Reply json (payjoin#606)

Fix payjoin#605

Author: DanGould

payjoin-cli/src/app/v2.rs

@@ -287,7 +287,8 @@ async fn handle_recoverable_error(
     mut receiver: UncheckedProposal,
     ohttp_relay: &payjoin::Url,
 ) -> anyhow::Error {
-    let (err_req, err_ctx) = match receiver.extract_err_req(&e, ohttp_relay) {
+    let to_return = anyhow!("Replied with error: {}", e);
+    let (err_req, err_ctx) = match receiver.extract_err_req(&e.into(), ohttp_relay) {
         Ok(req_ctx) => req_ctx,
         Err(e) => return anyhow!("Failed to extract error request: {}", e),
     };
@@ -306,7 +307,7 @@ async fn handle_recoverable_error(
         return anyhow!("Failed to process error response: {}", e);
     }
 
-    e.into()
+    to_return
 }
 
 fn try_contributing_inputs(

payjoin/src/error_codes.rs

@@ -1,14 +1,45 @@
 //! Well-known error codes as defined in BIP-78
 //! See: <https://github.com/bitcoin/bips/blob/master/bip-0078.mediawiki#receivers-well-known-errors>
 
-/// The payjoin endpoint is not available for now.
-pub const UNAVAILABLE: &str = "unavailable";
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ErrorCode {
+    /// The payjoin endpoint is not available for now.
+    Unavailable,
+    /// The receiver added some inputs but could not bump the fee of the payjoin proposal.
+    NotEnoughMoney,
+    /// This version of payjoin is not supported.
+    VersionUnsupported,
+    /// The receiver rejected the original PSBT.
+    OriginalPsbtRejected,
+}
 
-/// The receiver added some inputs but could not bump the fee of the payjoin proposal.
-pub const NOT_ENOUGH_MONEY: &str = "not-enough-money";
+impl ErrorCode {
+    pub const fn as_str(&self) -> &'static str {
+        match self {
+            Self::Unavailable => "unavailable",
+            Self::NotEnoughMoney => "not-enough-money",
+            Self::VersionUnsupported => "version-unsupported",
+            Self::OriginalPsbtRejected => "original-psbt-rejected",
+        }
+    }
+}
 
-/// This version of payjoin is not supported.
-pub const VERSION_UNSUPPORTED: &str = "version-unsupported";
+impl core::str::FromStr for ErrorCode {
+    type Err = ();
 
-/// The receiver rejected the original PSBT.
-pub const ORIGINAL_PSBT_REJECTED: &str = "original-psbt-rejected";
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "unavailable" => Ok(Self::Unavailable),
+            "not-enough-money" => Ok(Self::NotEnoughMoney),
+            "version-unsupported" => Ok(Self::VersionUnsupported),
+            "original-psbt-rejected" => Ok(Self::OriginalPsbtRejected),
+            _ => Err(()),
+        }
+    }
+}
+
+impl core::fmt::Display for ErrorCode {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.write_str(self.as_str())
+    }
+}

payjoin/src/receive/error.rs

@@ -1,7 +1,7 @@
 use std::{error, fmt};
 
-use crate::error_codes::{
-    NOT_ENOUGH_MONEY, ORIGINAL_PSBT_REJECTED, UNAVAILABLE, VERSION_UNSUPPORTED,
+use crate::error_codes::ErrorCode::{
+    self, NotEnoughMoney, OriginalPsbtRejected, Unavailable, VersionUnsupported,
 };
 
 pub type ImplementationError = Box<dyn error::Error + Send + Sync>;
@@ -48,7 +48,8 @@ impl error::Error for Error {
 /// 1. Provide structured error responses for protocol-level failures
 /// 2. Hide implementation details of external errors for security
 /// 3. Support proper error propagation through the receiver stack
-/// 4. Provide errors according to BIP-78 JSON error specifications for return using [`JsonError::to_json`]
+/// 4. Provide errors according to BIP-78 JSON error specifications for return
+///    after conversion into [`JsonReply`]
 #[derive(Debug)]
 pub enum ReplyableError {
     /// Error arising from validation of the original PSBT payload
@@ -62,41 +63,57 @@ pub enum ReplyableError {
     Implementation(ImplementationError),
 }
 
-/// A trait for errors that can be serialized to JSON in a standardized format.
+/// The standard format for errors that can be replied as JSON.
 ///
-/// The JSON output follows the structure:
+/// The JSON output includes the following fields:
 /// ```json
 /// {
 ///     "errorCode": "specific-error-code",
 ///     "message": "Human readable error message"
 /// }
 /// ```
-pub trait JsonError {
-    /// Converts the error into a JSON string representation.
-    fn to_json(&self) -> String;
+pub struct JsonReply {
+    /// The error code
+    error_code: ErrorCode,
+    /// The error message to be displayed only in debug logs
+    message: String,
+    /// Additional fields to be included in the JSON response
+    extra: serde_json::Map<String, serde_json::Value>,
 }
 
