fix(processors.snmp_lookup): Return empty tag-map on error to avoid panic

[Hipska]

Summary

Returning a tagMap with empty rows but created set, makes sure the rebuild of the table will only happen after min_time_between_updates.

Before

Telegraf crashes:

2024-06-05T08:32:43Z E! [processors.snmp_lookup] Building table for "172.16.43.2" failed: performing bulk walk for field ifName: request timeout (after 3 retries)
Worker exits from a panic: runtime error: invalid memory address or nil pointer dereference
Stack trace: goroutine 160 [running]:
runtime/debug.Stack()
/usr/local/go/src/runtime/debug/stack.go:24 +0x5e
github.com/alitto/pond.defaultPanicHandler({0x70a8180, 0xdc68f90})
/go/pkg/mod/github.com/alitto/pond@v1.8.3/pond.go:26 +0x25
github.com/alitto/pond.(*WorkerPool).executeTask.func1()
/go/pkg/mod/github.com/alitto/pond@v1.8.3/pond.go:437 +0x4a
panic({0x70a8180?, 0xdc68f90?})
/usr/local/go/src/runtime/panic.go:770 +0x132
github.com/influxdata/telegraf/plugins/processors/snmp_lookup.(*backlog).resolve(0xc03b210180, {0xc0256de590, 0xb}, 0x0)
/go/src/github.com/influxdata/telegraf/plugins/processors/snmp_lookup/backlog.go:79 +0x26e
github.com/influxdata/telegraf/plugins/processors/snmp_lookup.(*store).enqueue.func1()
/go/src/github.com/influxdata/telegraf/plugins/processors/snmp_lookup/store.go:80 +0x96
github.com/alitto/pond.(*WorkerPool).executeTask(0xc03b220000, 0x0?, 0x0?)
/go/pkg/mod/github.com/alitto/pond@v1.8.3/pond.go:454 +0x6c
github.com/alitto/pond.worker({0x8cdbd10, 0xc03aee5400}, 0x0?, 0x0?, 0xc02f837980, 0xc03aee1ee0)
/go/pkg/mod/github.com/alitto/pond@v1.8.3/worker.go:32 +0xc2
created by github.com/alitto/pond.(*WorkerPool).maybeStartWorker in goroutine 1
/go/pkg/mod/github.com/alitto/pond@v1.8.3/pond.go:423 +0x133

After

Processor returns the metrics unmodified:

2024-06-06T07:46:20Z E! [processors.snmp_lookup] Building table for "172.16.43.2" failed: performing bulk walk for field ifName: request timeout (after 3 retries)
2024-06-06T07:46:20Z W! [processors.snmp_lookup] Cannot resolve metrics because index "123" not found for agent "172.16.43.2"!

Checklist

• No AI generated code was used in this PR

Related issues

resolves #15465

[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 significantly change the Telegraf binary size (less than 1%)

📦 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]

Awesome fix @Hipska! Thanks a lot!