[erlang-patches] Limit maximum line length in interactive shells

Stefan Zegenhagen <>
Tue May 7 14:29:44 CEST 2013

Dear all,

one of our testers found out that he could reliably reboot our
erlang-based device by just sending tons of 'A' characters to an
interactive shell.

It appears that the I/O server of the interactive shell (in group.erl)
is always reading a full line before doing any end-of-input processing,
so that by sending bytes without a newline in between, it slowly eats up
all available memory.

The patch attached to this e-mail fixes that by introducing a new
io:setopt() option in group.erl named 'max_length' that is used to check
whether the current line length exceeds this maximum whenever the line
is edited. If an overlong line is detected, max_length bytes are
returned immediately (without the actual stop condition being fulfilled,
though, allowing I/O clients to detect this situation).

max_length is allowed to be an integer() > 0 or 'unlimited'. The default
is 'unlimited' to have the old behaviour by default.

Kind regards,

Dr. Stefan Zegenhagen

arcutronix GmbH
Garbsener Landstr. 10
30419 Hannover

Tel:   +49 511 277-2734
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