Documentation

Table of Contents

6 Header
- Overview
- Structure
- Examples
  - Python
  - Perl
  - PHP
  - Bash

Overview

The header is present in all request and response messages between Zabbix components. It is required to determine the message length, if it is compressed or not, if it is a large packet or not.

Zabbix communications protocol has 1GB packet size limit per connection. The limit of 1GB is applied to both the received packet data length and the uncompressed data length.

When sending configuration to Zabbix proxy, the packet size limit is increased to 4GB to allow syncing large configurations. When data length before compression exceeds 4GB, Zabbix server automatically starts using the large packet format (0x04 flag) which increases the packet size limit to 16GB.

Note that while a large packet format can be used for sending any data, currently only the Zabbix proxy configuration syncer can handle packets that are larger than 1GB.

Structure

The header consists of four fields. All numbers in the header are formatted as little-endian.

Field	Size	Size (large packet)	Description
`<PROTOCOL>`	4	4	`"ZBXD"` or `5A 42 58 44`
`<FLAGS>`	1	1	Protocol flags: `0x01` - Zabbix communications protocol `0x02` - compression `0x04` - large packet
`<DATALEN>`	4	8	Data length.
`<RESERVED>`	4	8	When compression is used (`0x02` flag) - the length of uncompressed data When compression is not used - `00 00 00 00` Contains item timeout value in passive check request.

Examples

Here are some code snippets showing how to add Zabbix protocol header to the data you want to send in order to obtain the packet you should send to Zabbix so that it is interpreted correctly. These code snippets assume that the data is not larger than 1GB, thus the large packet format is not used.

Python

packet = b"ZBXD\1" + struct.pack("<II", len(data), 0) + data

or

def zbx_create_header(plain_data_size, compressed_data_size=None):
           protocol = b"ZBXD"
           flags = 0x01
           if compressed_data_size is None:
               datalen = plain_data_size
               reserved = 0
           else:
               flags |= 0x02
               datalen = compressed_data_size
               reserved = plain_data_size
           return protocol + struct.pack("<BII", flags, datalen, reserved)
       
       packet = zbx_create_header(len(data)) + data

Perl

my $packet = "ZBXD\1" . pack("(II)<", length($data), 0) . $data;

or

sub zbx_create_header($;$)
       {
           my $plain_data_size = shift;
           my $compressed_data_size = shift;
       
           my $protocol = "ZBXD";
           my $flags = 0x01;
           my $datalen;
           my $reserved;
       
           if (!defined($compressed_data_size))
           {
               $datalen = $plain_data_size;
               $reserved = 0;
           }
           else
           {
               $flags |= 0x02;
               $datalen = $compressed_data_size;
               $reserved = $plain_data_size;
           }
       
           return $protocol . chr($flags) . pack("(II)<", $datalen, $reserved);
       }
       
       my $packet = zbx_create_header(length($data)) . $data;

PHP

$packet = "ZBXD\1" . pack("VV", strlen($data), 0) . $data;

or

function zbx_create_header($plain_data_size, $compressed_data_size = null)
       {
           $protocol = "ZBXD";
           $flags = 0x01;
           if (is_null($compressed_data_size))
           {
               $datalen = $plain_data_size;
               $reserved = 0;
           }
           else
           {
               $flags |= 0x02;
               $datalen = $compressed_data_size;
               $reserved = $plain_data_size;
           }
           return $protocol . chr($flags) . pack("VV", $datalen, $reserved);
       }
       
       $packet = zbx_create_header(strlen($data)) . $data;

Bash

datalen=$(printf "%08x" ${#data})
       datalen="\\x${datalen:6:2}\\x${datalen:4:2}\\x${datalen:2:2}\\x${datalen:0:2}"
       printf "ZBXD\1${datalen}\0\0\0\0%s" "$data"