Foreign API documentation and small cleanup (#31)

* verify slate messages documentation

* rustfmt

* foreign API documentation

* rustfmt

libwallet/src/api_impl/foreign.rs

@@ -44,16 +44,17 @@ pub fn verify_slate_messages(slate: &Slate) -> Result<(), Error> {
 /// Receive a tx as recipient
 pub fn receive_tx<T: ?Sized, C, K>(
 	w: &mut T,
-	slate: &mut Slate,
+	slate: &Slate,
 	dest_acct_name: Option<&str>,
 	message: Option<String>,
 	use_test_rng: bool,
-) -> Result<(), Error>
+) -> Result<Slate, Error>
 where
 	T: WalletBackend<C, K>,
 	C: NodeClient,
 	K: Keychain,
 {
+	let mut ret_slate = slate.clone();
 	let parent_key_id = match dest_acct_name {
 		Some(d) => {
 			let pm = w.get_acct_path(d.to_owned())?;
@@ -68,13 +69,13 @@ where
 	let tx = updater::retrieve_txs(
 		&mut *w,
 		None,
-		Some(slate.id),
+		Some(ret_slate.id),
 		Some(&parent_key_id),
 		use_test_rng,
 	)?;
 	for t in &tx {
 		if t.tx_type == TxLogEntryType::TxReceived {
-			return Err(ErrorKind::TransactionAlreadyReceived(slate.id.to_string()).into());
+			return Err(ErrorKind::TransactionAlreadyReceived(ret_slate.id.to_string()).into());
 		}
 	}
 
@@ -86,7 +87,14 @@ where
 		None => None,
 	};
 
-	tx::add_output_to_slate(&mut *w, slate, &parent_key_id, 1, message, use_test_rng)?;
-	tx::update_message(&mut *w, slate)?;
-	Ok(())
+	tx::add_output_to_slate(
+		&mut *w,
+		&mut ret_slate,
+		&parent_key_id,
+		1,
+		message,
+		use_test_rng,
+	)?;
+	tx::update_message(&mut *w, &mut ret_slate)?;
+	Ok(ret_slate)
 }