src/coins.h

   1 // Copyright (c) 2009-2010 Satoshi Nakamoto
   2 // Copyright (c) 2009-2016 The Bitcoin Core developers
   3 // Distributed under the MIT software license, see the accompanying
   4 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5
   6 #ifndef BITCOIN_COINS_H
   7 #define BITCOIN_COINS_H
   8
   9 #include "primitives/transaction.h"
  10 #include "compressor.h"
  11 #include "core_memusage.h"
  12 #include "hash.h"
  13 #include "memusage.h"
  14 #include "serialize.h"
  15 #include "uint256.h"
  16
  17 #include <assert.h>
  18 #include <stdint.h>
  19
  20 #include <boost/foreach.hpp>
  21 #include <unordered_map>
  22
  23 /**
  24  * Pruned version of CTransaction: only retains metadata and unspent transaction outputs
  25  *
  26  * Serialized format:
  27  * - VARINT(nVersion)
  28  * - VARINT(nCode)
  29  * - unspentness bitvector, for vout[2] and further; least significant byte first
  30  * - the non-spent CTxOuts (via CTxOutCompressor)
  31  * - VARINT(nHeight)
  32  *
  33  * The nCode value consists of:
  34  * - bit 0: IsCoinBase()
  35  * - bit 1: vout[0] is not spent
  36  * - bit 2: vout[1] is not spent
  37  * - The higher bits encode N, the number of non-zero bytes in the following bitvector.
  38  *   - In case both bit 1 and bit 2 are unset, they encode N-1, as there must be at
  39  *     least one non-spent output).
  40  *
  41  * Example: 0104835800816115944e077fe7c803cfa57f29b36bf87c1d358bb85e
  42  *          <><><--------------------------------------------><---->
  43  *          |  \                  |                             /
  44  *    version   code             vout[1]                  height
  45  *
  46  *    - version = 1
  47  *    - code = 4 (vout[1] is not spent, and 0 non-zero bytes of bitvector follow)
  48  *    - unspentness bitvector: as 0 non-zero bytes follow, it has length 0
  49  *    - vout[1]: 835800816115944e077fe7c803cfa57f29b36bf87c1d35
  50  *               * 8358: compact amount representation for 60000000000 (600 BTC)
  51  *               * 00: special txout type pay-to-pubkey-hash
  52  *               * 816115944e077fe7c803cfa57f29b36bf87c1d35: address uint160
  53  *    - height = 203998
  54  *
  55  *
  56  * Example: 0109044086ef97d5790061b01caab50f1b8e9c50a5057eb43c2d9563a4eebbd123008c988f1a4a4de2161e0f50aac7f17e7f9555caa486af3b
  57  *          <><><--><--------------------------------------------------><----------------------------------------------><---->
  58  *         /  \   \                     |                                                           |                     /
  59  *  version  code  unspentness       vout[4]                                                     vout[16]           height
  60  *
  61  *  - version = 1
  62  *  - code = 9 (coinbase, neither vout[0] or vout[1] are unspent,
  63  *                2 (1, +1 because both bit 1 and bit 2 are unset) non-zero bitvector bytes follow)
  64  *  - unspentness bitvector: bits 2 (0x04) and 14 (0x4000) are set, so vout[2+2] and vout[14+2] are unspent
  65  *  - vout[4]: 86ef97d5790061b01caab50f1b8e9c50a5057eb43c2d9563a4ee
  66  *             * 86ef97d579: compact amount representation for 234925952 (2.35 BTC)
  67  *             * 00: special txout type pay-to-pubkey-hash
  68  *             * 61b01caab50f1b8e9c50a5057eb43c2d9563a4ee: address uint160
  69  *  - vout[16]: bbd123008c988f1a4a4de2161e0f50aac7f17e7f9555caa4
  70  *              * bbd123: compact amount representation for 110397 (0.001 BTC)
  71  *              * 00: special txout type pay-to-pubkey-hash
  72  *              * 8c988f1a4a4de2161e0f50aac7f17e7f9555caa4: address uint160
  73  *  - height = 120891
  74  */
  75 class CCoins
  76 {
