ltm rule command ASN1 element

iRule(1)		      BIG-IP TMSH Manual		      iRule(1)



ASN1::element
       Returns ASN1.1 record elements.

SYNOPSIS
       ASN1::element init ('BER' | 'DER')

       ASN1::element next ELEMENT (NUM_ELEMENTS)?

       ASN1::element byte_offset ELEMENT (OFFSET)?

       ASN1::element tag ELEMENT

       ASN1::element size ELEMENT

       ASN1::element length ELEMENT (LENGTH)?

DESCRIPTION
       This command returns ASN1.1 record elements.

       ASN1::element init encodingType

	    * Returns an element (Tcl_Obj) handle used by the remaining commands.
	      encodingType specifies the encoding type that subsequent commands
	      should use (BER|DER).

       ASN1::element next element ?numberOfElements?

	    * Returns the next element found after element. If numberOfElements
	      is specified, the command will move ahead that many elements,
	      otherwise, the default is 1.

       ASN1::element byte_offset element ?offset?

	    * Returns the byte offset within the payload. This is often useful
	      when using the encode command along with the TCP::payload replace
	      command where a byte offset is used to indicate the location within
	      the payload. If offset is specified, the element offset is set to
	      the specified value. Changing the byte offset is generally
	      discouraged and should be done with caution as it affects the
	      behavior of any other command which takes an element object as an
	      argument.

       ASN1::element tag element

	    * Returns the id (integer) of the leading tag found in element.

       ASN1::element size element

	    * Returns the size (in number of bytes) of the element's full TLV.
	      This is useful for passing to TCP::release.

       ASN1::element length element ?length?

	    * Returns the length (in number of bytes) of the element's value.
	      This is the L coded in the TLV. If length is specified, the length
	      of the element is modified. Changing the byte offset is generally
	      discouraged and should be done with caution as it could affect the
	      behvior of any other command which takes an element object as an
	      argument.

RETURN VALUE
VALID DURING
EXAMPLES
	Optimize LDAP performance allowing reuse of server connections by detaching clients upon client unbind

	when CLIENT_ACCEPTED {
	  TCP::collect
	}
	when CLIENT_DATA {
	 set ele [ASN1::element init BER]
	  # Skip ahead two elements and check for an unbind tag (0x62)
	  if { [ASN1::element tag [ASN1::element next $ele 2]] == 0x62 } {
	    log local0. "unbind => detach"
	    TCP::payload replace 0 [TCP::payload length] ""
	    LB::detach
	  }
	  TCP::release
	  TCP::collect
	}


	Change LDAP protocol version upon bindRequest

	when CLIENT_ACCEPTED {
	  TCP::collect
	}
	when CLIENT_DATA {
	  set ldap_msg [ASN1::element init BER]
	  set ele [ASN1::element next $ldap_msg 2]
	  set tag [ASN1::element tag $ele]

	  if { $tag == 0x60} {	# bindRequest
	    # Offset of the version number
	    set version_ele [ASN1::element next $ele]
	    set offset [ASN1::element byte_offset $version_ele]

	    # Set the version to v2
	    set buf [ASN1::encode BER "i" 0x02]
	    set size [ASN1::element size $version_ele]

	    # Replace the original version TLV
	    TCP::payload replace $offset $size $buf
	  }
	  TCP::release
	  TCP::collect
	}

HINTS
SEE ALSO
CHANGE LOG
       @BIGIP-11.5.0 --First introduced the command.



BIG-IP				  2017-01-31			      iRule(1)