Bug #13949: String#unpack with 'M' directive can create strings with wrong code range - Ruby master - Ruby Issue Tracking System

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Bug #13949

closed

String#unpack with 'M' directive can create strings with wrong code range

Added by nirvdrum (Kevin Menard) about 7 years ago. Updated almost 7 years ago.

Status:

Closed

Assignee:

Target version:

ruby -v:

ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-linux]

Backport:

2.3: DONE, 2.4: DONE

[ruby-core:83055]

Description

I've noticed that String#unpack with the 'M' directive can create strings that should be CR_7BIT as CR_VALID. The issue appears to have been introduced in r30542, which assumes that all ASCII-8BIT strings must be CR_VALID. It's possible this was correct back during Ruby 1.9.3 development and just wasn't updated. I'm not familiar enough with the history to tell.

A simple reproduction showing the issue is:

res = '0123456789=\n'.unpack('M').first
p res
p res.encoding
p res.bytes
p res.ascii_only?

puts

packed = res.bytes.pack('c*')
p packed
p packed.encoding
p packed.bytes
p packed.ascii_only?

This yields the following output:

"0123456789=\\n"
#<Encoding:ASCII-8BIT>
[48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 61, 92, 110]
false

"0123456789=\\n"
#<Encoding:ASCII-8BIT>
[48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 61, 92, 110]
true

Both strings have exactly the same contents with the same encoding. But, depending on how you construct them, one is consider to be CR_7BIT value (indicated by the String#ascii_only? output), and one is considered to be CR_VALID. I believe CR_7BIT is the correct code range value in this situation.