Bug #20819
open
IO#readline does not process newlines correctly for wide character encodings
Description
When not performing character conversion, IO#readline only processes newline characters as ASCII when reading paragraphs. However, when character conversion is involved, even when converting between 2 ASCII incompatible encodings, newline handling is correct.
require "tempfile"
Tempfile.open(binmode: true) do |f|
f.set_encoding("utf-16le")
f.write("\n\n\n\nhello\n\nworld")
f.rewind
# No character conversion case.
# Expecting "hello\n\n".encode(Encoding::UTF_16LE)
f.readline("") # => "\0".force_encoding(Encoding::UTF_16LE) + "\n\n\nhello\n\nworld".encode(Encoding::UTF_16LE)
f.set_encoding("utf-16le:utf-32le")
f.rewind
# Character conversion case.
f.readline("") # => "hello\n\n".encode(Encoding::UTF_32LE)
end
In the failing case, a newline character appears in the first byte of the input due to the UTF-16LE encoding. This is discarded per the normal behavior of reading paragraphs, but the following null byte is not consumed as required to consume the entire newline character in UTF-16LE encoding. This leads to a leading and invalid null byte in the output of IO#readline. Furthermore, the newlines between "hello" and "world" are not seen as a pair of newline characters sufficient to end the first paragraph because they are not ASCII newlines and instead have a null byte between them.
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