Use consistent byte/char offsets when parsing invoice HRPs

When parsing lightning-invoice HRPs we want to read them
char-by-char, tracking at which offset different fields were. Prior
to this commit this was done first by reading char-by-char and then
by indexing using the byte offset which works for ASCII strings but
fails on multi-byte characters.

This commit fixes this issue by simply always walking byte-by-byte
and rejecting multi-byte characters which don't belong in HRPs.

diff --git a/lightning-invoice/src/de.rs b/lightning-invoice/src/de.rs
index 56e5c53ba1f281e01fb274914b108b0f026ff660..c38aeb8a5fea876235a0322c833e92c1aff92a32 100644 (file)
--- a/lightning-invoice/src/de.rs
+++ b/lightning-invoice/src/de.rs
@@ -43,7 +43,11 @@ mod hrp_sm {
        }
 
        impl States {
-               fn next_state(&self, read_symbol: char) -> Result<States, super::Bolt11ParseError> {
+               fn next_state(&self, read_byte: u8) -> Result<States, super::Bolt11ParseError> {
+                       let read_symbol = match char::from_u32(read_byte.into()) {
+                               Some(symb) if symb.is_ascii() => symb,
+                               _ => return Err(super::Bolt11ParseError::MalformedHRP),
+                       };
                        match *self {
                                States::Start => {
                                        if read_symbol == 'l' {
@@ -119,7 +123,7 @@ mod hrp_sm {
                        *range = Some(new_range);
                }
 
-               fn step(&mut self, c: char) -> Result<(), super::Bolt11ParseError> {
+               fn step(&mut self, c: u8) -> Result<(), super::Bolt11ParseError> {
                        let next_state = self.state.next_state(c)?;
                        match next_state {
                                States::ParseCurrencyPrefix => {
@@ -158,7 +162,7 @@ mod hrp_sm {
 
        pub fn parse_hrp(input: &str) -> Result<(&str, &str, &str), super::Bolt11ParseError> {
                let mut sm = StateMachine::new();
-               for c in input.chars() {
+               for c in input.bytes() {
                        sm.step(c)?;
                }