Fixes a panic in the outputs.heartbeat plugin introduced in v1.38.0.

[hklhai]

Summary

Fix a panic in the outputs.heartbeat plugin introduced in v1.38.0.

The issue was caused by unsafe type assertions in snapshot():

entry["buffer_limit"].(int64)
entry["buffer_size"].(int64)

This could lead to runtime panics when:

• fields are missing
• values are not int64 (e.g. float64 from decoded metrics)

The fix replaces these assertions with safe type checks and falls back
to a default buffer_fullness of 1.0 when values are invalid.

Additionally, selfstat.Metrics() is now wrapped in a package-level variable
to allow proper mocking in unit tests, improving testability.

Related issues

resolves #18559

[telegraf-tiger]

Download PR build artifacts for linux_amd64.tar.gz, darwin_arm64.tar.gz, and windows_amd64.zip.
Downloads for additional architectures and packages are available below.

👍 This pull request doesn't change the Telegraf binary size

📦 Click here to get additional PR build artifacts

Artifact URLs

. DEB	. RPM	. TAR . GZ	. ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz

[srebhan]

@hklhai your PR only shadows the real issue (see PR #18568). We know that a internal_write metric must contain the buffer-size and buffer-limit and those fields must be of type int64. That's why a raw type assertion makes sense because if those conditions are not true there is an internal programming error.

Therefore I would prefer my PR over yours.

[srebhan]

Closing this in favor of #18568 which solves the panic at the roots. Anyway, thanks for jumping on this so quickly @hklhai!

[hklhai]

Closing this in favor of #18568 which solves the panic at the roots. Anyway, thanks for jumping on this so quickly @hklhai!

😄 I didn’t really contribute much haha, but happy to see this resolved!