the most recent client could disconnect other clients (#19)

README.md

@@ -89,6 +89,7 @@ The DmdStreamHeader is defined as a struct:
     uint16_t width = 0;
     uint16_t height = 0;
     uint8_t buffered = 0;          // 0 => not buffered, 1 => buffered
+    uint8_t disconnectOthers = 0;  // 0 => no, 1 => yes
     uint32_t length = 0;
   };
 
@@ -121,7 +122,10 @@ grayscale content.
 So if you want to write a general purpose client to display images or text, you're adviced to use `Mode::RGB24` or `Mode::RGB216`!
 
 The `buffered` flag set to `1` means that the current data not just gets displayed, but also buffered for later use.
-As soon as some buffered data exists, it will be displayed instead of a black screen if a client disconnects. 
+As soon as some buffered data exists, it will be displayed instead of a black screen if a client disconnects.
+
+The `disconnectOthers` flag set to `1` means that any other client get disconnected except the most recent one.
+But only the most recent one is allowed to set this flag.
 
 ### Notes
 
@@ -139,6 +143,8 @@ To send a RGB24 image of 4x2 pixels, you have to sent these two packages, a head
 0x02 0x00 0x00 0x00                                // Mode::RGB24 (if your system is big endian, the byte order needs to be swapped)
 0x04 0x00                                          // width 4 (if your system is big endian, the byte order needs to be swapped)
 0x02 0x00                                          // height 2 (if your system is big endian, the byte order needs to be swapped)
+0x00                                               // not buffered
+0x00                                               // don't disconnect others
 0x18 0x00 0x00 0x00                                // payload length 24 (if your system is big endian, the byte order needs to be swapped)
 ```
 

include/DMDUtil/DMD.h

@@ -103,6 +103,7 @@ class DMDUTILAPI DMD
     uint16_t width = 0;
     uint16_t height = 0;
     uint8_t buffered = 0;  // 0 => unbuffered, 1 => buffered
+    uint8_t disconnectOthers = 0;  // 0 => no, 1 => yes
     uint32_t length = 0;
   };
 

src/dmdServer.cpp

@@ -18,6 +18,7 @@ using namespace std;
 
 DMDUtil::DMD* pDmd;
 uint32_t currentThreadId = 0;
+bool disconnectOtherClients = false;
 std::vector<uint32_t> threads;
 bool opt_verbose = false;
 bool opt_fixedAltColorPath = false;
@@ -74,7 +75,8 @@ void run(sockpp::tcp_socket sock, uint32_t threadId)
   DMDUtil::DMD::StreamHeader* pStreamHeader = (DMDUtil::DMD::StreamHeader*)malloc(sizeof(DMDUtil::DMD::StreamHeader));
   ssize_t n;
 
-  while ((n = sock.read_n(buffer, sizeof(DMDUtil::DMD::StreamHeader))) > 0)
+  while ((n = sock.read_n(buffer, sizeof(DMDUtil::DMD::StreamHeader))) > 0 &&
+         (!disconnectOtherClients || threadId == currentThreadId))
   {
     if (n == sizeof(DMDUtil::DMD::StreamHeader))
     {
@@ -90,6 +92,13 @@ void run(sockpp::tcp_socket sock, uint32_t threadId)
           if (pStreamHeader->buffered) DMDUtil::Log("Next data will be buffered");
         }
 
+        // Only the current (most recent) thread is allowed to disconnect other clients.
+        if (threadId == currentThreadId && pStreamHeader->disconnectOthers)
+        {
+          if (opt_verbose) DMDUtil::Log("Other clients will be disconnected");
+          disconnectOtherClients = true;
+        }
+
         switch (pStreamHeader->mode)
         {
           case DMDUtil::DMD::Mode::Data:
@@ -171,8 +180,8 @@ void run(sockpp::tcp_socket sock, uint32_t threadId)
     }
   }
 
-  // Display a buffered frame or clear the display.
-  if (!pDmd->QueueBuffer())
+  // Display a buffered frame or clear the display on disconnect of the current thread.
+  if (threadId == currentThreadId && !pDmd->QueueBuffer())
   {
     // Clear the DMD by sending a black screen.
     // Fixed dimension of 128x32 should be OK for all devices.
@@ -181,7 +190,8 @@ void run(sockpp::tcp_socket sock, uint32_t threadId)
   }
 
   threads.erase(remove(threads.begin(), threads.end(), threadId), threads.end());
-  currentThreadId = threads.back();
+  currentThreadId = (threads.size() >= 1) ? threads.back() : 0;
+  if (threads.size() <= 1) disconnectOtherClients = false;
 
   free(pStreamHeader);
 }
@@ -297,7 +307,7 @@ int main(int argc, char* argv[])
     else
     {
       if (opt_verbose) DMDUtil::Log("New DMD client connected");
-      currentThreadId = threadId++;
+      currentThreadId = ++threadId;
       threads.push_back(currentThreadId);
       // Create a thread and transfer the new stream to it.
       thread thr(run, std::move(sock), currentThreadId);