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# 4 Header and data length

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#### Overview

Header and data length are present in response and request messages
between Zabbix components. It is required to determine the length of
message.

    <HEADER> - "ZBXD\x01" (5 bytes)
    <DATALEN> - data length (8 bytes). 1 will be formatted as 01/00/00/00/00/00/00/00 (eight bytes, 64 bit number in little-endian format)

To not exhaust memory (potentially) Zabbix protocol is limited to accept
only 128MB in one connection.

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#### Implementation

Here are code snippets showing how to add Zabbix protocol header to the
`data` you *want* to send in order to obtain `packet` you *should* send
to Zabbix so it is interpreted correctly.

|Language|Code|
|--------|----|
|bash|`printf -v LENGTH '%016x' "${#DATA}"PACK=""for i in {14..0..-2}; do PACK="$PACK\\x${LENGTH:$i:2}"; doneprintf "ZBXD\1$PACK%s" $DATA`{.bash}|
|Java|`byte[] header = new byte[] {'Z', 'B', 'X', 'D', '\1',(byte)(data.length & 0xFF),(byte)((data.length >> 8) & 0xFF),(byte)((data.length >> 16) & 0xFF),(byte)((data.length >> 24) & 0xFF),'\0', '\0', '\0', '\0'};|
|<|byte[] packet = new byte[header.length + data.length];System.arraycopy(header, 0, packet, 0, header.length);System.arraycopy(data, 0, packet, header.length, data.length);`{.Java}|
|PHP|`$packet = "ZBXD\1" . pack('P', strlen($data)) . $data;`{.PHP}or`$packet = "ZBXD\1" . pack('V', strlen($data)) . "\0\0\0\0" . $data;`{.PHP}|
|Perl|`my $packet = "ZBXD\1" . pack('<Q', length($data)) . $data;`{.Perl}or`my $packet = "ZBXD\1" . pack('V', length($data)) . "\0\0\0\0" . $data;`{.Perl}|
|Python|`packet = "ZBXD\1" + struct.pack('<Q', len(data)) + data`{.Python}|

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