iRule Preprocessor

[Michael_Earnhar]

Problem this snippet solves:

The engine works by converting a template (which is a string, or a file) into a TCL script, and then running it. Nearly each line of text encountered will be returned as is. The exception is text between =<% ... %>= which is treated as Tcl code (the eval happens in a safe interp, see Safe Interps). This makes it very flexible and it leaves you freedom of doing what you want, dealing with any data and putting how much code you want in the template.

Also for convenience there is a

<%= ... %>

for spooling output (the proc _defaultSpool takes care of sending the text to the right place; you can change that: see Preprocessor Commands).

How to use this snippet:

Template Syntax

Delimiter/Command	Name	Description
<%	Code	the beginning of a template code block
<%=	Output	the beginning of a template code block that after it is evaluated by the tcl interpreter will hand the results to a function defined by printCommand option
<@%	Preprocessor Code	the beginning of an options block used to set template options such as printCommand, logCommand
<l%	Default Logging Code	the beginning of a logging code block with the log threshold set to 0
<l[0-9]%	Level Select Logging Code	the beginning of a logging code block with the log threshold set to [0-9]
<l%=	Default Logging Output	the beginning of a logging code block with the log threshold set to 0 which after it is evaluated by the tcl interpreter will hand the results to a function defined by logCommand option
<l[0-9]%=	Level Select Logging Output	the beginning of a logging code block with the log threshold set to [0-9] which after it is evaluated by the tcl interpreter will hand the results to a function defined by logCommand option
%>	Close Code/Output Block	ends the current block of template code for all types of template code blocks

Template Commands

Command	Arguments	Options	Returns	Explanation
ipp:import_irule_template	BIG-IP_file_object	none	string templateHandle	Reads the file referenced by the file object and returns a template handle
ipp::setVar	templateHandle templateVariable value	none	none	set the templateVariable to "value" which will be used when ipp::render is run
ipp::setLog	templateHandle logLevel	none	none	sets the global log level to a value 0-9 for the template specified by templateHandle which will be used when ipp::render is run
ipp::disableLog	templateHandle	none	none	globally disables template logging statements
ipp::render	templateHandle	none	string templateResult	renders out the template specified by templateHandle with all the information provided by the template and the other various methods mentioned above

Simple example

iRule Code

when HTTP_REQUEST {
    set uri [HTTP::uri]
    if {0} {
         log local0. "You should never see this"
    } elseif {[regexp {*.jpg$} $uri]} {
        pool /Common/test1
    } elseif {[regexp {^test*} $uri]} {
        pool /Common/test2
        log local0. "Sending connection from: [IP::remote_addr] to pool: /Common/test1"
    } else {
        log local0. "No match Found"
}
} 

Template Code

1.  when HTTP_REQUEST {
2.      set uri [HTTP::uri]
3.      
4.      
5.      
6.      
7.      if {0} {
8.           log local0. "You should never see this"
9.  <% foreach row $rows { %>
10. <% foreach {regex pool logEnabled} $row break %>
11.     } elseif {[regexp {<%=$regex%>} $uri]} {
12.         pool <%=$pool%>
13. <% if { $logEnabled {{}} "Yes" } { %>
14.         log local0. "Sending connection from: [IP::remote_addr] to pool: <%=$pool%>"
15. <% } } %>
16.     } else {
17.         log local0. "No match Found"
18.     }
19. }

Line by Line

Line	Explaination	Result
1	a literal line	put =when HTTP_REQUEST {= into content
2	a literal line	put =set uri [HTTP::uri]= into content
3	a log line with a log level threshold equal to 1	if logLevel >= 1; then put =log local0. "[HTTP::uri]"= into content
4	a log line with a log level threshold equal to 2	if logLevel >= 2; then put =log local0. "Client IP: [IP::client_addr]"= into content
5	a log line with a log level threshold equal to 4	if logLevel >= 4; then put =log local0. "Client Port: [TCP::remote_port]"= into content
6	a log line with a log level threshold equal to 3	if logLevel >= 3; then put =log local0. "Local IP: [IP::local_addr]"= into content
7	a literal line	put =if {0} {= into content
8	a literal line	put =log local0. "You should never see this"= into content
9	template Code	evaluate =foreach row $rows {=
10	template Code	evaluate =foreach {regex pool logEnabled} $row break=
11	literal with inline template Output code	put =} elseif {[regexp {[puts $regex]} elseif {[regexp {= where $regex is evaluated within the template scope into content
12	literal with inline template Output code	put =pool [put $pool]= where $pool is evaluated within the template scope into content
13	template Code	evaluate =if { $logEnabled }} "Yes" } {=
14	literal with inline template Output code	put =log local0. "Sending connection from: [IP::remote_addr] to pool: [puts $pool]"= where $pool is evaluated within the template scope into content
15	template Code	evaluate =} }=
16	literal line	put =} else {= into content
17	literal line	put =log local0. "No match Found"= into content
18	literal line	put } into content
19	literal line	put } into content

A few Crucial Notes

the

content

variable is the variable where the rendered result is built up and what is eventually returned to the user as the output of {{ipp::render

Preprocessor Configuration

proc _newLog {args} { 
      global content
      set txt "#[join $args]"
      append content $txt 
}

Versions

ipp.1.2.tcl.zip it works MORE perfectly (as of this writing)