Clean up docs on public chan_utils methods to be more useful

Author: TheBlueMatt

lightning/src/ln/chan_utils.rs

@@ -525,7 +525,11 @@ pub fn make_funding_redeemscript(broadcaster: &PublicKey, countersignatory: &Pub
 	}.push_opcode(opcodes::all::OP_PUSHNUM_2).push_opcode(opcodes::all::OP_CHECKMULTISIG).into_script()
 }
 
-/// panics if htlc.transaction_output_index.is_none()!
+/// Builds an unsigned HTLC-Success or HTLC-Timeout transaction from the given channel and HTLC
+/// parameters.
+///
+/// Panics if htlc.transaction_output_index.is_none() (as such HTLCs do not appear in the
+/// commitment transaction).
 pub fn build_htlc_transaction(prev_hash: &Txid, feerate_per_kw: u32, contest_delay: u16, htlc: &HTLCOutputInCommitment, broadcaster_delayed_payment_key: &PublicKey, revocation_key: &PublicKey) -> Transaction {
 	let mut txins: Vec<TxIn> = Vec::new();
 	txins.push(TxIn {
@@ -1177,7 +1181,11 @@ impl<'a> TrustedCommitmentTransaction<'a> {
 	}
 }
 
-/// Get the transaction number obscure factor
+/// Commitment transaction numbers which appear in the transactions themselves are XOR'd with a
+/// shared secret first. This prevents on-chain observers from discovering how many commitment
+/// transactions occurred in a channel before it was closed.
+///
+/// This function gets the shared secret from relevant channel public keys.
 pub fn get_commitment_transaction_number_obscure_factor(
 	broadcaster_payment_basepoint: &PublicKey,
 	countersignatory_payment_basepoint: &PublicKey,