feat(core): Updates to nut18 and nut26 payment request by KvngMikey · Pull Request #1059 · cashubtc/nutshell

KvngMikey · 2026-06-21T09:50:36Z

implements cashubtc/nuts#381 to keep Nutshell up to date !

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codecov · 2026-06-21T09:56:51Z

Codecov Report

❌ Patch coverage is 97.41379% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.87%. Comparing base (6691b1b) to head (ed186ad).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cashu/core/nuts/nut26.py	94.28%	2 Missing ⚠️
cashu/core/mint_info.py	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1059      +/-   ##
==========================================
+ Coverage   74.66%   74.87%   +0.20%     
==========================================
  Files         115      115              
  Lines       13205    13315     +110     
==========================================
+ Hits         9860     9969     +109     
- Misses       3345     3346       +1

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a1denvalu3 · 2026-06-22T14:02:19Z

@KvngMikey If I am not mistaken this only adds support for decoding such payment requests with the additional fields but does not add any logic to handle them or to create a payment request with them.

KvngMikey · 2026-06-22T14:28:15Z

@KvngMikey If I am not mistaken this only adds support for decoding such payment requests with the additional fields but does not add any logic to handle them or to create a payment request with them.

@a1denvalu3 you're right that this PR only adds encoding/decoding for the new ms / fr / sm fields and doesn't add enforcement logic.

Happy to either extend this PR with that handling + a request-creation path, or land this as the serialization layer and do the behavior in a focused follow-up. Which would you prefer?

a1denvalu3 · 2026-06-25T10:14:39Z

Happy to either extend this PR with that handling + a request-creation path

Yes please

robwoodgate · 2026-06-26T23:31:01Z

The nut has been updated: ms (mint_strict) is now flipped to mp (mint_preferred) to avoid the omitted=true antipattern.

a1denvalu3 · 2026-07-09T10:08:50Z

I think there are new changes to the spec @KvngMikey

robwoodgate · 2026-07-14T12:30:01Z

Noted by my agent while checking compliance to current spec:

Pay flow currently never reads pr.u: add "reject if pr.sm set and pr.u absent" plus "reject if pr.u != wallet.unit"
before calling payment_request_method_fee(pr.sm, wallet.unit). With that guard the existing wallet-unit resolution becomes correct as-is.
- Optionally a Pydantic validator on the model (u required if a or sm); the CLI request command already always sets u, so creation side is fine in practice.

a1denvalu3 · 2026-07-27T14:56:55Z

[P1] Reject negative method fees during validation — cashu/core/
base.py:1681-1683
A NUT-18 request can supply a negative mf, which passes model validation and is selected as the
lowest supported fee. When the fee applies, pay adds this negative value to amount_to_pay,
causing the wallet to send less than the requested amount. Constrain mf to the NUT-26 u64 range
so both encodings share safe semantics.
[P2] Require a positive payment-request amount — cashu/wallet/cli/
cli.py:529-530
The new request command accepts zero and negative amounts, so commands such as cashu request -1
emit requests that the corresponding pay path cannot process correctly (0 is rejected and
negative values reach send). Use a positive integer range at argument parsing time.
[P2] Validate the NUT-26 mint-preferred flag length — cashu/core/nuts/
nut26.py:342-343
For a malformed NUT-26 request whose 0x09 field is empty, indexing val[0] raises IndexError;
multi-byte values are also silently accepted despite the field being specified as u8. Validate
that the field is exactly one byte, as is already done for the adjacent single-use flag.

ss

robwoodgate · 2026-07-28T06:48:21Z

I had my agent give this an initial look-over. The findings:

Code review

Reviewed against NUT-18 and NUT-26 at current nuts main (e0a16f8), which includes the spec consolidation this implements (cashubtc/nuts#381).

Both frozen vectors check out byte-for-byte, and the mp strict/preferred logic, the fee applicability rule, the lowest-mf-among-supported-methods rule, and the sum(proofs) - input_fee >= a + mf invariant all match the spec. Matching mn against NUT-05 method rather than the new method_name is right too. Three issues:

1. Mint URL compared by exact string equality, so a trailing-slash mismatch silently overpays

Before this PR a mismatch produced a loud "not accepted" error. Now, with mp=true, the same mismatch classifies the payer's own mint as outside the list, and the payer silently pays mf more than they owe. The codebase already normalises for this comparison elsewhere (npc.py#L160-L162 uses rstrip("/")).

nutshell/cashu/wallet/cli/cli.py

Lines 303 to 306 in 27d35dd

    
           # The mint list is strict unless `mp` is explicitly true (preferred) 
        
           mint_outside_list = pr.m is not None and wallet.url not in pr.m 
        
           if mint_outside_list and not pr.mp: 
        
               print(

2. NUT-05 disabled is ignored when deciding whether the mint supports a requested method

The point of sm is that the receiver can melt out of the sender's mint ("the payer MUST send ecash from a mint that supports melting the request unit"). If that mint has melting switched off, that is false, but the payer still proceeds. Nutshell's own mint emits the flag next to methods (features.py#L112-L117), so it is available here.

nutshell/cashu/core/mint_info.py

Lines 86 to 91 in 27d35dd

    
               return None 
        
           nut_05 = self.nuts.get(MELT_NUT) 
        
           if not nut_05 or not nut_05.get("methods"): 
        
               return None 
        
           melt_methods = [MeltMethodSetting.model_validate(e) for e in nut_05["methods"]]

3. Fee message is wrong when the request carries no mint list

fee_applies is true when pr.m is None, but the message then claims the payer is outside a preferred list that does not exist.

nutshell/cashu/wallet/cli/cli.py

Lines 335 to 342 in 27d35dd

    
           # list, or when no mint list is set at all 
        
           fee_applies = pr.m is None or mint_outside_list 
        
           if fee_applies and method_fee: 
        
               amount_to_pay += method_fee 
        
               print( 
        
                   f"Adding method fee of {wallet.unit.str(method_fee)} " 
        
                   "(paying from a mint outside the preferred list)." 
        
