JackRequest: Add end marker and verify them on read

Without this marker partly written messages cannot be detected before
processing them.

Change-Id: I38802e9df2a09d1ad0371aba80fc1523cec2ddfe
Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>

common/JackRequest.h

@@ -94,6 +94,7 @@ struct JackRequest
     };
 
     static const int StartMarker = 'R' | ('e' << 8) | ('q' << 16) | ('S' << 24);
+    static const int EndMarker   = 'R' | ('e' << 8) | ('q' << 16) | ('E' << 24);
 
     static int ReadType(detail::JackChannelTransactionInterface* trans, RequestType& type)
     {
@@ -136,6 +137,8 @@ protected:
 public:
     DATA d;
 protected:
+    const int fEnd = JackRequest::EndMarker;
+
     template<typename... Args>
         JackRequestMessage(Args&... args) : fType(DATA::Type()),
             fSize(sizeof(JackRequestMessage<DATA>) - sizeof(fStart) - sizeof(fType) - sizeof(fSize)),
@@ -151,7 +154,16 @@ protected:
                 return -1;
             }
 
+            /* Size also contains fEnd */
             CheckRes(trans->Read(&d, fSize));
+            if (fEnd != JackRequest::EndMarker) {
+                jack_error("Request end marker not found (exp %08x act %08x). Request of type %d will be ignored!",
+                           JackRequest::EndMarker, fEnd, fType);
+
+                /* no need to sync here. Will be done by JackRequest::ReadType() */
+                return -1;
+            }
+
             return 0;
         }