1 files changed, 36 insertions, 0 deletions
diff --git a/lib/readbytes.rb b/lib/readbytes.rb
new file mode 100644
index 0000000000..d6a3b10afe
--- /dev/null
+++ b/lib/readbytes.rb
@@ -0,0 +1,36 @@
+# 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
+  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