Implement MultiSignReserve amendment [RIPD-1647]:

Reduces the account reserve for a multisigning SignerList from
(conditionally) 3 to 10 OwnerCounts to (unconditionally) 1
OwnerCount.  Includes a transition process.

src/ripple/app/tx/impl/SetSignerList.cpp

@@ -218,11 +218,19 @@ SetSignerList::replaceSignerList ()
     auto const sle = view().peek(accountKeylet);
 
     // Compute new reserve.  Verify the account has funds to meet the reserve.
-    auto const oldOwnerCount = (*sle)[sfOwnerCount];
-    std::uint32_t const addedOwnerCount = ownerCountDelta (signers_.size ());
+    std::uint32_t const oldOwnerCount {(*sle)[sfOwnerCount]};
 
-    auto const newReserve =
-        view().fees().accountReserve(oldOwnerCount + addedOwnerCount);
+    // The required reserve changes based on featureMultiSignReserve...
+    int addedOwnerCount {1};
+    std::uint32_t flags {lsfOneOwnerCount};
+    if (! ctx_.view().rules().enabled(featureMultiSignReserve))
+    {
+        addedOwnerCount = signerCountBasedOwnerCountDelta (signers_.size ());
+        flags = 0;
+    }
+
+    XRPAmount const newReserve {
+        view().fees().accountReserve(oldOwnerCount + addedOwnerCount)};
 
     // We check the reserve against the starting balance because we want to
     // allow dipping into the reserve to pay fees.  This behavior is consistent
@@ -233,15 +241,15 @@ SetSignerList::replaceSignerList ()
     // Everything's ducky.  Add the ltSIGNER_LIST to the ledger.
     auto signerList = std::make_shared<SLE>(signerListKeylet);
     view().insert (signerList);
-    writeSignersToSLE (signerList);
+    writeSignersToSLE (signerList, flags);
 
     auto viewJ = ctx_.app.journal ("View");
     // Add the signer list to the account's directory.
-    auto page = dirAdd(ctx_.view (), ownerDirKeylet,
+    auto const page = dirAdd (ctx_.view (), ownerDirKeylet,
         signerListKeylet.key, false, describeOwnerDir (account_), viewJ);
 
     JLOG(j_.trace()) << "Create signer list for account " <<
-        toBase58(account_) << ": " << (page ? "success" : "failure");
+        toBase58 (account_) << ": " << (page ? "success" : "failure");
 
     if (!page)
         return tecDIR_FULL;
@@ -283,8 +291,16 @@ SetSignerList::removeSignersFromLedger (Keylet const& accountKeylet,
     if (!signers)
         return tesSUCCESS;
 
-    STArray const& actualList = signers->getFieldArray (sfSignerEntries);
-    int const removeFromOwnerCount = ownerCountDelta (actualList.size()) * -1;
+    // There are two different ways that the OwnerCount could be managed.
+    // If the lsfOneOwnerCount bit is set then remove just one owner count.
+    // Otherwise use the pre-MultiSignReserve amendment calculation.
+    int removeFromOwnerCount = -1;
+    if ((signers->getFlags() & lsfOneOwnerCount) == 0)
+    {
+        STArray const& actualList = signers->getFieldArray (sfSignerEntries);
+        removeFromOwnerCount =
+            signerCountBasedOwnerCountDelta (actualList.size()) * -1;
+    }
 
     // Remove the node from the account directory.
     auto const hint = (*signers)[sfOwnerNode];
@@ -305,13 +321,14 @@ SetSignerList::removeSignersFromLedger (Keylet const& accountKeylet,
 }
 
 void
-SetSignerList::writeSignersToSLE (SLE::pointer const& ledgerEntry) const
+SetSignerList::writeSignersToSLE (
+    SLE::pointer const& ledgerEntry, std::uint32_t flags) const
 {
-    // Assign the quorum.
+    // Assign the quorum, default SignerListID, and flags.
     ledgerEntry->setFieldU32 (sfSignerQuorum, quorum_);
-
-    // For now, assign the default SignerListID.
     ledgerEntry->setFieldU32 (sfSignerListID, defaultSignerListID_);
+    if (flags) // Only set flags if they are non-default (default is zero).
+        ledgerEntry->setFieldU32 (sfFlags, flags);
 
