fix(payment-processor): pass custom quote amount over gRPC

Forward the optional custom melt quote amount in PaymentQuoteRequest so
remote processors can price and validate amount-aware custom payments.

Author: thesimplekid

crates/cdk-axum/src/custom_handlers.rs

@@ -1105,6 +1105,7 @@ mod tests {
             method: "venmo".to_string(),
             request: "test-payment-request".to_string(),
             unit: CurrencyUnit::Sat,
+            amount: None,
             extra: Value::Null,
         })
         .unwrap();
@@ -1144,6 +1145,7 @@ mod tests {
             method: "PayPal".to_string(),
             request: "test-payment-request".to_string(),
             unit: CurrencyUnit::Sat,
+            amount: None,
             extra: Value::Null,
         })
         .unwrap();

crates/cdk-fake-wallet/src/lib.rs

@@ -441,8 +441,19 @@ impl FakeWallet {
     async fn custom_outgoing_amount(
         &self,
         unit: &CurrencyUnit,
+        amount: Option<&Amount<CurrencyUnit>>,
         extra_json: &Option<String>,
     ) -> Result<Amount<CurrencyUnit>, Error> {
+        if let Some(amount) = amount {
+            return convert_currency_amount(
+                amount.value(),
+                amount.unit(),
+                unit,
+                &self.exchange_rate_cache,
+            )
+            .await;
+        }
+
         #[derive(Deserialize)]
         struct CustomAmountField {
             amount: Option<u64>,
@@ -587,7 +598,11 @@ impl MintPayment for FakeWallet {
                 self.ensure_custom_method_supported(&custom_options.method)?;
 
                 let amount = self
-                    .custom_outgoing_amount(unit, &custom_options.extra_json)
+                    .custom_outgoing_amount(
+                        unit,
+                        custom_options.amount.as_ref(),
+                        &custom_options.extra_json,
+                    )
                     .await?;
 
                 return Ok(PaymentQuoteResponse {
@@ -768,7 +783,11 @@ impl MintPayment for FakeWallet {
                 self.ensure_custom_method_supported(&custom_options.method)?;
 
                 let total_spent = self
-                    .custom_outgoing_amount(unit, &custom_options.extra_json)
+                    .custom_outgoing_amount(
+                        unit,
+                        custom_options.amount.as_ref(),
+                        &custom_options.extra_json,
+                    )
                     .await?;
 
                 Ok(MakePaymentResponse {
@@ -1070,8 +1089,8 @@ fn fake_secret_key(seed: &str) -> SecretKey {
 #[cfg(test)]
 mod tests {
     use cdk_common::payment::{
-        CustomIncomingPaymentOptions, IncomingPaymentOptions, MintPayment,
-        OnchainOutgoingPaymentOptions, OutgoingPaymentOptions, PaymentIdentifier,
+        CustomIncomingPaymentOptions, CustomOutgoingPaymentOptions, IncomingPaymentOptions,
+        MintPayment, OnchainOutgoingPaymentOptions, OutgoingPaymentOptions, PaymentIdentifier,
     };
 
     use super::*;
@@ -1093,6 +1112,22 @@ mod tests {
         test_wallet_with_delay(0)
     }
 
