looprpc: clarify loop quote response

Author: guggero

looprpc/client.pb.go

@@ -412,7 +412,7 @@ message QuoteRequest {
     publishing the HTLC on chain. Setting this to a larger value will give the
     server the opportunity to batch multiple swaps together, and wait for
     low-fee periods before publishing the HTLC, potentially resulting in a
-    lower total swap fee.
+    lower total swap fee. This only has an effect on loop out quotes.
     */
     uint64 swap_publication_deadline = 4;
 }
@@ -429,7 +429,13 @@ message QuoteResponse {
     int64 prepay_amt = 2;
 
     /**
-    An estimate of the on-chain fee that needs to be paid to sweep the HTLC.
+    An estimate of the on-chain fee that needs to be paid to sweep the HTLC for
+    a loop out or to pay to the HTLC for loop in. If a miner fee of 0 is
+    returned, it means the external_htlc flag was set for a loop in and the fee
+    estimation was skipped. If a miner fee of -1 is returned, it means lnd's
+    wallet tried to estimate the fee but was unable to create a sample
+    estimation transaction because not enough funds are available. An
+    information message should be shown to the user in this case.
     */
     int64 miner_fee = 3;
 

looprpc/client.proto

@@ -81,7 +81,7 @@
           },
           {
             "name": "swap_publication_deadline",
-            "description": "*\nThe latest time (in unix seconds) we allow the server to wait before\npublishing the HTLC on chain. Setting this to a larger value will give the\nserver the opportunity to batch multiple swaps together, and wait for\nlow-fee periods before publishing the HTLC, potentially resulting in a\nlower total swap fee.",
+            "description": "*\nThe latest time (in unix seconds) we allow the server to wait before\npublishing the HTLC on chain. Setting this to a larger value will give the\nserver the opportunity to batch multiple swaps together, and wait for\nlow-fee periods before publishing the HTLC, potentially resulting in a\nlower total swap fee. This only has an effect on loop out quotes.",
             "in": "query",
             "required": false,
             "type": "string",
@@ -176,7 +176,7 @@
           },
           {
             "name": "swap_publication_deadline",
-            "description": "*\nThe latest time (in unix seconds) we allow the server to wait before\npublishing the HTLC on chain. Setting this to a larger value will give the\nserver the opportunity to batch multiple swaps together, and wait for\nlow-fee periods before publishing the HTLC, potentially resulting in a\nlower total swap fee.",
+            "description": "*\nThe latest time (in unix seconds) we allow the server to wait before\npublishing the HTLC on chain. Setting this to a larger value will give the\nserver the opportunity to batch multiple swaps together, and wait for\nlow-fee periods before publishing the HTLC, potentially resulting in a\nlower total swap fee. This only has an effect on loop out quotes.",
             "in": "query",
             "required": false,
             "type": "string",
@@ -424,7 +424,7 @@
         "miner_fee": {
           "type": "string",
           "format": "int64",
-          "description": "*\nAn estimate of the on-chain fee that needs to be paid to sweep the HTLC."
+          "description": "*\nAn estimate of the on-chain fee that needs to be paid to sweep the HTLC for\na loop out or to pay to the HTLC for loop in. If a miner fee of 0 is\nreturned, it means the external_htlc flag was set for a loop in and the fee\nestimation was skipped. If a miner fee of -1 is returned, it means lnd's\nwallet tried to estimate the fee but was unable to create a sample\nestimation transaction because not enough funds are available. An\ninformation message should be shown to the user in this case."
         },
         "swap_payment_dest": {
           "type": "string",