Add channel_creation_fee_sat to funding rate

Creating a new channel has an additional cost compared to adding
liquidity to an existing channel: the channel will be closed in the
future, which will require paying on-chain fees. Node operators can
include some `channel_creation_fee_sat` to their liquidity ads to
cover some of that future cost.

Author: t-bast

07-routing-gossip.md

@@ -1134,6 +1134,7 @@ are selling.
     * [`u16`:`funding_weight`]
     * [`u16`:`funding_fee_basis`]
     * [`u32`:`funding_fee_base_sat`]
+    * [`u32`:`channel_creation_fee_sat`]
 
 Sellers also define how the fees can be paid by listing the `payment_type`s
 they support.
@@ -1201,16 +1202,27 @@ When `request_funds` and `will_fund` have been exchanged, the buyer agrees to
 pay fees to the seller for the funding they provide to the channel based on
 the proposed `funding_weight`, `funding_fee_basis` and `funding_fee_base_sat`.
 
+If the buyer is opening a new channel, an additional `channel_creation_fee_sat`
+is applied. This can be used to hedge some of the future cost of closing that
+channel, which doesn't apply when additional liquidity is purchased on an
+existing channel (since the creation fee has already been paid).
+
 The funding fee has three components:
 
-* a fixed amount: `funding_fee_base_sat`
+* a fixed amount:
+  * `funding_fee_base_sat` if liquidity is purchased on an existing channel
+  * `funding_fee_base_sat + channel_creation_fee_sat` when opening a channel
 * a proportional amount based on the seller's `funding_amount`:
   * `paid_funding_contribution = min(funding_amount, request_funds.requested_sats)`
   * `funding_fee_proportional_sat = paid_funding_contribution * funding_fee_basis / 10_000`
 * a contribution to the on-chain fees paid by the seller:
   * `funding_fee_mining_sat = funding_weight * funding_feerate_perkw / 1000`
 
-The total fee is then:
+The total fee for a channel creation is then:
+
+    funding_fee_total = funding_fee_base_sat + channel_creation_fee_sat + funding_fee_proportional_sat + funding_fee_mining_sat
+
+The total fee for buying liquidity on an existing channel is:
 
     funding_fee_total = funding_fee_base_sat + funding_fee_proportional_sat + funding_fee_mining_sat
 
@@ -1228,6 +1240,8 @@ A node advertising a `funding_rate`:
   - MUST set `min_funding_amount_sat` and `max_funding_amount_sat` to the
     minimum and maximum amount it will contribute at this rate.
   - MUST set `funding_fee_base_sat` to the base fee (in satoshi) it will charge.
+  - MUST set `channel_creation_fee_sat` to the additional fee it will charge for
+    channel creation.
   - MUST set `funding_fee_basis` to the amount it will charge per contributed
     satoshi (in basis points, ie 1/10_000).
   - MUST set `funding_weight` to the transaction weight that will be charged.
@@ -1254,28 +1268,30 @@ The seller contributes `1_100_000 sats` with the following funding rate:
 
 	funding_weight = 444
 	funding_fee_base_sat = 233 sats
+  channel_creation_fee_sat = 500 sats
 	funding_fee_basis = 22
 
 The funding fee is:
 
 	funding_fee_base_sat = 233 sats
+  channel_creation_fee_sat = 500 sats
 	funding_fee_proportional_sat = min(1_000_000, 1_100_000) * 22 / 10_000 = 2200 sats
 	funding_fee_mining_sat = 444 * 2500 / 1000 = 1110 sats
-	funding_fee_total = 3543 sats
+	funding_fee_total = 4043 sats
 
 The outputs to the peers in the commitment transaction will be
 
 	to-buyer:     500_000 sats
-	to-seller: 1_103_543 sats
+	to-seller: 1_104_043 sats
 
 The miner fee for the buyer will be `720 * 2500 / 1000 = 1800 sats`.
 
