From 08219f05ba81b16bd34afa82ef37f99d32d65e3b Mon Sep 17 00:00:00 2001
From: Lucas Schwiderski <lucas@lschwiderski.de>
Date: Thu, 31 Aug 2023 17:14:54 +0200
Subject: [PATCH] sdk: Fix reading strings

Fatshark has a few weird string fields, where they provide a length
field, but then sometimes write a shorter, NUL-terminated string into
that same field and adding padding up to the "advertised" length.
To properly read those strings, we can't rely on just the length field
anymore, but need to check for a NUL, too.
---
 lib/sdk/src/binary.rs | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/lib/sdk/src/binary.rs b/lib/sdk/src/binary.rs
index 1fcc90e..9348e1b 100644
--- a/lib/sdk/src/binary.rs
+++ b/lib/sdk/src/binary.rs
@@ -43,6 +43,7 @@ impl<T: FromBinary> FromBinary for Vec<T> {
 }
 
 pub mod sync {
+    use std::ffi::CStr;
     use std::io::{self, Read, Seek, SeekFrom};
 
     use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
@@ -165,25 +166,13 @@ pub mod sync {
         }
 
         fn read_string_len(&mut self, len: usize) -> Result<String> {
-            let mut buf = vec![0; len];
-            let res = self
-                .read_exact(&mut buf)
-                .map_err(Report::new)
-                .and_then(|_| {
-                    String::from_utf8(buf).map_err(|err| {
-                        let ascii = String::from_utf8_lossy(err.as_bytes()).to_string();
-                        let bytes = format!("{:?}", err.as_bytes());
-                        Report::new(err)
-                            .with_section(move || bytes.header("Bytes:"))
-                            .with_section(move || ascii.header("ASCII:"))
-                    })
-                });
+            let pos = self.stream_position();
 
+            let res = read_string_len(self, len);
             if res.is_ok() {
                 return res;
             }
 
-            let pos = self.stream_position();
             if pos.is_ok() {
                 res.with_section(|| {
                     format!("{pos:#X} ({pos})", pos = pos.unwrap()).header("Position: ")
@@ -243,4 +232,22 @@ pub mod sync {
 
         Err(err).with_section(|| format!("{pos:#X} ({pos})").header("Position: "))
     }
+
+    fn read_string_len(mut r: impl Read, len: usize) -> Result<String> {
+        let mut buf = vec![0; len];
+        r.read_exact(&mut buf)
+            .wrap_err_with(|| format!("Failed to read {} bytes", len))?;
+
+        let res = match CStr::from_bytes_until_nul(&buf) {
+            Ok(s) => {
+                let s = s.to_str()?;
+                Ok(s.to_string())
+            }
+            Err(_) => String::from_utf8(buf.clone()).map_err(Report::new),
+        };
+
+        res.wrap_err("Invalid binary for UTF8 string")
+            .with_section(|| format!("{}", String::from_utf8_lossy(&buf)).header("ASCI:"))
+            .with_section(|| format!("{:x?}", buf).header("Bytes:"))
+    }
 }