Log large HTTP payloads in chunks locally and remotely

Problem this snippet solves:

Log HTTP POST request payloads remotely via High Speed Logging (HSL) to a syslog server and locally.

Code :

# Log POST request payloads remotely via HSL to a syslog server and locally.

# Based on Steve Hillier's example and the HTTP::collect wiki page
# https://devcentral.f5.com/s/wiki/iRules.http__collect.ashx
# Note that although any size payload can theoretically be collected, the maximum size of a Tcl variable in v9 and v10 is 4MB 
#   with a smaller functional maximum after charset expansion of approximately 1Mb.
# In v11, the maximum variable size was increased to 32Mb.

when RULE_INIT {

# Log debug to /var/log/ltm? 1=yes, 0=no
set static::payload_dbg 1

# Limit payload collection to 5Mb
set static::max_collect_len 5242880

# HSL pool name
set static::hsl_pool "my_hsl_tcp_pool"

# Max characters to log locally (must be less than 1024 bytes)
# https://devcentral.f5.com/s/wiki/iRules.log.ashx
set static::max_chars 900
}
when HTTP_REQUEST {

# Only collect POST request payloads
if {[HTTP::method] equals "POST"}{

if {$static::payload_dbg}{log local0. "POST request"}

# Open HSL connection
set hsl [HSL::open -proto TCP -pool $static::hsl_pool]


# Get the content length so we can request the data to be processed in the HTTP_REQUEST_DATA event.
if {[HTTP::header exists "Content-Length"]}{
set content_length [HTTP::header "Content-Length"]
} else {
set content_length 0
}
# content_length of 0 indicates chunked data (of unknown size)
if {$content_length > 0 && $content_length < $static::max_collect_len}{
set collect_length $content_length
} else {
set collect_length $static::max_collect_len
}  
if {$static::payload_dbg}{log local0. "Content-Length: $content_length, Collect length: $collect_length"}
}
}

when HTTP_REQUEST_DATA {

# Log the bytes collected
if {$static::payload_dbg}{log local0. "Collected [HTTP::payload length] bytes"}

# Send all the collected payload to the remote syslog server
HSL::send $hsl "<190>[HTTP::payload]\n"

# Log the payload locally 
if {[HTTP::payload length] < $static::max_chars}{
log local0. "Payload=[HTTP::payload]"
} else {
# Initialize variables
set remaining $payload
set position 0
set count 1
set bytes_logged 0

# Loop through and log each chunk of the payload
while {[string length $remaining] > $static::max_chars}{

# Get the current chunk to log (subtract 1 from the end as string range is 0 indexed)
set current [string range $remaining $position [expr {$position + $static::max_chars -1}]]
log local0. "chunk $count=$current"

# Add the length of the current chunk to the position for the next chunk
incr position [string length $current]

# Get the next chunk to log
set remaining [string range $remaining $position end]
incr count
incr bytes_logged $position
log local0. "remaining bytes=[string length $remaining], \$position=$position, \$count=$count, \$bytes_logged=$bytes_logged"
}
if {[string length $remaining]}{
log local0. "chunk $count=$current"
incr bytes_logged [string length $remaining]
}
log local0. "Logged $count chunks for a total of $bytes_logged bytes"
}
}