"500 Internal Server Error" instead of "404 Not Found" on non-matching filter in API request

[peteeckel]

Describe the bug

When a filter expression does not match anything when, for example, creating a comment via the API, Icinga 2 returns a "500 Internal Server Error" instead of the expected "404 Not Found" as the result.

To Reproduce

1. Create some test hosts (e.g. test-host-0 ... test-host-9) and test services per host.
2. Create a sufficiently privileged test user (e.g. with "*" permission) on the Icinga 2 server
3. Run an API request (e.g. 'add-comment' for an existing host/service):

POST /v1/actions/add-comment HTTP/1.1
Accept: application/json
Authorization: Basic YWdncmVnYXRlZDpYb3QleWt5R3BPdG9wSGV4T3gldXFJcTROZ2loT0o0SzNOW3V3TDBnWVJdT2plTFY0cDNMUWk=
Content-Type: application/json; charset=utf-8
Host: 192.168.110.112:5665
Connection: close
User-Agent: Paw/3.1.10 (Macintosh; OS X/10.15.4) GCDHTTPRequest
Content-Length: 138

{"filter":"host.name==\"test-host-1\"&&service.name==\"test-service-1\"","author":"Test User","comment":"Test Comment","type":"Service"}

=> Works fine:

HTTP/1.1 200 OK
Server: Icinga/2.11.3-1
Content-Type: application/json
Content-Length: 263

{"results":[{"code":200.0,"legacy_id":21.0,"name":"test-host-1!test-service-1!8641bb23-a3ea-4372-88b9-4657761144c1","status":"Successfully added comment 'test-host-1!test-service-1!8641bb23-a3ea-4372-88b9-4657761144c1' for object 'test-host-1!test-service-1'."}]}

4. Now run the same API request with a non-existing service and/or host:

POST /v1/actions/add-comment HTTP/1.1
Accept: application/json
Authorization: Basic YWdncmVnYXRlZDpYb3QleWt5R3BPdG9wSGV4T3gldXFJcTROZ2loT0o0SzNOW3V3TDBnWVJdT2plTFY0cDNMUWk=
Content-Type: application/json; charset=utf-8
Host: 192.168.110.112:5665
Connection: close
User-Agent: Paw/3.1.10 (Macintosh; OS X/10.15.4) GCDHTTPRequest
Content-Length: 139

{"filter":"host.name==\"test-host-11\"&&service.name==\"test-service-1\"","author":"Test User","comment":"Test Comment","type":"Service"}

=> This time, an error 500 is reported:

HTTP/1.1 500 Internal Server Error
Server: Icinga/2.11.3-1
Content-Type: application/json
Content-Length: 14

{"results":[]}

Expected behavior

In accordance with the usual behaviour of the Icinga 2 API and REST services in general, I would expect a 404 error with a sensible error message ("No resource found" or something similar).

Your Environment

• Version used (icinga2 --version):

[root@master2 ~]# icinga2 --version 
icinga2 - The Icinga 2 network monitoring daemon (version: 2.11.3-1)

Copyright (c) 2012-2020 Icinga GmbH (https://icinga.com/)
License GPLv2+: GNU GPL version 2 or later <https://gnu.org/licenses/gpl2.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

System information:
  Platform: CentOS Linux
  Platform version: 7 (Core)
  Kernel: Linux
  Kernel version: 3.10.0-1062.9.1.el7.x86_64
  Architecture: x86_64

Build information:
  Compiler: GNU 4.8.5
  Build host: runner-LTrJQZ9N-project-322-concurrent-0

Application information:

General paths:
  Config directory: /etc/icinga2
  Data directory: /var/lib/icinga2
  Log directory: /var/log/icinga2
  Cache directory: /var/cache/icinga2
  Spool directory: /var/spool/icinga2
  Run directory: /run/icinga2

Old paths (deprecated):
  Installation root: /usr
  Sysconf directory: /etc
  Run directory (base): /run
  Local state directory: /var

Internal paths:
  Package data directory: /usr/share/icinga2
  State path: /var/lib/icinga2/icinga2.state
  Modified attributes path: /var/lib/icinga2/modified-attributes.conf
  Objects path: /var/cache/icinga2/icinga2.debug
  Vars path: /var/cache/icinga2/icinga2.vars
  PID path: /run/icinga2/icinga2.pid

• Config validation (icinga2 daemon -C):

[root@master2 ~]# icinga2 daemon -C 
[2020-04-01 16:43:48 +0000] information/cli: Icinga application loader (version: 2.11.3-1)
[2020-04-01 16:43:48 +0000] information/cli: Loading configuration file(s).
[2020-04-01 16:43:48 +0000] information/ConfigItem: Committing config item(s).
[2020-04-01 16:43:48 +0000] information/ApiListener: My API identity: master2.dev.evi.dfs
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 1 FileLogger.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 1 NotificationComponent.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 1 IcingaApplication.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 10 Hosts.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 1 ApiListener.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 6 Comments.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 1 CheckerComponent.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 4 Zones.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 4 Endpoints.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 2 ApiUsers.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 202 CheckCommands.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 1 IdoPgsqlConnection.
[2020-04-01 16:43:48 +0000] information/ConfigItem: Instantiated 200 Services.
[2020-04-01 16:43:48 +0000] information/ScriptGlobal: Dumping variables to file '/var/cache/icinga2/icinga2.vars'
[2020-04-01 16:43:48 +0000] information/cli: Finished validating the configuration file(s).

Additional context

The 500 error occurs also when I URLencode the parameters, or when I just use hosts, not services. I can reproduce it on any Icinga 2 instance I'm currently running.