-impl JsonError for ReplyableError {
-    fn to_json(&self) -> String {
-        match self {
-            Self::Payload(e) => e.to_json(),
-            #[cfg(feature = "v1")]
-            Self::V1(e) => e.to_json(),
-            Self::Implementation(_) => serialize_json_error(UNAVAILABLE, "Receiver error"),
-        }
+impl JsonReply {
+    /// Create a new Reply
+    pub fn new(error_code: ErrorCode, message: impl fmt::Display) -> Self {
+        Self { error_code, message: message.to_string(), extra: serde_json::Map::new() }
     }
-}
 
-pub(crate) fn serialize_json_error(code: &str, message: impl fmt::Display) -> String {
-    format!(r#"{{ "errorCode": "{}", "message": "{}" }}"#, code, message)
+    /// Add an additional field to the JSON response
+    pub fn with_extra(mut self, key: &str, value: impl Into<serde_json::Value>) -> Self {
+        self.extra.insert(key.to_string(), value.into());
+        self
+    }
+
+    /// Serialize the Reply to a JSON string
+    pub fn to_json(&self) -> serde_json::Value {
+        let mut map = serde_json::Map::new();
+        map.insert("errorCode".to_string(), self.error_code.to_string().into());
+        map.insert("message".to_string(), self.message.clone().into());
+        map.extend(self.extra.clone());
+
+        serde_json::Value::Object(map)
+    }
 }
 
-pub(crate) fn serialize_json_plus_fields(
-    code: &str,
-    message: impl fmt::Display,
-    additional_fields: &str,
-) -> String {
-    format!(r#"{{ "errorCode": "{}", "message": "{}", {} }}"#, code, message, additional_fields)
+impl From<ReplyableError> for JsonReply {
+    fn from(e: ReplyableError) -> Self {
+        use ReplyableError::*;
+        match e {
+            Payload(e) => e.into(),
+            #[cfg(feature = "v1")]
+            V1(e) => e.into(),
+            Implementation(_) => JsonReply::new(Unavailable, "Receiver error"),
+        }
+    }
 }
 
 impl fmt::Display for ReplyableError {
@@ -180,34 +197,34 @@ pub(crate) enum InternalPayloadError {
     FeeTooHigh(bitcoin::FeeRate, bitcoin::FeeRate),
 }
 
-impl JsonError for PayloadError {
-    fn to_json(&self) -> String {
+impl From<PayloadError> for JsonReply {
+    fn from(e: PayloadError) -> Self {
         use InternalPayloadError::*;
 
-        match &self.0 {
-            Utf8(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            ParsePsbt(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
+        match &e.0 {
+            Utf8(_)
+            | ParsePsbt(_)
+            | InconsistentPsbt(_)
+            | PrevTxOut(_)
+            | MissingPayment
+            | OriginalPsbtNotBroadcastable
+            | InputOwned(_)
+            | InputWeight(_)
+            | InputSeen(_)
+            | PsbtBelowFeeRate(_, _) => JsonReply::new(OriginalPsbtRejected, e),
+
+            FeeTooHigh(_, _) => JsonReply::new(NotEnoughMoney, e),
+
             SenderParams(e) => match e {
                 super::optional_parameters::Error::UnknownVersion { supported_versions } => {
                     let supported_versions_json =
                         serde_json::to_string(supported_versions).unwrap_or_default();
-                    serialize_json_plus_fields(
-                        VERSION_UNSUPPORTED,
-                        "This version of payjoin is not supported.",
-                        &format!(r#""supported": {}"#, supported_versions_json),
-                    )
+                    JsonReply::new(VersionUnsupported, "This version of payjoin is not supported.")
+                        .with_extra("supported", supported_versions_json)
                 }
-                _ => serialize_json_error("sender-params-error", self),
+                super::optional_parameters::Error::FeeRate =>
+                    JsonReply::new(OriginalPsbtRejected, e),
             },
-            InconsistentPsbt(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            PrevTxOut(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            MissingPayment => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            OriginalPsbtNotBroadcastable => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            InputOwned(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            InputWeight(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            InputSeen(_) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            PsbtBelowFeeRate(_, _) => serialize_json_error(ORIGINAL_PSBT_REJECTED, self),
-            FeeTooHigh(_, _) => serialize_json_error(NOT_ENOUGH_MONEY, self),
         }
     }
 }

payjoin/src/receive/mod.rs

@@ -14,7 +14,7 @@ use std::str::FromStr;
 use bitcoin::{psbt, AddressType, Psbt, TxIn, TxOut};
 pub(crate) use error::InternalPayloadError;
 pub use error::{
-    Error, ImplementationError, InputContributionError, JsonError, OutputSubstitutionError,
+    Error, ImplementationError, InputContributionError, JsonReply, OutputSubstitutionError,
     PayloadError, ReplyableError, SelectionError,
 };
 use optional_parameters::Params;

payjoin/src/receive/v1/exclusive/error.rs

@@ -1,7 +1,7 @@
 use core::fmt;
 use std::error;
 
