Switch CCoinsView and chainstate db from per-txid to per-txout

This patch makes several related changes:
* Changes the CCoinsView virtual methods (GetCoins, HaveCoins, ...)
  to be COutPoint/Coin-based rather than txid/CCoins-based.
* Changes the chainstate db to a new incompatible format that is also
  COutPoint/Coin based.
* Implements reconstruction code for hash_serialized_2.
* Adapts the coins_tests unit tests (thanks to Russell Yanofsky).

A side effect of the new CCoinsView model is that we can no longer
use the (unreliable) test for transaction outputs in the UTXO set
to determine whether we already have a particular transaction.

1 files changed, 7 insertions, 13 deletions

diff --git a/src/rest.cpp b/src/rest.cpp
index 4a71010094..16c8c4f529 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -47,6 +47,9 @@ struct CCoin {
 
     ADD_SERIALIZE_METHODS;
 
+    CCoin() : nHeight(0) {}
+    CCoin(Coin&& in) : nHeight(in.nHeight), out(std::move(in.out)) {}
+
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action)
     {
@@ -509,20 +512,11 @@ static bool rest_getutxos(HTTPRequest* req, const std::string& strURIPart)
             view.SetBackend(viewMempool); // switch cache backend to db+mempool in case user likes to query mempool
 
         for (size_t i = 0; i < vOutPoints.size(); i++) {
-            CCoins coins;
-            uint256 hash = vOutPoints[i].hash;
             bool hit = false;
-            if (view.GetCoins(hash, coins)) {
-                if (coins.IsAvailable(vOutPoints[i].n) && !mempool.isSpent(vOutPoints[i])) {
-                    hit = true;
-                    // Safe to index into vout here because IsAvailable checked if it's off the end of the array, or if
-                    // n is valid but points to an already spent output (IsNull).
-                    CCoin coin;
-                    coin.nHeight = coins.nHeight;
-                    coin.out = coins.vout.at(vOutPoints[i].n);
-                    assert(!coin.out.IsNull());
-                    outs.push_back(coin);
-                }
+            Coin coin;
+            if (view.GetCoins(vOutPoints[i], coin) && !mempool.isSpent(vOutPoints[i])) {
+                hit = true;
+                outs.emplace_back(std::move(coin));
             }
 
             hits.push_back(hit);