  77 public:
  78     //! whether transaction is a coinbase
  79     bool fCoinBase;
  80
  81     //! unspent transaction outputs; spent outputs are .IsNull(); spent outputs at the end of the array are dropped
  82     std::vector<CTxOut> vout;
  83
  84     //! at which height this transaction was included in the active block chain
  85     int nHeight;
  86
  87     //! version of the CTransaction; accesses to this value should probably check for nHeight as well,
  88     //! as new tx version will probably only be introduced at certain heights
  89     int nVersion;
  90
  91     void FromTx(const CTransaction &tx, int nHeightIn) {
  92         fCoinBase = tx.IsCoinBase();
  93         vout = tx.vout;
  94         nHeight = nHeightIn;
  95         nVersion = tx.nVersion;
  96         ClearUnspendable();
  97     }
  98
  99     //! construct a CCoins from a CTransaction, at a given height
 100     CCoins(const CTransaction &tx, int nHeightIn) {
 101         FromTx(tx, nHeightIn);
 102     }
 103
 104     void Clear() {
 105         fCoinBase = false;
 106         std::vector<CTxOut>().swap(vout);
 107         nHeight = 0;
 108         nVersion = 0;
 109     }
 110
 111     //! empty constructor
 112     CCoins() : fCoinBase(false), vout(0), nHeight(0), nVersion(0) { }
 113
 114     //!remove spent outputs at the end of vout
 115     void Cleanup() {
 116         while (vout.size() > 0 && vout.back().IsNull())
 117             vout.pop_back();
 118         if (vout.empty())
 119             std::vector<CTxOut>().swap(vout);
 120     }
 121
 122     void ClearUnspendable() {
 123         BOOST_FOREACH(CTxOut &txout, vout) {
 124             if (txout.scriptPubKey.IsUnspendable())
 125                 txout.SetNull();
 126         }
 127         Cleanup();
 128     }
 129
 130     void swap(CCoins &to) {
 131         std::swap(to.fCoinBase, fCoinBase);
 132         to.vout.swap(vout);
 133         std::swap(to.nHeight, nHeight);
 134         std::swap(to.nVersion, nVersion);
 135     }
 136
 137     //! equality test
 138     friend bool operator==(const CCoins &a, const CCoins &b) {
 139          // Empty CCoins objects are always equal.
 140          if (a.IsPruned() && b.IsPruned())
 141              return true;
 142          return a.fCoinBase == b.fCoinBase &&
 143                 a.nHeight == b.nHeight &&
 144                 a.nVersion == b.nVersion &&
 145                 a.vout == b.vout;
 146     }
 147     friend bool operator!=(const CCoins &a, const CCoins &b) {
 148         return !(a == b);
 149     }
 150
 151     void CalcMaskSize(unsigned int &nBytes, unsigned int &nNonzeroBytes) const;
 152
 153     bool IsCoinBase() const {
 154         return fCoinBase;
 155     }
 156
 157     template<typename Stream>
 158     void Serialize(Stream &s) const {
 159         unsigned int nMaskSize = 0, nMaskCode = 0;
 160         CalcMaskSize(nMaskSize, nMaskCode);
 161         bool fFirst = vout.size() > 0 && !vout[0].IsNull();
 162         bool fSecond = vout.size() > 1 && !vout[1].IsNull();
 163         assert(fFirst || fSecond || nMaskCode);
 164         unsigned int nCode = 8*(nMaskCode - (fFirst || fSecond ? 0 : 1)) + (fCoinBase ? 1 : 0) + (fFirst ? 2 : 0) + (fSecond ? 4 : 0);
 165         // version
 166         ::Serialize(s, VARINT(this->nVersion));
 167         // header code
 168         ::Serialize(s, VARINT(nCode));
 169         // spentness bitmask
 170         for (unsigned int b = 0; b<nMaskSize; b++) {
 171             unsigned char chAvail = 0;
 172             for (unsigned int i = 0; i < 8 && 2+b*8+i < vout.size(); i++)
 173                 if (!vout[2+b*8+i].IsNull())
 174                     chAvail |= (1 << i);
 175             ::Serialize(s, chAvail);
