Add support for field/tag keys to strings processor

[glinton]

Resolves #5928

This enables the string processor to work on tag and field keys with the config additions of tag_key and field_key.

Example

Config

[[processors.strings]]
  [[processors.strings.lowercase]]
    tag_key = "URI-Stem"
  [[processors.strings.replace]]
    tag_key = "uri-stem"
    old = "-"
    new = "_"

Input

iis_log,URI-Stem=/API/HealthCheck http_version=1.1 1519652321000000000

Output

iis_log,uri_stem=/API/HealthCheck,URI-Stem=/API/HealthCheck http_version=1.1 1519652321000000000

Try it here:

• linux/

  • amd64

    • telegraf
    • telegraf-1.12.0~f6226c6e-0.x86_64.rpm
    • telegraf-1.12.0~f6226c6e_linux_amd64.tar.gz
    • telegraf_1.12.0~f6226c6e-0_amd64.deb
  • arm64

    • telegraf
    • telegraf-1.12.0~f6226c6e-0.arm64.rpm
    • telegraf-1.12.0~f6226c6e_linux_arm64.tar.gz
    • telegraf_1.12.0~f6226c6e-0_arm64.deb
  • armel

    • telegraf
    • telegraf-1.12.0~f6226c6e-0.armel.rpm
    • telegraf-1.12.0~f6226c6e_linux_armel.tar.gz
    • telegraf_1.12.0~f6226c6e-0_armel.deb
  • armhf

    • telegraf
    • telegraf-1.12.0~f6226c6e-0.armv6hl.rpm
    • telegraf-1.12.0~f6226c6e_linux_armhf.tar.gz
    • telegraf_1.12.0~f6226c6e-0_armhf.deb
  • i386

    • telegraf
    • telegraf-1.12.0~f6226c6e-0.i386.rpm
    • telegraf-1.12.0~f6226c6e_linux_i386.tar.gz
    • telegraf_1.12.0~f6226c6e-0_i386.deb
  • mipsel

    • telegraf
    • telegraf-1.12.0~f6226c6e_linux_mipsel.tar.gz
    • telegraf_1.12.0~f6226c6e-0_mipsel.deb
  • s390x

    • telegraf
    • telegraf-1.12.0~f6226c6e-0.s390x.rpm
    • telegraf-1.12.0~f6226c6e_linux_s390x.tar.gz
    • telegraf_1.12.0~f6226c6e-0_s390x.deb
  • static_amd64

    • telegraf
    • telegraf-1.12.0~f6226c6e-static_linux_amd64.tar.gz
• windows/

  • amd64

    • telegraf-1.12.0~f6226c6e_windows_amd64.zip
    • telegraf.exe
  • i386

    • telegraf-1.12.0~f6226c6e_windows_i386.zip
    • telegraf.exe
• freebsd/

  • amd64

    • telegraf
    • telegraf-1.12.0~f6226c6e_freebsd_amd64.tar.gz
  • i386

    • telegraf
    • telegraf-1.12.0~f6226c6e_freebsd_i386.tar.gz

[danielnelson]

I guess we should remove the old key after each modification? I notice that dest doesn't really make sense with keys either, which is a little unfortunate.

[glinton]

Should we also remove the old key when dest is specified on regular tag/field? I didn't remove the old key after each modification in order to match the behavior of dest, but agree that the old key should be removed.

[danielnelson]

The dest operation is weird, perhaps we shouldn't include it in future processors and think about deprecating it. Maybe a copy processor would make more sense? Instead of using dest you use the copy processor, then you modify the copy. I think it will be tough to model this until we add a real language.

Looks like there are a few examples that need updated and then this is good.

[glinton]

For tags and fields, if dest is specified, we could add a metric.RemoveTag(key) to where we set dest = c.Dest to clean up the old keys, though now it seems it would need to be opt-in behavior.

[danielnelson]

I'm more inclined to move in the direction of deprecating the dest option, but let's think about it and not do anything more right now.