str.rs

// Copyright (C) 2022 Parity Technologies (UK) Ltd. (admin@parity.io)
// This file is a part of the scale-value crate.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//         http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use super::DecodeError;
use codec::{Compact, Decode};

/// This represents a string, but defers proper decoding of it until it's asked for,
/// and avoids allocating.
pub struct Str<'a> {
	len: usize,
	bytes: &'a [u8],
}

impl<'a> Str<'a> {
	pub(crate) fn new_from(bytes: &mut &'a [u8]) -> Result<Self, DecodeError> {
		// Strings are just encoded the same as bytes; a length prefix and then
		// the raw bytes. Pluck these out but don't do any further work.
		let len = <Compact<u32>>::decode(bytes)?.0 as usize;
		let str_bytes = &bytes[..len];
		*bytes = &bytes[len..];
		Ok(Str { len, bytes: str_bytes })
	}
	/// The length of the string.
	pub fn len(&self) -> usize {
		self.len
	}
	/// Is the string zero bytes long?
	pub fn is_empty(&self) -> bool {
		self.len == 0
	}
	/// return a string, failing if the bytes could not be properly utf8-decoded.
	pub fn as_str(&self) -> Result<&'a str, DecodeError> {
		std::str::from_utf8(self.bytes).map_err(DecodeError::InvalidStr)
	}
	/// Return the raw bytes representing this string.
	pub fn as_bytes(&self) -> &'a [u8] {
		self.bytes
	}
}