feat(nut04/05): optional amount

crates/cashu/src/nuts/nut04.rs

@@ -348,7 +348,11 @@ impl Settings {
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
 pub struct MintQuoteCustomRequest {
     /// Amount to mint
-    pub amount: Amount,
+    ///
+    /// Optional common field. Method-specific NUTs make it required or ignore
+    /// it as needed (e.g. NUT-23 requires `amount`).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub amount: Option<Amount>,
     /// Currency unit
     pub unit: CurrencyUnit,
     /// Optional description

crates/cashu/src/nuts/nut05.rs

@@ -460,6 +460,12 @@ pub struct MeltQuoteCustomRequest {
     pub request: String,
     /// Currency unit
     pub unit: CurrencyUnit,
+    /// Amount the wallet would like to pay
+    ///
+    /// Optional common field. Method-specific NUTs make it required or ignore
+    /// it as needed (e.g. NUT-30 requires `amount` for onchain melts).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub amount: Option<Amount>,
     /// Extra payment-method-specific fields
     ///
     /// These fields are flattened into the JSON representation, allowing

crates/cdk-axum/src/custom_handlers.rs

@@ -869,7 +869,7 @@ mod tests {
             .get_mint_quote(cdk::mint::MintQuoteRequest::Custom {
                 method: PaymentMethod::Custom(method.to_string()),
                 request: MintQuoteCustomRequest {
-                    amount: Amount::from(amount),
+                    amount: Some(Amount::from(amount)),
                     unit: CurrencyUnit::Sat,
                     description: None,
                     pubkey: None,

crates/cdk-common/src/melt.rs

@@ -489,6 +489,7 @@ mod tests {
             method: "cashapp".to_string(),
             unit: CurrencyUnit::Sat,
             request: "$tag".to_string(),
+            amount: None,
             extra: serde_json::Value::Null,
         };
         let req: MeltQuoteRequest = custom_req.into();

crates/cdk-common/src/mint_quote.rs

@@ -63,7 +63,7 @@ impl MintQuoteRequest {
             Self::Bolt11(request) => Some(request.amount),
             Self::Bolt12(request) => request.amount,
             Self::Onchain(_) => None,
-            Self::Custom { request, .. } => Some(request.amount),
+            Self::Custom { request, .. } => request.amount,
         }
     }
 

crates/cdk-common/src/payment.rs

@@ -222,8 +222,8 @@ pub struct CustomIncomingPaymentOptions {
     pub method: String,
     /// Optional description for the payment request
     pub description: Option<String>,
-    /// Amount for the payment request
-    pub amount: Amount<CurrencyUnit>,
+    /// Optional amount for the payment request
+    pub amount: Option<Amount<CurrencyUnit>>,
     /// Optional expiry time as Unix timestamp in seconds
     pub unix_expiry: Option<u64>,
     /// Extra payment-method-specific fields as JSON string
@@ -293,6 +293,8 @@ pub struct CustomOutgoingPaymentOptions {
     pub method: String,
     /// Payment request string (method-specific format)
     pub request: String,
+    /// Optional amount the wallet would like to pay (from the melt quote request)
+    pub amount: Option<Amount<CurrencyUnit>>,
     /// Maximum fee amount allowed for the payment
     pub max_fee_amount: Option<Amount<CurrencyUnit>>,
     /// Optional timeout in seconds
@@ -391,6 +393,8 @@ impl OutgoingPaymentOptions {
                 Box::new(CustomOutgoingPaymentOptions {
                     method: method.to_string(),
                     request: request.to_string(),
+                    // Payment is already quoted; correlation is via quote_id.
+                    amount: None,
                     max_fee_amount: Some(fee_reserve),
                     timeout_secs: None,
                     melt_options: melt_quote.options,

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

@@ -878,7 +878,9 @@ impl MintPayment for FakeWallet {
                 (
                     PaymentIdentifier::CustomId(custom_id),
                     request,
-                    custom_options.amount,
+                    custom_options
+                        .amount
+                        .unwrap_or_else(|| Amount::new(0, self.unit.clone())),
                     custom_options.unix_expiry,
                 )
             }
@@ -1110,7 +1112,7 @@ mod tests {
                 CustomIncomingPaymentOptions {
                     method: "venmo".to_string(),
                     description: None,
-                    amount: Amount::new(10, CurrencyUnit::Sat),
+                    amount: Some(Amount::new(10, CurrencyUnit::Sat)),
                     unix_expiry: None,
                     extra_json: None,
                 },

crates/cdk-integration-tests/tests/integration_tests_pure.rs

@@ -1753,6 +1753,7 @@ async fn test_direct_connector_custom_melt_enum_roundtrip() {
         method: "paypal".to_string(),
         request: "invoice-123".to_string(),
         unit: CurrencyUnit::Sat,
+        amount: None,
         extra: serde_json::Value::Null,
     });
 
