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I am working on a set of Helm templates for a web service, which takes as part of it's configuration an integer Id. That Id becomes part of the service endpoints, encoded to a web-safe base64 character set:

0=A
1=B
2=C
...
26=a
...
63=_

Within my Helm template I want to take that integer Id and determine the encoded value, so that I can insert it in an Nginx location block. The actual encoding logic is something like (psuedo-code):

func Encode(int i) {
  byte b = i << 2 # shift integer two bits
  string s = web_base64(b)
  char c = s[0] # return first char only
}

So far the closest I've gotten in Helm is just creating a lookup, like $d := dict "0" "A" "1" "B" "2" "C" ... and then using {{ .Values.Id | toString | get $d }}.

Is there another way?

superstator
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1 Answers1

1

I finally came up with this:

{{- with .Values.deployment.Id | int }}
  {{- if eq . 63 }}_
  {{- else if eq . 62 }}-
  {{- else if gt . 51 }}{{- sub . 52 | printf "%c" }}
  {{- else if gt . 25 }}{{- add . 71 | printf "%c" }}
  {{- else }}{{- add . 65 | printf "%c" }}
  {{- end }}
{{- end }}

Realizing I could do ordinal conversion via printf was the big a-ha moment, and this works great as long as the value for .Id isn't 0. If it is, the entire block just gets skipped. That seems to be a limitation of the with keyword. So, I'm left with this:

{{- if eq (int .Values.deployment.Id) 63 }}_
{{- else if eq (int .Values.deployment.Id) 62 }}-
{{- else if gt (int .Values.deployment.Id) 51 }}{{- sub (int .Values.deployment.Id) 52 | printf "%c" }}
{{- else if gt (int .Values.deployment.Id) 25 }}{{- add (int .Values.deployment.Id) 71 | printf "%c" }}
{{- else }}{{- add (int .Values.deployment.Id) 65 | printf "%c" }}
{{- end }}

Which is still a little ugly, but better than a huge lookup.

superstator
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