize_nar() {
+        let json_bytes = r#"
+        {
+            "hash": "08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba",
+            "hashAlgo": "r:sha256"
+        }"#;
+        let hash: CAHash = serde_json::from_str(json_bytes).expect("must parse");
+
+        let serialized = serde_json::to_string(&hash).expect("Serialize");
+        let hash2: CAHash = serde_json::from_str(&serialized).expect("must parse again");
+
+        assert_eq!(hash, hash2);
+    }
+
+    #[test]
+    fn serialize_deserialize_flat() {
+        let json_bytes = r#"
+        {
+            "hash": "08813cbee9903c62be4c5027726a418a300da4500b2d369d3af9286f4815ceba",
+            "hashAlgo": "sha256"
+        }"#;
+        let hash: CAHash = serde_json::from_str(json_bytes).expect("must parse");
+
+        let serialized = serde_json::to_string(&hash).expect("Serialize");
+        let hash2: CAHash = serde_json::from_str(&serialized).expect("must parse again");
+
+        assert_eq!(hash, hash2);
+    }
+}