Nginx File Upload

Nginx processes the request body incrementally rather than downloading the entire content first before checking its size. Here's a more detailed explanation of how it handles uploads:

1. Receiving the Request: When Nginx receives a request with a body (e.g., a file upload), it starts reading the body in chunks as they arrive, rather than waiting for the entire body to be received.

2. Incremental Size Check: As Nginx reads each chunk of the request body, it keeps a running total of the size of the body received so far. If at any point the total size exceeds the client_max_body_size limit, Nginx will immediately stop processing the request and return a 413 Request Entity Too Large error. This prevents Nginx from unnecessarily processing and storing large amounts of data that it will ultimately reject.

3. Storing the Data: If the size check passes, Nginx can then store the received data (in temporary files, buffers, or directly pass it upstream, depending on the configuration and the request).

4. Passing Data to Upstream: Once the entire request body is received and validated, Nginx can pass the data to an upstream server, such as a PHP-FPM backend, for further processing (like saving the uploaded file to disk or processing form data).

Here is a summary of the process:

• Nginx receives the request and starts reading the body.
• It checks the size of each chunk as it is received.
• If the cumulative size exceeds the client_max_body_size limit, Nginx returns a 413 error and discards the request body.
• If the body is within the size limit, Nginx continues to process the request as configured.

This approach ensures efficient handling of request bodies, especially for large file uploads, by rejecting oversized bodies as early as possible.