+    fn custom_outgoing_options(
+        amount: Option<Amount<CurrencyUnit>>,
+        extra_json: Option<String>,
+    ) -> OutgoingPaymentOptions {
+        OutgoingPaymentOptions::Custom(Box::new(CustomOutgoingPaymentOptions {
+            method: "venmo".to_string(),
+            request: "test-payment-request".to_string(),
+            amount,
+            max_fee_amount: None,
+            timeout_secs: None,
+            melt_options: None,
+            extra_json,
+            quote_id: cdk_common::QuoteId::new(),
+        }))
+    }
+
     #[tokio::test]
     async fn custom_payment_methods_are_configurable() {
         let settings = test_wallet()
@@ -1177,4 +1212,58 @@ mod tests {
         );
         assert_eq!(response.status, MeltQuoteState::Paid);
     }
+
+    #[tokio::test]
+    async fn custom_outgoing_quote_prefers_typed_amount() {
+        let wallet = test_wallet()
+            .with_custom_payment_methods(HashMap::from([("venmo".to_string(), "{}".to_string())]));
+
+        let response = wallet
+            .get_payment_quote(
+                &CurrencyUnit::Sat,
+                custom_outgoing_options(
+                    Some(Amount::new(20, CurrencyUnit::Sat)),
+                    Some(r#"{"amount":30}"#.to_string()),
+                ),
+            )
+            .await
+            .expect("configured custom method should quote outgoing payment");
+
+        assert_eq!(response.amount, Amount::new(20, CurrencyUnit::Sat));
+    }
+
+    #[tokio::test]
+    async fn custom_outgoing_payment_prefers_typed_amount() {
+        let wallet = test_wallet()
+            .with_custom_payment_methods(HashMap::from([("venmo".to_string(), "{}".to_string())]));
+
+        let response = wallet
+            .make_payment(
+                &CurrencyUnit::Sat,
+                custom_outgoing_options(
+                    Some(Amount::new(20, CurrencyUnit::Sat)),
+                    Some(r#"{"amount":30}"#.to_string()),
+                ),
+            )
+            .await
+            .expect("configured custom method should make outgoing payment");
+
+        assert_eq!(response.total_spent, Amount::new(21, CurrencyUnit::Sat));
+    }
+
+    #[tokio::test]
+    async fn custom_outgoing_amount_falls_back_to_extra_json() {
+        let wallet = test_wallet()
+            .with_custom_payment_methods(HashMap::from([("venmo".to_string(), "{}".to_string())]));
+
+        let response = wallet
+            .get_payment_quote(
+                &CurrencyUnit::Sat,
+                custom_outgoing_options(None, Some(r#"{"amount":30}"#.to_string())),
+            )
+            .await
+            .expect("configured custom method should quote outgoing payment");
+
+        assert_eq!(response.amount, Amount::new(30, CurrencyUnit::Sat));
+    }
 }

crates/cdk-payment-processor/src/proto/client.rs

@@ -288,6 +288,13 @@ impl MintPayment for PaymentProcessorClient {
             _ => None,
         };
 
+        let amount = match &options {
+            cdk_common::payment::OutgoingPaymentOptions::Custom(opts) => {
+                opts.amount.clone().into_proto()
+            }
+            _ => None,
+        };
+
         let quote_id = match &options {
             cdk_common::payment::OutgoingPaymentOptions::Custom(opts) => opts.quote_id.to_string(),
             cdk_common::payment::OutgoingPaymentOptions::Bolt11(opts) => opts.quote_id.to_string(),
@@ -304,6 +311,7 @@ impl MintPayment for PaymentProcessorClient {
                 extra_json,
                 quote_id,
                 onchain_options,
+                amount,
             }))
             .await
             .map_err(|err| {

crates/cdk-payment-processor/src/proto/payment_processor.proto

@@ -180,6 +180,8 @@ message PaymentQuoteRequest {
   // Structured options for onchain quote requests. Onchain processors need the
   // mint-generated quote_id and amount when preparing fee_options.
   optional OnchainOutgoingPaymentOptions onchain_options = 7;
+  // Optional amount the wallet would like to pay for custom payment methods.
+  optional AmountMessage amount = 8;
 }
 
 enum QuoteState {

crates/cdk-payment-processor/src/proto/server.rs

@@ -329,12 +329,17 @@ impl CdkPaymentProcessor for PaymentProcessorServer {
                 ))
             }
             OutgoingPaymentRequestType::Custom => {
+                let amount = request
+                    .amount
+                    .try_from_proto()
+                    .map_err(|_| Status::invalid_argument("Invalid amount"))?;
+
                 // Custom payment method - pass request as-is with no validation
                 cdk_common::payment::OutgoingPaymentOptions::Custom(Box::new(
                     cdk_common::payment::CustomOutgoingPaymentOptions {
                         method: String::new(), // Will be set from variant
                         request: request.request.clone(),
-                        amount: None,
+                        amount,
                         max_fee_amount: None,
                         timeout_secs: None,
                         melt_options: request.options.map(TryInto::try_into).transpose()?,

crates/cdk/src/wallet/mint_connector/http_client.rs

@@ -1346,6 +1346,7 @@ mod tests {
                 method: "paypal".to_string(),
                 request: "paypal://pay?id=123".to_string(),
                 unit: cdk_common::CurrencyUnit::Sat,
+                amount: None,
                 extra: serde_json::Value::Null,
             }))
             .await