A WebLN interface for creating Bitcoin Lightning powered web applications

A package that helps you to interact with WebLN providers by providing a FlutterWebln interface for creating Bitcoin Lightning powered web applications.

Features

There are methods to:

• Enable the provider (FlutterWebln.enable)
• Get information about a users Bitcoin Lightning node (FlutterWebln.getInfo)
• Send a payment (FlutterWebln.sendPayment)
• Create an invoice to receive a payment (FlutterWebln.makeInvoice)
• Request the user to send a keysend payment (FlutterWebln.keysend)
• Request a signature of an arbitrary message (FlutterWebln.signMessage)
• Verifies the signature against the raw message (FlutterWebln.verifyMessage)

Getting Started

You first need to install WebLN provider in order to use any of the FlutterWebln methods.

Detecting WebLN support

Before you start using FlutterWebln you need to check for browser support by checking if the variable FlutterWebln.webln is defined:

  void checkWebln() {
    try {
      final weblnValue = weblnDecode(FlutterWebln.webln);
      if (weblnValue.isEmpty) {
        isWallet = false;
      } else {
        isWallet = true;
      }
      print('[+] webln value is $weblnValue');
    } catch (e) {
      print("[!] Error in checkWebln method is $e");
    }
  }

weblnValue.isEmpty indicates that the WebLN provider is not installed and the user can’t use any of the FlutterWebln methods.

Enable WebLN

To begin interacting with FlutterWebln methods you’ll first need to enable the provider as:

await FlutterWebln.enable()

It will prompt the user for permission to use the WebLN capabilities of the browser. After that you are free to call any of the other FlutterWebln methods.

Get Info

With FlutterWebln.getInfo the user gets information about the connected node as:

 try {
   await FlutterWebln.enable();
   await FlutterWebln.getInfo().then(allowInterop((response) {
     print('[+] GetInfoResponse: ${weblnDecode(response)}');
   }));
 } catch (error) {
   print('[!] Error in getInfo method is $error');
 }

Response

Result: [+] GetInfoResponse: {node: {alias: ? getalby.com}}

Make Invoice

With FlutterWebln.makeInvoice the user creates an invoice to be used by the web app as:

 final invoice = FlutterWebln.requestInvoiceArgs(
   amount: 100,
   defaultMemo: 'Hello World',
 );
 try {
   await FlutterWebln.makeInvoice(requestInvoiceArgs: invoice)
       .then(allowInterop((result) {
     print('[+] RequestInvoiceResponse: ${weblnDecode(result)}');
   }));
 } catch (error) {
   print('[!] Error in makeInvoice method is $error');
 }

Response

[+] RequestInvoiceResponse: {paymentRequest: lnbc1u1p3jdmdzpp5aehslp0ts0wszr62lwl82qwzcgl6jtqudvg000ez75jx307vpcdqdqjfpjkcmr0yptk7unvvscqzpgxqyz5vqsp5npje0n0mct745acshv8dl5pz5kyznz2z6du45fwpyxgwvxvepdts9qyyssqdynz62hf8xh76pn4qfpswzcz4ezt6k9kj9mccf6lzwzkutm04rwjhzynctgphyk6xc0g2ftn7unjxvmszutzr07xq52h5qeja5mk3sqpqwwx7y, rHash: ee6f0f85eb83dd010f4afbbe7501c2c23fa92c1c6b10f7bf22f52468bfcc0e1a}

Send Payment

With FlutterWebln.sendPayment the user sends a payment for an invoice. The user needs to provide a BOLT-11 invoice.

 try {
   await FlutterWebln.sendPayment(invoice: invoiceController.text)
       .then(allowInterop((result) {
     print('[+] SendPaymentResponse: ${weblnDecode(result)}');
   }));
 } catch (error) {
   print('[!] Error in sendPayment method is $error');
 }

Response

[+] SendPaymentResponse: {preimage: 6662313533626135643134626265623164343134363734626261336263306630, paymentHash: ee6f0f85eb83dd010f4afbbe7501c2c23fa92c1c6b10f7bf22f52468bfcc0e1a, route: {total_amt: 100, total_fees: 0}}

Keysend

With FlutterWebln.keysend it request the user to send a keysend payment. This payment only needs a destination public key and amount.

 try {
   await FlutterWebln.keysend(keysendArgs: keysendArgs)
       .then(allowInterop((result) {
     print('[+] KeysendPaymentResponse: ${weblnDecode(result)}');
   }));
 } catch (error) {
   print('[!] Error in keysend method is $error');
 }

Response:

[+] KeysendPaymentResponse: {preimage: 3965373033306134316666323562396262333332393463653136383634636265, paymentHash: 20594ee7899bee252917bc44ec744309d0593adf0e79469bb067afb67b632ffc, route: {total_amt: 20, total_fees: 0}}

Sign Message

With “FlutterWebln.signMessage` it request that the user signs an arbitrary string message.

 try {
   await FlutterWebln.signMessage(message: 'Hello World!')
       .then(allowInterop((result) {
     print('[+] SignMessageResponse: ${weblnDecode(result)}');
   }));
 } catch (error) {
   print('[!] Error in signMessage method is $error');
 }

Signed messages can either be verified server-side using the LND RPC method, or by clients with FlutterWebln.verifyMessage.

Verify Message

With FlutterWebln.verifyMessage the users’s client verifies the signature against the raw message, and let’s the user know if it was valid.

 try {
   await FlutterWebln.verifyMessage(
           signature: signatureController.text,
           message: messageController.text,
      ).then(allowInterop((result) {
    print('[+] VerifyMessageResponse: ${weblnDecode(result)}');
   }));
 } catch (error) {
   print('[!] Error in verifyMessage method is $error');
 }

Example Project

The above flutter_webln_integration project can be found here

Reference

• WebLN Guide
• WebLN Dev
• TLV record registry

GitHub

View Github