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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity is distributed in the hope that it will be useful,
    // but WITHOUT ANY WARRANTY; without even the implied warranty of
    // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    // GNU General Public License for more details.

    // You should have received a copy of the GNU General Public License
    // along with Parity.  If not, see <http://www.gnu.org/licenses/>.

    use ::{UntrustedRlp, View, Compressible, encode, Stream, RlpStream};
    use commonrlps::{BLOCKS_RLP_SWAPPER, SNAPSHOT_RLP_SWAPPER};

    use std::collections::HashMap;
    use elastic_array::ElasticArray1024;

    /// Stores RLPs used for compression
    pub struct InvalidRlpSwapper<'a> {
    	invalid_to_valid: HashMap<&'a [u8], &'a [u8]>,
    	valid_to_invalid: HashMap<&'a [u8], &'a [u8]>,
    }

    impl<'a> InvalidRlpSwapper<'a> {
    	/// Construct a swapper from a list of common RLPs
    	pub fn new(rlps_to_swap: &[&'a [u8]], invalid_rlps: &[&'a [u8]]) -> Self {
    		if rlps_to_swap.len() > 0x7e {
    			panic!("Invalid usage, only 127 RLPs can be swappable.");
    		}
    		let mut invalid_to_valid = HashMap::new();
    		let mut valid_to_invalid = HashMap::new();
    		for (&rlp, &invalid) in rlps_to_swap.iter().zip(invalid_rlps.iter()) {
    			invalid_to_valid.insert(invalid, rlp);
    			valid_to_invalid.insert(rlp, invalid);
    		}
    		InvalidRlpSwapper {
    			invalid_to_valid: invalid_to_valid,
    			valid_to_invalid: valid_to_invalid
    		}
    	}
    	/// Get a valid RLP corresponding to an invalid one
    	fn get_valid(&self, invalid_rlp: &[u8]) -> Option<&[u8]> {
    		self.invalid_to_valid.get(invalid_rlp).cloned()
    	}
    	/// Get an invalid RLP corresponding to a valid one
    	fn get_invalid(&self, valid_rlp: &[u8]) -> Option<&[u8]> {
    		self.valid_to_invalid.get(valid_rlp).cloned()
    	}
    }

    /// Type of RLP indicating its origin database.
    pub enum RlpType {
    	/// RLP used in blocks database.
    	Blocks,
    	/// RLP used in snapshots.
    	Snapshot,
    }

    fn to_elastic(slice: &[u8]) -> ElasticArray1024<u8> {
    	let mut out = ElasticArray1024::new();
    	out.append_slice(slice);
    	out
    }

    fn map_rlp<F>(rlp: &UntrustedRlp, f: F) -> Option<ElasticArray1024<u8>> where
    	F: Fn(&UntrustedRlp) -> Option<ElasticArray1024<u8>> {
    	match rlp.iter()
    	.fold((false, RlpStream::new_list(rlp.item_count())),
    		|(is_some, mut acc), subrlp| {
      		let new = f(&subrlp);
      		if let Some(ref insert) = new {
      			acc.append_raw(&insert[..], 1);
      		} else {
      			acc.append_raw(subrlp.as_raw(), 1);
      		}
      		(is_some || new.is_some(), acc)
      	  }) {
      	(true, s) => Some(s.drain()),
      	_ => None,
      }
    }

    /// Replace common RLPs with invalid shorter ones.
    fn simple_compress(rlp: &UntrustedRlp, swapper: &InvalidRlpSwapper) -> ElasticArray1024<u8> {
    	if rlp.is_data() {
    		to_elastic(swapper.get_invalid(rlp.as_raw()).unwrap_or_else(|| rlp.as_raw()))
    	} else {
    		map_rlp(rlp, |r| Some(simple_compress(r, swapper))).unwrap_or_else(|| to_elastic(rlp.as_raw()))
    	}
    }

    /// Recover valid RLP from a compressed form.
    fn simple_decompress(rlp: &UntrustedRlp, swapper: &InvalidRlpSwapper) -> ElasticArray1024<u8> {
    	if rlp.is_data() {
    		to_elastic(swapper.get_valid(rlp.as_raw()).unwrap_or_else(|| rlp.as_raw()))
    	} else {
    		map_rlp(rlp, |r| Some(simple_decompress(r, swapper))).unwrap_or_else(|| to_elastic(rlp.as_raw()))
    	}
    }

