What are the key considerations when using fopen or fsockopen in PHP to read and transmit data in a file transfer scenario?

When using fopen or fsockopen in PHP for file transfer, key considerations include ensuring proper error handling, setting the correct file permissions, and securely transmitting data over a network. It is important to check for errors when opening or connecting to a file, handle exceptions gracefully, and close the file or network connection properly after use.

// Example of using fopen to read data from a file
$file = fopen("example.txt", "r");

if ($file) {
    while (($line = fgets($file)) !== false) {
        echo $line;
    }
    fclose($file);
} else {
    echo "Error opening file.";
}