Working

src/block.rs

@@ -1,6 +1,11 @@
 use std::fmt::Formatter;
 use std::str::FromStr;
 
+use rand::Rng;
+use rand::prelude::SliceRandom;
+
+use crate::embed::EmbedAlgorithm;
+
 /// Block mode for embedded data
 #[derive(Debug)]
 pub struct BlockMode {
@@ -68,3 +73,53 @@ impl FromStr for BlockMode {
 		})
 	}
 }
+
+#[derive(Debug)]
+pub struct BlockPlacement<'a> {
+	data: &'a mut [u8],
+	block_size: usize,
+	blocks: Vec<usize>,
+}
+
+impl<'a> BlockPlacement<'a>
+{
+	// Attempts to create a new block placement
+	//
+	// # Errors
+	//
+	// Will fail if the data is too small to hold all the blocks
+	pub fn new<R>(data: &'a mut [u8], block_size: usize, algorithm: &EmbedAlgorithm, embed_size: usize, rng: &mut R) -> Result<Self, String>
+    	where R: Rng + ?Sized
+	{
+		// Total size of the embed (crc included)
+		let embedded_size = algorithm.embedded_size(embed_size);
+
+		// Number of blocks
+		let blocks_num = (embedded_size as f64 / block_size as f64).ceil() as usize;
+
+
+		// Safe distance for spacing the blocks equally
+		let safe_spacing = data.len() / blocks_num;
+		if safe_spacing*blocks_num < embedded_size {
+			return Err(format!("Failed to determine a safe spacing size: {safe_spacing} < {}", embedded_size as f64 / blocks_num as f64))
+		}
+
+		// Blocks in the resulting data
+		let mut blocks = Vec::with_capacity(blocks_num);
+		for i in 0 .. blocks_num {
+			// Choose a random position within [0, safe_spacing[ for the block
+			let pos = rng.gen_range(i*safe_spacing..(i+1)*safe_spacing);
+
+			blocks.push(pos);
+		}
+
+		// Shuffle the block order
+		blocks.shuffle(rng);
+
+		Ok(Self {
+			data,
+			block_size,
+			blocks
+		})
+	}
+}

src/embed.rs

@@ -12,6 +12,15 @@ pub enum EmbedAlgorithm {
 }
 
 impl EmbedAlgorithm {
+	/// Get the size of the data (in bytes) once embedded by the algorithm
+	pub fn embedded_size(&self, size: usize) -> usize {
+		match self {
+			EmbedAlgorithm::Lo(bits) => {
+				((size * 8) as f64 / *bits as f64).ceil() as usize
+			}
+		}
+	}
+
 	pub fn max_size(&self, blockmode: &BlockMode, info: &Box<dyn ImageInfo>) -> usize {
 		let blocks_num = info.size() / blockmode.len;
 
@@ -22,7 +31,7 @@ impl EmbedAlgorithm {
 		}
 	}
 
-	pub fn next_block(&self, original_data: &mut [u8], embed_data: &BitVec<u8>, mut embed_offset: usize, blockmode: &BlockMode) -> usize {
+	pub fn next_block(&self, original_data: &mut [u8], mut data_pos: usize, embed_data: &BitVec<u8>, mut embed_offset: usize, blockmode: &BlockMode) -> (usize, usize) {
 		match self {
 			EmbedAlgorithm::Lo(bits) => {
 				let mask = (1<<bits) -1;
@@ -37,23 +46,27 @@ impl EmbedAlgorithm {
 					result
 				}
 
-				for i in 0..(blockmode.len-blockmode.crc_len)
+				let start = embed_offset;
+				while embed_offset-start < (blockmode.len-blockmode.crc_len)*8
 				{
-					let hi = std::cmp::min(embed_offset+*bits as usize, embed_data.len())-embed_offset;
+					let hi = std::cmp::min(*bits as usize, embed_data.len() - embed_offset);
 					let embed = bits_to_byte(embed_data.get(embed_offset..embed_offset+hi).unwrap(), hi as u8);
 
-					original_data[i] &= !mask;
-					original_data[i] |= embed;
+					original_data[data_pos] &= !mask;
+					original_data[data_pos] |= embed;
 					
+					data_pos += 1;
 					embed_offset += hi;
 				}
+
+				// TODO: WRITE CRC
 			}
 		}
 		
-		embed_offset
+		(data_pos, embed_offset)
 	}
 
-	pub fn read_block(&self, encoded_data: &[u8], incoming: &mut BitVec<u8>, blockmode: &BlockMode) {
+	pub fn read_block(&self, encoded_data: &[u8], mut data_pos: usize, incoming: &mut BitVec<u8>, blockmode: &BlockMode) -> usize {
 		match self {
 			EmbedAlgorithm::Lo(bits) => {
 				fn push(vec: &mut BitVec<u8>, bits: u8, b: u8)
@@ -64,17 +77,18 @@ impl EmbedAlgorithm {
 					}
 				}
 
