Supporting escape field when using comms::option::def::FrameLayerSeekField with SyncSuffixLayer.

Author: arobenko

include/comms/frame/SyncPrefixLayer.h

@@ -325,10 +325,10 @@ class SyncPrefixLayer : public comms::frame::details::SyncPrefixLayerBase<TField
         auto& thisObj = BaseImpl::thisLayer();
 
         auto limitIter = to;
-        std::advance(limitIter, -dist);
+        std::advance(limitIter, -static_cast<int>(dist));
 
         auto iter = to;
-        std::advance(iter, -EscField::minLength());
+        std::advance(iter, -static_cast<int>(EscField::minLength()));
         while (true) {
             auto iterTmp = iter;
             EscField escField;

include/comms/frame/SyncSuffixLayer.h

@@ -65,6 +65,10 @@ class SyncSuffixLayer : public comms::frame::details::SyncSuffixLayerBase<TField
     /// @brief Type of the field object used to read/write checksum value.
     using Field = typename BaseImpl::Field;
 
+    /// @brief Type of the escape field provided via @ref comms::option::def::FrameLayerSeekField option.
+    /// @details Same as @b void if not provided via said option.
+    using EscField = typename ParsedOptionsInternal::EscField;
+
     /// @brief Default constructor.
     SyncSuffixLayer() = default;
 
@@ -207,6 +211,18 @@ class SyncSuffixLayer : public comms::frame::details::SyncSuffixLayerBase<TField
         return field == Field();
     }
 
+    /// @brief Verify the validity of the escapte field provided via @ref comms::option::def::FrameLayerSeekField option.
+    /// @details Default implementation compares read field with default constructed type. @n
+    ///     May be overridden by the extending class in case
+    ///     more complex logic is required.
+    /// @param[out] field Field that has been read.
+    /// @note May be non-static in the extending class
+    template <typename TEscField>
+    static bool verifyEscFieldValue(const TEscField& field)
+    {
+        return field == TEscField();
+    }
+
     /// @brief Prepare field for writing.
     /// @details Default implementation does nothing. @n
     ///     May be overridden by the extending class in case
@@ -232,6 +248,12 @@ class SyncSuffixLayer : public comms::frame::details::SyncSuffixLayerBase<TField
     template <typename... TParams>
     using VerifyAfterReadTag = comms::details::tag::Tag4<>;
 
+    template <typename... TParams>
+    using EscapeSupportedTag = comms::details::tag::Tag5<>;
+
+    template <typename... TParams>
+    using NoEscapeTag = comms::details::tag::Tag6<>;
+
     template <typename TMsg, typename TIter, typename TReader, typename... TExtraValues>
     ErrorStatus verifyRead(
         Field& field,
@@ -336,6 +358,7 @@ class SyncSuffixLayer : public comms::frame::details::SyncSuffixLayerBase<TField
             }
 
             if ((fieldEs == ErrorStatus::Success) &&
+                (!fieldEscapedInternal(fromIter, iter)) &&
                 (thisObj.verifyFieldValue(field))) {
                 // Set iter to point after field
                 iter = iterTmp;
@@ -549,6 +572,65 @@ class SyncSuffixLayer : public comms::frame::details::SyncSuffixLayerBase<TField
         return thisObj.writeField(msgPtr, field, to, remSize);
     }
 
