Forum Discussion

Walter_Kacynski's avatar
Walter_Kacynski
Icon for Cirrostratus rankCirrostratus
Feb 25, 2016

ASCII LF (0a) in STREAM

Is there a way to represent the hex 0a in the target of a STREAM::expression? Everything I try causes the literal "0a" or "\n" to be inserted instead of the representation of LF.

STREAM::expression {@\x0d@\x0a@}

Result of replacement is "\x0a" (5c 78 30 61)

STREAM::expression {@\x0d@\n@}

STREAM::expression {@\r@\n@}

Both of these cause the replacement to be the literal "\n" (5c 6e). Is seems that the search operations handles regex/hex just fine, but the replacement chokes on anything other than ASCII.

application delivery
iRules
stream profile
  • Kai_Wilke's avatar
    Kai_Wilke
    Icon for MVP rankMVP
    Feb 25, 2016

    Hi Walther,

    the fix is rather simple. Don't use 

    {
    Curly-Braces
    }
    to allow the 
    \n
    to become substituted... 😉

    STREAM::expression "@\n@\n\n\n@"

    Cheers, Kai

  • Walter_Kacynski's avatar
    Walter_Kacynski
    Icon for Cirrostratus rankCirrostratus
    Feb 25, 2016

    In case someone else needs to perform a substitution on something not as simple as "\r" or "\n"... I just came up with this explanation...

    With some guidance from https://devcentral.f5.com/wiki/iRules.TCP__payload.ashx and some confusion over when to use decimal or hex, I came up with the following solution

    when CLIENT_ACCEPTED {
     Store hex 0a (Decimal of 10) as a binary format 
    set replacement [binary format c* {10}]
    STREAM::expression @\r@$replacement@
    STREAM::enable
}