lib/vmselectapi: do not send empty label names for labelNames request (…

…#4936)

* lib/vmselectapi: do not send empty label names for labelNames request
it breaks cluster communication, since vmselect incorrectly reads request buffer, leaving unread data on it
#4932

* typo fix

* wip

---------

Co-authored-by: Aliaksandr Valialkin <valyala@victoriametrics.com>

docs/CHANGELOG.md

@@ -26,6 +26,7 @@ The v1.87.x line will be supported for at least 12 months since [v1.87.0](https:
 * BUGFIX: vmselect: correctly handle requests with `/select/multitenant` prefix. Such requests must be rejected since vmselect does not support multitenancy endpoint. Previously, such requests were causing panic. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4910).
 * BUGFIX: [vminsert](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): properly check for [read-only state](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#readonly-mode) at `vmstorage`. Previously it wasn't properly checked, which could lead to increased resource usage and data ingestion slowdown when some of `vmstorage` nodes are in read-only mode. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4870).
 * BUGFIX: [vminsert](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): properly close broken vmstorage connection during [read-only state](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#readonly-mode) checks at `vmstorage`. Previously it wasn't properly closed, which prevents restoring `vmstorage` node from read-only mode. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4870).
+* BUGFIX: [vmstorage](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html):  prevent from breaking `vmselect` -> `vmstorage` RPC communication when `vmstorage` returns an empty label name at `/api/v1/labels` request. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4932).
 * BUGFIX: do not allow starting VictoriaMetrics components with improperly set boolean command-line flags in the form `-boolFlagName value`, since this leads to silent incomplete flags' parsing. This form should be replaced with `-boolFlagName=value`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4845).
 * BUGFIX: properly replace `:` chars in label names with `_` when `-usePromCompatibleNaming` command-line flag is passed to `vmagent`, `vminsert` or single-node VictoriaMetrics. This addresses [this comment](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3113#issuecomment-1275077071).
 * BUGFIX: [vmbackup](https://docs.victoriametrics.com/vmbackup.html): correctly check if specified `-dst` belongs to specified `-storageDataPath`. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4837).