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instance method

Psych::Parser#strip_bom

strip_bom(yaml)

ext/psych/lib/psych/parser.rb View on GitHub ↗

# File tmp/rubies/ruby-4.1.0-preview1/ext/psych/lib/psych/parser.rb, line 81
def strip_bom yaml
  if String === yaml
    bom = BOM[yaml.encoding]
    # delete_prefix copies even when there is no prefix, so keep the guard.
    return yaml.delete_prefix(bom) if bom && yaml.start_with?(bom)
  elsif yaml.respond_to?(:read) && yaml.respond_to?(:external_encoding) &&
        yaml.respond_to?(:pos) && yaml.respond_to?(:seek)
    bom = BOM[yaml.external_encoding]
    skip_io_bom yaml, bom.b if bom
  end
  yaml
end

libyaml only skips a leading byte order mark when it detects the stream encoding by itself. Psych passes the encoding explicitly whenever it is known, and on that path libyaml counts the BOM as a first-line character, which shifts the column of every token on the first line and silently terminates a block mapping at the second line [Bug #13615].