-use crate::receive::error::JsonError;
+use crate::receive::JsonReply;
 
 /// Error that occurs during validation of an incoming v1 payjoin request.
 ///
@@ -38,17 +38,17 @@ impl From<InternalRequestError> for super::ReplyableError {
     fn from(e: InternalRequestError) -> Self { super::ReplyableError::V1(e.into()) }
 }
 
-impl JsonError for RequestError {
-    fn to_json(&self) -> String {
+impl From<RequestError> for JsonReply {
+    fn from(e: RequestError) -> Self {
         use InternalRequestError::*;
 
-        use crate::receive::error::serialize_json_error;
-        match &self.0 {
-            Io(_) => serialize_json_error("original-psbt-rejected", self),
-            MissingHeader(_) => serialize_json_error("original-psbt-rejected", self),
-            InvalidContentType(_) => serialize_json_error("original-psbt-rejected", self),
-            InvalidContentLength(_) => serialize_json_error("original-psbt-rejected", self),
-            ContentLengthTooLarge(_) => serialize_json_error("original-psbt-rejected", self),
+        match &e.0 {
+            Io(_)
+            | MissingHeader(_)
+            | InvalidContentType(_)
+            | InvalidContentLength(_)
+            | ContentLengthTooLarge(_) =>
+                JsonReply::new(crate::error_codes::ErrorCode::OriginalPsbtRejected, e),
         }
     }
 }

payjoin/src/receive/v2/mod.rs

@@ -13,7 +13,7 @@ use url::Url;
 
 use super::error::{Error, InputContributionError};
 use super::{
-    v1, ImplementationError, InternalPayloadError, JsonError, OutputSubstitutionError,
+    v1, ImplementationError, InternalPayloadError, JsonReply, OutputSubstitutionError,
     ReplyableError, SelectionError,
 };
 use crate::hpke::{decrypt_message_a, encrypt_message_b, HpkeKeyPair, HpkePublicKey};
@@ -278,15 +278,15 @@ impl UncheckedProposal {
     /// a Receiver Error Response
     pub fn extract_err_req(
         &mut self,
-        err: &ReplyableError,
+        err: &JsonReply,
         ohttp_relay: impl IntoUrl,
     ) -> Result<(Request, ohttp::ClientResponse), SessionError> {
         let subdir = subdir(&self.context.directory, &id(&self.context.s));
         let (body, ohttp_ctx) = ohttp_encapsulate(
             &mut self.context.ohttp_keys,
             "POST",
             subdir.as_str(),
-            Some(err.to_json().as_bytes()),
+            Some(err.to_json().to_string().as_bytes()),
         )
         .map_err(InternalSessionError::OhttpEncapsulation)?;
         let req = Request::new_v2(&self.context.full_relay_url(ohttp_relay)?, &body);
@@ -620,19 +620,26 @@ mod test {
             context: SHARED_CONTEXT.clone(),
         };
 
-        let server_error = proposal
-            .clone()
-            .check_broadcast_suitability(None, |_| Err("mock error".into()))
-            .err()
-            .ok_or("expected error but got success")?;
-        assert_eq!(
-            server_error.to_json(),
-            r#"{ "errorCode": "unavailable", "message": "Receiver error" }"#
-        );
-        let (_req, _ctx) = proposal.clone().extract_err_req(&server_error, &*EXAMPLE_URL)?;
-
-        let internal_error = InternalPayloadError::MissingPayment.into();
-        let (_req, _ctx) = proposal.extract_err_req(&internal_error, &*EXAMPLE_URL)?;
+        let server_error = || {
+            proposal
+                .clone()
+                .check_broadcast_suitability(None, |_| Err("mock error".into()))
+                .expect_err("expected broadcast suitability check to fail")
+        };
+
+        let expected_json = serde_json::json!({
+            "errorCode": "unavailable",
+            "message": "Receiver error"
+        });
+
+        let actual_json = JsonReply::from(server_error()).to_json().clone();
+        assert_eq!(actual_json, expected_json);
+
+        let (_req, _ctx) =
+            proposal.clone().extract_err_req(&server_error().into(), &*EXAMPLE_URL)?;
+
+        let internal_error: ReplyableError = InternalPayloadError::MissingPayment.into();
+        let (_req, _ctx) = proposal.extract_err_req(&internal_error.into(), &*EXAMPLE_URL)?;
         Ok(())
     }