Call host parser only once when building light metricsets (elastic#20149

)

When using light modules, host parser is called twice. First by the actual implementation
of the metricset, and second after adding the configuration defined in the light module
manifest. Second call might be missing data as the original host is modified after the first
call, causing problems.

This change disables host parser in the registration created for light modules, and makes
only the "second call" inside the factory.

It also removes previous fix for URLs as it shouldn't be needed anymore.

CHANGELOG-developer.next.asciidoc

@@ -55,6 +55,7 @@ The list below covers the major changes between 7.0.0-rc2 and master only.
 ==== Bugfixes
 
 - Stop using `mage:import` in community beats. This was ignoring the vendorized beats directory for some mage targets, using the code available in GOPATH, this causes inconsistencies and compilation problems if the version of the code in the GOPATH is different to the vendored one. Use of `mage:import` will continue to be unsupported in custom beats till beats is migrated to go modules, or mage supports vendored dependencies. {issue}13998[13998] {pull}14162[14162]
+- Metricbeat module builders call host parser only once when instantiating light modules. {pull}20149[20149]
 
 ==== Added
 

metricbeat/mb/lightmetricset.go

@@ -18,9 +18,6 @@
 package mb
 
 import (
-	"fmt"
-	"net/url"
-
 	"github.com/pkg/errors"
 
 	"github.com/elastic/beats/v7/libbeat/common"
@@ -55,13 +52,17 @@ func (m *LightMetricSet) Registration(r *Register) (MetricSetRegistration, error
 	originalFactory := registration.Factory
 	registration.IsDefault = m.Default
 
+	// Disable the host parser, we will call it as part of the factory so the original
+	// host in the base module is not modified.
+	originalHostParser := registration.HostParser
+	registration.HostParser = nil
+
 	// Light modules factory has to override defaults and reproduce builder
 	// functionality with the resulting configuration, it does:
 	// - Override defaults
 	// - Call module factory if registered (it wouldn't have been called
 	//   if light module is really a registered mixed module)
-	// - Call host parser if defined (it would have already been called
-	//   without the light module defaults)
+	// - Call host parser if there was one defined
 	// - Finally, call the original factory for the registered metricset
 	registration.Factory = func(base BaseMetricSet) (MetricSet, error) {
 		// Override default config on base module and metricset
@@ -83,11 +84,9 @@ func (m *LightMetricSet) Registration(r *Register) (MetricSetRegistration, error
 			base.module = module
 		}
 
-		// At this point host parser was already run, we need to run this again
-		// with the overriden defaults
-		if registration.HostParser != nil {
-			host := m.useHostURISchemeIfPossible(base.host, base.hostData.URI)
-			base.hostData, err = registration.HostParser(base.module, host)
+		// Run the host parser if there was anyone defined
+		if originalHostParser != nil {
+			base.hostData, err = originalHostParser(base.module, base.host)
 			if err != nil {
 				return nil, errors.Wrapf(err, "host parser failed on light metricset factory for '%s/%s'", m.Module, m.Name)
 			}
@@ -100,18 +99,6 @@ func (m *LightMetricSet) Registration(r *Register) (MetricSetRegistration, error
 	return registration, nil
 }
 
-// useHostURISchemeIfPossible method parses given URI to extract protocol scheme and prepend it to the host.
-// It prevents from skipping protocol scheme (e.g. https) while executing HostParser.
-func (m *LightMetricSet) useHostURISchemeIfPossible(host, uri string) string {
-	u, err := url.ParseRequestURI(uri)
-	if err == nil {
-		if u.Scheme != "" {
-			return fmt.Sprintf("%s://%s", u.Scheme, u.Host)
-		}
-	}
-	return host
-}
-
 // baseModule does the configuration overrides in the base module configuration
 // taking into account the light metric set default configurations
 func (m *LightMetricSet) baseModule(from Module) (*BaseModule, error) {