@@ -2482,6 +2483,7 @@ async fn test_custom_melt_quote_status_preserves_extra_json() {
                 method: "test-custom".to_string(),
                 request: "custom-request".to_string(),
                 unit: CurrencyUnit::Sat,
+                amount: None,
                 extra: serde_json::json!({ "request_metadata": true }),
             },
         ))
@@ -2543,6 +2545,7 @@ async fn test_custom_melt_quote_id_propagates_to_payment_processor() {
                 method: "test-custom".to_string(),
                 request: "custom-request".to_string(),
                 unit: CurrencyUnit::Sat,
+                amount: None,
                 extra: serde_json::json!({ "request_metadata": true }),
             },
         ))

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

@@ -181,7 +181,7 @@ impl MintPayment for PaymentProcessorClient {
                 options: Some(super::incoming_payment_options::Options::Custom(
                     super::CustomIncomingPaymentOptions {
                         description: opts.description,
-                        amount: Some(opts.amount.into()),
+                        amount: opts.amount.map(Into::into),
                         unix_expiry: opts.unix_expiry,
                         extra_json: opts.extra_json.clone(),
                     },
@@ -330,6 +330,7 @@ impl MintPayment for PaymentProcessorClient {
                     options: Some(super::outgoing_payment_variant::Options::Custom(
                         super::CustomOutgoingPaymentOptions {
                             offer: opts.request.to_string(),
+                            amount: opts.amount.map(Into::into),
                             max_fee_amount: opts.max_fee_amount.into_proto(),
                             timeout_secs: opts.timeout_secs,
                             melt_options: opts.melt_options.map(Into::into),

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

@@ -2,7 +2,7 @@ syntax = "proto3";
 
 package cdk_payment_processor;
 
-service CdkPaymentProcessor {  
+service CdkPaymentProcessor {
     rpc GetSettings(EmptyRequest) returns (SettingsResponse) {}
     rpc CreatePayment(CreatePaymentRequest) returns (CreatePaymentResponse) {}
     rpc GetPaymentQuote(PaymentQuoteRequest) returns (PaymentQuoteResponse) {}
@@ -232,6 +232,8 @@ message CustomOutgoingPaymentOptions {
   string offer = 1;
   optional AmountMessage max_fee_amount = 2;
   optional uint64 timeout_secs = 3;
+  // Optional amount the wallet would like to pay (from the melt quote request)
+  optional AmountMessage amount = 4;
   optional MeltOptions melt_options = 5;
   // Extra payment-method-specific fields as JSON string
   // These fields are flattened into the JSON representation on the client side

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

@@ -224,11 +224,13 @@ impl CdkPaymentProcessor for PaymentProcessorServer {
             .ok_or_else(|| Status::invalid_argument("Missing options"))?
         {
             incoming_payment_options::Options::Custom(opts) => {
-                let amount = opts
-                    .amount
-                    .ok_or_else(|| Status::invalid_argument("Missing amount"))?
-                    .try_into()
-                    .map_err(|_| Status::invalid_argument("Invalid amount"))?;
+                let amount: Option<cdk_common::Amount<CurrencyUnit>> = match opts.amount {
+                    Some(a) => Some(
+                        a.try_into()
+                            .map_err(|_| Status::invalid_argument("Invalid amount"))?,
+                    ),
+                    None => None,
+                };
                 IncomingPaymentOptions::Custom(Box::new(
                     cdk_common::payment::CustomIncomingPaymentOptions {
                         method: "".to_string(),
@@ -332,6 +334,7 @@ impl CdkPaymentProcessor for PaymentProcessorServer {
                     cdk_common::payment::CustomOutgoingPaymentOptions {
                         method: String::new(), // Will be set from variant
                         request: request.request.clone(),
+                        amount: None,
                         max_fee_amount: None,
                         timeout_secs: None,
                         melt_options: request.options.map(TryInto::try_into).transpose()?,
@@ -450,11 +453,19 @@ impl CdkPaymentProcessor for PaymentProcessorServer {
                     .try_from_proto()
                     .map_err(|_| Status::invalid_argument("Invalid max_fee_amount"))?;
                 let quote_id = parse_quote_id(&opts.quote_id)?;
+                let amount: Option<cdk_common::Amount<CurrencyUnit>> = match opts.amount {
+                    Some(a) => Some(
+                        a.try_into()
+                            .map_err(|_| Status::invalid_argument("Invalid amount"))?,
+                    ),
+                    None => None,
+                };
 
