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/*******************************************************************************
*
* Copyright (c) 2026 Haixing Hu.
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0.
*
******************************************************************************/
use std::io::{
Error,
ErrorKind,
Read,
Result,
};
use std::string::FromUtf8Error;
use crate::{
BinaryReadExt,
Leb128ReadExt,
};
/// Extension methods for reading length-prefixed UTF-8 strings.
pub trait StringReadExt: Read {
/// Reads a UTF-8 string with an unsigned LEB128 byte-length prefix.
///
/// # Parameters
/// - `max_len`: Maximum accepted UTF-8 payload length in bytes.
///
/// # Returns
/// The decoded string.
///
/// # Errors
/// Returns an I/O error for length or payload reads, [`ErrorKind::InvalidData`]
/// when the encoded length exceeds `max_len`, or [`ErrorKind::InvalidData`]
/// when the payload is not valid UTF-8.
fn read_utf8_string_uleb(&mut self, max_len: usize) -> Result<String>;
/// Reads a UTF-8 string with a canonical unsigned LEB128 byte-length prefix.
///
/// # Parameters
/// - `max_len`: Maximum accepted UTF-8 payload length in bytes.
///
/// # Returns
/// The decoded string.
///
/// # Errors
/// Returns an I/O error for length or payload reads, [`ErrorKind::InvalidData`]
/// when the length prefix is malformed or non-canonical, [`ErrorKind::InvalidData`]
/// when the encoded length exceeds `max_len`, or [`ErrorKind::InvalidData`]
/// when the payload is not valid UTF-8.
fn read_utf8_string_uleb_strict(&mut self, max_len: usize) -> Result<String>;
/// Reads a UTF-8 string with a big-endian `u16` byte-length prefix.
///
/// # Parameters
/// - `max_len`: Maximum accepted UTF-8 payload length in bytes.
///
/// # Returns
/// The decoded string.
///
/// # Errors
/// Returns an I/O error for length or payload reads, [`ErrorKind::InvalidData`]
/// when the encoded length exceeds `max_len`, or [`ErrorKind::InvalidData`]
/// when the payload is not valid UTF-8.
fn read_utf8_string_u16_be(&mut self, max_len: usize) -> Result<String>;
/// Reads a UTF-8 string with a little-endian `u16` byte-length prefix.
///
/// # Parameters
/// - `max_len`: Maximum accepted UTF-8 payload length in bytes.
///
/// # Returns
/// The decoded string.
///
/// # Errors
/// Returns an I/O error for length or payload reads, [`ErrorKind::InvalidData`]
/// when the encoded length exceeds `max_len`, or [`ErrorKind::InvalidData`]
/// when the payload is not valid UTF-8.
fn read_utf8_string_u16_le(&mut self, max_len: usize) -> Result<String>;
/// Reads a UTF-8 string with a big-endian `u32` byte-length prefix.
///
/// # Parameters
/// - `max_len`: Maximum accepted UTF-8 payload length in bytes.
///
/// # Returns
/// The decoded string.
///
/// # Errors
/// Returns an I/O error for length or payload reads, [`ErrorKind::InvalidData`]
/// when the encoded length exceeds `max_len`, or [`ErrorKind::InvalidData`]
/// when the payload is not valid UTF-8.
fn read_utf8_string_u32_be(&mut self, max_len: usize) -> Result<String>;
/// Reads a UTF-8 string with a little-endian `u32` byte-length prefix.
///
/// # Parameters
/// - `max_len`: Maximum accepted UTF-8 payload length in bytes.
///
/// # Returns
/// The decoded string.
///
/// # Errors
/// Returns an I/O error for length or payload reads, [`ErrorKind::InvalidData`]
/// when the encoded length exceeds `max_len`, or [`ErrorKind::InvalidData`]
/// when the payload is not valid UTF-8.
fn read_utf8_string_u32_le(&mut self, max_len: usize) -> Result<String>;
}
impl<T> StringReadExt for T
where
T: Read + ?Sized,
{
#[inline]
fn read_utf8_string_uleb(&mut self, max_len: usize) -> Result<String> {
read_utf8_string_uleb_impl(self, max_len)
}
#[inline]
fn read_utf8_string_uleb_strict(&mut self, max_len: usize) -> Result<String> {
read_utf8_string_uleb_strict_impl(self, max_len)
}
#[inline]
fn read_utf8_string_u16_be(&mut self, max_len: usize) -> Result<String> {
read_utf8_string_u16_be_impl(self, max_len)
}
#[inline]
fn read_utf8_string_u16_le(&mut self, max_len: usize) -> Result<String> {
read_utf8_string_u16_le_impl(self, max_len)
}
#[inline]
fn read_utf8_string_u32_be(&mut self, max_len: usize) -> Result<String> {
read_utf8_string_u32_be_impl(self, max_len)
}
#[inline]
fn read_utf8_string_u32_le(&mut self, max_len: usize) -> Result<String> {
read_utf8_string_u32_le_impl(self, max_len)
}
}
fn read_utf8_string_uleb_impl<T>(reader: &mut T, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
let len = reader.read_uleb_usize()?;
read_utf8_payload(reader, len, max_len)
}
fn read_utf8_string_uleb_strict_impl<T>(reader: &mut T, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
let len = reader.read_uleb_usize_strict()?;
read_utf8_payload(reader, len, max_len)
}
fn read_utf8_string_u16_be_impl<T>(reader: &mut T, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
let len = reader.read_u16_be()? as usize;
read_utf8_payload(reader, len, max_len)
}
fn read_utf8_string_u16_le_impl<T>(reader: &mut T, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
let len = reader.read_u16_le()? as usize;
read_utf8_payload(reader, len, max_len)
}
fn read_utf8_string_u32_be_impl<T>(reader: &mut T, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
let len = reader.read_u32_be()? as usize;
read_utf8_payload(reader, len, max_len)
}
fn read_utf8_string_u32_le_impl<T>(reader: &mut T, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
let len = reader.read_u32_le()? as usize;
read_utf8_payload(reader, len, max_len)
}
fn read_utf8_payload<T>(reader: &mut T, len: usize, max_len: usize) -> Result<String>
where
T: Read + ?Sized,
{
if len > max_len {
return Err(length_exceeded_error(len, max_len));
}
let mut bytes = vec![0; len];
reader.read_exact(&mut bytes)?;
String::from_utf8(bytes).map_err(invalid_utf8_error)
}
fn length_exceeded_error(len: usize, max_len: usize) -> Error {
Error::new(
ErrorKind::InvalidData,
format!("string length {len} exceeds maximum length of {max_len} bytes"),
)
}
fn invalid_utf8_error(error: FromUtf8Error) -> Error {
Error::new(
ErrorKind::InvalidData,
format!("length-prefixed string is not valid UTF-8: {error}"),
)
}