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Clarify about the length of a r field in invoice #865

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Clarify about the length of a r field in invoice #865

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14 changes: 8 additions & 6 deletions 11-payment-encoding.md
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Original file line number Diff line number Diff line change
Expand Up @@ -145,12 +145,14 @@ Currently defined tagged fields are:
* `x` (6): `data_length` variable. `expiry` time in seconds (big-endian). Default is 3600 (1 hour) if not specified.
* `c` (24): `data_length` variable. `min_final_cltv_expiry` to use for the last HTLC in the route. Default is 18 if not specified.
* `f` (9): `data_length` variable, depending on version. Fallback on-chain address: for Bitcoin, this starts with a 5-bit `version` and contains a witness program or P2PKH or P2SH address.
* `r` (3): `data_length` variable. One or more entries containing extra routing information for a private route; there may be more than one `r` field
* `pubkey` (264 bits)
* `short_channel_id` (64 bits)
* `fee_base_msat` (32 bits, big-endian)
* `fee_proportional_millionths` (32 bits, big-endian)
* `cltv_expiry_delta` (16 bits, big-endian)
* `r` (3): `data_length` variable. One or more entries containing extra routing information for a private route; there may be more than one `r` field.
* Fields are
* `pubkey` (264 bits)
* `short_channel_id` (64 bits)
* `fee_base_msat` (32 bits, big-endian)
* `fee_proportional_millionths` (32 bits, big-endian)
* `cltv_expiry_delta` (16 bits, big-endian)
* Be aware that `data_length` can express `2^10` (=1024 bits) as the longest, and a single hop will be 51 bytes (= 408 bits). So currently there is no way to specify a hint with more than two hops.
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Weirdly, data_length is expressed in 5-bit amounts, so there is 5120 bits. You can fit 12 hops in there.

* `9` (5): `data_length` variable. One or more 5-bit values containing features
supported or required for receiving this payment.
See [Feature Bits](#feature-bits).
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