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

Author: arobenko

doxygen/page_frame.dox

@@ -408,7 +408,7 @@
 ///     comms::frame::SyncPrefixLayer<
 ///         SyncField,
 ///         MyChecksum<TMessage, TInputMessages, TAllocationOptions>,
-///         comms::option::def::FrameLayerSeekField
+///         comms::option::def::FrameLayerSeekField<>
 ///     >;
 /// @endcode
 /// Similar to the @ref page_frame_tutorial_checksum the @ref page_frame_tutorial_sync

include/comms/frame/SyncPrefixLayer.h

@@ -14,6 +14,7 @@
 #include "comms/frame/details/SyncPrefixLayerBase.h"
 #include "comms/frame/details/SyncPrefixLayerOptionsParser.h"
 
+#include <algorithm>
 #include <iterator>
 
 COMMS_MSVC_WARNING_PUSH
@@ -57,6 +58,10 @@ class SyncPrefixLayer : public comms::frame::details::SyncPrefixLayerBase<TField
     /// @brief Type of the field object used to read/write "sync" 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
     SyncPrefixLayer() = default;
 
@@ -180,6 +185,18 @@ class SyncPrefixLayer : public comms::frame::details::SyncPrefixLayerBase<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
@@ -199,6 +216,12 @@ class SyncPrefixLayer : public comms::frame::details::SyncPrefixLayerBase<TField
     template <typename... TParams>
     using InstantOpTag = comms::details::tag::Tag2<>;
 
+    template <typename... TParams>
+    using EscapeSupportedTag = comms::details::tag::Tag3<>;
+
+    template <typename... TParams>
+    using NoEscapeTag = comms::details::tag::Tag4<>;
+
     template <typename TMsg, typename TIter, typename TReader, typename... TExtraValues>
     ErrorStatus readInternal(
         Field& field,
@@ -230,6 +253,7 @@ class SyncPrefixLayer : public comms::frame::details::SyncPrefixLayerBase<TField
             }
 
             if ((fieldEs == ErrorStatus::Success) &&
+                (!fieldEscapedInternal(fromIter, iter)) &&
                 (thisObj.verifyFieldValue(field))) {
                 // Set iter to point after field
                 iter = iterTmp;
@@ -280,6 +304,65 @@ class SyncPrefixLayer : public comms::frame::details::SyncPrefixLayerBase<TField
         auto fieldLen = static_cast<std::size_t>(std::distance(beforeReadIter, iter));
         return nextLayerReader.read(msg, iter, size - fieldLen, extraValues...);
     }
+
+    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, -dist);
+
+        auto iter = to;
+        std::advance(iter, -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());
+    }
 };
 
 namespace details

include/comms/frame/details/MsgSizeLayerBase.h

@@ -36,7 +36,7 @@ class MsgSizeLayerBaseHelper
             TField,
             TNextLayer,
             ActualLayer,
-            comms::option::FrameLayerDisallowReadUntilDataSplit
+            comms::option::def::FrameLayerDisallowReadUntilDataSplit
         >;
 
 public:

include/comms/frame/details/SyncPrefixLayerOptionsParser.h

@@ -30,6 +30,8 @@ class SyncPrefixLayerOptionsParser<>
 
     using ExtendingClass = void;
 
+    using EscField = void;
+
     template <typename TLayer>
     using DefineExtendingClass = TLayer;
 };
@@ -46,11 +48,12 @@ class SyncPrefixLayerOptionsParser<comms::option::def::ExtendingClass<T>, TOptio
     using DefineExtendingClass = ExtendingClass;
 };
 
-template <typename... TOptions>
-class SyncPrefixLayerOptionsParser<comms::option::def::FrameLayerSeekField, TOptions...> :
+template <typename TEscField, typename... TOptions>
+class SyncPrefixLayerOptionsParser<comms::option::def::FrameLayerSeekField<TEscField>, TOptions...> :
         public SyncPrefixLayerOptionsParser<TOptions...>
 {
 public:
+    using EscField = TEscField;
     static constexpr bool HasSeekField = true;
 };
 

include/comms/frame/details/SyncSuffixLayerOptionsParser.h

@@ -31,6 +31,8 @@ class SyncSuffixLayerOptionsParser<>
 
     using ExtendingClass = void;
 
+    using EscField = void;
+
     template <typename TLayer>
     using DefineExtendingClass = TLayer;
 };
@@ -55,11 +57,12 @@ class SyncSuffixLayerOptionsParser<comms::option::def::ExtendingClass<T>, TOptio
     using DefineExtendingClass = ExtendingClass;
 };
 
