Plus signs in `OTEL_RESOURCE_ATTRIBUTES` values are incorrectly decoded as spaces

[trask]

Only noticed this via inspection, didn't run into this in the real world.

OTEL_RESOURCE_ATTRIBUTES=abc=x+y should result in resource attribute with key abc and value x+y.

But because the implementation is using URLDecoder#decode

opentelemetry-java/sdk-extensions/autoconfigure/src/main/java/io/opentelemetry/sdk/autoconfigure/ResourceConfiguration.java

Line 77 in 87b0d9a

URLDecoder.decode(entry.getValue(), StandardCharsets.UTF_8.displayName()));

+ is decoded as a space ( )

and this results in a resource attribute with key abc and value x y.

[jack-berg]

So is this a deviation between URLDecoder#decode and the baggage encoding spec?

[trask]

yeah, in particular a small deviation between application/x-www-form-urlencoded MIME format and regular percent encoding (https://datatracker.ietf.org/doc/html/rfc3986#section-2.1)

noticed it when reviewing open-telemetry/opentelemetry-specification#4856 (comment)

[arnav-dasgupta]

Hi @trask and @jack-berg , can I work on this as my first issue? I use the otel java sdk at work so I was looking for a chance to contribute to get started on my open source contributions. Let me know if I can work on this. Thanks.