                 cdk_common::payment::OutgoingPaymentOptions::Custom(Box::new(
                     cdk_common::payment::CustomOutgoingPaymentOptions {
                         method: String::new(), // Method will be determined from context
                         request: opts.offer,   // Reusing offer field for custom request string
+                        amount,
                         max_fee_amount,
                         timeout_secs: opts.timeout_secs,
                         melt_options: opts.melt_options.map(TryInto::try_into).transpose()?,

crates/cdk/src/mint/issue/mod.rs

@@ -312,7 +312,7 @@ impl Mint {
                     let custom_options = CustomIncomingPaymentOptions {
                         method: payment_method.to_string(),
                         description: request.description,
-                        amount: request.amount.with_unit(unit.clone()),
+                        amount: request.amount.map(|a| a.with_unit(unit.clone())),
                         unix_expiry: Some(quote_expiry),
                         extra_json,
                     };

crates/cdk/src/mint/melt/mod.rs

@@ -682,6 +682,7 @@ impl Mint {
                 request,
                 unit,
                 method,
+                amount,
                 extra,
             } = melt_request;
 
@@ -720,6 +721,7 @@ impl Mint {
                 OutgoingPaymentOptions::Custom(Box::new(CustomOutgoingPaymentOptions {
                     method: method.to_string(),
                     request: request.clone(),
+                    amount: (*amount).map(|a| a.with_unit(unit.clone())),
                     max_fee_amount: None,
                     timeout_secs: None,
                     melt_options: None,

crates/cdk/src/wallet/issue/mod.rs

@@ -155,7 +155,7 @@ impl Wallet {
                 MintQuoteRequest::Custom {
                     method: method.clone(),
                     request: cdk_common::nuts::MintQuoteCustomRequest {
-                        amount,
+                        amount: Some(amount),
                         unit: unit.clone(),
                         description,
                         pubkey: Some(secret_key.public_key()),

crates/cdk/src/wallet/melt/custom.rs

@@ -27,6 +27,7 @@ impl Wallet {
             method: method.to_string(),
             request: request.clone(),
             unit: self.unit.clone(),
+            amount: None,
             extra: extra.unwrap_or(serde_json::Value::Null),
         };
         let quote_res = self

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

@@ -980,7 +980,7 @@ mod tests {
         let request = MintQuoteRequest::Custom {
             method: PaymentMethod::Custom("paypal".to_string()),
             request: MintQuoteCustomRequest {
-                amount: cdk_common::Amount::from(1000),
+                amount: Some(cdk_common::Amount::from(1000)),
                 unit: cdk_common::CurrencyUnit::Sat,
                 description: None,
                 pubkey: None,
@@ -1016,7 +1016,7 @@ mod tests {
 
         // Verify the actual field values round-tripped correctly
         let parsed = parsed.expect("already checked");
-        assert_eq!(parsed.amount, cdk_common::Amount::from(1000));
+        assert_eq!(parsed.amount, Some(cdk_common::Amount::from(1000)));
         assert_eq!(parsed.unit, cdk_common::CurrencyUnit::Sat);
     }
 
@@ -1033,7 +1033,7 @@ mod tests {
             .post_mint_quote(MintQuoteRequest::Custom {
                 method: invalid_method.clone(),
                 request: MintQuoteCustomRequest {
-                    amount: cdk_common::Amount::from(1000),
+                    amount: Some(cdk_common::Amount::from(1000)),
                     unit: cdk_common::CurrencyUnit::Sat,
                     description: None,
                     pubkey: None,
@@ -1088,6 +1088,7 @@ mod tests {
                 method: "../../v1/swap".to_string(),
                 request: "custom-payment-request".to_string(),
                 unit: cdk_common::CurrencyUnit::Sat,
+                amount: None,
                 extra: serde_json::Value::Null,
             }))
             .await;