    /// Replace common RLPs with invalid shorter ones, None if no compression achieved.
    /// Tries to compress data insides.
    fn deep_compress(rlp: &UntrustedRlp, swapper: &InvalidRlpSwapper) -> Option<ElasticArray1024<u8>> {
    	let simple_swap = ||
    		swapper.get_invalid(rlp.as_raw()).map(to_elastic);
    	if rlp.is_data() {
    		// Try to treat the inside as RLP.
    		return match rlp.payload_info() {
    			// Shortest decompressed account is 70, so simply try to swap the value.
    			Ok(ref p) if p.value_len < 70 => simple_swap(),
    			_ => {
    				if let Ok(d) = rlp.data() {
    					let internal_rlp = UntrustedRlp::new(d);
    					if let Some(new_d) = deep_compress(&internal_rlp, swapper) {
    						// If compressed put in a special list, with first element being invalid code.
    						let mut rlp = RlpStream::new_list(2);
    						rlp.append_raw(&[0x81, 0x7f], 1);
    						rlp.append_raw(&new_d[..], 1);
    						return Some(rlp.drain());
    					}
    				}
    				simple_swap()
    			},
    		};
    	}
    	// Iterate through RLP while checking if it has been compressed.
    	map_rlp(rlp, |r| deep_compress(r, swapper))
    }

    /// Recover valid RLP from a compressed form, None if no decompression achieved.
    /// Tries to decompress compressed data insides.
    fn deep_decompress(rlp: &UntrustedRlp, swapper: &InvalidRlpSwapper) -> Option<ElasticArray1024<u8>> {
    	let simple_swap = ||
    		swapper.get_valid(rlp.as_raw()).map(to_elastic);
    	// Simply decompress data.
    	if rlp.is_data() { return simple_swap(); }
    	match rlp.item_count() {
    		// Look for special compressed list, which contains nested data.
    		2 if rlp.at(0).map(|r| r.as_raw() == &[0x81, 0x7f]).unwrap_or(false) =>
    			rlp.at(1).ok().map_or(simple_swap(),
    			|r| deep_decompress(&r, swapper).map(|d| { let v = d.to_vec(); encode(&v) })),
    		// Iterate through RLP while checking if it has been compressed.
    		_ => map_rlp(rlp, |r| deep_decompress(r, swapper)),
      	}
    }

    impl<'a> Compressible for UntrustedRlp<'a> {
    	type DataType = RlpType;

    	fn compress(&self, t: RlpType) -> ElasticArray1024<u8> {
    		match t {
    			RlpType::Snapshot => simple_compress(self, &SNAPSHOT_RLP_SWAPPER),
    			RlpType::Blocks => deep_compress(self, &BLOCKS_RLP_SWAPPER).unwrap_or_else(|| to_elastic(self.as_raw())),
    		}
    	}

    	fn decompress(&self, t: RlpType) -> ElasticArray1024<u8> {
    		match t {
    			RlpType::Snapshot => simple_decompress(self, &SNAPSHOT_RLP_SWAPPER),
    			RlpType::Blocks => deep_decompress(self, &BLOCKS_RLP_SWAPPER).unwrap_or_else(|| to_elastic(self.as_raw())),
    		}
    	}
    }

    #[cfg(test)]
    mod tests {
    	use ::{UntrustedRlp, Compressible, View, RlpType};
    	use rlpcompression::InvalidRlpSwapper;

    	#[test]
    	fn invalid_rlp_swapper() {
    		let to_swap: &[&[u8]] = &[&[0x83, b'c', b'a', b't'], &[0x83, b'd', b'o', b'g']];
    		let invalid_rlp: &[&[u8]] = &[&[0x81, 0x00], &[0x81, 0x01]];
    		let swapper = InvalidRlpSwapper::new(to_swap, invalid_rlp);
    		assert_eq!(Some(invalid_rlp[0]), swapper.get_invalid(&[0x83, b'c', b'a', b't']));
    		assert_eq!(None, swapper.get_invalid(&[0x83, b'b', b'a', b't']));
    		assert_eq!(Some(to_swap[1]), swapper.get_valid(invalid_rlp[1]));
    	}