 176         }
 177         // txouts themself
 178         for (unsigned int i = 0; i < vout.size(); i++) {
 179             if (!vout[i].IsNull())
 180                 ::Serialize(s, CTxOutCompressor(REF(vout[i])));
 181         }
 182         // coinbase height
 183         ::Serialize(s, VARINT(nHeight));
 184     }
 185
 186     template<typename Stream>
 187     void Unserialize(Stream &s) {
 188         unsigned int nCode = 0;
 189         // version
 190         ::Unserialize(s, VARINT(this->nVersion));
 191         // header code
 192         ::Unserialize(s, VARINT(nCode));
 193         fCoinBase = nCode & 1;
 194         std::vector<bool> vAvail(2, false);
 195         vAvail[0] = (nCode & 2) != 0;
 196         vAvail[1] = (nCode & 4) != 0;
 197         unsigned int nMaskCode = (nCode / 8) + ((nCode & 6) != 0 ? 0 : 1);
 198         // spentness bitmask
 199         while (nMaskCode > 0) {
 200             unsigned char chAvail = 0;
 201             ::Unserialize(s, chAvail);
 202             for (unsigned int p = 0; p < 8; p++) {
 203                 bool f = (chAvail & (1 << p)) != 0;
 204                 vAvail.push_back(f);
 205             }
 206             if (chAvail != 0)
 207                 nMaskCode--;
 208         }
 209         // txouts themself
 210         vout.assign(vAvail.size(), CTxOut());
 211         for (unsigned int i = 0; i < vAvail.size(); i++) {
 212             if (vAvail[i])
 213                 ::Unserialize(s, REF(CTxOutCompressor(vout[i])));
 214         }
 215         // coinbase height
 216         ::Unserialize(s, VARINT(nHeight));
 217         Cleanup();
 218     }
 219
 220     //! mark a vout spent
 221     bool Spend(uint32_t nPos);
 222
 223     //! check whether a particular output is still available
 224     bool IsAvailable(unsigned int nPos) const {
 225         return (nPos < vout.size() && !vout[nPos].IsNull());
 226     }
 227
 228     //! check whether the entire CCoins is spent
 229     //! note that only !IsPruned() CCoins can be serialized
 230     bool IsPruned() const {
 231         BOOST_FOREACH(const CTxOut &out, vout)
 232             if (!out.IsNull())
 233                 return false;
 234         return true;
 235     }
 236
 237     size_t DynamicMemoryUsage() const {
 238         size_t ret = memusage::DynamicUsage(vout);
 239         BOOST_FOREACH(const CTxOut &out, vout) {
 240             ret += RecursiveDynamicUsage(out.scriptPubKey);
 241         }
 242         return ret;
 243     }
 244 };
 245
 246 class SaltedTxidHasher
 247 {
 248 private:
 249     /** Salt */
 250     const uint64_t k0, k1;
 251
 252 public:
 253     SaltedTxidHasher();
 254
 255     /**
 256      * This *must* return size_t. With Boost 1.46 on 32-bit systems the
 257      * unordered_map will behave unpredictably if the custom hasher returns a
 258      * uint64_t, resulting in failures when syncing the chain (#4634).
 259      */
 260     size_t operator()(const uint256& txid) const {
 261         return SipHashUint256(k0, k1, txid);
 262     }
 263 };
 264
 265 struct CCoinsCacheEntry
 266 {
 267     CCoins coins; // The actual cached data.
 268     unsigned char flags;
 269
 270     enum Flags {
 271         DIRTY = (1 << 0), // This cache entry is potentially different from the version in the parent view.
 272         FRESH = (1 << 1), // The parent view does not have this entry (or it is pruned).
 273         /* Note that FRESH is a performance optimization with which we can
 274          * erase coins that are fully spent if we know we do not need to
 275          * flush the changes to the parent cache.  It is always safe to
 276          * not mark FRESH if that condition is not guaranteed.
