filebeat/input/tcp: add support for TCP input metrics

CHANGELOG.next.asciidoc

@@ -164,6 +164,7 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 - Allow user configuration of keep-alive behaviour for HTTPJSON and CEL inputs. {issue}33951[33951] {pull}34014[34014]
 - Add support for polling system UDP stats for UDP input metrics. {pull}34070[34070]
 - Add support for recognizing the log level in Elasticsearch JVM logs {pull}34159[34159]
+- Add metrics for TCP packet processing. {pull}34333[34333]
 
 *Auditbeat*
 

filebeat/docs/inputs/input-tcp.asciidoc

@@ -27,6 +27,24 @@ The `tcp` input supports the following configuration options plus the
 
 include::../inputs/input-common-tcp-options.asciidoc[]
 
+[float]
+=== Metrics
+
+This input exposes metrics under the <<http-endpoint, HTTP monitoring endpoint>>.
+These metrics are exposed under the `/dataset` path. They can be used to
+observe the activity of the input.
+
+[options="header"]
+|=======
+| Metric                         | Description
+| `device`                       | Host/port of the TCP stream.
+| `received_events_total`        | Total number of packets (events) that have been received.
+| `received_bytes_total`         | Total number of bytes received.
+| `receive_queue_length`         | Size of the system receive queue (linux only) (guage).
+| `arrival_period`               | Histogram of the time between successive packets in nanoseconds.
+| `processing_time`              | Histogram of the time taken to process packets in nanoseconds.
+|=======
+
 [id="{beatname_lc}-input-{type}-common-options"]
 include::../inputs/input-common-options.asciidoc[]
 

filebeat/input/default-inputs/inputs.go

@@ -21,6 +21,7 @@ import (
 	"github.com/elastic/beats/v7/filebeat/beater"
 	"github.com/elastic/beats/v7/filebeat/input/filestream"
 	"github.com/elastic/beats/v7/filebeat/input/kafka"
+	"github.com/elastic/beats/v7/filebeat/input/tcp"
 	"github.com/elastic/beats/v7/filebeat/input/udp"
 	"github.com/elastic/beats/v7/filebeat/input/unix"
 	v2 "github.com/elastic/beats/v7/filebeat/input/v2"
@@ -39,6 +40,7 @@ func genericInputs(log *logp.Logger, components beater.StateStore) []v2.Plugin {
 	return []v2.Plugin{
 		filestream.Plugin(log, components),
 		kafka.Plugin(),
+		tcp.Plugin(),
 		udp.Plugin(),
 		unix.Plugin(),
 	}