How Do PHP\'s `post_max_size` and `upload_max_filesize` Work Together for File Uploads?

Understanding PHP File Upload Size Limits

The PHP configuration settings post_max_size and upload_max_filesize play crucial roles in handling file uploads. However, their interaction can be confusing.

The Confusion

In the provided example, post_max_size is set to 8Mb, while upload_max_filesize is set to 16Mb. Logically, one might assume that files up to 16Mb could be uploaded. However, the smaller post_max_size limit overrides this assumption, resulting in errors when attempting to upload files larger than 8Mb.

Definition of Limits

• upload_max_filesize: Specifies the maximum size of a single uploaded file.
• post_max_size: Specifies the maximum size of the entire HTTP POST request body, which includes all data being submitted, including files.

Interaction of Limits

post_max_size acts as a total limit on the combined size of all files and other data being submitted via POST. This means that even if upload_max_filesize allows for larger files, the overall request size must adhere to post_max_size.

Solution for Large File Uploads

To allow for the upload of files larger than post_max_size, one needs to find an alternative way to transmit the file without using POST. This could involve:

• Multipart/form-data: Utilizing a custom script that handles file uploads independently of the HTTP request size limitations.
• PUT/PATCH HTTP Methods: Using these methods to upload large files over a REST API.

Error Detection

When post_max_size is exceeded, $_POST and $_FILES will be empty. However, $_SERVER['CONTENT_LENGTH'] will be greater than 0. It's important to note that if no post variables or files are transmitted, $_SERVER['CONTENT_LENGTH'] will be 0.

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