Development of new DHCP Plugin - undefined method merge

sl12 · July 15, 2020, 6:14pm

I try to develop a new DHCP plugin.

At the find_record_by_mac function I have the following line:

return Proxy::DHCP::Record.new(ipaddress, mac_address,Proxy::DHCP::Subnet.new(subnet_address,"255.255.255.0"))

When I call “/unattended/built?token=xxx” I get the following error in the log:

proxy.log:

2020-07-15T20:02:28 d784b476 [I] Finished GET /dhcp/192.168.2.0/mac/56:6f:5f:b7:00:05 with 200 (261.72 ms)

production.log

2020-07-15T20:02:28 [W|app|d784b476] ProxyAPI operation FAILED
2020-07-15T20:02:28 [D|app|d784b476] Backtrace for 'ProxyAPI operation FAILED' error (ProxyAPI::ProxyException): ERF12-4395 [ProxyAPI::ProxyException]: DHCP-Eintrag für 56:6f:5f:b7:00:05 konnte nicht abgerufen werden ([NoMethodError]: undefined method `merge' for "192.168.2.60 / 56:6f:5f:b7:00:05":String) für Proxy https://theforeman.tkv.int:8443/dhcp
/usr/share/foreman/lib/proxy_api/dhcp.rb:56:in `rescue in record'
/usr/share/foreman/lib/proxy_api/dhcp.rb:45:in `record'
/usr/share/foreman/lib/net/dhcp/record.rb:57:in `conflicts'
...

Any idea how to solve this error ?

ekohl · July 16, 2020, 11:59am

I took the liberty to edit your post to add some code tags.

This suggests that it’s calling merge() on a String, but typically that’s called on a Hash.

I wonder what the JSON returned by the proxy is. Can you share that?

sl12 · July 16, 2020, 6:27pm

If I call the proxy with curl http://theforeman:8000/dhcp/192.168.2.0/mac/56:6f:5f:b7:00:03 I get the following string:

“192.168.2.60 / 56:6f:5f:b7:00:03”

Do I need to return something different in the find_record_by_mac function to get an JSON output ?

ekohl · July 17, 2020, 10:20am

The code in between isn’t very strict in what it sends back which makes it easy to create an invalid API response:

github.com

theforeman/smart-proxy/blob/e138e2309d38eabc06b7251f15ad28ad5a264c4f/modules/dhcp/dhcp_api.rb#L73-L75


record = server.find_record_by_mac(param_network, param_mac)
log_halt 404, "No DHCP record for MAC #{param_network}/#{param_mac} found" unless record
record.to_json

Sadly, the API is barely specified and the specific API isn’t even mentioned on API - Smart Proxy - Foreman

Digging in the source, it appears the data types have the json serialization defined:

github.com

theforeman/smart-proxy/blob/e138e2309d38eabc06b7251f15ad28ad5a264c4f/modules/dhcp_common/record/reservation.rb#L25-L27


def to_json(*opts)
  Hash[[:name, :ip, :mac, :subnet, :type].map { |s| [s, send(s)] }].merge(options).to_json(*opts)
end

github.com

theforeman/smart-proxy/blob/e138e2309d38eabc06b7251f15ad28ad5a264c4f/modules/dhcp_common/record/lease.rb#L24-L26


def to_json(*opts)
  Hash[[:name, :ip, :mac, :subnet, :starts, :ends, :state, :type].map { |s| [s, send(s)] }].merge(options).to_json(*opts)
end

So it’s recommended to use these data structures and return them instead of the raw Proxy::DHCP::Record. Also note how both reservation and lease extend `Record.

lzap · July 17, 2020, 12:11pm

Yeah, you need to explicitly call to_json otherwise the object is converted to String via its to_s implementation, which in this case returns IP / MAC.

ekohl · July 17, 2020, 12:47pm

No, this is wrong. The DHCP API already calls to_json but you are calling Proxy::DHCP::Record. This class has no to_json defined so it falls back to to_s.

sl12 · July 18, 2020, 10:28am

thanks.

using Proxy::DHCP::Reservation in find_record_by_mac did fix the problem.

ekohl · July 18, 2020, 2:07pm

Out of interest, which DHCP server are you talking to? Any chance it will be relevant for others and you’ll open source it?

sl12 · July 18, 2020, 2:58pm

Univention Corporate Server (UCS) and yes I will publish it on github.