 Minimum funds that the buyer must contribute to the funding transaction:
 
 	open_channel2.funding_satoshis: 500_000 sats
-	funding fee:                      3_543 sats
+	funding fee:                      4_043 sats
 	miner fee:                        1_800 sats
-	total required contribution:    505_343 sats
+	total required contribution:    505_843 sats
 
 Minimum funds that the seller must contribute to the funding transaction:
 

bolt07/liquidity-ads.json

@@ -20,15 +20,17 @@
             "funding_weight": 550,
             "funding_fee_basis": 100,
             "funding_fee_base_sat": 5000,
-            "encoded": "000186a0 0007a120 0226 0064 00001388"
+            "channel_creation_fee_sat": 1000,
+            "encoded": "000186a0 0007a120 0226 0064 00001388 000003e8"
           },
           {
             "min_funding_amount_sat": 500000,
             "max_funding_amount_sat": 5000000,
             "funding_weight": 1100,
             "funding_fee_basis": 75,
             "funding_fee_base_sat": 0,
-            "encoded": "0007a120 004c4b40 044c 004b 00000000"
+            "channel_creation_fee_sat": 1500,
+            "encoded": "0007a120 004c4b40 044c 004b 00000000 000005dc"
           }
         ],
         "payment_types": {
@@ -39,8 +41,8 @@
         }
       }
     },
-    "signature": "a822c88c3807659ce1c74866f3346444d0fe6ceb25f86804b245af064f77d0a83b8457732d77386a3b10cf4c80a1811d02f34770eefbef9548ab3a3ce3d629df",
-    "encoded": "0101 a822c88c3807659ce1c74866f3346444d0fe6ceb25f86804b245af064f77d0a83b8457732d77386a3b10cf4c80a1811d02f34770eefbef9548ab3a3ce3d629df 0000 661cebc9 03ca9b880627d2d4e3b33164f66946349f820d26aa9572fe0e525e534850cbd413 2a7557 4c4e2d4c69717569646974790000000000000000000000000000000000000000 0000 01250002000186a00007a12002260064000013880007a120004c4b40044c004b00000000000101"
+    "signature": "22ec2e2a6e02f54d949e332cbce571d123ae20dda98d0340ac7e64f60f11d413659a2a9645adea8f886bb5dd40cc589bd3e0f4f8b2ab333d323b74b7762b4ca1",
+    "encoded": "0101 22ec2e2a6e02f54d949e332cbce571d123ae20dda98d0340ac7e64f60f11d413659a2a9645adea8f886bb5dd40cc589bd3e0f4f8b2ab333d323b74b7762b4ca1 0000 661cebc9 03ca9b880627d2d4e3b33164f66946349f820d26aa9572fe0e525e534850cbd413 2a7557 4c4e2d4c69717569646974790000000000000000000000000000000000000000 0000 012d0002000186a00007a1200226006400001388000003e80007a120004c4b40044c004b00000000000005dc000101"
   },
   "open_channel2": {
     "chainHash": "6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000",
@@ -72,16 +74,17 @@
           "max_funding_amount_sat": 5000000,
           "funding_weight": 1100,
           "funding_fee_basis": 75,
-          "funding_fee_base_sat": 0
+          "funding_fee_base_sat": 0,
+          "channel_creation_fee_sat": 1500
         },
         "payment_type": {
           "type": "from_channel_balance",
           "encoded": "0000"
         },
-        "encoded": "03 1a 00000000000b71b0 0007a120004c4b40044c004b00000000 0000"
+        "encoded": "03 1e 00000000000b71b0 0007a120004c4b40044c004b00000000000005dc 0000"
       }
     },
-    "encoded": "0040 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000 0100000000000000000000000000000000000000000000000000000000000000 00001388 00000fa0 000000000003d090 00000000000001f4 000000000000c350 000000000000000f 0090 01e3 0009eb10 031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f 024d4b6cd1361032ca9bd2aeb9d900aa4d45d9ead80ac9423374c451a7254d0766 02531fe6068134503d2723133227c867ac8fa6c83c537e9a44c3c5bdbdcb1fe337 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b 0362c0a046dacce86ddd0343c6d3c7c79c2208ba0d9c9cf24a6d046d21d21f90f7 03f006a18d5653c4edf5391ff23a61f03ff83d237e880ee61187fa9f379a028e0a 02989c0b76cb563971fdc9bef31ec06c3560f3249d6ee9e5d83c57625596e05f6f 01 031a00000000000b71b00007a120004c4b40044c004b000000000000"
