Create short_channel_id utils

Util converts parts into u64 SCID
Util extracts block height from u64 SCID

Both will be used when processing gossip_query messages.

Author: bmancini55

lightning/src/util/mod.rs

@@ -22,6 +22,7 @@ pub(crate) mod chacha20;
 pub(crate) mod poly1305;
 pub(crate) mod chacha20poly1305rfc;
 pub(crate) mod transaction_utils;
+pub(crate) mod scid_utils;
 
 #[macro_use]
 pub(crate) mod ser_macros;

lightning/src/util/scid_utils.rs

@@ -0,0 +1,60 @@
+// This file is Copyright its original authors, visible in version control
+// history.
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+/// A `short_channel_id` construction error
+#[derive(Debug, PartialEq)]
+pub enum ShortChannelIdError {
+	BlockOverflow,
+	TxIndexOverflow,
+}
+
+/// Extracts the block height (most significant 3-bytes) from the `short_channel_id`
+#[allow(dead_code)]
+pub fn block_from_scid(short_channel_id: &u64) -> u32 {
+	return (short_channel_id >> 40) as u32;
+}
+
+/// Constructs a `short_channel_id` using the components pieces. Results in an error
+/// if the block height or tx index overflow the 3-bytes for each component.
+#[allow(dead_code)]
+pub fn scid_from_parts(block: u32, tx_index: u32, vout_index: u16) -> Result<u64, ShortChannelIdError> {
+	if block > 0x00ffffff {
+		return Err(ShortChannelIdError::BlockOverflow);
+	}
+
+	if	tx_index > 0x00ffffff {
+		return Err(ShortChannelIdError::TxIndexOverflow);
+	}
+
+	Ok(((block as u64) << 40) | ((tx_index as u64) << 16) | (vout_index as u64))
+}
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	#[test]
+	fn test_block_from_scid() {
+		assert_eq!(block_from_scid(&0x000000_000000_0000), 0);
+		assert_eq!(block_from_scid(&0x000001_000000_0000), 1);
+		assert_eq!(block_from_scid(&0x000001_ffffff_ffff), 1);
+		assert_eq!(block_from_scid(&0x800000_ffffff_ffff), 0x800000);
+		assert_eq!(block_from_scid(&0xffffff_ffffff_ffff), 0xffffff);
+	}
+
+	#[test]
+	fn test_scid_from_parts() {
+		assert_eq!(scid_from_parts(0x00000000, 0x00000000, 0x0000).unwrap(), 0x000000_000000_0000);
+		assert_eq!(scid_from_parts(0x00000001, 0x00000002, 0x0003).unwrap(), 0x000001_000002_0003);
+		assert_eq!(scid_from_parts(0x00111111, 0x00222222, 0x3333).unwrap(), 0x111111_222222_3333);
+		assert_eq!(scid_from_parts(0x00ffffff, 0x00ffffff, 0xffff).unwrap(), 0xffffff_ffffff_ffff);
+		assert_eq!(scid_from_parts(0x01ffffff, 0x00000000, 0x0000).err().unwrap(), ShortChannelIdError::BlockOverflow);
+		assert_eq!(scid_from_parts(0x00000000, 0x01ffffff, 0x0000).err().unwrap(), ShortChannelIdError::TxIndexOverflow);
+	}
+}