feat(core/rust): improve behavior of from_c_str / from_c_array

core/embed/rust/src/ui/screens.rs

@@ -7,25 +7,15 @@ pub use super::model_tr::screens::*;
 pub use super::model_tt::screens::*;
 use crate::ui::util::from_c_str;
 
-macro_rules! convert_str {
-    ($str:expr) => {
-        if ($str).is_null() {
-            ""
-        } else {
-            unwrap!(unsafe { from_c_str($str) })
-        }
-    };
-}
-
 #[no_mangle]
 extern "C" fn screen_fatal_error_rust(
     title: *const cty::c_char,
     msg: *const cty::c_char,
     footer: *const cty::c_char,
 ) {
-    let title = convert_str!(title);
-    let msg = convert_str!(msg);
-    let footer = convert_str!(footer);
+    let title = unsafe { from_c_str(title) }.unwrap_or("");
+    let msg = unsafe { from_c_str(msg) }.unwrap_or("");
+    let footer = unsafe { from_c_str(footer) }.unwrap_or("");
 
     screen_fatal_error(title, msg, footer);
 }

core/embed/rust/src/ui/util.rs

@@ -45,11 +45,13 @@ pub fn u32_to_str(num: u32, buffer: &mut [u8]) -> Option<&str> {
 /// # Safety
 ///
 /// The caller is responsible that the pointer is valid, which means that:
-/// (a) it is not null,
-/// (b) it points to a memory containing a valid C string (zero-terminated
+/// (a) it points to a memory containing a valid C string (zero-terminated
 /// sequence of characters), and
-/// (c) that the pointer has appropriate lifetime.
+/// (b) that the pointer has appropriate lifetime.
 pub unsafe fn from_c_str<'a>(c_str: *const cty::c_char) -> Option<&'a str> {
+    if c_str.is_null() {
+        return None;
+    }
     unsafe {
         let bytes = CStr::from_ptr(c_str).to_bytes();
         if bytes.is_ascii() {
@@ -65,11 +67,13 @@ pub unsafe fn from_c_str<'a>(c_str: *const cty::c_char) -> Option<&'a str> {
 /// # Safety
 ///
 /// The caller is responsible that the pointer is valid, which means that:
-/// (a) it is not null,
-/// (b) it points to a memory containing array of characters, with length `len`,
+/// (a) it points to a memory containing array of characters, with length `len`,
 /// and
-/// (c) that the pointer has appropriate lifetime.
+/// (b) that the pointer has appropriate lifetime.
 pub unsafe fn from_c_array<'a>(c_str: *const cty::c_char, len: usize) -> Option<&'a str> {
+    if c_str.is_null() {
+        return None;
+    }
     unsafe {
         let slice = core::slice::from_raw_parts(c_str as *const u8, len);
         if slice.is_ascii() {