fix: missing UDP field in checkType (#14885)

* fix: missing UDP field in checkType

* Add changelog

* Update doc

.changelog/14885.txt

@@ -0,0 +1,4 @@
+```release-note:bug
+checks: Fixed a bug that prevented registration of UDP health checks from agent configuration files, such as service definition files with embedded health check definitions.
+```
+

agent/config/builder.go

@@ -1562,6 +1562,7 @@ func (b *builder) checkVal(v *CheckDefinition) *structs.CheckDefinition {
 		Body:                           stringVal(v.Body),
 		DisableRedirects:               boolVal(v.DisableRedirects),
 		TCP:                            stringVal(v.TCP),
+		UDP:                            stringVal(v.UDP),
 		Interval:                       b.durationVal(fmt.Sprintf("check[%s].interval", id), v.Interval),
 		DockerContainerID:              stringVal(v.DockerContainerID),
 		Shell:                          stringVal(v.Shell),

agent/config/builder_test.go

@@ -326,6 +326,24 @@ func TestBuilder_ServiceVal_MultiError(t *testing.T) {
 	require.Contains(t, b.err.Error(), "cannot have both socket path")
 }
 
+func TestBuilder_ServiceVal_with_Check(t *testing.T) {
+	b := builder{}
+	svc := b.serviceVal(&ServiceDefinition{
+		Name: strPtr("unbound"),
+		ID:   strPtr("unbound"),
+		Port: intPtr(12345),
+		Checks: []CheckDefinition{
+			{
+				Interval: strPtr("5s"),
+				UDP:      strPtr("localhost:53"),
+			},
+		},
+	})
+	require.NoError(t, b.err)
+	require.Equal(t, 1, len(svc.Checks))
+	require.Equal(t, "localhost:53", svc.Checks[0].UDP)
+}
+
 func intPtr(v int) *int {
 	return &v
 }

docs/service-discovery/health-checks.md

@@ -24,10 +24,11 @@ be reviewed and tested.
    on `config.Config` in [agent/config/config.go].
 5. Config [Service.Checks](https://www.consul.io/docs/discovery/services) - the
    `Checks` and `Check` fields on `ServiceDefinition` in [agent/config/config.go].
-6. CLI [consul services register](https://www.consul.io/commands/services/register) - the
+6. The returned fields of `ServiceDefinition` in [agent/config/builder.go].
+7. CLI [consul services register](https://www.consul.io/commands/services/register) - the
    `Checks` and `Check` fields on `api.AgentServiceRegistration`. The entrypoint is
    `ServicesFromFiles` in [command/services/config.go].
-7. API [/v1/txn](https://www.consul.io/api-docs/txn) - the `Transaction` API allows for registering a check.
+8. API [/v1/txn](https://www.consul.io/api-docs/txn) - the `Transaction` API allows for registering a check.
 
 
 [agent/catalog_endpoint.go]: https://github.com/hashicorp/consul/blob/main/agent/catalog_endpoint.go