Add LNURL support for amountless Lightning receives

src/components/ExpandAddresses.tsx

@@ -19,6 +19,7 @@ interface ExpandAddressesProps {
   boardingAddr: string
   offchainAddr: string
   invoice: string
+  lnurl?: string
   onClick: (arg0: string) => void
 }
 
@@ -27,6 +28,7 @@ export default function ExpandAddresses({
   boardingAddr,
   offchainAddr,
   invoice,
+  lnurl,
   onClick,
 }: ExpandAddressesProps) {
   const [copied, setCopied] = useState('')
@@ -99,6 +101,7 @@ export default function ExpandAddresses({
             {boardingAddr ? <ExpandLine testId='btc' title='BTC address' value={boardingAddr} /> : null}
             {offchainAddr ? <ExpandLine testId='ark' title='Arkade address' value={offchainAddr} /> : null}
             {invoice ? <ExpandLine testId='invoice' title='Lightning invoice' value={invoice} /> : null}
+            {lnurl ? <ExpandLine testId='lnurl' title='LNURL' value={lnurl} /> : null}
           </FlexCol>
         </div>
       ) : null}

src/hooks/useLnurlSession.ts

@@ -0,0 +1,134 @@
+import { useCallback, useEffect, useRef, useState } from 'react'
+import { lnurlServerUrl } from '../lib/constants'
+import { consoleError } from '../lib/logs'
+
+interface LnurlSession {
+  /** LNURL bech32 string to display/share */
+  lnurl: string
+  /** Whether the SSE session is active */
+  active: boolean
+  /** Error message if session failed */
+  error: string | undefined
+}
+
+interface InvoiceRequest {
+  amountMsat: number
+  comment?: string
+}
+
+/**
+ * Hook that manages an LNURL session with the lnurl-server.
+ *
+ * Opens an SSE stream to receive invoice requests from payers.
+ * When a payer requests an invoice, calls `onInvoiceRequest` so the wallet
+ * can create a reverse swap and return the bolt11.
+ *
+ * The session (and LNURL) is active as long as the component is mounted.
+ */
+export function useLnurlSession(
+  enabled: boolean,
+  onInvoiceRequest: (req: InvoiceRequest) => Promise<string>,
+): LnurlSession {
+  const [lnurl, setLnurl] = useState('')
+  const [active, setActive] = useState(false)
+  const [error, setError] = useState<string | undefined>()
+  const sessionIdRef = useRef<string | null>(null)
+  const abortRef = useRef<AbortController | null>(null)
+  const onInvoiceRequestRef = useRef(onInvoiceRequest)
+  onInvoiceRequestRef.current = onInvoiceRequest
+
+  const postInvoice = useCallback(async (sessionId: string, pr: string) => {
+    try {
+      await fetch(`${lnurlServerUrl}/lnurl/session/${sessionId}/invoice`, {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ pr }),
+      })
+    } catch (err) {
+      consoleError(err, 'Failed to post invoice to lnurl-server')
+    }
+  }, [])
+
+  useEffect(() => {
+    if (!enabled || !lnurlServerUrl) return
+
+    const abort = new AbortController()
+    abortRef.current = abort
+
+    const connect = async () => {
+      try {
+        const response = await fetch(`${lnurlServerUrl}/lnurl/session`, {
+          method: 'POST',
+          signal: abort.signal,
+        })
+
+        if (!response.ok || !response.body) {
+          setError('Failed to open LNURL session')
+          return
+        }
+
+        const reader = response.body.getReader()
+        const decoder = new TextDecoder()
+        let buffer = ''
+
+        while (!abort.signal.aborted) {
+          const { done, value } = await reader.read()
+          if (done) break
+
+          buffer += decoder.decode(value, { stream: true })
+          const lines = buffer.split('\n')
+          // Keep the last incomplete line in the buffer
+          buffer = lines.pop() ?? ''
+
+          let eventType = ''
+          for (const line of lines) {
+            if (line.startsWith('event: ')) {
+              eventType = line.slice(7).trim()
+            } else if (line.startsWith('data: ') && eventType) {
+              const data = JSON.parse(line.slice(6))
+
+              if (eventType === 'session_created') {
+                sessionIdRef.current = data.sessionId
+                setLnurl(data.lnurl)
+                setActive(true)
+                setError(undefined)
+              } else if (eventType === 'invoice_request') {
+                const req: InvoiceRequest = {
+                  amountMsat: data.amountMsat,
+                  comment: data.comment,
+                }
+                try {
+                  const pr = await onInvoiceRequestRef.current(req)
+                  if (sessionIdRef.current) {
+                    await postInvoice(sessionIdRef.current, pr)
+                  }
+                } catch (err) {
+                  consoleError(err, 'Failed to handle invoice request')
+                }
+              }
+
+              eventType = ''
+            }
+          }
+        }
+      } catch (err) {
+        if (!abort.signal.aborted) {
+          consoleError(err, 'LNURL session error')
+          setError('LNURL session disconnected')
+        }
+      } finally {
+        setActive(false)
+        sessionIdRef.current = null
+      }
+    }
+
+    connect()
+
+    return () => {
+      abort.abort()
+      abortRef.current = null
+    }
+  }, [enabled, postInvoice])
+
+  return { lnurl, active, error }
+}

src/lib/bip21.ts

@@ -73,12 +73,12 @@ export const decodeBip21 = (uri: string): Bip21Decoded => {
   return result
 }
 