     // Create the SignerListArray one SignerEntry at a time.
     STArray toLedger (signers_.size ());
@@ -330,8 +347,12 @@ SetSignerList::writeSignersToSLE (SLE::pointer const& ledgerEntry) const
 
 // The return type is signed so it is compatible with the 3rd argument
 // of adjustOwnerCount() (which must be signed).
+//
+// NOTE: This way of computing the OwnerCount associated with a SignerList
+// is valid until the featureMultiSignReserve amendment passes.  Once it
+// passes then just 1 OwnerCount is associated with a SignerList.
 int
-SetSignerList::ownerCountDelta (std::size_t entryCount)
+SetSignerList::signerCountBasedOwnerCountDelta (std::size_t entryCount)
 {
     // We always compute the full change in OwnerCount, taking into account:
     //  o The fact that we're adding/removing a SignerList and

src/ripple/app/tx/impl/SetSignerList.h

@@ -87,9 +87,14 @@ private:
 
     TER removeSignersFromLedger (Keylet const& accountKeylet,
         Keylet const& ownerDirKeylet, Keylet const& signerListKeylet);
-    void writeSignersToSLE (SLE::pointer const& ledgerEntry) const;
+    void writeSignersToSLE (
+        SLE::pointer const& ledgerEntry, std::uint32_t flags) const;
 
-    static int ownerCountDelta (std::size_t entryCount);
+    // Way of computing owner count prior to featureMultiSignReserve.
+    // This needs to stay in the code base until no signerLists remain
+    // in the ledger that were created prior to acceptance of
+    // featureMultiSignReserve...  Effectively forever.
+    static int signerCountBasedOwnerCountDelta (std::size_t entryCount);
 };
 
 } // ripple

src/ripple/protocol/Feature.h

@@ -81,7 +81,8 @@ class FeatureCollections
         "fix1623",
         "DepositPreauth",
         "fix1515",
-        "fix1578"
+        "fix1578",
+        "MultiSignReserve"
     };
 
     std::vector<uint256> features;
@@ -369,6 +370,7 @@ extern uint256 const fix1623;
 extern uint256 const featureDepositPreauth;
 extern uint256 const fix1515;
 extern uint256 const fix1578;
+extern uint256 const featureMultiSignReserve;
 
 } // ripple
 

src/ripple/protocol/LedgerFormats.h

@@ -152,6 +152,9 @@ enum LedgerSpecificFlags
     lsfHighNoRipple     = 0x00200000,
     lsfLowFreeze        = 0x00400000,   // True, low side has set freeze flag
     lsfHighFreeze       = 0x00800000,   // True, high side has set freeze flag
+
+    // ltSIGNER_LIST
+    lsfOneOwnerCount    = 0x00010000,   // True, uses only one OwnerCount
 };
 
 //------------------------------------------------------------------------------

src/ripple/protocol/impl/Feature.cpp

@@ -114,7 +114,8 @@ detail::supportedAmendments ()
         { "3CBC5C4E630A1B82380295CDA84B32B49DD066602E74E39B85EF64137FA65194 DepositPreauth" },
         // Use liquidity from strands that consume max offers, but mark as dry
         { "5D08145F0A4983F23AFFFF514E83FAD355C5ABFBB6CAB76FB5BC8519FF5F33BE fix1515" },
-        { "FBD513F1B893AC765B78F250E6FFA6A11B573209D1842ADC787C850696741288 fix1578" }
+        { "FBD513F1B893AC765B78F250E6FFA6A11B573209D1842ADC787C850696741288 fix1578" },
+        { "586480873651E106F1D6339B0C4A8945BA705A777F3F4524626FF1FC07EFE41D MultiSignReserve" }
     };
     return supported;
 }
@@ -170,5 +171,6 @@ uint256 const fix1623 = *getRegisteredFeature("fix1623");
 uint256 const featureDepositPreauth = *getRegisteredFeature("DepositPreauth");
 uint256 const fix1515 = *getRegisteredFeature("fix1515");
 uint256 const fix1578 = *getRegisteredFeature("fix1578");
+uint256 const featureMultiSignReserve = *getRegisteredFeature("MultiSignReserve");
 
 } // ripple