Add capture_content_types configuration option

[felixbarny]

Description of the issue

I propose adding the following configuration option to our agents:

Key: capture_body_content_types
Type: List of wildcard matchers
Default: application/x-www-form-urlencoded*, text/*, application/json*, application/xml*
Description:

Configures which content types should be recorded.

The defaults end with a wildcard so that content types like text/plain; charset=utf-8 are captured as well.

Rationale

Users might only want to record certain content types, like application/json but don't want to record others, like binary data.

The Java agent can also be more efficient if it knows upfront whether it should record the request body. That is because it has to register a wrapper for the input stream which records and decodes the request body stream as it is read by the application.

Timeline

There's no specific timeline for implementing this configuration. But I hope we can agree on wether to add the option soon so that I can proceed with this PR: elastic/apm-agent-java#498

What we are voting on

@elastic/apm-agent-devs Please tick the box if you are ok with adding that configuration option.

If all are ok with adding the option, I'll create issues for each agent. You can then decide on your own about the priority.

Please tick the box if you are ok with some agents adding this configuration option

Vote

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[mikker]

Is this something we could just hard-code instead of providing an option? We're drowning in config options already ⚓️

[felixbarny]

We definitely could but I guess sooner or later, someone wants to record a content type we didn't think of yet. Another option would be to make it a "hidden" configuration option - one that is not documented but we can easily add more defaults to it or "reveal" the option to users with those (one off?) use cases.

EDIT: I think I'll go with that until we made a decision here so that the PR is not blocked.

[watson]

Meeting update:

• We decided that this would not be a required config option to be added by the agents
• The config option should be renamed to make it more clear that it's related to the body and not for instance request sampling. New name: capture_body_content_types

[felixbarny]

Added in version 1.5.0 of the Java agent: https://www.elastic.co/guide/en/apm/agent/java/current/config-http.html#config-capture-body-content-types

Other agents can but don't have to add this option. Closing.