Strongly typed wrapper for Payment Channels ledger object

This commit introduces implementation for the said wrapper. Occurences of PayChan keylet have been modified to indicate the new type.
One function in PayChan_test.cpp:channelAndSle(...) uses the readSLE API. It has a dependency on inOwnerDir(...) function. This can be ported only after completion of the Directory ledger object wrapper.

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

@@ -252,7 +252,7 @@ PayChanCreate::doApply()
     //
     // Note that we we use the value from the sequence or ticket as the
     // payChan sequence.  For more explanation see comments in SeqProxy.h.
-    Keylet const payChanKeylet =
+    PayChanKeylet const payChanKeylet =
         keylet::payChan(account, dst, ctx_.tx.getSeqProxy().value());
     auto const slep = std::make_shared<SLE>(payChanKeylet);
 

src/ripple/ledger/ApplyView.h

@@ -343,7 +343,7 @@ class ApplyView : public ReadView
     std::optional<std::uint64_t>
     dirInsert(
         Keylet const& directory,
-        Keylet const& key,
+        KeyletBase const& key,
         std::function<void(std::shared_ptr<SLE> const&)> const& describe)
     {
         return dirAdd(false, directory, key.key, describe);

src/ripple/protocol/Indexes.h

@@ -222,7 +222,7 @@ Keylet
 escrow(AccountID const& src, std::uint32_t seq) noexcept;
 
 /** A PaymentChannel */
-Keylet
+PayChanKeylet
 payChan(AccountID const& src, AccountID const& dst, std::uint32_t seq) noexcept;
 
 /** NFT page keylets

src/ripple/protocol/Keylet.h

@@ -95,6 +95,21 @@ static_assert(std::is_move_assignable_v<Keylet>);
 static_assert(std::is_nothrow_destructible_v<Keylet>);
 #endif
 
+template <bool>
+class PayChanImpl;
+
+struct PayChanKeylet final : public KeyletBase
+{
+    template <bool Writable>
+    using TWrapped = PayChanImpl<Writable>;
+
+    using KeyletBase::check;
+
+    explicit PayChanKeylet(uint256 const& key) : KeyletBase(ltPAYCHAN, key)
+    {
+    }
+};
+
 template <bool>
 class AcctRootImpl;
 

src/ripple/protocol/PayChan.h

@@ -27,6 +27,39 @@
 
 namespace ripple {
 
+template <bool Writable>
+class PayChanImpl final : public LedgerEntryWrapper<Writable>
+{
+    using Base = LedgerEntryWrapper<Writable>;
+    using SleT = typename Base::SleT;
+    using Base::wrapped_;
+
+    // This constructor is private so only the factory functions can
+    // construct an PayChanImpl.
+    PayChanImpl(std::shared_ptr<SleT>&& w) : Base(std::move(w))
+    {
+    }
+
+    // Friend declarations of factory functions.
+    //
+    // For classes that contain factories we must declare the entire class
+    // as a friend unless the class declaration is visible at this point.
+    friend class ReadView;
+    friend class ApplyView;
+
+public:
+    // Conversion operator from PayChanImpl<true> to PayChanImpl<false>.
+    operator PayChanImpl<true>() const
+    {
+        return PayChanImpl<false>(
+            std::const_pointer_cast<std::shared_ptr<STLedgerEntry const>>(
+                wrapped_));
+    }
+};
+
+using PayChan = PayChanImpl<true>;
+using PayChanRd = PayChanImpl<false>;
+
 inline void
 serializePayChanAuthorization(
     Serializer& msg,

src/ripple/protocol/impl/Indexes.cpp

@@ -320,12 +320,11 @@ escrow(AccountID const& src, std::uint32_t seq) noexcept
     return {ltESCROW, indexHash(LedgerNameSpace::ESCROW, src, seq)};
 }
 
-Keylet
+PayChanKeylet
 payChan(AccountID const& src, AccountID const& dst, std::uint32_t seq) noexcept
 {
-    return {
-        ltPAYCHAN,
-        indexHash(LedgerNameSpace::XRP_PAYMENT_CHANNEL, src, dst, seq)};
+    return PayChanKeylet(
+        indexHash(LedgerNameSpace::XRP_PAYMENT_CHANNEL, src, dst, seq));
 }
 
 Keylet

src/test/app/AccountDelete_test.cpp

@@ -405,7 +405,7 @@ class AccountDelete_test : public beast::unit_test::suite
         env(escrowCancel(becky, alice, escrowSeq));
         env.close();
 
-        Keylet const alicePayChanKey{
+        PayChanKeylet const alicePayChanKey{
             keylet::payChan(alice, becky, env.seq(alice))};
 
         env(payChanCreate(
@@ -426,7 +426,7 @@ class AccountDelete_test : public beast::unit_test::suite
 
         // Lambda to close a PayChannel.
         auto payChanClose = [](jtx::Account const& account,
-                               Keylet const& payChanKeylet,
+                               KeyletBase const& payChanKeylet,
                                PublicKey const& pk) {
             Json::Value jv;
             jv[jss::TransactionType] = jss::PaymentChannelClaim;
@@ -447,7 +447,8 @@ class AccountDelete_test : public beast::unit_test::suite
         // gw creates a PayChannel with alice as the destination.  With the
         // amendment passed this should prevent alice from deleting her
         // account.
-        Keylet const gwPayChanKey{keylet::payChan(gw, alice, env.seq(gw))};
+        PayChanKeylet const gwPayChanKey{
+            keylet::payChan(gw, alice, env.seq(gw))};
 
         env(payChanCreate(gw, alice, XRP(68), 4s, env.now() + 2s, alice.pk()));
         env.close();
@@ -492,7 +493,8 @@ class AccountDelete_test : public beast::unit_test::suite
         BEAST_EXPECT(env.closed()->exists(beckyAcctKey));
 
         using namespace std::chrono_literals;
-        Keylet const payChanKey{keylet::payChan(alice, becky, env.seq(alice))};
+        PayChanKeylet const payChanKey{
+            keylet::payChan(alice, becky, env.seq(alice))};
         auto const payChanXRP = XRP(37);
 
         env(payChanCreate(

src/test/app/PayChan_test.cpp

@@ -44,6 +44,8 @@ struct PayChan_test : public beast::unit_test::suite
         return k.key;
     }
 
+    // Keshava: Modify this function to use read() after keylet::ownerDir has
+    // been updated. inOwnerDir(...) has a dependency on ltDirNode.
     static std::pair<uint256, std::shared_ptr<SLE const>>
     channelKeyAndSle(
         ReadView const& view,
@@ -81,8 +83,8 @@ struct PayChan_test : public beast::unit_test::suite
     static bool
     channelExists(ReadView const& view, uint256 const& chan)
     {
-        auto const slep = view.readSLE(Keylet(ltPAYCHAN, chan));
-        return bool(slep);
+        auto const slep = view.read(PayChanKeylet(chan));
+        return slep.has_value();
     }
 
     static STAmount