-template <typename... TOptions>
-class SyncSuffixLayerOptionsParser<comms::option::def::FrameLayerSeekField, TOptions...> :
+template <typename TEscField, typename... TOptions>
+class SyncSuffixLayerOptionsParser<comms::option::def::FrameLayerSeekField<TEscField>, TOptions...> :
         public SyncSuffixLayerOptionsParser<TOptions...>
 {
 public:
+    using EscField = TEscField;
     static constexpr bool HasSeekField = true;
 };
 

include/comms/options.h

@@ -1087,7 +1087,9 @@ using ChecksumLayerVerifyBeforeRead = FrameLayerVerifyBeforeRead;
 
 /// @brief Force the layer to seek its field before
 ///     forwarding read to the wrapped layer(s).
+/// @tparam TEscField - Escape field to avoid detection of the field being seeked.
 /// @headerfile comms/options.h
+template <typename TEscField = void>
 struct FrameLayerSeekField {};
 
 /// @brief Force field not to be serialized during read/write operations

test/SyncPrefixLayer.th

@@ -29,6 +29,7 @@ public:
     void test7();
     void test8();
     void test9();
+    void test10();
 
 private:
 
@@ -94,10 +95,22 @@ private:
             comms::option::DefaultNumValue<0xabcd>
         >;
 
+    template <typename TField, std::size_t TSize>
+    using EscField =
+        comms::field::IntValue<
+            TField,
+            unsigned,
+            comms::option::FixedLength<TSize>,
+            comms::option::DefaultNumValue<0xdead>
+        >;
+
     template <typename TField>
     using SyncField2 = SyncField<TField, 2>;
+    template <typename TField>
+    using EscField2 = EscField<TField, 2>;
     using BeSyncField2 = SyncField2<BeField>;
     using LeSyncField2 = SyncField2<LeField>;
+    using BeEscField2 = EscField2<BeField>;
     using BeBackInsertSyncField2 = SyncField2<BeBackInsertField>;
 
     template <typename TField, std::size_t TSize, std::size_t TOffset = 0>
@@ -172,7 +185,23 @@ private:
                     comms::frame::MsgDataLayer<>
                 >
             >,
-            comms::option::def::FrameLayerSeekField
+            comms::option::def::FrameLayerSeekField<>
+        >;
+
+    template <typename TSyncField, typename TEscField, typename TSizeField, typename TIdField, typename TMessage>
+    using SeekFieldWithEscFrame =
+        comms::frame::SyncPrefixLayer<
+            TSyncField,
+            comms::frame::MsgSizeLayer<
+                TSizeField,
+                comms::frame::MsgIdLayer<
+                    TIdField,
+                    TMessage,
+                    AllTestMessages<TMessage>,
+                    comms::frame::MsgDataLayer<>
+                >
+            >,
+            comms::option::def::FrameLayerSeekField<TEscField>
         >;
 };
 
@@ -406,6 +435,35 @@ void SyncPrefixLayerTestSuite::test9()
             BeMsgBase
         >;
 
+    TestFrame frame;
+    TestFrame::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(), MessageType1);
+    auto& msg1 = dynamic_cast<BeMsg1&>(*msg);
+    TS_ASSERT_EQUALS(std::get<0>(msg1.fields()).value(), 0x0102);
+}
+
+void SyncPrefixLayerTestSuite::test10()
+{
+    static const char Buf[] = {
+        0x0, 0x1, static_cast<char>(0xde), static_cast<char>(0xad), static_cast<char>(0xab), static_cast<char>(0xcd), // garbage with esc
+        static_cast<char>(0xab), static_cast<char>(0xcd), 0x0, 0x3, MessageType1, 0x01, 0x02, static_cast<char>(0x3f)
+    };
+
+    static const std::size_t BufSize = std::extent<decltype(Buf)>::value;
+
+    using TestFrame =
+        SeekFieldWithEscFrame<
+            BeSyncField2,
+            BeEscField2,
+            BeSizeField20,
+            BeIdField1,
+            BeMsgBase
+        >;
+
     TestFrame frame;
     TestFrame::MsgPtr msg;
     auto readIter = comms::readIteratorFor(msg, Buf);

test/SyncSuffixLayer.th

@@ -99,7 +99,7 @@ private:
                 AllTestMessages<BeMsgBase>,
                 comms::frame::MsgDataLayer<>
             >,
-            comms::option::def::FrameLayerSeekField
+            comms::option::def::FrameLayerSeekField<>
         >;
 };