rpc: Allow empty JSON object value for consensus_param_updates in /block_results response

.changelog/unreleased/bug/1440-allow-empty-consensus-params-updates.md

@@ -0,0 +1,3 @@
+- `[tendermint-rpc]` Deserialize an empty JSON object as `None` for the `consensus_param_updates`
+  field in the `/block_results` response.
+  ([\#1440](https://github.com/informalsystems/tendermint-rs/issues/1440))

rpc/src/endpoint/block_results.rs

@@ -1,6 +1,7 @@
 //! `/block_results` endpoint JSON-RPC wrapper
 
 use serde::{Deserialize, Serialize};
+use tendermint::deserializers::allow_empty_object::allow_empty_object;
 use tendermint::{abci, block, consensus, serializers, validator, AppHash};
 
 use crate::dialect::{self, Dialect};
@@ -78,6 +79,7 @@ pub struct Response {
     pub validator_updates: Vec<validator::Update>,
 
     /// New consensus params (might be explicit null)
+    #[serde(deserialize_with = "allow_empty_object")]
     pub consensus_param_updates: Option<consensus::Params>,
 
     /// Merkle hash of the application state

tendermint/src/consensus/params.rs

@@ -2,7 +2,9 @@
 
 use serde::{Deserialize, Serialize};
 
-use crate::{block, evidence, prelude::*, public_key};
+use crate::{
+    block, deserializers::allow_empty_object::allow_empty_object, evidence, prelude::*, public_key,
+};
 
 /// All consensus-relevant parameters that can be adjusted by the ABCI app.
 ///
@@ -15,8 +17,8 @@ pub struct Params {
     pub evidence: evidence::Params,
     /// Parameters limiting the types of public keys validators can use.
     pub validator: ValidatorParams,
-    /// The ABCI application version.
-    #[serde(skip)] // FIXME: kvstore /genesis returns '{}' instead of '{app_version: "0"}'
+    /// The ABCI application version. Will default to None if not present.
+    #[serde(default, deserialize_with = "allow_empty_object")]
     pub version: Option<VersionParams>,
     /// Parameters specific to the Application Blockchain Interface.
     ///

tendermint/src/deserializers/allow_empty_object.rs

@@ -0,0 +1,26 @@
+use serde::{Deserialize, Deserializer};
+
+/// Deserialize `null` or an empty object `{}` as `None`.
+pub fn allow_empty_object<'de, D, T>(deserializer: D) -> Result<Option<T>, D::Error>
+where
+    D: Deserializer<'de>,
+    T: Deserialize<'de>,
+{
+    #[derive(Deserialize)]
+    #[serde(
+        untagged,
+        deny_unknown_fields,
+        expecting = "object, empty object or null"
+    )]
+    enum Helper<T> {
+        Data(T),
+        Empty {},
+        Null,
+    }
+
+    match Helper::deserialize(deserializer) {
+        Ok(Helper::Data(data)) => Ok(Some(data)),
+        Ok(Helper::Empty {} | Helper::Null) => Ok(None),
+        Err(e) => Err(e),
+    }
+}

tendermint/src/deserializers/mod.rs

@@ -0,0 +1 @@
+pub mod allow_empty_object;

tendermint/src/lib.rs

@@ -35,6 +35,7 @@ pub mod chain;
 pub mod channel;
 pub mod consensus;
 pub mod crypto;
+pub mod deserializers;
 pub mod evidence;
 pub mod genesis;
 pub mod hash;