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# readbytes.rb
#
# add IO#readbytes, which reads fixed sized data.
# it guarantees read data size.
class TruncatedDataError<IOError
def initialize(mesg, data)
@data = data
super(mesg)
end
attr_reader :data
end
class IO
# reads exactly n bytes from the IO stream.
# If the data read is nil, raises EOFError.
# If the data read is too short, raises TruncatedDataError.
# The method TruncatedDataError#data may be used to obtain
# the truncated message.
def readbytes(n)
str = read(n)
if str == nil
raise EOFError, "End of file reached"
end
if str.size < n
raise TruncatedDataError.new("data truncated", str)
end
str
end
end
if __FILE__ == $0
begin
loop do
print STDIN.readbytes(6)
end
rescue TruncatedDataError
p $!.data
raise
end
end
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