Limit file manager string size to avoid stack explosion

Author: nseidle

Firmware/RTK_Everywhere/WebServer.ino

@@ -217,7 +217,7 @@ void getFileList(String &returnText)
     returnText += "sdFreeSpace," + freeSpace + ",";
 
     char fileName[50]; // Handle long file names
-
+    
     // Attempt to gain access to the SD card
     if (xSemaphoreTake(sdCardSemaphore, fatSemaphore_longWait_ms) == pdPASS)
     {
@@ -239,6 +239,18 @@ void getFileList(String &returnText)
                 String fileSize;
                 stringHumanReadableSize(fileSize, file.fileSize());
                 returnText += "fmName," + String(fileName) + ",fmSize," + fileSize + ",";
+
+                const int maxFiles = 20; //40 is too much
+                const int fileNameLength = 50;
+                const int maxStringLength = maxFiles * fileNameLength;
+                // It is not uncommon to have SD cards with 100+ files on them. String can get huge.
+                // Here we arbitrarily limit it. 
+                // This could be larger but, left unchecked, it will absolutely explode the stack.
+                if(returnText.length() > maxStringLength)
+                {
+                    systemPrintf("Limiting file list to %d characters\r\n", maxStringLength);
+                    break;
+                }
             }
         }