    	#[test]
    	fn simple_compression() {
    		let basic_account_rlp = vec![248, 68, 4, 2, 160, 86, 232, 31, 23, 27, 204, 85, 166, 255, 131, 69, 230, 146, 192, 248, 110, 91, 72, 224, 27, 153, 108, 173, 192, 1, 98, 47, 181, 227, 99, 180, 33, 160, 197, 210, 70, 1, 134, 247, 35, 60, 146, 126, 125, 178, 220, 199, 3, 192, 229, 0, 182, 83, 202, 130, 39, 59, 123, 250, 216, 4, 93, 133, 164, 112];
    		let rlp = UntrustedRlp::new(&basic_account_rlp);
    		let compressed = rlp.compress(RlpType::Snapshot).to_vec();
    		assert_eq!(compressed, vec![198, 4, 2, 129, 0, 129, 1]);
    		let compressed_rlp = UntrustedRlp::new(&compressed);
    		assert_eq!(compressed_rlp.decompress(RlpType::Snapshot).to_vec(), basic_account_rlp);
    	}

    	#[test]
    	fn data_compression() {
    		let data_basic_account_rlp = vec![184, 70, 248, 68, 4, 2, 160, 86, 232, 31, 23, 27, 204, 85, 166, 255, 131, 69, 230, 146, 192, 248, 110, 91, 72, 224, 27, 153, 108, 173, 192, 1, 98, 47, 181, 227, 99, 180, 33, 160, 197, 210, 70, 1, 134, 247, 35, 60, 146, 126, 125, 178, 220, 199, 3, 192, 229, 0, 182, 83, 202, 130, 39, 59, 123, 250, 216, 4, 93, 133, 164, 112];
    		let data_rlp = UntrustedRlp::new(&data_basic_account_rlp);
    		let compressed = data_rlp.compress(RlpType::Blocks).to_vec();
    		assert_eq!(compressed, vec![201, 129, 127, 198, 4, 2, 129, 0, 129, 1]);
    		let compressed_rlp = UntrustedRlp::new(&compressed);
    		assert_eq!(compressed_rlp.decompress(RlpType::Blocks).to_vec(), data_basic_account_rlp);
    	}

    	#[test]
    	fn nested_list_rlp() {
    		let nested_basic_account_rlp = vec![228, 4, 226, 2, 160, 86, 232, 31, 23, 27, 204, 85, 166, 255, 131, 69, 230, 146, 192, 248, 110, 91, 72, 224, 27, 153, 108, 173, 192, 1, 98, 47, 181, 227, 99, 180, 33];
    		let nested_rlp = UntrustedRlp::new(&nested_basic_account_rlp);
    		let compressed = nested_rlp.compress(RlpType::Blocks).to_vec();
    		assert_eq!(compressed, vec![197, 4, 195, 2, 129, 0]);
    		let compressed_rlp = UntrustedRlp::new(&compressed);
    		assert_eq!(compressed_rlp.decompress(RlpType::Blocks).to_vec(), nested_basic_account_rlp);
    		let compressed = nested_rlp.compress(RlpType::Snapshot).to_vec();
    		assert_eq!(compressed, vec![197, 4, 195, 2, 129, 0]);
    		let compressed_rlp = UntrustedRlp::new(&compressed);
    		assert_eq!(compressed_rlp.decompress(RlpType::Snapshot).to_vec(), nested_basic_account_rlp);
    	}

    	#[test]
    	fn malformed_rlp() {
    		let malformed = vec![248, 81, 128, 128, 128, 128, 128, 160, 12, 51, 241, 93, 69, 218, 74, 138, 79, 115, 227, 44, 216, 81, 46, 132, 85, 235, 96, 45, 252, 48, 181, 29, 75, 141, 217, 215, 86, 160, 109, 130, 160, 140, 36, 93, 200, 109, 215, 100, 241, 246, 99, 135, 92, 168, 149, 170, 114, 9, 143, 4, 93, 25, 76, 54, 176, 119, 230, 170, 154, 105, 47, 121, 10, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128];
    		let malformed_rlp = UntrustedRlp::new(&malformed);
    		assert_eq!(malformed_rlp.decompress(RlpType::Blocks).to_vec(), malformed);
    	}
    }

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