xref: /aosp_15_r20/external/pigweed/pw_tokenizer/rust/pw_tokenizer/internal.rs (revision 61c4878ac05f98d0ceed94b57d316916de578985)

// Copyright 2023 The Pigweed Authors
//
// 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
//
//     https://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 core::cmp::min;

use pw_status::{Error, Result};
use pw_stream::{Cursor, Write};
use pw_varint::VarintEncode;

use crate::MessageWriter;

// The `Argument` enum is used to marshal arguments to pass to the tokenization
// engine.
pub enum Argument<'a> {
    String(&'a str),
    Varint(i32),
    Varint64(i64),
    Char(u8),
}

impl<'a> From<&'a str> for Argument<'a> {
    fn from(val: &'a str) -> Self {
        Self::String(val)
    }
}

impl<'a> From<i32> for Argument<'a> {
    fn from(val: i32) -> Self {
        Self::Varint(val)
    }
}

impl<'a> From<u32> for Argument<'a> {
    fn from(val: u32) -> Self {
        Self::Varint64(val as i64)
    }
}

// Wraps a `Cursor` so that `tokenize_to_buffer` and `tokenize_to_writer` can
// share implementations.  It is not meant to be used outside of
// `tokenize_to_buffer`.
struct CursorMessageWriter<'a> {
    cursor: Cursor<&'a mut [u8]>,
}

impl MessageWriter for CursorMessageWriter<'_> {
    fn new() -> Self {
        // Ensure `tokenize_to_buffer` never calls `new()`.
        unimplemented!();
    }

    fn write(&mut self, data: &[u8]) -> Result<()> {
        self.cursor.write_all(data)
    }

    fn remaining(&self) -> usize {
        self.cursor.remaining()
    }

    fn finalize(self) -> Result<()> {
        // Ensure `tokenize_to_buffer` never calls `finalize()`.
        unimplemented!();
    }
}

// Encode a string in Tokenizer format: length byte + data with the high bit of
// the length byte used to signal that the string was truncated.
pub fn encode_string<W: MessageWriter>(writer: &mut W, value: &str) -> Result<()> {
    const MAX_STRING_LENGTH: usize = 0x7f;

    let string_bytes = value.as_bytes();

    // Limit the encoding to the lesser of 127 or the available space in the buffer.
    let max_len = min(MAX_STRING_LENGTH, writer.remaining() - 1);
    let overflow = max_len < string_bytes.len();
    let len = min(max_len, string_bytes.len());

    // First byte of an encoded string is it's length.
    let mut header = len as u8;

    // The high bit of the first byte is used to indicate if the string was
    // truncated.
    if overflow {
        header |= 0x80;
    }
    writer.write(&[header])?;

    writer.write(&string_bytes[..len])
}

// Write out a tokenized message to an already created `MessageWriter`.
fn tokenize_engine<W: crate::MessageWriter>(
    writer: &mut W,
    token: u32,
    args: &[Argument<'_>],
) -> Result<()> {
    writer.write(&token.to_le_bytes()[..])?;
    for arg in args {
        match arg {
            Argument::String(s) => encode_string(writer, s)?,
            Argument::Varint(i) => {
                let mut encode_buffer = [0u8; 10];
                let len = i.varint_encode(&mut encode_buffer)?;
                writer.write(&encode_buffer[..len])?;
            }
            Argument::Varint64(i) => {
                let mut encode_buffer = [0u8; 10];
                let len = i.varint_encode(&mut encode_buffer)?;
                writer.write(&encode_buffer[..len])?;
            }
            Argument::Char(c) => writer.write(&[*c])?,
        }
    }

    Ok(())
}

#[inline(never)]
pub fn tokenize_to_buffer(buffer: &mut [u8], token: u32, args: &[Argument<'_>]) -> Result<usize> {
    let mut writer = CursorMessageWriter {
        cursor: Cursor::new(buffer),
    };
    tokenize_engine(&mut writer, token, args)?;
    Ok(writer.cursor.position())
}

#[inline(never)]
pub fn tokenize_to_buffer_no_args(buffer: &mut [u8], token: u32) -> Result<usize> {
    let token_bytes = &token.to_le_bytes()[..];
    let token_len = token_bytes.len();
    if buffer.len() < token_len {
        return Err(Error::OutOfRange);
    }
    buffer[..token_len].copy_from_slice(token_bytes);

    Ok(token_len)
}

#[inline(never)]
pub fn tokenize_to_writer<W: crate::MessageWriter>(
    token: u32,
    args: &[Argument<'_>],
) -> Result<()> {
    let mut writer = W::new();
    tokenize_engine(&mut writer, token, args)?;
    writer.finalize()
}

#[inline(never)]
pub fn tokenize_to_writer_no_args<W: crate::MessageWriter>(token: u32) -> Result<()> {
    let mut writer = W::new();
    writer.write(&token.to_le_bytes()[..])?;
    writer.finalize()
}

#[cfg(test)]
mod test {
    use pw_stream::Seek;

    use super::*;

    fn do_string_encode_test<const BUFFER_LEN: usize>(value: &str, expected: &[u8]) {
        let mut buffer = [0u8; BUFFER_LEN];
        let mut writer = CursorMessageWriter {
            cursor: Cursor::new(&mut buffer),
        };
        encode_string(&mut writer, value).unwrap();

        let len = writer.cursor.stream_position().unwrap() as usize;
        let buffer = writer.cursor.into_inner();

        assert_eq!(len, expected.len());
        assert_eq!(&buffer[..len], expected);
    }

    #[test]
    fn test_string_encode() {
        do_string_encode_test::<64>("test", b"\x04test");
        do_string_encode_test::<4>("test", b"\x83tes");
        do_string_encode_test::<1>("test", b"\x80");

        // Truncates when the string does not fit.
        do_string_encode_test::<64>(
            "testtesttesttesttesttesttesttesttesttesttesttesttesttesttesttest",
            b"\xbftesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttes",
        );

        // Truncates when string is over 127 bytes.
        do_string_encode_test::<1024>(
            "testtesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttest",
            b"\xfftesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttesttes",
        );
    }
}