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use std::mem;
/// A type that represents an object that consumes a memory slice on demand.
/// The consumer lives as long as the slice is alive.
pub struct ByteConsumer<'b> {
/// The memory slice that get's consumed.
buffer: &'b [u8],
}
impl<'b> ByteConsumer<'b> {
/// Creates a new ByteConsumer from a stream of bytes.
pub fn new(stream: &'b [u8]) -> ByteConsumer {
ByteConsumer { buffer: stream }
}
/// Consumes `nr_bytes` from the original slice and returns an `Option` that holds a reference
/// to a memory slice which is `nr_bytes` long. If `nr_bytes` is greater than the remaining
/// bytes of the consumer's slice then `None` is returned.
///
/// *Note*: The memory slice returned is not copied, it's a reference to the initial slice
///
/// # Arguments
///
/// * `nr_bytes` - A number representing the number of bytes to consume
///
///
/// # Examples
///
/// ```
/// use byte_consumer::ByteConsumer;
/// let mut consumer = ByteConsumer::new(&[10, 20, 30, 40]);
/// let first_two = consumer.consume(2);
/// let second_two = consumer.consume(2);
///
/// assert!(first_two.is_some());
/// assert_eq!(first_two.unwrap(), [10, 20]);
///
/// assert!(second_two.is_some());
/// assert_eq!(second_two.unwrap(), [30, 40]);
///
/// assert_eq!(consumer.consume(1), None);
/// ```
///
#[inline]
pub fn consume(&mut self, nr_bytes: usize) -> Option<&'b [u8]> {
if nr_bytes > self.buffer.len() || nr_bytes == 0 {
None
} else {
let (res, remaining) = self.buffer.split_at(nr_bytes);
self.buffer = remaining;
Some(res)
}
}
/// Consumes `nr_bytes` from the original slice and returns a reference to a memory slice which is `nr_bytes` long.
///
/// *Note*: The memory slice returned is not copied, it's a reference to the initial slice
///
/// # Arguments
///
/// * `nr_bytes` - A number representing the number of bytes to consume
///
/// # Panics
///
/// If `nr_bytes` is greater than the remaining bytes in the consumer's slice then
/// then it panics with a custom message.
///
/// # Examples
///
/// ```
/// use byte_consumer::ByteConsumer;
/// let mut consumer = ByteConsumer::new(&[10, 20, 30, 40]);
/// let first_two = consumer.consume_unchecked(2);
/// let second_two = consumer.consume_unchecked(2);
///
/// assert_eq!(first_two, [10, 20]);
/// assert_eq!(second_two, [30, 40]);
///
/// // let next = consumer.consume_unchecked(1) <-- This should panic.
/// ```
#[inline]
pub fn consume_unchecked(&mut self, nr_bytes: usize) -> &'b [u8] {
self.consume(nr_bytes).expect(format!(
"[ByteConsumer]: The number of bytes requested ({}) is greater that the number of bytes available ({}).",
nr_bytes,
self.buffer.len()
).as_str())
}
/// Consumes as many bytes as the size of type `T` and converts them to an object of type `T`.
/// If the size of type `T` in number of bytes is greater than the remaining bytes in the consumer's buffer
/// then it returns None.
///
/// *Note*: The type `T` must implement the `Copy` trait as we are moving the bytes out of the slice
///
/// # Examples
///
/// ```
/// use byte_consumer::ByteConsumer;
///
/// let mut consumer = ByteConsumer::new(&[0x1, 0x2, 0x1, 0x1]);
/// let first_byte_as_u8: Option<u8> = consumer.consume_as();
/// let second_byte_as_u8 = consumer.consume_as::<u8>();
/// let last_two_as_u16 = consumer.consume_as::<u16>();
///
/// assert!(first_byte_as_u8.is_some());
/// assert_eq!(first_byte_as_u8.unwrap(), 1);
///
/// assert!(second_byte_as_u8.is_some());
/// assert_eq!(second_byte_as_u8.unwrap(), 2);
///
/// assert!(last_two_as_u16.is_some());
/// assert_eq!(last_two_as_u16.unwrap(), 257);
///
/// assert_eq!(consumer.consume_as::<u32>(), None);
/// ```
#[inline]
pub fn consume_as<T>(&mut self) -> Option<T> {
let bytes = self.consume(mem::size_of::<T>());
match bytes {
Some(bytes) => unsafe { Some(std::ptr::read(bytes.as_ptr() as *const T)) },
None => None,
}
}
/// Consumes as many bytes as the size of type `T` and converts them to an object of type `T`.
///
/// *Note*: The type `T` must implement the `Copy` trait as we are moving the bytes out of the slice
///
/// # Panics
///
/// If size of type `T` in bytes is greater than the remaining bytes in the consumer's buffer
/// then it panics with a custom message.
