XLS-85d: Token-Enabled Escrows

include/xrpl/protocol/Feature.h

@@ -80,7 +80,7 @@ namespace detail {
 // Feature.cpp. Because it's only used to reserve storage, and determine how
 // large to make the FeatureBitset, it MAY be larger. It MUST NOT be less than
 // the actual number of amendments. A LogicError on startup will verify this.
-static constexpr std::size_t numFeatures = 88;
+static constexpr std::size_t numFeatures = 89;
 
 /** Amendments that this server supports and the default voting behavior.
    Whether they are enabled depends on the Rules defined in the validated

include/xrpl/protocol/LedgerFormats.h

@@ -145,7 +145,8 @@ enum LedgerSpecificFlags {
         0x10000000,               // True, reject new paychans
     lsfDisallowIncomingTrustline =
         0x20000000,               // True, reject new trustlines (only if no issued assets)
-    // 0x40000000 is available
+    lsfAllowTokenLocking =
+        0x40000000,               // True, enable token locking
     lsfAllowTrustLineClawback =
         0x80000000,               // True, enable clawback
 

include/xrpl/protocol/STAmount.h

@@ -684,6 +684,48 @@ isXRP(STAmount const& amount)
     return amount.native();
 }
 
+/** returns true if adding or subtracting results in less than or equal to
+ * 0.01% precision loss **/
+inline bool
+isAddable(STAmount const& amt1, STAmount const& amt2)
+{
+    // special case: adding anything to zero is always fine
+    if (amt1 == beast::zero || amt2 == beast::zero)
+        return true;
+
+    // special case: adding two xrp amounts together.
+    // this is just an overflow check
+    if (isXRP(amt1) && isXRP(amt2))
+    {
+        XRPAmount A = (amt1.signum() == -1 ? -(amt1.xrp()) : amt1.xrp());
+        XRPAmount B = (amt2.signum() == -1 ? -(amt2.xrp()) : amt2.xrp());
+
+        XRPAmount finalAmt = A + B;
+        return (finalAmt >= A && finalAmt >= B);
+    }
+
+    static const STAmount one{IOUAmount{1, 0}, noIssue()};
+    static const STAmount maxLoss{IOUAmount{1, -4}, noIssue()};
+
+    STAmount A = amt1;
+    STAmount B = amt2;
+
+    if (isXRP(A))
+        A = STAmount{IOUAmount{A.xrp().drops(), -6}, noIssue()};
+
+    if (isXRP(B))
+        B = STAmount{IOUAmount{B.xrp().drops(), -6}, noIssue()};
+
+    A.setIssue(noIssue());
+    B.setIssue(noIssue());
+
+    STAmount lhs = divide((A - B) + B, A, noIssue()) - one;
+    STAmount rhs = divide((B - A) + A, B, noIssue()) - one;
+
+    return ((rhs.negative() ? -rhs : rhs) + (lhs.negative() ? -lhs : lhs)) <=
+        maxLoss;
+}
+
 // Since `canonicalize` does not have access to a ledger, this is needed to put
 // the low-level routine stAmountCanonicalize on an amendment switch. Only
 // transactions need to use this switchover. Outside of a transaction it's safe

include/xrpl/protocol/TER.h

@@ -344,6 +344,7 @@ enum TECcodes : TERUnderlyingType {
     tecARRAY_TOO_LARGE = 191,
     tecLOCKED = 192,
     tecBAD_CREDENTIALS = 193,
+    tecPRECISION_LOSS = 194,
 };
 
 //------------------------------------------------------------------------------

include/xrpl/protocol/TxFlags.h

@@ -91,6 +91,7 @@ constexpr std::uint32_t asfDisallowIncomingCheck           = 13;
 constexpr std::uint32_t asfDisallowIncomingPayChan         = 14;
 constexpr std::uint32_t asfDisallowIncomingTrustline       = 15;
 constexpr std::uint32_t asfAllowTrustLineClawback          = 16;
+constexpr std::uint32_t asfAllowTokenLocking               = 17;
 
 // OfferCreate flags:
 constexpr std::uint32_t tfPassive                          = 0x00010000;

include/xrpl/protocol/detail/features.macro

@@ -29,6 +29,7 @@
 // If you add an amendment here, then do not forget to increment `numFeatures`
 // in include/xrpl/protocol/Feature.h.
 
