What is the difference between reading outgoing HTTP headers and incoming HTTP headers in PHP?

When working with HTTP headers in PHP, it's important to understand the distinction between outgoing and incoming headers. Outgoing headers are sent from the server to the client, while incoming headers are received by the server from the client. To read outgoing headers, you can use the `headers_list()` function, which returns an array of all headers that have been sent. To read incoming headers, you can access them directly from the `$_SERVER` superglobal array. 

// Reading outgoing headers
$outgoingHeaders = headers_list();
foreach ($outgoingHeaders as $header) {
    echo $header . "<br>";
}

// Reading incoming headers
$incomingHeaders = getallheaders();
foreach ($incomingHeaders as $key => $value) {
    echo $key . ": " . $value . "<br>";
}

Keywords

HTTP headers outgoing incoming PHP difference

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