[ruby-core:91184] [Ruby trunk Bug#15517] Net::HTTP not recognizing valid UTF-8

Issue #15517 has been updated by duerst (Martin Dテシrst).


I think this issue is not a duplicate of issue #2567, but it is clearly related.

Checking whether the string is valid UTF-8 is rather easy;
```
string.force_encoding('UTF-8').valid_encoding?
```
should do.

There are some security issues with browsers accepting certain mime types in certain encodings, and servers might mislabel stuff, but for `text/plain; charset=utf-8`, the text/plain part isn't a security issue, and text/plain doesn't have any way of indicating the encoding inside the document, so there should be no problems declaring the encoding of the resulting string as UTF-8.

----------------------------------------
Bug #15517: Net::HTTP not recognizing valid UTF-8
https://bugs.ruby-lang.org/issues/15517#change-76415

* Author: cohen (Cohen Carlisle)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.6.0
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
I created a case at https://github.com/Cohen-Carlisle/utf8app that shows Net::HTTP labeling a response body as ASCII-8BIT encoded because it contains a non-ascii character (specifically, the double prime symbol: 窶ウ), but recognizing ascii-only strings as UTF-8 encoded. The example is live on heroku but because it's a free dyno, it will go to sleep and take a while to start up the first time it is hit after a while.

As explained there, I would expect response body strings with the double prime symbol to still have an encoding of UTF-8 since they are valid UTF-8.

The README from the repo (which shows the behavior) is reproduced below:



The purpose of this app is to demonstrate unexpected behavior in Ruby's net/http library. Valid UTF-8 response bodies are encoded as ASCII-8BIT, which apparently means Ruby is treating them as pure binary data, even when Content-Type headers label the body as UTF-8.

In the example below, I would expect the response body to have UTF-8 encoding. Especially because when I copy and paste the body into a new string literal in my console, that string is UTF-8 encoded.

~~~
require 'net/http'
uri = URI('https://utf8app.herokuapp.com')
uri.path = '/utf8/example'
res = Net::HTTP.get_response(uri)
res['Content-Type']
# => "text/plain; charset=utf-8"
puts res.body
# The symbol for the inch unit of measurement is 窶ウ.
res.body.encoding
# => #<Encoding:ASCII-8BIT>
res.body.ascii_only?
# => false
'The symbol for the inch unit of measurement is 窶ウ.'.encoding
# => #<Encoding:UTF-8>
~~~

We can demonstrate that the encoding issue is due to the non-ascii inches symbol by replacing it with a double quote instead.

~~~
uri.path = '/ascii/example'
res = Net::HTTP.get_response(uri)
res['Content-Type']
# => "text/plain; charset=utf-8"
puts res.body
# The symbol for the inch unit of measurement is ".
res.body.encoding
# => #<Encoding:UTF-8>
res.body.ascii_only?
# => true
~~~

Finally, as an extra WTF, JSON.parse recognizes the non-ascii characters as valid UTF-8 in a JSON example.

~~~
require 'json'
uri.path = '/utf8/example_json'
res = Net::HTTP.get_response(uri)
res['Content-Type']
# => "application/json; charset=utf-8"
puts res.body
# {"feet":"窶イ","inches":"窶ウ"}
res.body.encoding
# => #<Encoding:ASCII-8BIT>
json = JSON.parse(res.body)
# => {"feet"=>"窶イ", "inches"=>"窶ウ"}
json.values.map { |v| [v.encoding.to_s, v] }
# => [["UTF-8", "窶イ"], ["UTF-8", "窶ウ"]]
~~~




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