StringScanner#skip returns nil inside an invalid character in non-UTF-8 strings (was an exception in 3.1.6)
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调研方向
Start by comparing StringScanner#skip behavior in the reported strscan versions for the Shift_JIS and UTF-16LE examples, then inspect the implementation and tests for skip on non-UTF-8 strings. Decide whether returning nil is intended or should raise consistently with the prior behavior; done means the behavior is specified and covered by regression tests, including the reported encodings.
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描述
Thanks for maintaining strscan.
On Ruby master (strscan 3.1.9.dev), StringScanner#skip returns nil when the scan position is inside an invalid or misaligned character in a non-UTF-8 string. strscan 3.1.6 (Ruby 4.0.9) raises there:
require "strscan"
[["/\xFF".dup.force_encoding("Shift_JIS"), "Shift_JIS"], ["/a".encode("UTF-16LE"), "UTF-16LE"]].each do |str, name|
s = StringScanner.new(str)
s.pos = 1
p [name, (s.skip(/./) rescue $!.class)]
end
# master (strscan 3.1.9.dev): ["Shift_JIS", nil] ["UTF-16LE", nil]
# 4.0.9 (strscan 3.1.6): ["Shift_JIS", ArgumentError] ["UTF-16LE", Encoding::CompatibilityError]
The same input as UTF-8 ("/\xFF", pos 1) raises ArgumentError on both.
Is returning nil here intended? We noticed it because Rails' route-path scanner advances with pos += 1 and then relies on skip(/./) either matching or raising. With nil, its loop never advances, so ActionDispatch::Journey::Parser.parse hangs on master for paths such as "/\xFF|bc" in Shift_JIS. Such paths are rare, and Rails could guard its loop. We'd just like to know whether the new result is deliberate before we propose anything there.
Found while comparing Rails' request path on Ruby master and Ruby 4.0.9 (record, part of my research project Lowrail).
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