fix(rpc): Return detailed errors to the RPC client when a block proposal fails

zebra-rpc/src/methods/get_block_template_rpcs/get_block_template.rs

@@ -10,7 +10,7 @@ use zebra_chain::{
     block::{
         self,
         merkle::{self, AuthDataRoot},
-        ChainHistoryBlockTxAuthCommitmentHash, Height,
+        Block, ChainHistoryBlockTxAuthCommitmentHash, Height,
     },
     chain_sync_status::ChainSyncStatus,
     chain_tip::ChainTip,
@@ -108,8 +108,18 @@ where
         + Sync
         + 'static,
 {
-    let Ok(block) = block_proposal_bytes.zcash_deserialize_into::<block::Block>() else {
-         return Ok(ProposalRejectReason::Rejected.into())
+    let block: Block = match block_proposal_bytes.zcash_deserialize_into() {
+        Ok(block) => block,
+        Err(parse_error) => {
+            tracing::info!(
+                ?parse_error,
+                "error response from block parser in CheckProposal request"
+            );
+
+            return Ok(
+                ProposalResponse::rejected("invalid proposal format", parse_error.into()).into(),
+            );
+        }
     };
 
     let chain_verifier_response = chain_verifier
@@ -127,11 +137,11 @@ where
         .map(|_hash| ProposalResponse::Valid)
         .unwrap_or_else(|verify_chain_error| {
             tracing::info!(
-                verify_chain_error,
-                "Got error response from chain_verifier CheckProposal request"
+                ?verify_chain_error,
+                "error response from chain_verifier in CheckProposal request"
             );
 
-            ProposalRejectReason::Rejected.into()
+            ProposalResponse::rejected("invalid proposal", verify_chain_error)
         })
         .into())
 }

zebra-rpc/src/methods/get_block_template_rpcs/types/get_block_template.rs

@@ -31,7 +31,7 @@ pub mod parameters;
 pub mod proposal;
 
 pub use parameters::{GetBlockTemplateCapability, GetBlockTemplateRequestMode, JsonParameters};
-pub use proposal::{proposal_block_from_template, ProposalRejectReason, ProposalResponse};
+pub use proposal::{proposal_block_from_template, ProposalResponse};
 
 /// A serialized `getblocktemplate` RPC response in template mode.
 #[derive(Clone, Debug, Eq, PartialEq, serde::Serialize, serde::Deserialize)]

zebra-rpc/src/methods/get_block_template_rpcs/types/get_block_template/proposal.rs

@@ -2,13 +2,14 @@
 //!
 //! `ProposalResponse` is the output of the `getblocktemplate` RPC method in 'proposal' mode.
 
-use std::{num::ParseIntError, str::FromStr, sync::Arc};
+use std::{error::Error, num::ParseIntError, str::FromStr, sync::Arc};
 
 use zebra_chain::{
     block::{self, Block, Height},
     serialization::{DateTime32, SerializationError, ZcashDeserializeInto},
     work::equihash::Solution,
 };
+use zebra_node_services::BoxError;
 
 use crate::methods::{
     get_block_template_rpcs::types::{
@@ -18,47 +19,46 @@ use crate::methods::{
     GetBlockHash,
 };
 
