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