b64decode errors...

Question

&nbsp; I'm doing some testing on an iRule that uses b64decode to decode the cookie contents. The documentation (Wiki) says that b64decode returns the decoded string, OR "" if an error occurs. 
&nbsp;  
&nbsp; However what I'm finding is that b64decode either works (If given a valid b64encoded string), or causes a TCL error if it's fed something else (e.g. Corrupt cookie) and the connection is reset. 
&nbsp;  
&nbsp; Is this a bug (In 9.3.1HF4)? Or bad documentation?

colin_walker_12 · Answer

I'll have to poke around to see if this is an issue on your particular version or a broader problem. I haven't run into this yet, personally. 
  
 In the meantime you can use the catch command to stop the connection from being reset on error. 
  
 something like:

[catch [b64decode ...]]

Colin

hoolio · Answer

I think it's been this way for a while.  I have rules going back about two years where I was using catch to handle b64decode errors.  The general method I've tried is to use catch and check that the result is not null length:

Try to base64 decode $string_b64encoded. Handle errors using catch. 
    Successful execution of b64decode by catch will return 0 and the output will be written to $string_b64decoded 
 if {[catch {b64decode $string_b64encoded} string_b64decoded] == 0 and $string_b64decoded ne ""}{ 
     base64 decoding succeeded 
 } else { 
     base64 decoding failed 
 }

Aaron

hamish · Answer

Ah! 
&nbsp;  
&nbsp; Cheers Hoolio! 
&nbsp;  
&nbsp;  
&nbsp; H

hoolio · Answer

I added some notes to the b64decode wiki page to describe this (Click here).  
&nbsp; Aaron

luke_lehman · Answer

Hey all, &nbsp;
&nbsp;I'm using Aaron's code in an iRule I'm working on, but I'm having trouble validating the content a little further down. &nbsp;
&nbsp;Initially, I use this code: &nbsp;&nbsp;
 Try to base64 decode $string_b64encoded. Handle errors using catch.
 Successful execution of b64decode by catch will return 0 and the output will be written to $b64decoded_member_ip
if {[catch {b64decode $query_b64encoded_member_ip} b64decoded_member_ip] == 0 and $b64decoded_member_ip ne ""}{
    base64 decoding succeeded
   if { $::debug } {log local0. "b64 decoding successful: $b64decoded_member_ip"}
   set b64decoded_member_ip_2 $b64decoded_member_ip
} else {
    base64 decoding failed = non-valid IP Address
   set member_ip_valid "false"
   if { $::debug } {log local0. "b64 decoding failed"}
}&nbsp;&nbsp;&nbsp;
&nbsp;So if the decoding works, then in the var $b64decoded_member_ip is set. 
&nbsp;If the decoding fails, it toggles the switch $member_ip_valid so that the iRule won't try to use the value later. &nbsp;
&nbsp;At this point, I want to validate that the decoded value is a valid IP address, so I use the following code: &nbsp;&nbsp; log local0. "catch $b64decoded_member_ip =&gt; [catch {IP::addr $b64decoded_member_ip mask 255.255.255.255} ]"
set a "256.256.256.256"
log local0. "catch $a =&gt; [catch {IP::addr $a mask 255.255.255.255} ]"
set b "192.168.130.157"
log local0. "catch $b =&gt; [catch {IP::addr $b mask 255.255.255.255} ]" &nbsp;
&nbsp;The logs look like this: &nbsp;&nbsp; Feb 22 14:54:45 local/tmm info tmm[5018]: Rule iRule : b64 decoding successful: 192.168.130.156
Feb 22 14:54:45 local/tmm info tmm[5018]: Rule iRule : catch 192.168.130.156 =&gt; 1
Feb 22 14:54:45 local/tmm info tmm[5018]: Rule iRule : catch 256.256.256.256 =&gt; 1
Feb 22 14:54:45 local/tmm info tmm[5018]: Rule iRule : catch 192.168.130.157 =&gt; 0
Feb 22 14:54:45 local/tmm info tmm[5018]: Rule iRule : catch 192.168.130.156 =&gt; 0 &nbsp;
&nbsp;It's the 2nd line there that baffles me. As you can see the 5th line has the exact same value, but passes the doesn't match the catch. &nbsp;
&nbsp;Does this have something to do with variable types that IP:addr can or can't handle? &nbsp;
&nbsp;Thanks!

Forum Discussion

Jonathan - March 2026 Featured Member

F5 AppWorld 2026 Las Vegas - iRules Contest Winners!

2026 F5 DevCentral MVP Announcement

Recent Discussions

Related Content

Error post F5 upgrade

error code 503 redirect irule

winscp error

File Permissions Errors When Installing F5 Application Study Tool? Here’s Why.

BIG-IP methods to Fix the “421 Misdirected Request” Error

ABOUT DEVCENTRAL

RESOURCES

SUPPORT

PARTNERS