Fix: Replace hardcoded 256-byte shared memory buffer with 4096-byte SHM_SIZE constant (#514)

The C++ shared memory implementation in concore.hpp and concoredocker.hpp
allocated a fixed 256-byte buffer for inter-node data exchange and silently
truncated any payload exceeding 255 characters.

Changes:
- Add static constexpr SHM_SIZE = 4096 in both concore.hpp and concoredocker.hpp
- Replace all hardcoded 256 in shmget(), strnlen(), and strncpy() with SHM_SIZE
- Add overflow detection: stderr error message when payload exceeds SHM_SIZE
- Add explicit null termination after strncpy() to prevent read overruns
- Buffer now supports ~200+ double values (up from ~25)

Fixes #514

Author: GaneshPatil7517

concore.hpp

@@ -40,6 +40,8 @@ class Concore{
     string inpath = "./in";
     string outpath = "./out";
 
+    static constexpr size_t SHM_SIZE = 4096;
+
     int shmId_create = -1;
     int shmId_get = -1;
 
@@ -259,7 +261,7 @@ class Concore{
      */
     void createSharedMemory(key_t key)
     {
-        shmId_create = shmget(key, 256, IPC_CREAT | 0666);
+        shmId_create = shmget(key, SHM_SIZE, IPC_CREAT | 0666);
 
         if (shmId_create == -1) {
             std::cerr << "Failed to create shared memory segment." << std::endl;
@@ -284,7 +286,7 @@ class Concore{
         const int MAX_RETRY = 100;
         while (retry < MAX_RETRY) {
             // Get the shared memory segment created by Writer
-            shmId_get = shmget(key, 256, 0666);
+            shmId_get = shmget(key, SHM_SIZE, 0666);
             // Check if shared memory exists
             if (shmId_get != -1) {
                 break; // Break the loop if shared memory exists
@@ -490,7 +492,7 @@ class Concore{
         try {
         if (shmId_get != -1) {
             if (sharedData_get && sharedData_get[0] != '\0') {
-                std::string message(sharedData_get, strnlen(sharedData_get, 256));
+                std::string message(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
                 ins = message;
             } 
             else 
@@ -515,7 +517,7 @@ class Concore{
             this_thread::sleep_for(timespan);
             try{
                 if(shmId_get != -1) {
-                    std::string message(sharedData_get, strnlen(sharedData_get, 256));
+                    std::string message(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
                     ins = message;
                     retrycount++;
                 }
@@ -664,7 +666,13 @@ class Concore{
                     outfile<<val[i]<<',';
                 outfile<<val[val.size()-1]<<']';
                 std::string result = outfile.str();
-                std::strncpy(sharedData_create, result.c_str(), 256 - 1);
+                if (result.size() >= SHM_SIZE) {
+                    std::cerr << "ERROR: write_SM payload (" << result.size()
+                              << " bytes) exceeds " << SHM_SIZE - 1
+                              << "-byte shared memory limit. Data truncated!" << std::endl;
+                }
+                std::strncpy(sharedData_create, result.c_str(), SHM_SIZE - 1);
+                sharedData_create[SHM_SIZE - 1] = '\0';
                 // simtime must not be mutated here (issue #385).
                 }
             else{
@@ -689,7 +697,13 @@ class Concore{
         this_thread::sleep_for(timespan);
         try {
             if(shmId_create != -1){
-                std::strncpy(sharedData_create, val.c_str(), 256 - 1);
+                if (val.size() >= SHM_SIZE) {
+                    std::cerr << "ERROR: write_SM payload (" << val.size()
+                              << " bytes) exceeds " << SHM_SIZE - 1
+                              << "-byte shared memory limit. Data truncated!" << std::endl;
+                }
+                std::strncpy(sharedData_create, val.c_str(), SHM_SIZE - 1);
+                sharedData_create[SHM_SIZE - 1] = '\0';
             }
             else throw 505;
         }

concoredocker.hpp

@@ -26,6 +26,8 @@
 
 class Concore {
 private:
+    static constexpr size_t SHM_SIZE = 4096;
+
     int shmId_create = -1;
     int shmId_get = -1;
     char* sharedData_create = nullptr;
@@ -233,7 +235,7 @@ class Concore {
 
 #ifdef __linux__
     void createSharedMemory(key_t key) {
-        shmId_create = shmget(key, 256, IPC_CREAT | 0666);
+        shmId_create = shmget(key, SHM_SIZE, IPC_CREAT | 0666);
         if (shmId_create == -1) {
             std::cerr << "Failed to create shared memory segment.\n";
             return;
@@ -249,7 +251,7 @@ class Concore {
         int retry = 0;
         const int MAX_RETRY = 100;
         while (retry < MAX_RETRY) {
-            shmId_get = shmget(key, 256, 0666);
+            shmId_get = shmget(key, SHM_SIZE, 0666);
             if (shmId_get != -1)
                 break;
             std::cout << "Shared memory does not exist. Make sure the writer process is running.\n";
@@ -345,7 +347,7 @@ class Concore {
         std::string ins;
         try {
             if (shmId_get != -1 && sharedData_get && sharedData_get[0] != '\0')
-                ins = std::string(sharedData_get, strnlen(sharedData_get, 256));
+                ins = std::string(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
             else
                 throw 505;
         } catch (...) {
@@ -359,7 +361,7 @@ class Concore {
             std::this_thread::sleep_for(std::chrono::seconds(delay));
             try {
                 if (shmId_get != -1 && sharedData_get) {
-                    ins = std::string(sharedData_get, strnlen(sharedData_get, 256));
+                    ins = std::string(sharedData_get, strnlen(sharedData_get, SHM_SIZE));
                     retrycount++;
                 } else {
                     retrycount++;
@@ -426,7 +428,13 @@ class Concore {
                 outfile << val[i] << ',';
             outfile << val[val.size() - 1] << ']';
             std::string result = outfile.str();
-            std::strncpy(sharedData_create, result.c_str(), 256 - 1);
+            if (result.size() >= SHM_SIZE) {
+                std::cerr << "ERROR: write_SM payload (" << result.size()
+                          << " bytes) exceeds " << SHM_SIZE - 1
+                          << "-byte shared memory limit. Data truncated!" << std::endl;
+            }
+            std::strncpy(sharedData_create, result.c_str(), SHM_SIZE - 1);
+            sharedData_create[SHM_SIZE - 1] = '\0';
         } catch (...) {
             std::cerr << "skipping +" << outpath << port << "/" << name << "\n";
         }