[ruby-core:108159] [Ruby master Bug#16672] net/http leaves original content-length header intact after inflating response

Issue #16672 has been updated by st0012 (Stan Lo).


@MSP-Greg I've also noticed this today and reported it in the net/http repo: https://github.com/ruby/net-http/issues/49
And also proposed a fix for it: https://github.com/ruby/net-http/pull/50

----------------------------------------
Bug #16672: net/http leaves original content-length header intact after inflating response
https://bugs.ruby-lang.org/issues/16672#change-97136

* Author: jmreid (Justin Reid)
* Status: Closed
* Priority: Normal
* Assignee: naruse (Yui NARUSE)
* ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin19]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
When using net/http to make a request to a resource, the default request headers are the following (when you have ZLIB available):
`"accept-encoding"=>["gzip;q=1.0,deflate;q=0.6,identity;q=0.3"], "accept"=>["*/*"], "user-agent"=>["Ruby"]`

This means that a resource will return a gzipped response if it can provide it. Take this URL for example:
`https://storage.googleapis.com/justin-reid-test/test.js`

This is a JS file that has a `content-length` of `2733` when gzipped and `9995` when inflated:

```
curl "https://storage.googleapis.com/justin-reid-test/test.js" -H "accept-encoding: gzip;q=1.0,deflate;q=0.6,identity;q=0.3" | wc -c
2733

curl "https://storage.googleapis.com/justin-reid-test/test.js" | wc -c
9995
```


When making a simple request for this asset using net/http:
```
uri = URI('https://storage.googleapis.com/justin-reid-test/test.js')
res = Net::HTTP.get_response(uri)
```

Ruby will (https://github.com/ruby/ruby/blob/f08cd708b11dd5b293986b92bb5e227731665b36/lib/net/http/response.rb#L264-L278):
- Delete the `content-encoding` header
- inflate the body
- return the inflated body

The issue here is that Ruby also leaves the `content-length` header set to the original request's value:
```
require 'net/http'

uri = URI('https://storage.googleapis.com/justin-reid-test/test.js')
res = Net::HTTP.get_response(uri)

puts "Fetching: https://storage.googleapis.com/justin-reid-test/test.js"
puts "Body size using String#bytesize: #{res.body.to_s.bytesize}"
puts "Content-Length response header: #{res.content_length}"
```

Results in:
```
Fetching: https://storage.googleapis.com/justin-reid-test/test.js
Body size using String#bytesize: 9995
Content-Length response header: 2733
```

This means that an incorrect `content-length` header is passed back when net/http makes requests for gzip objects and inflates them. 


This issue was noticed when Rack changed their behaviour in how they compute content-length. They used to compute the content-length for each body, but that changed in 2.0.8:
https://github.com/rack/rack/commit/8c62821f4a464858a6b6ca3c3966ec308d2bb53e#diff-10b933d2c1fdc82ceecade456c64e1c2L92
https://github.com/rack/rack/issues/1472#issuecomment-574362342

Using `Rack::ContentLength` is now the method they prefer if you need to compute the content-length. However, `Rack::ContentLength` will not try to re-compute the value if that header already exists:
https://github.com/rack/rack/blob/6196377654b7ff7ce7abaecea62bb285d77d53aa/lib/rack/content_length.rb#L21

Should Ruby:
- Do a `self.delete 'content-length'` in the inflater?
- Compute the `content-length` itself and update the header? (Hacky example: https://github.com/ruby/ruby/compare/master...jmreid:content-length)





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