Fix and simplify string property parsing, add test

I figured out what the actual layout of this property is (instead of
guessing, which created some bad results.) And added tests of course!

Also fixed a bug in read_string_with_length() that didn't handle the
case where the string length is zero.

src/common.rs

@@ -1,3 +1,4 @@
+use std::io::Seek;
 use binrw::{BinRead, BinReaderExt, BinResult};
 
 pub(crate) fn read_bool_from<T: From<u8> + PartialEq>(x: T) -> bool {
@@ -6,8 +7,12 @@ pub(crate) fn read_bool_from<T: From<u8> + PartialEq>(x: T) -> bool {
 
 #[binrw::parser(reader, endian)]
 pub(crate) fn read_string_with_length() -> BinResult<String> {
+    let length = u32::read_le(reader)? as usize;
+    if length == 0 {
+        return Ok(String::default());;
+    }
     // last byte is the null terminator which Rust ignores
-    let length = u32::read_le(reader)? as usize - 1;
+    let length = length - 1;
     let mut bytes: Vec<u8> = vec![0u8; length];
     // TODO: there was to be way to read this all in one go?
     for i in 0..length {

src/str_property.rs

@@ -1,14 +1,63 @@
 use binrw::binrw;
+use crate::common::read_string_with_length;
 
 #[binrw]
 #[derive(Debug)]
 pub struct StrProperty {
-    #[br(temp)]
-    #[bw(ignore)]
     #[br(pad_after = 5)]
-    pub name_length: u32,
+    pub size_in_bytes: u32,
-    #[br(count = name_length)]
+
-    #[bw(map = |x : &String | x.as_bytes())]
+    #[br(parse_with = read_string_with_length)]
-    #[br(map = | x: Vec<u8> | String::from_utf8(x).unwrap().trim_matches(char::from(0)).to_string())]
+    #[bw(ignore)]
-    pub name: String,
+    pub value: String,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use binrw::BinRead;
+    use std::io::Cursor;
+
+    #[test]
+    fn empty_string() {
+        // From Slot.sav
+        let data = [
+            0x04, 0x00, 0x00,
+            0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00,
+            0x00, 0x0b, 0x00,
+            0x00, 0x00, 0x4c,
+            0x6f, 0x61, 0x64,
+            0x4f, 0x70, 0x74,
+            0x69, 0x6f, 0x6e,
+            0x00,
+        ];
+        let mut cursor = Cursor::new(data);
+        let decoded = StrProperty::read_le(&mut cursor).unwrap();
+        assert_eq!(decoded.value, "");
+    }
+
+    #[test]
+    fn regular_string() {
+        // From Slot.sav
+        let data = [
+            0x1e, 0x00, 0x00,
+            0x00, 0x00, 0x00,
+            0x00, 0x00, 0x00,
+            0x1a, 0x00, 0x00,
+            0x00, 0x41, 0x52,
+            0x30, 0x58, 0x4a,
+            0x47, 0x46, 0x57,
+            0x41, 0x36, 0x48,
+            0x4e, 0x49, 0x51,
+            0x31, 0x41, 0x41,
+            0x55, 0x4a, 0x39,
+            0x55, 0x52, 0x38,
+            0x32, 0x38, 0x00,
+        ];
+        let mut cursor = Cursor::new(data);
+        let decoded = StrProperty::read_le(&mut cursor).unwrap();
+        assert_eq!(decoded.value, "AR0XJGFWA6HNIQ1AAUJ9UR828");
+    }
 }