-export const encodeBip21 = (address: string, arkAddress: string, invoice: string, sats: number) => {
+export const encodeBip21 = (address: string, arkAddress: string, invoice: string, sats: number, lnurl?: string) => {
   return (
     `bitcoin:${address}` +
     `?ark=${arkAddress}` +
-    (invoice ? `&lightning=${invoice}` : '') +
-    `&amount=${prettyNumber(fromSatoshis(sats))}`
+    (invoice ? `&lightning=${invoice}` : lnurl ? `&lightning=${lnurl}` : '') +
+    (sats ? `&amount=${prettyNumber(fromSatoshis(sats))}` : '')
   )
 }
 

src/lib/constants.ts

@@ -12,6 +12,7 @@ export const minSatsToNudge = 100_000
 export const maxPercentage = import.meta.env.VITE_MAX_PERCENTAGE ?? 10
 export const psaMessage = import.meta.env.VITE_PSA_MESSAGE ?? ''
 export const enableChainSwapsReceive = import.meta.env.VITE_CHAIN_SWAPS_RECEIVE_ENABLED === 'true'
+export const lnurlServerUrl: string | undefined = import.meta.env.VITE_LNURL_SERVER_URL
 
 export const defaultArkServer = () => {
   if (import.meta.env.VITE_ARK_SERVER) return import.meta.env.VITE_ARK_SERVER

src/screens/Wallet/Receive/QrCode.tsx

@@ -1,4 +1,4 @@
-import { useContext, useEffect, useState } from 'react'
+import { useCallback, useContext, useEffect, useState } from 'react'
 import Button from '../../../components/Button'
 import Padded from '../../../components/Padded'
 import QrCode from '../../../components/QrCode'
@@ -19,10 +19,11 @@ import Loading from '../../../components/Loading'
 import { SwapsContext } from '../../../providers/swaps'
 import { encodeBip21, encodeBip21Asset } from '../../../lib/bip21'
 import { PendingChainSwap, PendingReverseSwap } from '@arkade-os/boltz-swap'
-import { enableChainSwapsReceive } from '../../../lib/constants'
+import { enableChainSwapsReceive, lnurlServerUrl } from '../../../lib/constants'
 import { centsToUnits } from '../../../lib/assets'
 import WarningBox from '../../../components/Warning'
 import ErrorMessage from '../../../components/Error'
+import { useLnurlSession } from '../../../hooks/useLnurlSession'
 
 export default function ReceiveQRCode() {
   const { navigate } = useContext(NavigationContext)
@@ -51,6 +52,30 @@ export default function ReceiveQRCode() {
   const [bip21Uri, setBip21Uri] = useState('')
   const [invoice, setInvoice] = useState('')
 
+  // LNURL session for amountless Lightning receives
+  const isAmountlessLnurl = !satoshis && !isAssetReceive && !!lnurlServerUrl
+  const handleInvoiceRequest = useCallback(
+    async (req: { amountMsat: number }) => {
+      const sats = Math.floor(req.amountMsat / 1000)
+      const pendingSwap = await createReverseSwap(sats)
+      if (!pendingSwap) throw new Error('Failed to create reverse swap')
+      // Auto-claim in background
+      if (arkadeSwaps) {
+        arkadeSwaps
+          .waitAndClaim(pendingSwap)
+          .then(() => {
+            setRecvInfo({ ...recvInfo, satoshis: pendingSwap.response.onchainAmount })
+            notifyPaymentReceived(pendingSwap.response.onchainAmount)
+            navigate(Pages.ReceiveSuccess)
+          })
+          .catch((err) => consoleError(err, 'Error claiming LNURL reverse swap'))
+      }
+      return pendingSwap.response.invoice
+    },
+    [arkadeSwaps, createReverseSwap, setRecvInfo, recvInfo, navigate, notifyPaymentReceived],
+  )
+  const lnurlSession = useLnurlSession(isAmountlessLnurl, handleInvoiceRequest)
+
   const createBtcAddress = () => {
     return new Promise((resolve, reject) => {
       if (!enableChainSwapsReceive) return reject()
@@ -153,14 +178,15 @@ export default function ReceiveQRCode() {
 
     const bip21uri = isAssetReceive
       ? encodeBip21Asset(arkAddress, assetId, centsToUnits(satoshis, assetMeta?.metadata?.decimals))
-      : encodeBip21(btcAddress, arkAddress, invoice, satoshis)
+      : encodeBip21(btcAddress, arkAddress, invoice, satoshis, lnurlSession.lnurl)
 
-    setNoPaymentMethods(!arkAddress && !btcAddress && !invoice && !isAssetReceive)
+    const hasLnurl = isAmountlessLnurl && lnurlSession.active
+    setNoPaymentMethods(!arkAddress && !btcAddress && !invoice && !hasLnurl && !isAssetReceive)
     setArkAddress(arkAddress)
     setBtcAddress(btcAddress)
     setQrCodeValue(bip21uri)
     setBip21Uri(bip21uri)
-  }, [showQrCode, swapAddress, invoice])
+  }, [showQrCode, swapAddress, invoice, lnurlSession.lnurl, lnurlSession.active])
 
   useEffect(() => {
     if (!svcWallet) return
@@ -242,6 +268,7 @@ export default function ReceiveQRCode() {
                 boardingAddr={btcAddress}
                 offchainAddr={arkAddress}
                 invoice={invoice || ''}
+                lnurl={lnurlSession.lnurl}
                 onClick={setQrCodeValue}
               />
               {swapsTimedOut && !invoice && !isAssetReceive ? (