mikrotik_rs/protocol/sentence.rs
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use super::word::{Word, WordError};
/// A parser for parsing bytes into sentences in the Mikrotik API sentence format.
///
/// The Mikrotik API uses a custom protocol to communicate. Each message is a sentence
/// composed of words. This structure represents a sentence and allows iterating over
/// its words.
///
/// Each word in a sentence is encoded with a length prefix, followed by the word's bytes.
/// The length is encoded in a variable number of bytes to save space for short words.
///
/// More details about the protocol can be found in the Mikrotik Wiki:
/// [Mikrotik API Protocol](https://wiki.mikrotik.com/wiki/Manual:API#Protocol)
#[derive(Debug)]
pub struct Sentence<'a> {
data: &'a [u8],
position: usize,
}
impl<'a> Sentence<'a> {
/// Creates a new `Sentence` instance for parsing the given data slice.
///
/// # Arguments
///
/// * `data` - A slice of bytes representing the data of the Mikrotik sentence.
pub fn new(data: &'a [u8]) -> Self {
Self { data, position: 0 }
}
}
impl<'a> Iterator for Sentence<'a> {
type Item = Result<Word<'a>, SentenceError>;
/// Advances the [`Iterator`] and returns the next [`Word`] in the [`Sentence`].
///
/// The word is returned as a slice of the original data. This avoids copying
/// data but means the lifetime of the returned slice is tied to the lifetime
/// of the data passed to `Sentence::new`.
///
/// # Errors
///
/// Returns an `Err` if there's an issue decoding the length of the next word
/// or if the data cannot be interpreted as a valid UTF-8 string slice.
fn next(&mut self) -> Option<Self::Item> {
if self.position >= self.data.len() {
return None;
}
let mut start = self.position;
match read_length(&self.data[start..]) {
Ok((lenght, bytes_read)) => {
// Last word is empty, so we are done.
if lenght == 0 {
return None;
}
// Start reading the content skipping the length bytes
start += bytes_read;
// Will never run on architectures where usize is < 32 bits so converting to usize is safe.
let end = start + lenght as usize;
let word = || -> Result<Word, SentenceError> {
// Parse the word
let data = &self
.data
.get(start..end)
.ok_or(SentenceError::PrefixLength)?;
let word = Word::try_from(*data).map_err(SentenceError::from)?;
Ok(word)
}();
// Update the position for the next iteration
self.position = end;
Some(word)
}
Err(e) => Some(Err(e)),
}
}
}
/// Specific errors that can occur while processing a byte sequence into a [`Sentence`].
///
/// Provides information about issues related to converting a sequence of bytes into a [`Sentence`].
#[derive(Debug, PartialEq)]
pub enum SentenceError {
/// Error indicating that a sequence of bytes could not be parsed into a [`Word`].
WordError(WordError),
/// Error indicating that the prefix lenght of a [`Sentence`] is incorrect.
/// This could happen if the length of the word is invalid or the data is corrupted.
PrefixLength,
// Error indicating that the category of the sentence is missing.
// This could happen if the sentence does not start with a recognized category.
// Valid categories are `!done`, `!re`, `!trap`, and `!fatal`.
//Category,
}
impl From<WordError> for SentenceError {
fn from(e: WordError) -> Self {
Self::WordError(e)
}
}
/// Returns the length and the number of bytes read.
