Plugin: network

• infos = Information about network plugin is in keys below
• infos/author = Markus Raab elekt.nosp@m.ra@l.nosp@m.ibele.nosp@m.ktra.nosp@m..org
• infos/licence = BSD
• infos/provides = check
• infos/needs =
• infos/placements = presetstorage
• infos/status = maintained unittest nodep libc
• infos/metadata = check/ipaddr check/port check/port/listen
• infos/description = Checks keys if they contain a valid ip address

Introduction

This plugin is a check plugin that checks if a key contains a valid ip address. It uses the POSIX.1-2001 interface getaddrinfo() in order to check if an ip address is valid.

Furthermore getaddrinfo() is used in check/port to resolve a port by its service name which is defined under /etc/services. The portname is translated to the respective portnumber. The plugin can be used to check for valid port numbers and if the set port is free to use.

Purpose

While, in theory, a regular expression can express if a string is a network address, in practice, such an attempt does not work well. The reason is that an unmanageable number of valid shortenings for IPv6 addresses makes the regular expression hard to write and understand.

So the idea of building such a complicated regular expression was discarded, but instead a dedicated checker was introduced. The idea is to use the operating system facilities to resolve the network address. If this succeeds, it is guaranteed that this network address will be valid when it is resolved by the same interface afterwards.

Many network address translators coexist. In POSIX.1-2001 a powerful address translator is provided with the interface getaddrinfo(). It is a common network address translation for both IPv4 and IPv6. We used it to implement this plugin.

Usage

Every key tagged with the metakey check/ipaddr will be checked using getaddrinfo(). If additionally the values ipv4 or ipv6 are supplied, the address family will be specified.

Example

# Mount Network plugin to `user:/tests/network`
sudo kdb mount config.file user:/tests/network network
 
# Set valid IPv4 address
kdb set user:/tests/network/host 127.0.0.1
# Check for valid IPv4 address
kdb meta-set user:/tests/network/host check/ipaddr ipv4
 
# Try to set invalid IPv4 address
kdb set user:/tests/network/host 133.133.133.1337
# RET: 5
# STDERR:.*Validation Semantic: name:.*133.133.133.1337.*
kdb get user:/tests/network/host
#> 127.0.0.1
 
# Set valid IPv4 address
kdb set user:/tests/network/host 1.2.3.4
#> Set string to "1.2.3.4"
kdb get user:/tests/network/host
#> 1.2.3.4
 
# Check for any valid network address
kdb meta-set user:/tests/network/host check/ipaddr ''
# If identifier `localhost` is not a valid network address it is not part of /etc/hosts
kdb set user:/tests/network/host localhost || ! grep -q localhost /etc/hosts
 
kdb get user:/tests/network/host
# STDOUT-REGEX: localhost|1.2.3.4
 
# Undo modifications to the key database
kdb rm -r user:/tests/network
sudo kdb umount user:/tests/network

If check/port is specified on a given key, the plugin will validate if the port is a correct number between 1 and 65535.

If check/port/listen is specified, the plugin will check if the application can be started and listen on the given port.

If gethostbyname() returns a "try again" error, two retries will be attempted. If all retries were consumed, the plugin will proceed in the same manner as with other errors.

Future Work

check/port/connect to check if the port can be pinged/reached (usually for clients). If not reachable, users receive a warning. A correct timeout setting will be problematic though.