How Can I Parse Multipart/Form-Data POST Requests in PHP Without Using Built-in Functions?

Parsing Multipart/Form-Data POST Requests without PHP's Intervention

Despite the limitations of php://input and $HTTP_RAW_POST_DATA in handling multipart/form-data POST requests, there is a way to access the raw data directly.

The Challenge of RAW multipart/form-Data Parsing

PHP automatically parses multipart/form-data requests, making it impossible to obtain the raw data directly. This can be a problem when dealing with incorrectly formatted data that PHP cannot parse.

Hacking Around the Limitation

The solution lies in modifying the request header using an Apache configuration directive. By changing the Content-Type from multipart/form-data to multipart/form-data-alternate, PHP is tricked into not parsing the request.

Apache Configuration Modification

The following code can be added to the Apache configuration:

<location>
    SetEnvIf Content-Type ^(multipart/form-data)(.*) NEW_CONTENT_TYPE=multipart/form-data-alternate OLD_CONTENT_TYPE=
    RequestHeader set Content-Type %{NEW_CONTENT_TYPE}e env=NEW_CONTENT_TYPE
</location> 

This directive changes the Content-Type header of incoming requests to /backend/XXX.php from multipart/form-data to multipart/form-data-alternate, preventing PHP from attempting to parse the request.

Retrieving Raw Data and Parsing

After modifying the configuration, the raw data can be retrieved from php://input and parsed manually. However, this method has one caveat: the $_FILES array will be empty.

This workaround is not ideal, but it provides a solution for situations where the default PHP parsing fails.

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