+    "encoded": "0040 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000 0100000000000000000000000000000000000000000000000000000000000000 00001388 00000fa0 000000000003d090 00000000000001f4 000000000000c350 000000000000000f 0090 01e3 0009eb10 031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f 024d4b6cd1361032ca9bd2aeb9d900aa4d45d9ead80ac9423374c451a7254d0766 02531fe6068134503d2723133227c867ac8fa6c83c537e9a44c3c5bdbdcb1fe337 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b 0362c0a046dacce86ddd0343c6d3c7c79c2208ba0d9c9cf24a6d046d21d21f90f7 03f006a18d5653c4edf5391ff23a61f03ff83d237e880ee61187fa9f379a028e0a 02989c0b76cb563971fdc9bef31ec06c3560f3249d6ee9e5d83c57625596e05f6f 01 031e00000000000b71b00007a120004c4b40044c004b00000000000005dc0000"
   },
   "accept_channel2": {
     "temporaryChannelId": "0100000000000000000000000000000000000000000000000000000000000000",
@@ -106,13 +109,14 @@
           "max_funding_amount_sat": 5000000,
           "funding_weight": 1100,
           "funding_fee_basis": 75,
-          "funding_fee_base_sat": 0
+          "funding_fee_base_sat": 0,
+          "channel_creation_fee_sat": 1500
         },
         "funding_script": "00202ec38203f4cf37a3b377d9a55c7ae0153c643046dbdbe2ffccfb11b74420103c",
-        "signature": "35962783e077e3c5214ba829752be2a3994a7c5e0e9d735ef5a9dab3ce1d6dda6282c3252b20af52e58c33c0e164167fd59e19114a8a8f9eb76b33008205dcb6",
-        "encoded": "03 74 0007a120004c4b40044c004b00000000 002200202ec38203f4cf37a3b377d9a55c7ae0153c643046dbdbe2ffccfb11b74420103c 35962783e077e3c5214ba829752be2a3994a7c5e0e9d735ef5a9dab3ce1d6dda6282c3252b20af52e58c33c0e164167fd59e19114a8a8f9eb76b33008205dcb6"
+        "signature": "c57cf393f6bd534472ec08cbfbbc7268501b32f563a21cdf02a99127c4f25168249acd6509f96b2e93843c3b838ee4808c75d0a15ff71ba886fda980b8ca954f",
+        "encoded": "03 78 0007a120004c4b40044c004b00000000000005dc 002200202ec38203f4cf37a3b377d9a55c7ae0153c643046dbdbe2ffccfb11b74420103c c57cf393f6bd534472ec08cbfbbc7268501b32f563a21cdf02a99127c4f25168249acd6509f96b2e93843c3b838ee4808c75d0a15ff71ba886fda980b8ca954f"
       }
     },
-    "encoded": "0041 0100000000000000000000000000000000000000000000000000000000000000 00000000000aae60 00000000000001d9 0000000005f5e100 0000000000000001 00000006 0090 0032 031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f 024d4b6cd1361032ca9bd2aeb9d900aa4d45d9ead80ac9423374c451a7254d0766 02531fe6068134503d2723133227c867ac8fa6c83c537e9a44c3c5bdbdcb1fe337 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b 0362c0a046dacce86ddd0343c6d3c7c79c2208ba0d9c9cf24a6d046d21d21f90f7 03f006a18d5653c4edf5391ff23a61f03ff83d237e880ee61187fa9f379a028e0a 02989c0b76cb563971fdc9bef31ec06c3560f3249d6ee9e5d83c57625596e05f6f 03740007a120004c4b40044c004b00000000002200202ec38203f4cf37a3b377d9a55c7ae0153c643046dbdbe2ffccfb11b74420103c35962783e077e3c5214ba829752be2a3994a7c5e0e9d735ef5a9dab3ce1d6dda6282c3252b20af52e58c33c0e164167fd59e19114a8a8f9eb76b33008205dcb6"
+    "encoded": "0041 0100000000000000000000000000000000000000000000000000000000000000 00000000000aae60 00000000000001d9 0000000005f5e100 0000000000000001 00000006 0090 0032 031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f 024d4b6cd1361032ca9bd2aeb9d900aa4d45d9ead80ac9423374c451a7254d0766 02531fe6068134503d2723133227c867ac8fa6c83c537e9a44c3c5bdbdcb1fe337 03462779ad4aad39514614751a71085f2f10e1c7a593e4e030efb5b8721ce55b0b 0362c0a046dacce86ddd0343c6d3c7c79c2208ba0d9c9cf24a6d046d21d21f90f7 03f006a18d5653c4edf5391ff23a61f03ff83d237e880ee61187fa9f379a028e0a 02989c0b76cb563971fdc9bef31ec06c3560f3249d6ee9e5d83c57625596e05f6f 03780007a120004c4b40044c004b00000000000005dc002200202ec38203f4cf37a3b377d9a55c7ae0153c643046dbdbe2ffccfb11b74420103cc57cf393f6bd534472ec08cbfbbc7268501b32f563a21cdf02a99127c4f25168249acd6509f96b2e93843c3b838ee4808c75d0a15ff71ba886fda980b8ca954f"
   }
 }