Adds FundingGenerationReady Event Handling section

Author: Conor Okus

docs/tutorials/building-a-node-with-ldk/opening-a-channel.md

@@ -67,6 +67,129 @@ val createChannelResult = channelManager.create_channel(
   </template>
 </CodeSwitcher>
 
+# FundingGenerationReady Event Handling
+
+At this point, an outbound channel has been initiated with your peer and it will appear in `ChannelManager::list_channels`. However, the channel is not yet funded. Once your peer accepts the channel, you will be notified with a `FundingGenerationReady` event. It's then your responsibility to construct the funding transaction and pass it to ChannelManager, which will broadcast it once it receives your channel counterparty's signature.
+
+
+<CodeSwitcher :languages="{rust:'Rust', java:'Java', kotlin:'Kotlin'}">
+<template v-slot:rust>
+
+```rust
+// In the event handler passed to BackgroundProcessor::start
+match event {
+	Event::FundingGenerationReady {
+		temporary_channel_id,
+		channel_value_satoshis,
+		output_script,
+		user_channel_id,
+	} => {
+		// This is the same channel created earler.
+		assert_eq!(event.user_channel_id, 42);
+
+		// Construct the raw transaction with one output, that is paid the amount of the
+		// channel.
+		let network = bitcoin_bech32::constants::Network::Testnet;
+		let address = WitnessProgram::from_scriptpubkey(&output_script[..], network)
+			.unwrap().to_address;
+		let mut outputs = vec![HashMap::with_capacity(1)];
+		outputs[0].insert(address, channel_value_satoshis as f64 / 100_000_000.0);
+		let raw_tx = bitcoind_client.create_raw_transaction(outputs).await;
+
+		// Have your wallet put the inputs into the transaction such that the output is
+		// satisfied.
+		let funded_tx = bitcoind_client.fund_raw_transaction(raw_tx).await;
+		assert!(funded_tx.changepos == 0 || funded_tx.changepos == 1);
+
+		// Sign the funding transaction and give it to ChannelManager to broadcast.
+		let signed_tx = bitcoind_client.sign_raw_transaction_with_wallet(funded_tx.hex).await;
+		assert_eq!(signed_tx.complete, true);
+		let final_tx: Transaction =
+			encode::deserialize(&hex_utils::to_vec(&signed_tx.hex).unwrap()).unwrap();
+		channel_manager.funding_transaction_generated(&temporary_channel_id, final_tx).unwrap();
+	}
+	// ...
+}
+```
+
+</template>
+
+<template v-slot:java>
+
+```java
+// After the peer responds with an `accept_channel` message, an
+// Event.FundingGenerationReady event will be generated.
+
+// In the `handle_event` method of ChannelManagerPersister implementation
+if (e instanceof Event.FundingGenerationReady) {
+	Event.FundingGenerationReady event = (Event.FundingGenerationReady) e;
+	byte[] funding_scriptpubkey = event.output_script;
+	long output_value = event.channel_value_satoshis;
+
+	// This is the same channel created earler
+	assert event.user_channel_id == 42;
+
+	// The output is always a P2WSH:
+	assert funding_scriptpubkey.length == 34 && funding_scriptpubkey[0] == 0 &&
+		funding_scriptpubkey[1] == 32;
+
+	// Generate the funding transaction for the channel based on the channel amount
+	// The following uses the bitcoinj library to do so, but you can use any
+	// standard Bitcoin library for on-chain logic.
+	NetworkParameters bitcoinj_net =
+		NetworkParameters.fromID(NetworkParameters.ID_MAINNET);
+	Transaction funding_tx = new Transaction(bitcoinj_net);
+	funding_tx.addInput(new TransactionInput(bitcoinj_net, funding, new byte[0]));
+	// Note that all inputs in the funding transaction MUST spend SegWit outputs
+	// (and have witnesses)
+	funding_tx.getInputs().get(0).setWitness(new TransactionWitness(2));
+	funding_tx.getInput(0).getWitness().setPush(0, new byte[]{0x1});
+	funding_tx.addOutput(Coin.SATOSHI.multiply(output_value),
+		new Script(funding_scriptpubkey));
+
+	// Give the funding transaction back to the ChannelManager.
+	Result_NoneAPIErrorZ funding_res = channel_manager.funding_transaction_generated(
+		event.temporary_channel_id, funding_tx.bitcoinSerialize());
+	// funding_transaction_generated should only generate an error if the
+	// transaction didn't meet the required format (or the counterparty already
+	// closed the channel on us):
+	assert funding_res instanceof Result_NoneAPIErrorZ.Result_NoneAPIErrorZ_OK;
+}
+```
+
+</template>
+
+<template v-slot:kotlin>
+
+```kotlin
+// After the peer responds with an `accept_channel` message, an
+// Event.FundingGenerationReady event will be generated.
+
+if (event is Event.FundingGenerationReady) {
+    val funding_spk = event.output_script
+
+    if (funding_spk.size == 34 && funding_spk[0].toInt() == 0 && funding_spk[1].toInt() == 32) {
+      // Generate the funding transaction for the channel based on the channel amount
+      // The following uses BDK for on-chain logic
+        val rawTx = OnchainWallet.buildFundingTx(event.channel_value_satoshis, event.output_script)
+
+        channelManager.funding_transaction_generated(
+            event.temporary_channel_id,
+            event.counterparty_node_id,
+            rawTx
+        )
+    }
+  }
+```
+
+</template>
+
+
+
+
+</CodeSwitcher>
+
+