lnd.xprv/docs/grpc/ruby.md

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# How to write a Ruby gRPC client for the Lightning Network Daemon
This section enumerates what you need to do to write a client that communicates
with `lnd` in Ruby.
### Introduction
`lnd` uses the `gRPC` protocol for communication with clients like `lncli`.
`gRPC` is based on protocol buffers and as such, you will need to compile
the `lnd` proto file in Ruby before you can use it to communicate with `lnd`.
### Setup
Install gRPC rubygems:
```
$ gem install grpc
$ gem install grpc-tools
```
Clone the Google APIs repository:
```
$ git clone https://github.com/googleapis/googleapis.git
```
Fetch the `rpc.proto` file (or copy it from your local source directory):
```
$ curl -o rpc.proto -s https://raw.githubusercontent.com/lightningnetwork/lnd/master/lnrpc/rpc.proto
```
Compile the proto file:
```
$ grpc_tools_ruby_protoc --proto_path googleapis:. --ruby_out=. --grpc_out=. rpc.proto
```
Two files will be generated in the current directory:
* `rpc_pb.rb`
* `rpc_services_pb.rb`
### Examples
#### Simple client to display wallet balance
Every time you use the Ruby gRPC you need to require the `rpc_services_pb` file.
We assume that `lnd` runs on the default `localhost:10009`.
We further assume you run `lnd` with `--no-macaroons`.
```ruby
#!/usr/bin/env ruby
$:.unshift(File.dirname(__FILE__))
require 'grpc'
require 'rpc_services_pb'
# Due to updated ECDSA generated tls.cert we need to let gprc know that
# we need to use that cipher suite otherwise there will be a handhsake
# error when we communicate with the lnd rpc server.
ENV['GRPC_SSL_CIPHER_SUITES'] = "HIGH+ECDSA"
certificate = File.read(File.expand_path("~/.lnd/tls.cert"))
credentials = GRPC::Core::ChannelCredentials.new(certificate)
stub = Lnrpc::Lightning::Stub.new('127.0.0.1:10009', credentials)
response = stub.wallet_balance(Lnrpc::WalletBalanceRequest.new())
puts "Total balance: #{response.total_balance}"
```
This will show the `total_balance` of the wallet.
#### Streaming client for invoice payment updates
```ruby
#!/usr/bin/env ruby
$:.unshift(File.dirname(__FILE__))
require 'grpc'
require 'rpc_services_pb'
ENV['GRPC_SSL_CIPHER_SUITES'] = "HIGH+ECDSA"
certificate = File.read(File.expand_path("~/.lnd/tls.cert"))
credentials = GRPC::Core::ChannelCredentials.new(certificate)
stub = Lnrpc::Lightning::Stub.new('127.0.0.1:10009', credentials)
stub.subscribe_invoices(Lnrpc::InvoiceSubscription.new) do |invoice|
puts invoice.inspect
end
```
Now, create an invoice on your node:
```bash
$ lncli addinvoice --amt=590
{
"r_hash": <R_HASH>,
"pay_req": <PAY_REQ>
}
```
Next send a payment to it from another node:
```
$ lncli sendpayment --pay_req=<PAY_REQ>
```
You should now see the details of the settled invoice appear.
#### Using Macaroons
To authenticate using macaroons you need to include the macaroon in the metadata of the request.
```ruby
# Lnd admin macaroon is at ~/.lnd/data/chain/bitcoin/simnet/admin.macaroon on Linux and
# ~/Library/Application Support/Lnd/data/chain/bitcoin/simnet/admin.macaroon on Mac
macaroon_binary = File.read(File.expand_path("~/.lnd/data/chain/bitcoin/simnet/admin.macaroon"))
macaroon = macaroon_binary.each_byte.map { |b| b.to_s(16).rjust(2,'0') }.join
```
The simplest approach to use the macaroon is to include the metadata in each request as shown below.
```ruby
stub.get_info(Lnrpc::GetInfoRequest.new, metadata: {macaroon: macaroon})
```
However, this can get tiresome to do for each request. We can use gRPC interceptors to add this metadata to each request automatically. Our interceptor class would look like this.
```ruby
class MacaroonInterceptor < GRPC::ClientInterceptor
attr_reader :macaroon
def initialize(macaroon)
@macaroon = macaroon
super
end
def request_response(request:, call:, method:, metadata:)
metadata['macaroon'] = macaroon
yield
end
def server_streamer(request:, call:, method:, metadata:)
metadata['macaroon'] = macaroon
yield
end
end
```
And then we would include it when we create our stub like so.
```ruby
certificate = File.read(File.expand_path("~/.lnd/tls.cert"))
credentials = GRPC::Core::ChannelCredentials.new(certificate)
macaroon_binary = File.read(File.expand_path("~/.lnd/data/chain/bitcoin/simnet/admin.macaroon"))
macaroon = macaroon_binary.each_byte.map { |b| b.to_s(16).rjust(2,'0') }.join
stub = Lnrpc::Lightning::Stub.new(
'localhost:10009',
credentials,
interceptors: [MacaroonInterceptor.new(macaroon)]
)
# Now we don't need to pass the metadata on a request level
p stub.get_info(Lnrpc::GetInfoRequest.new)
```
#### Receive Large Responses
A GRPC::ResourceExhausted exception is raised when a server response is too large. In particular, this will happen with mainnet DescribeGraph calls. The solution is to raise the default limits by including a channel_args hash when creating our stub.
```ruby
stub = Lnrpc::Lightning::Stub.new(
'localhost:10009',
credentials,
channel_args: {"grpc.max_receive_message_length" => 1024 * 1024 * 50}
)
```