-				let mut i = 0;
 				let start = incoming.len();
 				while incoming.len()-start < (blockmode.len-blockmode.crc_len)*8
 				{
-					push(incoming, *bits, encoded_data[i]);
-					i += 1;
+					push(incoming, *bits, encoded_data[data_pos]);
+					data_pos += 1;
 				}
 
 				// TODO: Read CRC and verify
 			}
 		}
+
+		data_pos
 	}
 }
 

src/main.rs

@@ -13,6 +13,7 @@ use std::str::FromStr;
 
 use bitvec::vec::BitVec;
 use block::BlockMode;
+use block::BlockPlacement;
 use embed::EmbedAlgorithm;
 use getopts::Matches;
 use getopts::Options;
@@ -121,16 +122,17 @@ fn decode(image: String, matches: Matches, header_only: bool) -> Result<(), Stri
 
 	// Read header
 	let mut read_data = BitVec::<u8>::new();
+	let mut data_pos = 0;
 	while read_data.len() < 9*8
 	{
-		algorithm.read_block(&data[read_data.len()/8..], &mut read_data, &blockmode);
+		data_pos = algorithm.read_block(&data, data_pos, &mut read_data, &blockmode);
 	}
 
 	let (version, blockmode, data_len, comment_len) = Header::from_data(read_data.as_bitslice());
 	// Read header comment
 	while read_data.len() < (9+comment_len as usize)*8
 	{
-		algorithm.read_block(&data[read_data.len()/8..], &mut read_data, &blockmode);
+		data_pos = algorithm.read_block(&data, data_pos, &mut read_data, &blockmode);
 	}
 
 	// Extract comment:
@@ -157,10 +159,10 @@ fn decode(image: String, matches: Matches, header_only: bool) -> Result<(), Stri
 	let data_start = 9+comment_len as usize;
 	while read_data.len() < (data_start + data_len as usize)*8
 	{
-		algorithm.read_block(&data[read_data.len()/8..], &mut read_data, &blockmode);
+		data_pos = algorithm.read_block(&data, data_pos, &mut read_data, &blockmode);
 	}
 
-	for i in 0..32
+	for i in 60..80
 	{
 		let b = read_byte(&read_data[(data_start+i)*8..(data_start+1+i)*8]);
 		println!("{i} : {b:08b} ({})", b as char);
@@ -192,11 +194,18 @@ fn encode(image: String, matches: Matches) -> Result<Vec<u8>, String> {
 			.unwrap_or(format!("{}x{}", info.width(), info.height()))
 			.as_str(),
 	)?;
+
+
 	let max_size = algorithm.max_size(&blockmode, &info);
 
 	let embed_data = std::fs::read(&embed_file)
 		.map_err(|err| format!("Failed to read embed file `{embed_file}`: {err}"))?;
 
+	let mut rand = ChaCha8Rng::from_seed(seed);
+	//let placement = BlockPlacement::new(data.as_mut_slice(), blockmode.len, &algorithm, embed_data.len(), &mut rand)?;
+
+	//return Ok(vec![]);
+
 	// Get header
 	let header = Header {
 		blockmode,
@@ -252,24 +261,33 @@ fn encode(image: String, matches: Matches) -> Result<Vec<u8>, String> {
 
 
 	let mut embed_offset = 0;
+	let mut data_pos = 0;
 	for i in 0 .. blocks_num
 	{
-		let mut new_offset = algorithm.next_block(
-			&mut data.as_mut_slice()[i*header.blockmode.len..],
+		println!("block: {i}/{embed_offset}/{data_pos}");
+		(data_pos, embed_offset) = algorithm.next_block(
+			&mut data.as_mut_slice(),
+			data_pos,
 			&bv,
 			embed_offset,
 			&header.blockmode);
-		new_offset += header.blockmode.crc_len*8;
-
-		embed_offset = new_offset;
 	}
 	println!("{}", bv.len());
-	// TODO: WRITE CRC
 
 
-	for i in 70..99 {
+	for i in 10..80 {
 		let b = (data[i*2] & 0b1111) | ((data[i*2+1] & 0b1111) << 4);
-		println!("{b:08b}, {}", b as char);
+		println!("{i}: {b:08b}, {}", b as char);
+		fn read_byte(slice: &bitvec::slice::BitSlice<u8>) -> u8
+		{
+			let mut result = 0;
+			for i in 0..8
+			{
+				result |= (slice[i as usize] as u8) << i;
+			}
+			result
+		}
+		println!("{i}+ {b:08b}, {}", read_byte(&bv[i*8..(i+1)*8]) as char);
 	}
 	let outfile = File::create("out.png").unwrap();
 	let ref mut w = BufWriter::new(Box::new(outfile) as Box<dyn Write>);