Introduce the ability to return 413: payload too large for requests

[shayonj]

Description

When receiving large payload objects, the server can often slowdown or get fully exhausted if bunch of requests with large payload body size come in. When request with large payload comes in, lot of the time is spent reading the body into buffer, writing it to the IO for rack, before the request is passed to the rails app for further processing.

While there are some workarounds around limiting large request sizes, like at nginx layer by setting client_max_body_size, which would return a 413 back to the client, today that is not possible with puma.

This would be a very nice feature to have, especially when there is no reverse proxy in between client and server.

This approach - allows a user to set http_content_length_limit via a config variable (defaults to nil). This value is then compared against Content-Length http header (when present) before reading the body into buffer. If the user value is higher than the header value, the request body is not loaded and an immediate 413 (Payload too large) http response is returned, from Puma::Request.handle_request.

Without having to buffer in the huge request and return the 413 immediately to the clients that send a Content-Length - could be a nice feature and helpful protection to have.

Additionally, when no Content-Length http header is present, it is compared against the size of the body of the request.
During this time, the body is already loaded, so there isn't much we can do, but it still respects the limit and
returns the 413 status from puma itself, before passing down the request to the app.

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[shayonj]

Trying it out locally

# config.rb

http_content_length_limit 100

 bundle exec bin/puma -C config.rb test/rackup/hello.ru

Sending a curl with standard body body above 100 bytes

curl -kso /dev/null -XPOST http://localhost:9292 -d "Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum" -w "==============\n\n        
| dnslookup: %{time_namelookup}\n    
| connect: %{time_connect}\n             
| appconnect: %{time_appconnect}\n 
| pretransfer: %{time_pretransfer}\n 
| starttransfer: %{time_starttransfer}\n 
| total: %{time_total}\n
| size: %{size_download}\n
| HTTPCode=%{http_code}\n\n"
==============

 
| dnslookup: 0.003017
 
| connect: 0.003273
 
| appconnect: 0.000000
 
| pretransfer: 0.003293
 
| starttransfer: 0.003995
 
| total: 0.004048
 
| size: 17
 
| HTTPCode=413

With a large json (40mb)

curl -kso /dev/null -XPOST http://localhost:9292/1 -d @40mb.json -w "==============\n\n      
| dnslookup: %{time_namelookup}\n
| connect: %{time_connect}\n
| appconnect: %{time_appconnect}\n
| pretransfer: %{time_pretransfer}\n
| starttransfer: %{time_starttransfer}\n
| total: %{time_total}\n
| size: %{size_download}\n
| HTTPCode=%{http_code}\n\n"
==============

 
| dnslookup: 0.002976
 
| connect: 0.003273
 
| appconnect: 0.000000
 
| pretransfer: 0.003293
 
| starttransfer: 0.003568
 
| total: 0.004242
 
| size: 17
 
| HTTPCode=413

[nateberkopec]

Great idea. I want to look at the code in a little more depth later, but I think this is a great feature for inclusion.

[nateberkopec]

This is a very important path so we'll need to be careful with anything we add here.

[shayonj]

Sounds good, appreciate the review. Yeah, definitely feels like something very useful. Especially when keeping puma workers snappy and fast by rejecting large requests.

I have been using it locally with our @tines monolith and works well (but ofc its local only). I will try to see if I can roll this out on some test stacks to test internally (but in prod) as well.

[nateberkopec]

Thank you for your change @shayonj 🙇

[shayonj]

Thanks @nateberkopec! Any ideas, when we can expect a release with this change? 🙌

[nateberkopec]

Probably in about 4 weeks? When I'm not busy, I try to release on a 4-week cadence. We just did a patch release so your commit was the first commit since that.