+    template <typename TIter>
+    bool fieldEscapedInternal(TIter from, TIter to, NoEscapeTag<>)
+    {
+        static_cast<void>(from);
+        static_cast<void>(to);
+        return false;
+    }
+
+    template <typename TIter>
+    bool fieldEscapedInternal(TIter from, TIter to, EscapeSupportedTag<>)
+    {
+        auto dist = static_cast<std::size_t>(std::distance(from, to));
+        dist = std::min(dist, EscField::maxLength());
+        if (dist < EscField::minLength()) {
+            return false;
+        }
+
+        auto& thisObj = BaseImpl::thisLayer();
+
+        auto limitIter = to;
+        std::advance(limitIter, -static_cast<int>(dist));
+
+        auto iter = to;
+        std::advance(iter, -static_cast<int>(EscField::minLength()));
+        while (true) {
+            auto iterTmp = iter;
+            EscField escField;
+            auto len = static_cast<std::size_t>(std::distance(iterTmp, to));
+            auto es = escField.read(iterTmp, len);
+            if ((es == comms::ErrorStatus::Success) &&
+                (iterTmp == to) &&
+                (thisObj.verifyEscFieldValue(escField))) {
+                return true;
+            }
+
+            if (iter == limitIter) {
+                break;
+            }
+
+            std::advance(iter, -1);
+        }
+
+        return false;
+    }
+
+    template <typename TIter>
+    bool fieldEscapedInternal(TIter from, TIter to)
+    {
+        using EscTag =
+            typename comms::util::LazyShallowConditional<
+                std::is_same<EscField, void>::value
+            >::template Type<
+                NoEscapeTag,
+                EscapeSupportedTag
+            >;
+
+        return fieldEscapedInternal(from, to, EscTag());
+    }
+
     static_assert(!(hasVerifyBeforeRead() && hasSeekField()),
         "Usage of both comms::option::def::FrameLayerVerifyBeforeRead and comms::option::def::FrameLayerSeekField at the same time are not allowed");
 };

test/CommsTestCommon.h

@@ -962,13 +962,11 @@ class CountHandler
     template <typename TMsg>
     void handle(TMsg&)
     {
-        //std::cout << "Dispatching actual type!!!" << std::endl;
         ++m_custom;
     }
 
     void handle(TMsgBase&)
     {
-        //std::cout << "Dispatching base!!!" << std::endl;
         ++m_base;
     }
 

test/SyncSuffixLayer.th

@@ -23,6 +23,7 @@ public:
     void test1();
     void test2();
     void test3();
+    void test4();
 
 private:
 
@@ -48,6 +49,20 @@ private:
             comms::option::DefaultNumValue<0xabcd>
         >;
 
+    using BeSyncField2 =
+        comms::field::IntValue<
+            BeField,
+            std::uint16_t,
+            comms::option::DefaultNumValue<0x3d3d> // ==
+        >;
+
+    using BeEscField =
+        comms::field::IntValue<
+            BeField,
+            std::uint16_t,
+            comms::option::DefaultNumValue<0x4040> // @@
+        >;
+
     using BeSizeField =
         comms::field::IntValue<
             BeField,
@@ -101,6 +116,18 @@ private:
             >,
             comms::option::def::FrameLayerSeekField<>
         >;
+
+    using SeekFieldWithEscFrame =
+        comms::frame::SyncSuffixLayer<
+            BeSyncField2,
+            comms::frame::MsgIdLayer<
+                BeIdField,
+                BeMsgBase,
+                AllTestMessages<BeMsgBase>,
+                comms::frame::MsgDataLayer<>
+            >,
+            comms::option::def::FrameLayerSeekField<BeEscField>
+        >;
 };
 
 void SyncSuffixLayerTestSuite::test1()
@@ -154,3 +181,22 @@ void SyncSuffixLayerTestSuite::test3()
     TS_ASSERT_EQUALS(std::get<0>(msg11.fields()).value(), "hello");
 }
 
+void SyncSuffixLayerTestSuite::test4()
+{
+    static const char Buf[] = {
+        MessageType11, 'h', 'e', '@', '@', '=', '=', 'l', 'l', 'o', '=', '=', static_cast<char>(0x3f)
+    };
+
+    static const std::size_t BufSize = std::extent<decltype(Buf)>::value;
+
+    SeekFieldWithEscFrame frame;
+    SeekFieldWithEscFrame::MsgPtr msg;
+    auto readIter = comms::readIteratorFor(msg, Buf);
+    auto es = frame.read(msg, readIter, BufSize);
+    TS_ASSERT_EQUALS(es, comms::ErrorStatus::Success);
+    TS_ASSERT(msg);
+    TS_ASSERT_EQUALS(msg->getId(), MessageType11);
+    auto& msg11 = dynamic_cast<BeMsg11&>(*msg);
+    TS_ASSERT_EQUALS(std::get<0>(msg11.fields()).value(), "he@@==llo");
+}
+