-/// Error response to a `getblocktemplate` RPC request in proposal mode.
-///
-/// See <https://en.bitcoin.it/wiki/BIP_0022#Appendix:_Example_Rejection_Reasons>
-#[derive(Copy, Clone, Debug, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
-#[serde(rename_all = "kebab-case")]
-pub enum ProposalRejectReason {
-    /// Block proposal rejected as invalid.
-    Rejected,
-}
-
 /// Response to a `getblocktemplate` RPC request in proposal mode.
 ///
-/// See <https://en.bitcoin.it/wiki/BIP_0023#Block_Proposal>
+/// <https://en.bitcoin.it/wiki/BIP_0022#Appendix:_Example_Rejection_Reasons>
+///
+/// Note:
+/// The error response specification at <https://en.bitcoin.it/wiki/BIP_0023#Block_Proposal>
+/// seems to have a copy-paste issue, or it is under-specified. We follow the `zcashd`
+/// implementation instead, which returns a single raw string.
 #[derive(Clone, Debug, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 #[serde(untagged, rename_all = "kebab-case")]
 pub enum ProposalResponse {
-    /// Block proposal was rejected as invalid, returns `reject-reason` and server `capabilities`.
-    ErrorResponse {
-        /// Reason the proposal was invalid as-is.
-        reject_reason: ProposalRejectReason,
-
-        /// The getblocktemplate RPC capabilities supported by Zebra.
-        capabilities: Vec<String>,
-    },
+    /// Block proposal was rejected as invalid.
+    /// Contains the reason that the proposal was invalid.
+    ///
+    /// TODO: turn this into a typed error enum?
+    Rejected(String),
 
     /// Block proposal was successfully validated, returns null.
     Valid,
 }
 
-impl From<ProposalRejectReason> for ProposalResponse {
-    fn from(reject_reason: ProposalRejectReason) -> Self {
-        Self::ErrorResponse {
-            reject_reason,
-            capabilities: GetBlockTemplate::capabilities(),
-        }
+impl ProposalResponse {
+    /// Return a rejected response containing an error kind and detailed error info.
+    pub fn rejected<S: ToString>(kind: S, error: BoxError) -> Self {
+        let kind = kind.to_string();
+
+        // Pretty-print the detailed error for now
+        ProposalResponse::Rejected(format!("{kind}: {error:#?}"))
+    }
+
+    /// Return a rejected response containing just the detailed error information.
+    pub fn error(error: BoxError) -> Self {
+        // Pretty-print the detailed error for now
+        ProposalResponse::Rejected(format!("{error:#?}"))
     }
 }
 
-impl From<ProposalRejectReason> for Response {
-    fn from(error_response: ProposalRejectReason) -> Self {
-        Self::ProposalMode(ProposalResponse::from(error_response))
+impl<E: Error + Send + Sync + 'static> From<E> for ProposalResponse {
+    fn from(error: E) -> Self {
+        Self::error(error.into())
     }
 }
 

zebra-rpc/src/methods/tests/snapshot/snapshots/get_block_template_invalid-proposal@mainnet_10.snap

@@ -2,9 +2,4 @@
 source: zebra-rpc/src/methods/tests/snapshot/get_block_template_rpcs.rs
 expression: block_template
 ---
-{
-  "reject_reason": "rejected",
-  "capabilities": [
-    "proposal"
-  ]
-}
+"invalid proposal format: Io(\n    Error {\n        kind: UnexpectedEof,\n        message: \"failed to fill whole buffer\",\n    },\n)"

zebra-rpc/src/methods/tests/snapshot/snapshots/get_block_template_invalid-proposal@testnet_10.snap

@@ -2,9 +2,4 @@
 source: zebra-rpc/src/methods/tests/snapshot/get_block_template_rpcs.rs
 expression: block_template
 ---
-{
-  "reject_reason": "rejected",
-  "capabilities": [
-    "proposal"
-  ]
-}
+"invalid proposal format: Io(\n    Error {\n        kind: UnexpectedEof,\n        message: \"failed to fill whole buffer\",\n    },\n)"

zebrad/tests/common/get_block_template_rpcs/get_block_template.rs

@@ -167,7 +167,7 @@ async fn try_validate_block_template(client: &RPCRequestClient) -> Result<()> {
             "got getblocktemplate proposal response"
         );
 
-        if let ProposalResponse::ErrorResponse { reject_reason, .. } = json_result {
+        if let ProposalResponse::Rejected(reject_reason) = json_result {
             Err(eyre!(
                 "unsuccessful block proposal validation, reason: {reject_reason:?}"
             ))?;