///
/// # Examples
///
/// ```
/// use byte_consumer::ByteConsumer;
///
/// let mut consumer = ByteConsumer::new(&[0x1, 0x2, 0x1, 0x1]);
/// let first_byte_as_u8: u8 = consumer.consume_as_unchecked();
/// let second_byte_as_u8 = consumer.consume_as_unchecked::<u8>();
/// let last_two_as_u16 = consumer.consume_as_unchecked::<u16>();
///
/// assert_eq!(first_byte_as_u8, 1);
/// assert_eq!(second_byte_as_u8, 2);
/// assert_eq!(last_two_as_u16, 257);
///
/// // let next = consumer.consume_as_unchecked::<u32>() <-- This should panic.
/// ```
#[inline]
pub fn consume_as_unchecked<T: Copy>(&mut self) -> T {
self.consume_as::<T>().expect(format!(
"[ByteConsumer]: The number of bytes ({}) in the type ({}) is greater that the number of bytes available ({}).",
mem::size_of::<T>(),
std::any::type_name::<T>(),
self.buffer.len()
).as_str())
}
/// Returns whether there are remaining bytes to consume or not.
/// # Examples
///
/// ```
/// // Calling has_remaining on a consumer with an empty slice should return false.
/// use byte_consumer::ByteConsumer;
/// let mut consumer = ByteConsumer::new(&[]);
/// assert!(!consumer.has_remaining());
/// ```
///
/// ```
/// // Calling has_remaining on a non consumed or partially consumed slice should return true.
/// // After consuming everything, we should get false
/// use byte_consumer::ByteConsumer;
/// let mut consumer = ByteConsumer::new(&[1, 2, 3, 4]);
/// assert!(consumer.has_remaining());
/// consumer.consume(3);
/// assert!(consumer.has_remaining());
/// consumer.consume(1);
/// assert!(!consumer.has_remaining());
/// ```
#[inline]
pub fn has_remaining(&mut self) -> bool {
self.buffer.len() != 0
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_consume_bytes() {
let mut consumer = ByteConsumer::new(&[10, 20, 30, 40, 50]);
let first_two = consumer.consume(2);
let third = consumer.consume(1);
let last_two = consumer.consume(2);
assert!(first_two.is_some());
assert_eq!(first_two.unwrap(), [10, 20]);
assert!(third.is_some());
assert_eq!(third.unwrap(), [30]);
assert!(last_two.is_some());
assert_eq!(last_two.unwrap(), [40, 50]);
assert!(consumer.consume(10).is_none());
assert!(consumer.consume(100).is_none());
}
#[test]
fn test_consume_bytes_unchecked() {
let mut consumer = ByteConsumer::new(&[10, 20, 30, 40, 50]);
assert_eq!(consumer.consume_unchecked(2), [10, 20]);
assert_eq!(consumer.consume_unchecked(3), [30, 40, 50]);
}
#[test]
fn test_consume_bytes_iteratively() {
let view = [10, 20, 30, 40, 50];
let mut index = 0;
let mut consumer = ByteConsumer::new(&view);
while let Some(bytes) = consumer.consume(1) {
assert!(!bytes.is_empty());
assert_eq!(bytes.len(), 1);
assert_eq!(view[index], bytes[0]);
index += 1;
}
assert_eq!(index, view.len());
}
#[test]
fn test_consume_bytes_iteratively_unchecked() {
let view = [10, 20, 30, 40, 50];
let mut index = 0;
let mut consumer = ByteConsumer::new(&view);
while consumer.has_remaining() {
assert_eq!(view[index], consumer.consume_unchecked(1)[0]);
index += 1;
}
assert_eq!(index, view.len());
}
#[test]
#[should_panic]
fn test_panic_on_uncecked_consume() {
let mut consumer = ByteConsumer::new(&[10, 20, 30, 40]);
assert_eq!(consumer.consume_unchecked(4), [10, 20, 30, 40]); // This should not panic
consumer.consume_unchecked(1); // This should panic
}
#[test]
#[should_panic]
fn test_panic_on_unchecked_consume_iteratively() {
let view = [10, 20, 30, 40];
let mut consumer = ByteConsumer::new(&view);
for _ in 0..view.len() + 1 {
consumer.consume_unchecked(1);
}
}
#[test]
fn test_consume_on_empty_slice() {
let mut consumer = ByteConsumer::new(&[]);
assert!(consumer.consume(1).is_none());
assert!(consumer.consume_as::<u128>().is_none());
}
#[test]
fn test_has_remaining_on_empty_slice() {
let mut consumer = ByteConsumer::new(&[]);
assert!(!consumer.has_remaining());
}
#[test]
fn test_has_remaining_on_unconsumed_slice() {
let mut consumer = ByteConsumer::new(&[1, 2, 3, 4]);
assert!(consumer.has_remaining());
}
#[test]
fn test_has_remaining_on_partially_consumed_slice() {
let mut consumer = ByteConsumer::new(&[1, 2, 3, 4]);
consumer.consume(3);
assert!(consumer.has_remaining());
}
#[test]
fn test_has_remaining_on_totaly_consumed_slice() {
let mut consumer = ByteConsumer::new(&[1, 2, 3, 4]);
consumer.consume(4);
assert!(!consumer.has_remaining());
}
}