Add file locking to counter update process to ensure data integrity

- Implement file locking with `flock()` to synchronize access to the counter file.
- Use `ftruncate()` and `rewind()` to ensure correct file writes after incrementing the counter.
- Add detailed inline comments explaining each step and functionality in the script for better maintainability and clarity.

script.php

@@ -1,9 +1,9 @@
 <?php
-// Define paths and file names for the counter file and the generated image output
+// Define paths and filenames for the counter file and generated image output
 $counterFile = "example.txt";
 $imageFile = "example.png";
 
-// Background image URL for the counter display image
+// Background image URL for the counter display
 $backgroundImageUrl = "https://datakra.sh/assets/example_counter.jpg"; // Replace this with your actual background image URL
 
 // Text settings to be displayed on the image
@@ -25,13 +25,27 @@ $numberColorRGB = ['red' => 255, 'green' => 255, 'blue' => 255]; // Color for th
 $frameColorRGB = ['red' => 255, 'green' => 238, 'blue' => 0]; // Color for the frame
 $drawFrame = true; // Boolean to toggle drawing a frame around the image
 
-// Increment the visit counter stored in the counter file
+// Ensure the counter file exists, and initialize if not
 if (!file_exists($counterFile)) {
-    file_put_contents($counterFile, "0"); // If the file does not exist, create it with an initial value of 0
+    file_put_contents($counterFile, "0"); // Create the file with an initial value of 0 if it doesn't exist
 }
-$number = (int)file_get_contents($counterFile); // Read the current count from the file
-$number++; // Increment the counter by 1
-file_put_contents($counterFile, (string)$number); // Write the new count back to the file
+
+// Open the file for reading and writing (c+ creates the file if it does not exist)
+$fp = fopen($counterFile, "c+");
+if (flock($fp, LOCK_EX)) { // Lock to synchronize file access
+    // Read and increment the counter
+    $number = (int)fread($fp, filesize($counterFile));
+    $number++; // Increment the counter by 1
+
+    // Prepare the file for writing the updated counter
+    ftruncate($fp, 0); // Clear file content
+    rewind($fp); // Reset the file pointer to the start of the file
+    fwrite($fp, (string)$number); // Write the new counter value to the file
+
+    // Release the lock on the file
+    flock($fp, LOCK_UN);
+}
+fclose($fp); // Close the file
 
 // Load the background image and determine its type (JPEG or PNG)
 list($width, $height, $type) = getimagesize($backgroundImageUrl); // Get image dimensions and type
@@ -43,7 +57,7 @@ switch ($type) {
         $backgroundImage = imagecreatefrompng($backgroundImageUrl); // Load PNG image
         break;
     default:
-        die("Unsupported image format: " . $backgroundImageUrl); // Terminate script if image format is not supported
+        die("Unsupported image format: " . $backgroundImageUrl); // Exit script if image format is not supported
 }
 
 // Allocate colors for the text and frame on the image
@@ -68,7 +82,7 @@ imagestring($backgroundImage, 3, $numberPositionX, $numberPositionY, (string)$nu
 imagepng($backgroundImage, $imageFile); // Save the image to a file
 imagedestroy($backgroundImage); // Free up memory used by the image
 
-// Set headers for browser to interpret the output as an image
+// Set headers for the browser to interpret the output as an image
 header('Content-Type: image/png'); // MIME type for PNG image
 header('Content-Disposition: filename="' . $imageFile . '"'); // Suggested filename for download
 readfile($imageFile); // Output the image file