               )

Minor: SupportedMethod.mn is not constrained to non-empty, so --method ":5" encodes an empty method name; and the payment_request_method_fee docstring omits the sm empty/None -> 0 case, which is what separates "no requirement" from None = "unsupported".

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…quest that carries fields

Drop `fr` and replace `sm: List[str]` with `sm: List[SupportedMethod]` (`mn`, optional `mf`) per cashubtc/nuts#381. NUT-26 tag 0x0a is now a repeatable supported_method sub-TLV (0x01=method, 0x02=fee u64 BE); 0x0b removed. Also fixes a mis-scoped guard error message (tag 0x01 is id, not transport). Byte-verified against frozen spec vectors.

Add MintInfo.payment_request_method_fee (mirrors supports_mpp): reject when the mint melts none of a request's `sm` methods, else return the lowest matching mf, unit-filtered. Wire it into `pay`: fee applies only when paying from a mint outside a strict/preferred list, or when no mint list is set. Fix `request` command's --method/--fee-reserve to match the new SupportedMethod shape (fr no longer exists).

… path the creq pay path already selects proofs via include_fees=True, which enforces sum(proofs) - input_fee(proofs) >= amount. Add a dust-proof regression test (20x 1-sat proofs at 250 ppk) proving the payer tops up rather than underpays. No CDK oracle exists for this clause.

--method now accepts name or name:fee (e.g. bolt11:50), rejecting non-integer or negative fees. Help text states the fee only applies when the payer mint is outside a preferred mint list. Full suite green (839 passed); no fr references remain outside unrelated tor binaries.

a and mf are denominated in the request unit u: reject when sm is set without u, and when u differs from the wallet unit, before the method fee lookup.

A negative mf passed model validation and was picked as the lowest fee, making the payer send less than the requested amount; constrain mf to the NUT-26 u64 range so both encodings agree. Require a positive request amount at parse time, and reject 0x09 values that are not exactly one byte (empty raised IndexError, multi-byte was silently accepted).

…e reason. Also say the request has no mint list when the fee applies for that reason, and require a non-empty method name.

callebtc · 2026-08-11T15:57:53Z

+    def payment_request_method_fee(
+        self, sm: Optional[List[SupportedMethod]], unit: Unit
+    ) -> Optional[int]:
+        """
+        Given the `sm` (supported methods) list from a NUT-18/26 payment request,
+        return the lowest per-method fee this mint owes for melting via one of the
+        listed methods in `unit`. Returns 0 when `sm` is unset, i.e. the request
+        makes no method requirement, and `None` when this mint cannot melt via any
+        of the listed methods.
+        """


does this really belong into mint_info.py?

Copilot AI review requested due to automatic review settings June 21, 2026 09:50

github-project-automation Bot added this to nutshell Jun 21, 2026

github-project-automation Bot moved this to Backlog in nutshell Jun 21, 2026

Copilot AI reviewed Jun 21, 2026

KvngMikey mentioned this pull request Jun 21, 2026

NUT-18: Payment request consolidation (and extra fees for non-preferred mints) cashubtc/nuts#381

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4 tasks

KvngMikey changed the title ~~feat(core): new properties added to nut18 and nut26 payment request~~ feat(core): Updates to nut18 and nut26 payment request Jun 21, 2026

ye0man assigned KvngMikey Jun 26, 2026

ye0man added the nut hold label Jun 26, 2026

a1denvalu3 previously approved these changes Jul 1, 2026

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KvngMikey force-pushed the payment_request_update branch from 11612fe to 91195fd Compare July 10, 2026 17:03

KvngMikey removed the nut hold label Jul 29, 2026

KvngMikey added 9 commits August 10, 2026 15:33

feat(core): new properties added to nut18 and nut26

0d8d23c

chore: tests added

37b961d

chore: failing test

169f7a5

chore: wallet now acts on fields when paying and creates a payment re…

7fc06be

…quest that carries fields

chore: updated ms to mp(mint_preferred)

33988d6

KvngMikey added 3 commits August 10, 2026 15:36

fix(wallet): reject payment requests with missing or mismatched unit

fc2c66c

a and mf are denominated in the request unit u: reject when sm is set without u, and when u differs from the wallet unit, before the method fee lookup.

fix(wallet): normalise mint URLs, honour disabled melting, correct fe…

ed186ad

…e reason. Also say the request has no mint list when the fee applies for that reason, and require a non-empty method name.

KvngMikey force-pushed the payment_request_update branch from 49d09a5 to ed186ad Compare August 10, 2026 14:52

callebtc reviewed Aug 11, 2026

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feat(core): Updates to nut18 and nut26 payment request - #1059

feat(core): Updates to nut18 and nut26 payment request#1059
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