[pkg/ottl] OTTL Base64Encode function

[alexcams]

Description

Add Base64Encode OTTL converter function to encode strings into base64 format with support for multiple variants (base64, base64-raw, base64-url, base64-raw-url). This function addresses the need to handle characters not allowed by certain exporters like NATS Core.

Link to tracking issue

Fixes #46071

Testing

Tested manually and added unit and e2e tests.
Test config:

processors:
  transform:
    log_statements:
      - context: log
        statements:
          - set(attributes["encoded_default"], Base64Encode(attributes["plain_text"]))
          
          - set(attributes["encoded_base64_raw"], Base64Encode(attributes["plain_text"], "base64-raw"))
          
          - set(attributes["encoded_base64_url"], Base64Encode(attributes["plain_text"], "base64-url"))
          
          - set(attributes["encoded_base64_raw_url"], Base64Encode(attributes["plain_text"], "base64-raw-url"))

Test input:

{"plain_text": "test string"}
{"plain_text": "hello world"}
{"plain_text": "special chars: @#$%"}
{"plain_text": "URL encoding test: https://example.com?param=value&other=123"}

Test result:

LogRecord #0
Body: Str({"plain_text": "test string"})
Attributes:
     -> log.file.name: Str(test_data.log)
     -> plain_text: Str(test string)
     -> encoded_default: Str(dGVzdCBzdHJpbmc=)
     -> encoded_base64_raw: Str(dGVzdCBzdHJpbmc)
     -> encoded_base64_url: Str(dGVzdCBzdHJpbmc=)
     -> encoded_base64_raw_url: Str(dGVzdCBzdHJpbmc)
LogRecord #1
Body: Str({"plain_text": "hello world"})
Attributes:
     -> log.file.name: Str(test_data.log)
     -> plain_text: Str(hello world)
     -> encoded_default: Str(aGVsbG8gd29ybGQ=)
     -> encoded_base64_raw: Str(aGVsbG8gd29ybGQ)
     -> encoded_base64_url: Str(aGVsbG8gd29ybGQ=)
     -> encoded_base64_raw_url: Str(aGVsbG8gd29ybGQ)
LogRecord #2
Body: Str({"plain_text": "special chars: @#$%"})
Attributes:
     -> log.file.name: Str(test_data.log)
     -> plain_text: Str(special chars: @#$%)
     -> encoded_default: Str(c3BlY2lhbCBjaGFyczogQCMkJQ==)
     -> encoded_base64_raw: Str(c3BlY2lhbCBjaGFyczogQCMkJQ)
     -> encoded_base64_url: Str(c3BlY2lhbCBjaGFyczogQCMkJQ==)
     -> encoded_base64_raw_url: Str(c3BlY2lhbCBjaGFyczogQCMkJQ)
LogRecord #3
Body: Str({"plain_text": "URL encoding test: https://example.com?param=value&other=123"})
Attributes:
     -> log.file.name: Str(test_data.log)
     -> plain_text: Str(URL encoding test: https://example.com?param=value&other=123)
     -> encoded_default: Str(VVJMIGVuY29kaW5nIHRlc3Q6IGh0dHBzOi8vZXhhbXBsZS5jb20/cGFyYW09dmFsdWUmb3RoZXI9MTIz)
     -> encoded_base64_raw: Str(VVJMIGVuY29kaW5nIHRlc3Q6IGh0dHBzOi8vZXhhbXBsZS5jb20/cGFyYW09dmFsdWUmb3RoZXI9MTIz)
     -> encoded_base64_url: Str(VVJMIGVuY29kaW5nIHRlc3Q6IGh0dHBzOi8vZXhhbXBsZS5jb20_cGFyYW09dmFsdWUmb3RoZXI9MTIz)
     -> encoded_base64_raw_url: Str(VVJMIGVuY29kaW5nIHRlc3Q6IGh0dHBzOi8vZXhhbXBsZS5jb20_cGFyYW09dmFsdWUmb3RoZXI9MTIz)

Documentation

Updated README.md with function documentation, usage examples, and supported variants.

[alexcams]

/rerun

[alexcams]

/rerun

[edmocosta]

Hi @alexcams, could you please address the lint issues and re-request review when it's done? Thanks!

[alexcams]

/rerun

[otelbot]

Thank you for your contribution @alexcams! 🎉 We would like to hear from you about your experience contributing to OpenTelemetry by taking a few minutes to fill out this survey. If you are getting started contributing, you can also join the CNCF Slack channel #opentelemetry-new-contributors to ask for guidance and get help.

[agardnerIT]

Hi all. Nothing to do with the functionality of this PR but I thought I'd mention (here in context) a pain point in relation to finding which release this PR takes effect in.

It'd be great for each PR to have a tag saying "first available in collector version X.Y.Z".

This would also help AIs detect when people think there's a bug (feature X doesn't work) the AI could say "please run otelcol-contrib --version and provide the output" then "ahh you're using X.Y.Z and this functionality isn't available until version Z.Y.X"

For example, I know that this was merged 5 days ago. Now I need to jump to the releases repo and check when the last collector release was ("last week"). OK so maybe I'm in luck because 5 days could be "last week". I download 0.146.0 and it doesn't seem to have this. Looking at the release notes I don't see it, so I assume I just need to wait?

[edmocosta]

Hi @agardnerIT, thanks for the feedback, that's a fair request, and I agree those labels could be very helpful. Please feel free to open an issue and bring this topic into discussion. Regarding this specific OTTL feature, it was merged after v0.146.0 was released, so it will only be available on next release (v0.147.0), which BTW is today.