JSON de-serialization error on /status API call

[okushchenko]

What did you do?
I called the StatusAPI.Get() of the Alertmanager's Go client in order to get a server status info. https://github.com/prometheus/alertmanager/blob/master/client/client.go#L125

What did you expect to see?
No errors being returned.

What did you see instead? Under which circumstances?
An error being returned in the format of json: cannot unmarshal string into Go struct field GlobalConfig.configJSON.global.smtp_smarthost of type config.HostPort.

Environment

• System information:

  Centos 7

• Alertmanager version:

  0.20.0-rc0

• Alertmanager configuration file:

global:
  http_config: {}
  smtp_from: prometheus@localhost
  smtp_require_tls: false
  smtp_smarthost: localhost:25

route:
  receiver: "test"
  group_by: ['alertname']
  group_wait:      15s
  group_interval:  15s
  repeat_interval: 1m

receivers:
- name: "test"
  webhook_configs:
  - url: 'http://webhook.service:8080/api/webhooks/prometheus'
    send_resolved: true
    http_config:
      basic_auth:
        username: admin@localhost
        password: test

[simonpasquier]

Thanks for the report!

I didn't think about github.com/prometheus/alertmanager/client when I submitted #2086 to remove support for JSON unmarshaling so in addition to the problem you're seeing, other issues exist. I'll do a revert of #2086 and a fix for this issue.