+XRPL_FEATURE(TokenEscrow,                Supported::yes, VoteBehavior::DefaultNo)
 // Check flags in Credential transactions
 XRPL_FIX    (InvalidTxFlags,             Supported::yes, VoteBehavior::DefaultNo)
 XRPL_FIX    (FrozenLPTokenTransfer,      Supported::yes, VoteBehavior::DefaultNo)

include/xrpl/protocol/detail/ledger_entries.macro

@@ -350,6 +350,8 @@ LEDGER_ENTRY(ltESCROW, 0x0075, Escrow, escrow, ({
     {sfPreviousTxnID,        soeREQUIRED},
     {sfPreviousTxnLgrSeq,    soeREQUIRED},
     {sfDestinationNode,      soeOPTIONAL},
+    {sfTransferRate,         soeOPTIONAL},
+    {sfIssuerNode,           soeOPTIONAL},
 }))
 
 /** A ledger object describing a single unidirectional XRP payment channel.

include/xrpl/protocol/detail/transactions.macro

@@ -43,7 +43,7 @@ TRANSACTION(ttPAYMENT, 0, Payment, ({
 /** This transaction type creates an escrow object. */
 TRANSACTION(ttESCROW_CREATE, 1, EscrowCreate, ({
     {sfDestination, soeREQUIRED},
-    {sfAmount, soeREQUIRED},
+    {sfAmount, soeREQUIRED, soeMPTSupported},
     {sfCondition, soeOPTIONAL},
     {sfCancelAfter, soeOPTIONAL},
     {sfFinishAfter, soeOPTIONAL},

src/libxrpl/protocol/TER.cpp

@@ -117,6 +117,7 @@ transResults()
         MAKE_ERROR(tecARRAY_TOO_LARGE,               "Array is too large."),
         MAKE_ERROR(tecLOCKED,                        "Fund is locked."),
         MAKE_ERROR(tecBAD_CREDENTIALS,               "Bad credentials."),
+        MAKE_ERROR(tecPRECISION_LOSS,                "The amounts used by the transaction cannot interact."),
 
         MAKE_ERROR(tefALREADY,                     "The exact transaction was already in this ledger."),
         MAKE_ERROR(tefBAD_ADD_AUTH,                "Not authorized to add account."),

src/test/app/AccountDelete_test.cpp

@@ -403,6 +403,34 @@ class AccountDelete_test : public beast::unit_test::suite
                 jv[sfOfferSequence.jsonName] = seq;
                 return jv;
             };
+
+        bool const withTokenEscrow =
+            env.current()->rules().enabled(featureTokenEscrow);
+        if (withTokenEscrow)
+        {
+            Account const carol("carol");
+            auto const USD = gw["USD"];
+            env.fund(XRP(100000), carol);
+            env(fset(gw, asfAllowTokenLocking));
+            env.close();
+            env.trust(USD(10000), carol);
+            env.close();
+            env(pay(gw, carol, USD(100)));
+            env.close();
+
+            std::uint32_t const escrowSeq{env.seq(carol)};
+            env(escrowCreate(carol, becky, USD(1), env.now() + 2s));
+            env.close();
+
+            env(acctdelete(gw, becky),
+                fee(acctDelFee),
+                ter(tecHAS_OBLIGATIONS));
+            env.close();
+
+            env(escrowCancel(becky, carol, escrowSeq));
+            env.close();
+        }
+
         env(escrowCancel(becky, alice, escrowSeq));
         env.close();