coredhcp.go is not the entrypoint of main (that's cmds/coredhcp) and
contains many tightly-coupled things that could be separated.
This separates the logic into:
* server/serve.go handles setting up connections
* server/handle.go handles parsing and entry into handlers (in
preparation of a larger rewrite)
* plugins/plugin.go gets plugin loading (and doesn't need to access the
Server struct either)
Signed-off-by: Anatole Denis <anatole@unverle.fr>
Fixes#45
Do not use `init()` magic to register plugins, do it explicitly. This is
done by requiring plugins to declare a populated `Plugin` symbol of type
`plugins.Plugin`.
Signed-off-by: Andrea Barberio <insomniac@slackware.it>
This is useful to automatically provide context about what component of
the framework is emitting a log line.
Example output:
```
$ go build && sudo ./coredhcp
[2019-08-25T21:39:26+01:00] INFO plugins: Registering plugin "dns"
[2019-08-25T21:39:26+01:00] INFO plugins: Registering plugin "file"
[2019-08-25T21:39:26+01:00] INFO plugins: Registering plugin "netmask"
[2019-08-25T21:39:26+01:00] INFO plugins: Registering plugin "range"
[2019-08-25T21:39:26+01:00] INFO plugins: Registering plugin "router"
[2019-08-25T21:39:26+01:00] INFO plugins: Registering plugin "server_id"
[2019-08-25T21:39:26+01:00] INFO config: Loading configuration
[2019-08-25T21:39:26+01:00] INFO config: DHCPv4: found plugin `server_id` with 1 args: [10.10.10.1]
[2019-08-25T21:39:26+01:00] INFO config: DHCPv4: found plugin `dns` with 2 args: [8.8.8.8 8.8.4.4]
[2019-08-25T21:39:26+01:00] INFO config: DHCPv4: found plugin `router` with 1 args: [10.10.10.1]
[2019-08-25T21:39:26+01:00] INFO config: DHCPv4: found plugin `netmask` with 1 args: [255.255.255.0]
[2019-08-25T21:39:26+01:00] INFO config: DHCPv4: found plugin `range` with 4 args: [leases.txt 10.10.10.100 10.10.10.200 60s]
[2019-08-25T21:39:26+01:00] INFO coredhcp: Loading plugins...
[2019-08-25T21:39:26+01:00] INFO coredhcp: DHCPv4: loading plugin `server_id`
[2019-08-25T21:39:26+01:00] INFO plugins/server_id: plugins/server_id: loading `server_id` plugin for DHCPv4
[2019-08-25T21:39:26+01:00] INFO coredhcp: DHCPv4: loading plugin `dns`
[2019-08-25T21:39:26+01:00] INFO plugins/dns: loaded plugin for DHCPv4.
[2019-08-25T21:39:26+01:00] INFO plugins/dns: loaded 2 DNS servers.
[2019-08-25T21:39:26+01:00] INFO coredhcp: DHCPv4: loading plugin `router`
[2019-08-25T21:39:26+01:00] INFO plugins/router: plugins/router: loaded plugin for DHCPv4.
[2019-08-25T21:39:26+01:00] INFO plugins/router: plugins/router: loaded 1 router IP addresses.
[2019-08-25T21:39:26+01:00] INFO coredhcp: DHCPv4: loading plugin `netmask`
[2019-08-25T21:39:26+01:00] INFO plugins/netmask: plugins/netmask: loaded plugin for DHCPv4.
[2019-08-25T21:39:26+01:00] INFO plugins/netmask: plugins/netmask: loaded client netmask
[2019-08-25T21:39:26+01:00] INFO coredhcp: DHCPv4: loading plugin `range`
[2019-08-25T21:39:26+01:00] INFO plugins/range: plugins/range: reading leases from leases.txt
[2019-08-25T21:39:26+01:00] INFO plugins/range: plugins/range: loaded 1 leases from leases.txt
[2019-08-25T21:39:26+01:00] INFO coredhcp: Starting DHCPv4 listener on 0.0.0.0:67
[2019-08-25T21:39:26+01:00] INFO coredhcp: Waiting
```
Signed-off-by: Andrea Barberio <insomniac@slackware.it>