 277          */
 278     };
 279
 280     CCoinsCacheEntry() : coins(), flags(0) {}
 281 };
 282
 283 typedef std::unordered_map<uint256, CCoinsCacheEntry, SaltedTxidHasher> CCoinsMap;
 284
 285 /** Cursor for iterating over CoinsView state */
 286 class CCoinsViewCursor
 287 {
 288 public:
 289     CCoinsViewCursor(const uint256 &hashBlockIn): hashBlock(hashBlockIn) {}
 290     virtual ~CCoinsViewCursor();
 291
 292     virtual bool GetKey(uint256 &key) const = 0;
 293     virtual bool GetValue(CCoins &coins) const = 0;
 294     virtual unsigned int GetValueSize() const = 0;
 295
 296     virtual bool Valid() const = 0;
 297     virtual void Next() = 0;
 298
 299     //! Get best block at the time this cursor was created
 300     const uint256 &GetBestBlock() const { return hashBlock; }
 301 private:
 302     uint256 hashBlock;
 303 };
 304
 305 /** Abstract view on the open txout dataset. */
 306 class CCoinsView
 307 {
 308 public:
 309     //! Retrieve the CCoins (unspent transaction outputs) for a given txid
 310     virtual bool GetCoins(const uint256 &txid, CCoins &coins) const;
 311
 312     //! Just check whether we have data for a given txid.
 313     //! This may (but cannot always) return true for fully spent transactions
 314     virtual bool HaveCoins(const uint256 &txid) const;
 315
 316     //! Retrieve the block hash whose state this CCoinsView currently represents
 317     virtual uint256 GetBestBlock() const;
 318
 319     //! Do a bulk modification (multiple CCoins changes + BestBlock change).
 320     //! The passed mapCoins can be modified.
 321     virtual bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
 322
 323     //! Get a cursor to iterate over the whole state
 324     virtual CCoinsViewCursor *Cursor() const;
 325
 326     //! As we use CCoinsViews polymorphically, have a virtual destructor
 327     virtual ~CCoinsView() {}
 328 };
 329
 330
 331 /** CCoinsView backed by another CCoinsView */
 332 class CCoinsViewBacked : public CCoinsView
 333 {
 334 protected:
 335     CCoinsView *base;
 336
 337 public:
 338     CCoinsViewBacked(CCoinsView *viewIn);
 339     bool GetCoins(const uint256 &txid, CCoins &coins) const;
 340     bool HaveCoins(const uint256 &txid) const;
 341     uint256 GetBestBlock() const;
 342     void SetBackend(CCoinsView &viewIn);
 343     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
 344     CCoinsViewCursor *Cursor() const;
 345 };
 346
 347
 348 class CCoinsViewCache;
 349
 350 /**
 351  * A reference to a mutable cache entry. Encapsulating it allows us to run
 352  *  cleanup code after the modification is finished, and keeping track of
 353  *  concurrent modifications.
 354  */
 355 class CCoinsModifier
 356 {
 357 private:
 358     CCoinsViewCache& cache;
 359     CCoinsMap::iterator it;
 360     size_t cachedCoinUsage; // Cached memory usage of the CCoins object before modification
 361     CCoinsModifier(CCoinsViewCache& cache_, CCoinsMap::iterator it_, size_t usage);
 362
 363 public:
 364     CCoins* operator->() { return &it->second.coins; }
 365     CCoins& operator*() { return it->second.coins; }
 366     ~CCoinsModifier();
 367     friend class CCoinsViewCache;
 368 };
 369
 370 /** CCoinsView that adds a memory cache for transactions to another CCoinsView */
 371 class CCoinsViewCache : public CCoinsViewBacked
 372 {
 373 protected:
 374     /* Whether this cache has an active modifier. */
 375     bool hasModifier;
 376
 377
 378     /**
 379      * Make mutable so that we can "fill the cache" even from Get-methods
 380      * declared as "const".
