feat(mintd): allow multiple lightning backends per currency unit#1949
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Micah-Shallom wants to merge 5 commits into
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feat(mintd): allow multiple lightning backends per currency unit#1949Micah-Shallom wants to merge 5 commits into
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Micah-Shallom
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asmogo
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May 11, 2026
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Thanks for your contribution.
I have a minor change request regarding the grpc processor configuration. Apart from that, this looks good to me.
| tracing::debug!("Adding unit: {:?}", unit); | ||
| let processor = grpc_processor | ||
| .setup(settings, unit.clone(), None, work_dir, None) | ||
| for unit in grpc_processor.clone().supported_units { |
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I believe we should deprecate the supported_units variable and instead use ln_entry units in this context. With this setup, we may need to define the unit twice in the configuration, once for the supported_units variable and once for the ln_entry variable.
[grpc_processor]
addr = "http://127.0.0.1"
port = 50051
supported_units = ["sat"]
[[ln]]
ln_backend = "grpcprocessor"
unit = "sat"
I’m not sure if we should do this in the same pull request.
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A single mintd instance can now run several Lightning backends, each serving a different currency unit (for example CLN for sat, LNbits for eur). The legacy single [ln] config block is still accepted unchanged; multi-backend setups repeat [[ln]] with a unit field on each entry. Closes cashubtc#1465
Adds two round-trip parsing tests: - test_multi_backend_config_parses verifies a TOML with two [[ln]] blocks (sat and eur) deserializes into a 2-element Vec<Ln> with correct units and per-entry limits. - test_legacy_ln_block_parses verifies the old single [ln] form produces a 1-element Vec with unit defaulted to Sat, locking in backwards compatibility.
Updates example.config.toml to show the new [[ln]] array form alongside the existing single [ln] block, and adds a "Multiple Lightning Backends" section to the cdk-mintd README explaining per-unit configuration, duplicate (unit, method) rejection, and backwards compatibility.
Replaces the internal supported_units iteration with a single registration driven by [[ln]].unit, matching the pattern used by the other Lightning backends. Operators no longer need to declare the same unit twice (once in [fake_wallet]/[grpc_processor] and again in [[ln]]). The supported_units field stays in the config structs so legacy configs still parse, but it no longer affects registration. Operators using multiple supported_units should switch to one [[ln]] block per unit.
Verifies that when an operator configures [[ln]] backend = "fakewallet" with a non-default unit, the resulting mint registers that unit and not whatever [fake_wallet].supported_units says. This guards against the supported_units iteration creeping back into the dispatcher.
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Summary
Adds support for running multiple Lightning backends in a single
cdk-mintd, with each backend serving a different currency unit. So one mint can hand out sat-denominated ecash via CLN and eur-denominated ecash via LNbits, all through the same mint URL.The mint engine itself already supported this (its payment-processor map is keyed by
(unit, method)); the only thing blocking it wascdk-mintd's config and startup, which assumed a single backend. This PR removes that assumption.Closes #1465
What operators see
Existing configs keep working. The old single
[ln]block is still accepted and behaves identically to today.For a multi-backend setup, repeat
[[ln]]instead, one entry per(unit, method):Each entry has its own mint/melt limits. Two entries pointing to the same
(unit, method)are rejected at startup with a clear error.