Moved util from game module to crate level to add functions more global, outside of game.

Removed all `as` conversions lints and fixed code using them.

src/util/null_ascii_string.rs

@@ -0,0 +1,47 @@
+//! Null-terminated ascii string helpers
+
+// Modules
+pub mod error;
+
+// Exports
+pub use error::{ReadError, WriteError};
+
+/// Trait for reading null terminated ascii strings from a buffer
+pub trait NullAsciiString {
+	/// Reads a null terminated ascii string from this buffer and returns it
+	fn read_string(&self) -> Result<&ascii::AsciiStr, ReadError>;
+
+	/// Writes a null terminated ascii string to this buffer and returns it
+	fn write_string(&mut self, s: &ascii::AsciiStr) -> Result<&Self, WriteError>;
+}
+
+impl NullAsciiString for [u8] {
+	fn read_string(&self) -> Result<&ascii::AsciiStr, ReadError> {
+		// Find the first null and trim the buffer until it
+		let buf = match self.iter().position(|&b| b == b'\0') {
+			Some(idx) => &self[0..idx],
+			None => return Err(ReadError::NoNull),
+		};
+
+		// Then convert it from Ascii
+		ascii::AsciiStr::from_ascii(buf).map_err(ReadError::NotAscii)
+	}
+
+	fn write_string(&mut self, input: &ascii::AsciiStr) -> Result<&Self, WriteError> {
+		// If the input string doesn't fit into the buffer (excluding the null byte), return Err
+		if input.len() >= self.len() {
+			return Err(WriteError::TooLarge {
+				input_len:  input.len(),
+				buffer_len: self.len(),
+			});
+		}
+
+		// Else copy everything over and set the last byte to null
+		// Note: We leave all other bytes as they are, no need to set them to 0
+		self[0..input.len()].copy_from_slice(input.as_bytes());
+		self[input.len()] = 0;
+
+		// And return Ok with the buffer
+		Ok(self)
+	}
+}