Expose BIP39 Mnemonic generation in bindings

We already re-export the `bip39` crate to allow users to generate
Mnemonics. However, doing the same is not trivial in bindings.

Here we expose a simple convenience function that returns a random
mnemonic, allowig users to generate them without relying on a
third-party library.

Author: tnull

bindings/ldk_node.udl

@@ -1,4 +1,5 @@
 namespace ldk_node {
+	Mnemonic generate_entropy_mnemonic();
 };
 
 dictionary Config {

src/io/utils.rs

@@ -12,6 +12,7 @@ use lightning::routing::scoring::{ProbabilisticScorer, ProbabilisticScoringParam
 use lightning::util::logger::Logger;
 use lightning::util::ser::{Readable, ReadableArgs, Writeable};
 
+use bip39::Mnemonic;
 use bitcoin::hash_types::{BlockHash, Txid};
 use bitcoin::hashes::hex::FromHex;
 use rand::{thread_rng, RngCore};
@@ -24,6 +25,20 @@ use std::sync::Arc;
 
 use super::KVStore;
 
+/// Generates a random [BIP 39] mnemonic.
+///
+/// The result may be used to initialize the [`Node`] entropy, i.e., can be given to
+/// [`Builder::set_entropy_bip39_mnemonic`].
+///
+/// [BIP 39]: https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
+/// [`Builder::set_entropy_bip39_mnemonic`]: crate::Builder::set_entropy_bip39_mnemonic
+pub fn generate_entropy_mnemonic() -> Mnemonic {
+	// bip39::Mnemonic supports 256 bit entropy max
+	let mut entropy = [0; 32];
+	thread_rng().fill_bytes(&mut entropy);
+	Mnemonic::from_entropy(&entropy).unwrap()
+}
+
 pub(crate) fn read_or_generate_seed_file(keys_seed_path: &str) -> [u8; WALLET_KEYS_SEED_LEN] {
 	if Path::new(&keys_seed_path).exists() {
 		let seed = fs::read(keys_seed_path).expect("Failed to read keys seed file");
@@ -236,3 +251,16 @@ where
 			Error::PersistenceFailed
 		})
 }
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn mnemonic_to_entropy_to_mnemonic() {
+		let mnemonic = generate_entropy_mnemonic();
+
+		let entropy = mnemonic.to_entropy();
+		assert_eq!(mnemonic, Mnemonic::from_entropy(&entropy).unwrap());
+	}
+}

src/lib.rs

@@ -93,7 +93,6 @@ mod wallet;
 pub use bip39;
 pub use bitcoin;
 pub use lightning;
-use lightning::ln::msgs::RoutingMessageHandler;
 pub use lightning_invoice;
 
 pub use error::Error as NodeError;
@@ -102,6 +101,8 @@ use error::Error;
 pub use event::Event;
 pub use types::NetAddress;
 
+pub use io::utils::generate_entropy_mnemonic;
+
 #[cfg(feature = "uniffi")]
 use {bitcoin::OutPoint, lightning::ln::PaymentSecret, uniffi_types::*};
 
@@ -126,6 +127,7 @@ use lightning::chain::{chainmonitor, BestBlock, Confirm, Watch};
 use lightning::ln::channelmanager::{
 	self, ChainParameters, ChannelManagerReadArgs, PaymentId, RecipientOnionFields, Retry,
 };
+use lightning::ln::msgs::RoutingMessageHandler;
 use lightning::ln::peer_handler::{IgnoringMessageHandler, MessageHandler};
 use lightning::ln::{PaymentHash, PaymentPreimage};
 use lightning::routing::scoring::{ProbabilisticScorer, ProbabilisticScoringParameters};