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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_COMPRESSOR_H
#define BITCOIN_COMPRESSOR_H
#include <prevector.h>
#include <primitives/transaction.h>
#include <script/script.h>
#include <serialize.h>
#include <span.h>
/**
* This saves us from making many heap allocations when serializing
* and deserializing compressed scripts.
*
* This prevector size is determined by the largest .resize() in the
* CompressScript function. The largest compressed script format is a
* compressed public key, which is 33 bytes.
*/
using CompressedScript = prevector<33, unsigned char>;
bool CompressScript(const CScript& script, CompressedScript& out);
unsigned int GetSpecialScriptSize(unsigned int nSize);
bool DecompressScript(CScript& script, unsigned int nSize, const CompressedScript& in);
/**
* Compress amount.
*
* nAmount is of type uint64_t and thus cannot be negative. If you're passing in
* a CAmount (int64_t), make sure to properly handle the case where the amount
* is negative before calling CompressAmount(...).
*
* @pre Function defined only for 0 <= nAmount <= MAX_MONEY.
*/
uint64_t CompressAmount(uint64_t nAmount);
uint64_t DecompressAmount(uint64_t nAmount);
/** Compact serializer for scripts.
*
* It detects common cases and encodes them much more efficiently.
* 3 special cases are defined:
* * Pay to pubkey hash (encoded as 21 bytes)
* * Pay to script hash (encoded as 21 bytes)
* * Pay to pubkey starting with 0x02, 0x03 or 0x04 (encoded as 33 bytes)
*
* Other scripts up to 121 bytes require 1 byte + script length. Above
* that, scripts up to 16505 bytes require 2 bytes + script length.
*/
struct ScriptCompression
{
/**
* make this static for now (there are only 6 special scripts defined)
* this can potentially be extended together with a new version for
* transactions, in which case this value becomes dependent on version
* and nHeight of the enclosing transaction.
*/
static const unsigned int nSpecialScripts = 6;
template<typename Stream>
void Ser(Stream &s, const CScript& script) {
CompressedScript compr;
if (CompressScript(script, compr)) {
s << Span{compr};
return;
}
unsigned int nSize = script.size() + nSpecialScripts;
s << VARINT(nSize);
s << Span{script};
}
template<typename Stream>
void Unser(Stream &s, CScript& script) {
unsigned int nSize = 0;
s >> VARINT(nSize);
if (nSize < nSpecialScripts) {
CompressedScript vch(GetSpecialScriptSize(nSize), 0x00);
s >> Span{vch};
DecompressScript(script, nSize, vch);
return;
}
nSize -= nSpecialScripts;
if (nSize > MAX_SCRIPT_SIZE) {
// Overly long script, replace with a short invalid one
script << OP_RETURN;
s.ignore(nSize);
} else {
script.resize(nSize);
s >> Span{script};
}
}
};
struct AmountCompression
{
template<typename Stream, typename I> void Ser(Stream& s, I val)
{
s << VARINT(CompressAmount(val));
}
template<typename Stream, typename I> void Unser(Stream& s, I& val)
{
uint64_t v;
s >> VARINT(v);
val = DecompressAmount(v);
}
};
/** wrapper for CTxOut that provides a more compact serialization */
struct TxOutCompression
{
FORMATTER_METHODS(CTxOut, obj) { READWRITE(Using<AmountCompression>(obj.nValue), Using<ScriptCompression>(obj.scriptPubKey)); }
};
#endif // BITCOIN_COMPRESSOR_H
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