fn read_length(data: &[u8]) -> Result<(u32, usize), SentenceError> {
let mut c: u32 = data[0] as u32;
if c & 0x80 == 0x00 {
Ok((c, 1))
} else if c & 0xC0 == 0x80 {
c &= !0xC0;
c <<= 8;
c += data[1] as u32;
return Ok((c, 2));
} else if c & 0xE0 == 0xC0 {
c &= !0xE0;
c <<= 8;
c += data[1] as u32;
c <<= 8;
c += data[2] as u32;
return Ok((c, 3));
} else if c & 0xF0 == 0xE0 {
c &= !0xF0;
c <<= 8;
c += data[1] as u32;
c <<= 8;
c += data[2] as u32;
c <<= 8;
c += data[3] as u32;
return Ok((c, 4));
} else if c & 0xF8 == 0xF0 {
c = data[1] as u32;
c <<= 8;
c += data[2] as u32;
c <<= 8;
c += data[3] as u32;
c <<= 8;
c += data[4] as u32;
return Ok((c, 5));
} else {
Err(SentenceError::PrefixLength)
}
}
#[cfg(test)]
mod tests {
use crate::protocol::word::{Word, WordCategory};
use super::*;
#[test]
fn test_sentence_iterator() {
let data: &[u8] = &[
0x05, b'!', b'd', b'o', b'n', b'e', // Word: !done
0x08, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Word: .tag=123
0x0C, b'=', b'n', b'a', b'm', b'e', b'=', b'e', b't', b'h', b'e', b'r',
b'1', // Word: =name=ether1
0x00, // End of sentence
];
let mut sentence = Sentence::new(data);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Category(WordCategory::Done)
);
assert_eq!(sentence.next().unwrap().unwrap(), Word::Tag(123));
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Attribute(("name", Some("ether1")).into())
);
assert_eq!(sentence.next(), None);
}
#[test]
fn test_sentence_category_error() {
// Test case where the first word is not a category
let data: &[u8] = &[
0x0A, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Word: .tag=123
0x0D, b'=', b'n', b'a', b'm', b'e', b'=', b'e', b't', b'h', b'e', b'r',
b'1', // Word: =name=ether1
];
let mut sentence = Sentence::new(data);
assert!(sentence.next().unwrap().is_err());
}
#[test]
fn test_sentence_length_error() {
// Test case where length is invalid
let data: &[u8] = &[
0xF8, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Invalid length prefix
];
let mut sentence = Sentence::new(data);
assert!(sentence.next().unwrap().is_err());
}
#[test]
fn test_complete_sentence_parsing() {
let data: &[u8] = &[
0x05, b'!', b'd', b'o', b'n', b'e', // Word: !done
0x08, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Word: .tag=123
0x0C, b'=', b'n', b'a', b'm', b'e', b'=', b'e', b't', b'h', b'e', b'r',
b'1', // Word: =name=ether1
0x00, // End of sentence
];
let mut sentence = Sentence::new(data);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Category(WordCategory::Done)
);
assert_eq!(sentence.next().unwrap().unwrap(), Word::Tag(123));
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Attribute(("name", Some("ether1")).into())
);
assert_eq!(sentence.next(), None);
}
#[test]
fn test_sentence_with_invalid_length() {
let data: &[u8] = &[
0xF8, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Invalid length prefix
];
let mut sentence = Sentence::new(data);
assert!(sentence.next().unwrap().is_err());
}
#[test]
fn test_sentence_without_category() {
let data: &[u8] = &[
0x0A, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Word: .tag=123
0x0D, b'=', b'n', b'a', b'm', b'e', b'=', b'e', b't', b'h', b'e', b'r',
b'1', // Word: =name=ether1
];
let mut sentence = Sentence::new(data);
assert!(sentence.next().unwrap().is_err());
}
#[test]
fn test_mixed_words_sentence() {
let data: &[u8] = &[
0x03, b'!', b'r', b'e', // Word: !re
0x04, b'=', b'a', b'=', b'b', // Word: =a=b
0x08, b'.', b't', b'a', b'g', b'=', b'4', b'5', b'6', // Word: .tag=456
0x00, // End of sentence
];
let mut sentence = Sentence::new(data);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Category(WordCategory::Reply)
);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Attribute(("a", Some("b")).into())
);
assert_eq!(sentence.next().unwrap().unwrap(), Word::Tag(456));
assert_eq!(sentence.next(), None);
}
#[test]
fn test_sentence_with_fatal_message() {
let data: &[u8] = &[
0x06, b'!', b'f', b'a', b't', b'a', b'l', 0x0B, b's', b'e', b'r', b'v', b'e', b'r',
b' ', b'd', b'o', b'w', b'n', // Word: !fatal server down
0x00, // End of sentence
];
let mut sentence = Sentence::new(data);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Category(WordCategory::Fatal)
);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Message("server down")
);
assert_eq!(sentence.next(), None);
}
#[test]
fn test_complete_sentence_with_extra_data() {
let data: &[u8] = &[
0x05, b'!', b'd', b'o', b'n', b'e', // Word: !done
0x08, b'.', b't', b'a', b'g', b'=', b'1', b'2', b'3', // Word: .tag=123
0x0C, b'=', b'n', b'a', b'm', b'e', b'=', b'e', b't', b'h', b'e', b'r',
b'1', // Word: =name=ether1
0x00, // End of sentence
0x07, b'!', b'd', b'o', b'n', b'e', // Extra data: !done
];
let mut sentence = Sentence::new(data);
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Category(WordCategory::Done)
);
assert_eq!(sentence.next().unwrap().unwrap(), Word::Tag(123));
assert_eq!(
sentence.next().unwrap().unwrap(),
Word::Attribute(("name", Some("ether1")).into())
);
assert_eq!(sentence.next(), None);
// Confirm that extra data is ignored after the end of the sentence
assert_eq!(sentence.next(), None);
}
}