Issue #11410 has been reported by Ethan Brown.

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Bug #11410: Win32 Registry enumeration performs unnecessary string re-encoding which cause UndefinedConversionError exceptions
https://bugs.ruby-lang.org/issues/11410

* Author: Ethan Brown
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.1.5p273 (2014-11-13 revision 48405) [x64-mingw32]
* Backport: 2.0.0: DONTNEED, 2.1: REQUIRED, 2.2: REQUIRED
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When enumerating keys with `Win32::Registry#each_key` / `Win32::Registry#keys` or values with `Win32::Registry#each_value` / `Win32::Registry#values`, Ruby will take a `UTF-16LE` string returned from the Windows API and convert it to the local codepage.  In the case of `each_value`, the string is then immediately converted back to `UTF16-LE` before being used in subsequent Windows API calls.  Not only is this conversion unnecessary, but it may cause encoding exceptions when the local codepage does not support all of the characters present in the original Unicode string.

One such example of this is when a Unicode en-dash `U+2013` appears in a string, and the local codepage is `IBM437`, which has no equivalent character. But this is just one of many examples that may trigger this behavior. 


~~~
[1] pry(main)> RUBY_VERSION
=> "2.1.5"
[2] pry(main)> ENDASH_UTF_16 = [0x2013]
=> [8211]
[3] pry(main)> utf_16_str = ENDASH_UTF_16.pack('s*').force_encoding(Encoding::UTF_16LE)
=> "\u2013"
[4] pry(main)> utf_16_str.encode(Encoding::IBM437)
Encoding::UndefinedConversionError: U+2013 to IBM437 in conversion from UTF-16LE to UTF-8 to IBM437
from (pry):4:in `encode'
~~~


NOTE: Normal registry reads of a value at a particular key are not problematic - the bad behavior is triggered specifically during enumeration. 

This is primarily as a result of the `export_string` function which re-encodes strings
https://github.com/ruby/ruby/blob/ruby_2_1/ext/win32/lib/win32/registry.rb#L894-L896


It is used by `each_value` and `each_key`, which return `UTF-16LE` strings:

https://github.com/ruby/ruby/blob/ruby_2_1/ext/win32/lib/win32/registry.rb#L561
https://github.com/ruby/ruby/blob/ruby_2_1/ext/win32/lib/win32/registry.rb#L598


In the `each_value` method, this LOCALE re-encoded string is then passed to the `read` method, where it is turned back into a `UTF16-LE` string to be passed to `RegQueryValueExW`

https://github.com/ruby/ruby/blob/v2_1_5/ext/win32/lib/win32/registry.rb#L563
https://github.com/ruby/ruby/blob/v2_1_5/ext/win32/lib/win32/registry.rb#L631
https://github.com/ruby/ruby/blob/v2_1_5/ext/win32/lib/win32/registry.rb#L307


Inside Puppet, we employed a solution that avoids Ruby's `Win32::Registry` when performing enumeration, and relies on internal helpers instead (avoiding unnecessary string encodings).  This was unfortunate, but necessary:
https://github.com/puppetlabs/puppet/commit/c610cd01eeef3fafa7aa2761a3435dd6c1b0d8d4

Note also that we typically convert `UTF-16LE` strings to `UTF-8` internally (since this is almost always guaranteed to be a lossless conversion), until we reach an end-user boundary where they absolutely need a specific encoding rendered. For instance, our version of `read` converts to `UTF8`:
https://github.com/puppetlabs/puppet/blob/c610cd01eeef3fafa7aa2761a3435dd6c1b0d8d4/lib/puppet/util/windows/registry.rb#L211-L214



I suggest that other locations where strings are re-encoded be examined for potential issues, as locale codepage conversions are generally considered dangerous given Win32 APIs use `UTF-16LE`.



-- 
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