 381      */
 382     mutable uint256 hashBlock;
 383     mutable CCoinsMap cacheCoins;
 384
 385     /* Cached dynamic memory usage for the inner CCoins objects. */
 386     mutable size_t cachedCoinsUsage;
 387
 388 public:
 389     CCoinsViewCache(CCoinsView *baseIn);
 390     ~CCoinsViewCache();
 391
 392     // Standard CCoinsView methods
 393     bool GetCoins(const uint256 &txid, CCoins &coins) const;
 394     bool HaveCoins(const uint256 &txid) const;
 395     uint256 GetBestBlock() const;
 396     void SetBestBlock(const uint256 &hashBlock);
 397     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
 398
 399     /**
 400      * Check if we have the given tx already loaded in this cache.
 401      * The semantics are the same as HaveCoins(), but no calls to
 402      * the backing CCoinsView are made.
 403      */
 404     bool HaveCoinsInCache(const uint256 &txid) const;
 405
 406     /**
 407      * Return a pointer to CCoins in the cache, or NULL if not found. This is
 408      * more efficient than GetCoins. Modifications to other cache entries are
 409      * allowed while accessing the returned pointer.
 410      */
 411     const CCoins* AccessCoins(const uint256 &txid) const;
 412
 413     /**
 414      * Return a modifiable reference to a CCoins. If no entry with the given
 415      * txid exists, a new one is created. Simultaneous modifications are not
 416      * allowed.
 417      */
 418     CCoinsModifier ModifyCoins(const uint256 &txid);
 419
 420     /**
 421      * Return a modifiable reference to a CCoins. Assumes that no entry with the given
 422      * txid exists and creates a new one. This saves a database access in the case where
 423      * the coins were to be wiped out by FromTx anyway.  This should not be called with
 424      * the 2 historical coinbase duplicate pairs because the new coins are marked fresh, and
 425      * in the event the duplicate coinbase was spent before a flush, the now pruned coins
 426      * would not properly overwrite the first coinbase of the pair. Simultaneous modifications
 427      * are not allowed.
 428      */
 429     CCoinsModifier ModifyNewCoins(const uint256 &txid, bool coinbase);
 430
 431     /**
 432      * Push the modifications applied to this cache to its base.
 433      * Failure to call this method before destruction will cause the changes to be forgotten.
 434      * If false is returned, the state of this cache (and its backing view) will be undefined.
 435      */
 436     bool Flush();
 437
 438     /**
 439      * Removes the transaction with the given hash from the cache, if it is
 440      * not modified.
 441      */
 442     void Uncache(const uint256 &txid);
 443
 444     //! Calculate the size of the cache (in number of transactions)
 445     unsigned int GetCacheSize() const;
 446
 447     //! Calculate the size of the cache (in bytes)
 448     size_t DynamicMemoryUsage() const;
 449
 450     /**
 451      * Amount of bitcoins coming in to a transaction
 452      * Note that lightweight clients may not know anything besides the hash of previous transactions,
 453      * so may not be able to calculate this.
 454      *
 455      * @param[in] tx    transaction for which we are checking input total
 456      * @return  Sum of value of all inputs (scriptSigs)
 457      */
 458     CAmount GetValueIn(const CTransaction& tx) const;
 459
 460     //! Check whether all prevouts of the transaction are present in the UTXO set represented by this view
 461     bool HaveInputs(const CTransaction& tx) const;
 462
 463     const CTxOut &GetOutputFor(const CTxIn& input) const;
 464
 465     friend class CCoinsModifier;
 466
 467 private:
 468     CCoinsMap::const_iterator FetchCoins(const uint256 &txid) const;
 469
 470     /**
 471      * By making the copy constructor private, we prevent accidentally using it when one intends to create a cache on top of a base cache.
 472      */
 473     CCoinsViewCache(const CCoinsViewCache &);
 474 };
 475
 476 #endif // BITCOIN_COINS_H