Implementing the Read Trait in Rust

Rust's standard library provides powerful traits for handling input and output operations. The std::io::Read trait is fundamental for consuming data from various sources. This challenge will test your understanding of this trait by implementing it for a custom data structure.

Problem Description

Your task is to implement the std::io::Read trait for a custom struct, MemoryBuffer. This struct will hold a slice of bytes in memory and will be treated as a readable source of data. You'll need to correctly handle reading data into a provided buffer, keeping track of the current position within your MemoryBuffer, and returning the appropriate number of bytes read or an error.

Key Requirements:

• Implement the std::io::Read trait for a struct MemoryBuffer<'a>.
• The MemoryBuffer should wrap a &'a [u8] (a byte slice).
• The read method should copy data from the MemoryBuffer's internal slice into the provided buf.
• The read method should advance an internal cursor to track the position within the MemoryBuffer.
• The read method should return the number of bytes actually read.
• The read method should return io::ErrorKind::UnexpectedEof when there is no more data to read.

Expected Behavior:

When read is called, it should attempt to fill the provided buf with data from the MemoryBuffer, starting from the current position. It should not read beyond the end of the MemoryBuffer's data. Subsequent calls to read should continue from where the previous read left off.

Edge Cases:

• Reading when the MemoryBuffer is empty.
• Reading when the requested buffer size is larger than the remaining data in the MemoryBuffer.
• Reading when the provided buffer buf is empty.
• Multiple consecutive reads.

Examples

Example 1:

Input:
let data = vec![1, 2, 3, 4, 5];
let mut memory_buffer = MemoryBuffer::new(&data);
let mut buffer = [0; 3];

// Call read
let bytes_read = memory_buffer.read(&mut buffer).unwrap();

Output:
bytes_read = 3
buffer = [1, 2, 3]
Explanation: The first read attempts to fill a buffer of size 3. The `MemoryBuffer` has 5 bytes, so it successfully copies the first 3 bytes into `buffer`. The internal cursor advances by 3.

Example 2:

Input:
let data = vec![1, 2, 3, 4, 5];
let mut memory_buffer = MemoryBuffer::new(&data);
let mut buffer = [0; 3];

// First read
memory_buffer.read(&mut buffer).unwrap(); // bytes_read = 3, buffer = [1, 2, 3]

let mut buffer2 = [0; 3];
// Second read
let bytes_read_2 = memory_buffer.read(&mut buffer2).unwrap();

Output:
bytes_read_2 = 2
buffer2 = [4, 5, 0]
Explanation: The second read also attempts to fill a buffer of size 3. However, only 2 bytes remain in the `MemoryBuffer` (bytes 4 and 5). So, only these 2 bytes are copied. The `buffer2` will contain `[4, 5]` in its first two positions, followed by its initial value (0 in this case).

Example 3: (End of stream)

Input:
let data = vec![1, 2];
let mut memory_buffer = MemoryBuffer::new(&data);
let mut buffer = [0; 3];

// First read
memory_buffer.read(&mut buffer).unwrap(); // bytes_read = 2

let mut buffer2 = [0; 3];
// Second read, should result in EOF
let result = memory_buffer.read(&mut buffer2);

Output:
result = Err(io::Error { kind: UnexpectedEof, .. })
Explanation: After reading all available data (2 bytes), the `MemoryBuffer` is exhausted. The subsequent read attempt returns an `io::Error` with the kind `io::ErrorKind::UnexpectedEof`.

Constraints

• The MemoryBuffer will store a slice of bytes (&'a [u8]).
• The read method's buf parameter will be a mutable slice &mut [u8].
• You must use std::io::Read and std::io::Result.
• The implementation should be efficient for in-memory operations.

Notes

• Remember to manage an internal cursor or index to keep track of the current reading position within the MemoryBuffer.
• The read method is expected to return Ok(0) only if the provided buf is empty and there is no data to read. If buf is non-empty and there's no data, UnexpectedEof is the correct error.
• Consider the behavior of std::io::Read::read when buf.len() is 0. It should return Ok(0).