Add helper type for writing to UTF-16 buffers

Author: FenrirWolf

ctru-rs/src/applets/error.rs

@@ -2,10 +2,13 @@
 //!
 //! This applet displays error text as a pop-up message on the lower screen.
 
+use crate::Utf16Writer;
 use crate::services::{apt::Apt, gfx::Gfx};
 
 use ctru_sys::{errorConf, errorDisp, errorInit};
 
+use std::fmt::Write;
+
 /// Configuration struct to set up the Error applet.
 #[doc(alias = "errorConf")]
 pub struct PopUp {
@@ -59,14 +62,9 @@ impl PopUp {
     /// 1900 UTF-16 code units in length after conversion.
     #[doc(alias = "errorText")]
     pub fn set_text(&mut self, text: &str) {
-        for (idx, code_unit) in text
-            .encode_utf16()
-            .take(self.state.Text.len() - 1)
-            .chain(std::iter::once(0))
-            .enumerate()
-        {
-            self.state.Text[idx] = code_unit;
-        }
+        let mut writer = Utf16Writer::new(&mut self.state.Text);
+
+        let _ = writer.write_str(text);
     }
 
     /// Launches the error applet.

ctru-rs/src/applets/swkbd.rs

@@ -3,7 +3,9 @@
 //! This applet opens a virtual keyboard on the console's bottom screen which lets the user write UTF-16 valid text.
 #![doc(alias = "keyboard")]
 
+use crate::Utf16Writer;
 use crate::services::{apt::Apt, gfx::Gfx};
+
 use ctru_sys::{
     APPID_SOFTWARE_KEYBOARD, APT_SendParameter, APTCMD_MESSAGE, NS_APPID, SwkbdButton,
     SwkbdDictWord, SwkbdLearningData, SwkbdState, SwkbdStatusData, aptLaunchLibraryApplet,
@@ -13,8 +15,7 @@ use ctru_sys::{
 use bitflags::bitflags;
 
 use std::borrow::Cow;
-use std::fmt::Display;
-use std::iter::once;
+use std::fmt::{Display, Write};
 use std::str;
 
 type CallbackFunction = dyn FnMut(&str) -> CallbackResult;
@@ -445,14 +446,9 @@ impl SoftwareKeyboard {
     #[doc(alias = "swkbdSetHintText")]
     pub fn set_hint_text(&mut self, text: Option<&str>) {
         if let Some(text) = text {
-            for (idx, code_unit) in text
-                .encode_utf16()
-                .take(self.state.hint_text.len() - 1)
-                .chain(once(0))
-                .enumerate()
-            {
-                self.state.hint_text[idx] = code_unit;
-            }
+            let mut writer = Utf16Writer::new(&mut self.state.hint_text);
+
+            let _ = writer.write_str(text);
         } else {
             self.state.hint_text[0] = 0;
         }
@@ -551,14 +547,9 @@ impl SoftwareKeyboard {
     pub fn configure_button(&mut self, button: Button, text: &str, submit: bool) {
         let button_text = &mut self.state.button_text[button as usize];
 
-        for (idx, code_unit) in text
-            .encode_utf16()
-            .take(button_text.len() - 1)
-            .chain(once(0))
-            .enumerate()
-        {
-            button_text[idx] = code_unit;
-        }
+        let mut writer = Utf16Writer::new(button_text);
+
+        let _ = writer.write_str(text);
 
         self.state.button_submits_text[button as usize] = submit;
     }
@@ -678,20 +669,13 @@ impl SoftwareKeyboard {
 
         // Copy stuff to shared mem
         if let Some(initial_text) = self.initial_text.as_deref() {
-            swkbd.initial_text_offset = 0;
-
-            let mut initial_text_cursor = swkbd_shared_mem_ptr.cast();
-
-            for code_unit in initial_text
-                .encode_utf16()
-                .take(swkbd.max_text_len as _)
-                .chain(once(0))
-            {
-                unsafe {
-                    *initial_text_cursor = code_unit;
-                    initial_text_cursor = initial_text_cursor.add(1);
-                }
-            }
+            let slice = unsafe {
+                std::slice::from_raw_parts_mut(swkbd_shared_mem_ptr.cast(), initial_text.len())
+            };
+
+            let mut writer = Utf16Writer::new(slice);
+
+            let _ = writer.write_str(initial_text);
         }
 
         if !extra.dict.is_null() {
@@ -838,14 +822,9 @@ impl SoftwareKeyboard {
         swkbd.callback_result = result.discriminant().into();
 
         if let CallbackResult::Retry(msg) | CallbackResult::Close(msg) = result {
-            for (idx, code_unit) in msg
-                .encode_utf16()
-                .take(swkbd.callback_msg.len() - 1)
-                .chain(once(0))
-                .enumerate()
-            {
-                swkbd.callback_msg[idx] = code_unit;
-            }
+            let mut writer = Utf16Writer::new(&mut swkbd.callback_msg);
+
+            let _ = writer.write_str(&msg);
         }
 
         let _ = unsafe {

ctru-rs/src/lib.rs

@@ -84,3 +84,38 @@ pub use crate::error::{Error, Result};
 pub fn set_panic_hook(call_old_hook: bool) {
     crate::applets::error::set_panic_hook(call_old_hook);
 }
+
+/// A helper type for writing string data into UTF-16 text buffers. Useful for interoperating with `libctru` APIs that expect UTF-16 as input.
+///
+/// The writer ensures that the text is written in-bounds and properly nul-terminated.
+pub struct Utf16Writer<'a> {
+    buf: &'a mut [u16],
+    index: usize,
+}
+
+impl<'a> Utf16Writer<'a> {
+    /// Creates a new [Utf16Writer] that writes its output into the provided buffer.
+    pub fn new(buf: &'a mut [u16]) -> Self {
+        Self { buf, index: 0 }
+    }
+}
+
+impl std::fmt::Write for Utf16Writer<'_> {
+    fn write_str(&mut self, s: &str) -> std::fmt::Result {
+        let max = self.buf.len() - 1;
+
+        for code_unit in s.encode_utf16() {
+            if self.index == max {
+                self.buf[self.index] = 0;
+                return Err(std::fmt::Error);
+            } else {
+                self.buf[self.index] = code_unit;
+                self.index += 1;
+            }
+        }
+
+        self.buf[self.index] = 0;
+
+        Ok(())
+    }
+}