rpc: Fix AppHash decoding failure in /block_results response (#1449)

* If AppHash decoding fails, try with decoding with base64

* Add changelog entry

* Update .changelog/unreleased/improvements/1449-allow-base64-apphash.md

Co-authored-by: Romain Ruetschi <romain@informal.systems>

---------

Co-authored-by: Romain Ruetschi <romain@informal.systems>

.changelog/unreleased/improvements/1449-allow-base64-apphash.md

@@ -0,0 +1,2 @@
+- `[tendermint-rpc]` If `AppHash` fails to decode as hex, try to decode it as base64.
+  ([\#1449](https://github.com/informalsystems/tendermint-rs/issues/1449))

tendermint/src/hash.rs

@@ -7,7 +7,7 @@ use core::{
 
 use bytes::Bytes;
 use serde::{de::Error as _, Deserialize, Deserializer, Serialize, Serializer};
-use subtle_encoding::{Encoding, Hex};
+use subtle_encoding::{base64, Encoding, Hex};
 use tendermint_proto::Protobuf;
 
 use crate::{error::Error, prelude::*};
@@ -253,6 +253,12 @@ impl AppHash {
             .map_err(Error::subtle_encoding)?;
         Ok(AppHash(h))
     }
+
+    /// Decode a `Hash` from base64-encoded string
+    pub fn from_base64(s: &str) -> Result<Self, Error> {
+        let h = base64::decode(s).map_err(Error::subtle_encoding)?;
+        Ok(AppHash(h))
+    }
 }
 
 impl AsRef<[u8]> for AppHash {
@@ -285,6 +291,52 @@ impl FromStr for AppHash {
     type Err = Error;
 
     fn from_str(s: &str) -> Result<Self, Error> {
-        Self::from_hex_upper(s)
+        Self::from_hex_upper(s).or_else(|_| Self::from_base64(s))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[derive(Debug, serde::Deserialize)]
+    struct Test {
+        #[serde(default)]
+        #[serde(with = "crate::serializers::apphash")]
+        pub app_hash: AppHash,
+    }
+
+    #[test]
+    fn apphash_decode_base64() {
+        let test = serde_json::from_str::<Test>(
+            r#"{"app_hash":"MfX9f+bYoI8IioRb4YT/8/VhPvtNjgWFgTi4mmMSkBc="}"#,
+        )
+        .unwrap();
+
+        assert_eq!(
+            test.app_hash.as_ref(),
+            &[
+                0x31, 0xF5, 0xFD, 0x7F, 0xE6, 0xD8, 0xA0, 0x8F, 0x08, 0x8A, 0x84, 0x5B, 0xE1, 0x84,
+                0xFF, 0xF3, 0xF5, 0x61, 0x3E, 0xFB, 0x4D, 0x8E, 0x05, 0x85, 0x81, 0x38, 0xB8, 0x9A,
+                0x63, 0x12, 0x90, 0x17
+            ]
+        );
+    }
+
+    #[test]
+    fn apphash_decode_hex() {
+        let test = serde_json::from_str::<Test>(
+            r#"{"app_hash":"31F5FD7FE6D8A08F088A845BE184FFF3F5613EFB4D8E05858138B89A63129017"}"#,
+        )
+        .unwrap();
+
+        assert_eq!(
+            test.app_hash.as_ref(),
+            &[
+                0x31, 0xF5, 0xFD, 0x7F, 0xE6, 0xD8, 0xA0, 0x8F, 0x08, 0x8A, 0x84, 0x5B, 0xE1, 0x84,
+                0xFF, 0xF3, 0xF5, 0x61, 0x3E, 0xFB, 0x4D, 0x8E, 0x05, 0x85, 0x81, 0x38, 0xB8, 0x9A,
+                0x63, 0x12, 0x90, 0x17
+            ]
+        );
     }
 }

tendermint/src/serializers/apphash.rs

@@ -1,9 +1,10 @@
 //! AppHash serialization with validation
 
+use core::str::FromStr;
+
 use alloc::borrow::Cow;
 
-use serde::{de, ser, Deserialize, Deserializer, Serializer};
-use subtle_encoding::hex;
+use serde::{de, Deserialize, Deserializer, Serializer};
 
 use crate::{prelude::*, AppHash};
 
@@ -13,16 +14,14 @@ where
     D: Deserializer<'de>,
 {
     let hexstring = Option::<Cow<'_, str>>::deserialize(deserializer)?.unwrap_or(Cow::Borrowed(""));
-    AppHash::from_hex_upper(&hexstring).map_err(de::Error::custom)
+    AppHash::from_str(&hexstring).map_err(de::Error::custom)
 }
 
 /// Serialize from AppHash into hexstring
 pub fn serialize<S>(value: &AppHash, serializer: S) -> Result<S::Ok, S::Error>
 where
     S: Serializer,
 {
-    let hex_bytes = hex::encode_upper(value.as_ref());
-    let hex_string = String::from_utf8(hex_bytes).map_err(ser::Error::custom)?;
     // Serialize as Option<String> for symmetry with deserialize
-    serializer.serialize_some(&hex_string)
+    serializer.serialize_some(&value.to_string())
 }