Support for bytes encoding for "gnmi" input plugin

[hellt]

Required for all PRs:

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

Purpose of the PR

This PR adds support for bytes encoding for the gNMI messages as per 2.3.2 of gNMI specification.

The code already had a support for bytes encoded values, it was just not allowed to specify this encoding in the appropriate check before.

The only changes made to the plugin were to allow to specify bytes as the encoding.

Example

Config file:

[[inputs.gnmi]]
  addresses = ["r1:14946"]
  username = "admin"
  password = "nokia"

  encoding = "bytes"

  redial = "10s"

  [[inputs.gnmi.subscription]]
    name = "test-bytes-encoding"
    path = "/state/system/version/version-number"
    subscription_mode = "sample"
    sample_interval = "2s"

[[outputs.file]]
  files = ["stdout", "/tmp/metrics.out"]
  data_format = "influx"

Output:

❯ ./telegraf --config __test_config.toml
2020-08-04T09:29:36Z I! Starting Telegraf 
2020-08-04T09:29:36Z I! Loaded inputs: gnmi
2020-08-04T09:29:36Z I! Loaded aggregators: 
2020-08-04T09:29:36Z I! Loaded processors: 
2020-08-04T09:29:36Z I! Loaded outputs: file
2020-08-04T09:29:36Z I! Tags enabled: host=mbp-2.local
2020-08-04T09:29:36Z I! [agent] Config: Interval:10s, Quiet:false, Hostname:"mbp-2.local", Flush Interval:10s
test-bytes-encoding,host=mbp-2.local,path=/state/system/version,source=0.tcp.eu.ngrok.io version_number="B-20.5.R1" 1596533379127528433

[hellt]

Hi @danielnelson, I am not sure if you are the intended reviewer for that domain?

[ssoroka]

This is great. There's also an ASCII encoding. should we be supporting that, too?

[hellt]

Thanks for the approval. Technically ascii should be allowed to be specified as well

…

On Wed, 28 Oct 2020, 22:56 Steven Soroka, ***@***.***> wrote: ***@***.**** approved this pull request. This is great. There's also an ASCII encoding. should we be supporting that, too? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#7938 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABLKV5MOHWMT4D7GP7OFYDDSNCHR3ANCNFSM4PUGXMFQ> .

[ssoroka]

looks like at the moment ascii is not part of the docs and will complain that it's not a supported type.

[hellt]

Correct, it needs to be added in the same fashion as this PR adds `bytes` support.

…

On Thu, Oct 29, 2020 at 4:08 PM Steven Soroka ***@***.***> wrote: looks like at the moment ascii is not part of the docs and will complain that it's not a supported type. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#7938 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABLKV5IJBLCUWQGK7YPF4YLSNGAORANCNFSM4PUGXMFQ> .

[hellt]

@ssoroka can we merge this one and address ASCII later? Thank you

[ssoroka]

Merged. Thank you!