x-pack/filebeat/input/cel: add support for http+{unix,npipe} schemes

.github/CODEOWNERS

@@ -76,6 +76,7 @@ CHANGELOG*
 /x-pack/filebeat/docs/ # Listed without an owner to avoid maintaining doc ownership for each input and module.
 /x-pack/filebeat/input/awscloudwatch/ @elastic/obs-cloud-monitoring
 /x-pack/filebeat/input/awss3/ @elastic/obs-cloud-monitoring
+/x-pack/filebeat/input/cel/ @elastic/security-external-integrations
 /x-pack/filebeat/input/gcppubsub/ @elastic/security-external-integrations
 /x-pack/filebeat/input/http_endpoint/ @elastic/security-external-integrations
 /x-pack/filebeat/input/httpjson/ @elastic/security-external-integrations

CHANGELOG.next.asciidoc

@@ -163,7 +163,8 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 - Modified `aws-s3` input to reduce mutex contention when multiple SQS message are being processed concurrently. {pull}33658[33658]
 - Disable "event normalization" processing for the aws-s3 input to reduce allocations. {pull}33673[33673]
 - Add Common Expression Language input. {pull}31233[31233]
-- Add support for http+unix and http+npipe schemes. {issue}33571[33571] {pull}33610[33610]
+- Add support for http+unix and http+npipe schemes in httpjson input. {issue}33571[33571] {pull}33610[33610]
+- Add support for http+unix and http+npipe schemes in cel input. {issue}33571[33571] {pull}33712[33712]
 
 *Auditbeat*
 

x-pack/filebeat/docs/inputs/input-cel.asciidoc

@@ -425,6 +425,9 @@ with `auth.oauth2.google.jwt_file` or `auth.oauth2.google.jwt_json`.
 
 The URL of the HTTP API. Required.
 
+The API endpoint may be accessed via unix socket and Windows named pipes by adding  `+unix` or `+npipe`
+to the URL scheme, for example, `http+unix:///var/socket/`.
+
 [float]
 ==== `resource.timeout`
 

x-pack/filebeat/input/cel/input.go

@@ -47,6 +47,7 @@ import (
 	"github.com/elastic/elastic-agent-libs/mapstr"
 	"github.com/elastic/elastic-agent-libs/monitoring"
 	"github.com/elastic/elastic-agent-libs/monitoring/adapter"
+	"github.com/elastic/elastic-agent-libs/transport"
 	"github.com/elastic/elastic-agent-libs/transport/httpcommon"
 	"github.com/elastic/elastic-agent-libs/useragent"
 	"github.com/elastic/go-concert/ctxtool"
@@ -640,10 +641,7 @@ func newClient(ctx context.Context, cfg config, log *logp.Logger) (*http.Client,
 	if !wantClient(cfg) {
 		return nil, nil
 	}
-	c, err := cfg.Resource.Transport.Client(
-		httpcommon.WithAPMHTTPInstrumentation(),
-		httpcommon.WithKeepaliveSettings{Disable: true},
-	)
+	c, err := cfg.Resource.Transport.Client(clientOptions(cfg.Resource.URL.URL)...)
 	if err != nil {
 		return nil, err
 	}
@@ -684,14 +682,57 @@ func newClient(ctx context.Context, cfg config, log *logp.Logger) (*http.Client,
 }
 
 func wantClient(cfg config) bool {
-	switch cfg.Resource.URL.Scheme {
+	switch scheme, _, _ := strings.Cut(cfg.Resource.URL.Scheme, "+"); scheme {
 	case "http", "https":
 		return true
 	default:
 		return false
 	}
 }
 
+// clientOption returns constructed client configuration options, including
+// setting up http+unix and http+npipe transports if requested.
+func clientOptions(u *url.URL) []httpcommon.TransportOption {
+	scheme, trans, ok := strings.Cut(u.Scheme, "+")
+	var dialer transport.Dialer
+	switch {
+	default:
+		fallthrough
+	case !ok:
+		return []httpcommon.TransportOption{
+			httpcommon.WithAPMHTTPInstrumentation(),
+			httpcommon.WithKeepaliveSettings{Disable: true},
+		}
+
+	// We set the host for the unix socket and Windows named
+	// pipes schemes because the http.Transport expects to
+	// have a host and will error out if it is not present.
+	// The values here are just non-zero with a helpful name.
+	// They are not used in any logic.
+	case trans == "unix":
+		u.Host = "unix-socket"
+		dialer = socketDialer{u.Path}
+	case trans == "npipe":
+		u.Host = "windows-npipe"
+		dialer = npipeDialer{u.Path}
+	}
+	u.Scheme = scheme
+	return []httpcommon.TransportOption{
+		httpcommon.WithAPMHTTPInstrumentation(),
+		httpcommon.WithKeepaliveSettings{Disable: true},
+		httpcommon.WithBaseDialer(dialer),
+	}
+}
+
+// socketDialer implements transport.Dialer to a constant socket path.
+type socketDialer struct {
+	path string
+}
+
+func (d socketDialer) Dial(_, _ string) (net.Conn, error) {
+	return net.Dial("unix", d.path)
+}
+
 func checkRedirect(cfg *ResourceConfig, log *logp.Logger) func(*http.Request, []*http.Request) error {
 	return func(req *http.Request, via []*http.Request) error {
 		log.Debug("http client: checking redirect")

x-pack/filebeat/input/cel/transport_other.go

@@ -0,0 +1,21 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+//go:build !windows
+
+package cel
+
+import (
+	"errors"
+	"net"
+)
+
+// npipeDialer implements transport.Dialer.
+type npipeDialer struct {
+	path string
+}
+
+func (npipeDialer) Dial(_, _ string) (net.Conn, error) {
+	return nil, errors.New("named pipe only available on windows")
+}

x-pack/filebeat/input/cel/transport_windows.go

@@ -0,0 +1,23 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+//go:build windows
+
+package cel
+
+import (
+	"net"
+	"path/filepath"
+
+	"github.com/Microsoft/go-winio"
+)
+
+// npipeDialer implements transport.Dialer to a constant named pipe path.
+type npipeDialer struct {
+	path string
+}
+
+func (d npipeDialer) Dial(_, _ string) (net.Conn, error) {
+	return winio.DialPipe(`\\.\pipe`+filepath.FromSlash(d.path), nil)
+}