[processor/resourcedetection] Add host.mac to system detector (#29588)

**Description:**

Adds support for `host.mac` detection to the `system` detector on the
resource detection processor.

This convention is defined in the specification [on the host
document](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/resource/host.md).

**Link to tracking Issue:** Fixes #29587 and therefore fixes #22045

**Testing:** 

Unit tests; manually Tested on my laptop with the following
configuration:

```
receivers:
  hostmetrics:
    collection_interval: 10s
    scrapers:
      load:

processors:
  resourcedetection:
    detectors: ["system"]
    system:
      resource_attributes:
        host.mac:
          enabled: true

exporters:
  debug:
    verbosity: detailed

service:
  pipelines:
    metrics:
      receivers: [hostmetrics]
      processors: [resourcedetection]
      exporters: [debug]
```

---------

Co-authored-by: Curtis Robert <[email protected]>

Author: mx-psi

.chloggen/mx-psi_host.mac.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: resourcedetectionprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add detection of host.mac to system detector.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [29587]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

internal/metadataproviders/system/metadata.go

@@ -66,6 +66,9 @@ type Provider interface {
 
 	// HostIPs returns the host's IP interfaces
 	HostIPs() ([]net.IP, error)
+
+	// HostMACs returns the host's MAC addresses
+	HostMACs() ([]net.HardwareAddr, error)
 }
 
 type systemMetadataProvider struct {
@@ -196,3 +199,20 @@ func (p systemMetadataProvider) HostIPs() (ips []net.IP, err error) {
 	}
 	return ips, err
 }
+
+func (p systemMetadataProvider) HostMACs() (macs []net.HardwareAddr, err error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, iface := range ifaces {
+		// skip if the interface is down or is a loopback interface
+		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
+			continue
+		}
+
+		macs = append(macs, iface.HardwareAddr)
+	}
+	return macs, err
+}

processor/resourcedetectionprocessor/README.md

@@ -49,6 +49,7 @@ Queries the host machine to retrieve the following resource attributes:
     * host.name
     * host.id
     * host.ip
+    * host.mac
     * host.cpu.vendor.id
     * host.cpu.family
     * host.cpu.model.id

processor/resourcedetectionprocessor/internal/system/internal/metadata/generated_config.go

@@ -19,6 +19,8 @@ all_set:
       enabled: true
     host.ip:
       enabled: true
+    host.mac:
+      enabled: true
     host.name:
       enabled: true
     os.description:
@@ -45,6 +47,8 @@ none_set:
       enabled: false
     host.ip:
       enabled: false
+    host.mac:
+      enabled: false
     host.name:
       enabled: false
     os.description:

processor/resourcedetectionprocessor/internal/system/internal/metadata/generated_config_test.go

@@ -27,6 +27,10 @@ resource_attributes:
     description: IP addresses for the host
     type: slice
     enabled: false
+  host.mac:
+    description: MAC addresses for the host
+    type: slice
+    enabled: false
   host.cpu.vendor.id:
     description: The host.cpu.vendor.id
     type: string

processor/resourcedetectionprocessor/internal/system/internal/metadata/generated_resource.go

@@ -7,7 +7,9 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
 	"strconv"
+	"strings"
 
 	"github.com/shirou/gopsutil/v3/cpu"
 	"go.opentelemetry.io/collector/featuregate"
@@ -69,6 +71,17 @@ func NewDetector(p processor.CreateSettings, dcfg internal.DetectorConfig) (inte
 	}, nil
 }
 
+// toIEEERA converts a MAC address to IEEE RA format.
+// Per the spec: "MAC Addresses MUST be represented in IEEE RA hexadecimal form: as hyphen-separated
+// octets in uppercase hexadecimal form from most to least significant."
+// Golang returns MAC addresses as colon-separated octets in lowercase hexadecimal form from most
+// to least significant, so we need to:
+// - Replace colons with hyphens
+// - Convert to uppercase
+func toIEEERA(mac net.HardwareAddr) string {
+	return strings.ToUpper(strings.ReplaceAll(mac.String(), ":", "-"))
+}
+
 // Detect detects system metadata and returns a resource with the available ones
 func (d *Detector) Detect(ctx context.Context) (resource pcommon.Resource, schemaURL string, err error) {
 	var hostname string
@@ -94,6 +107,17 @@ func (d *Detector) Detect(ctx context.Context) (resource pcommon.Resource, schem
 		}
 	}
 
+	var hostMACAttribute []any
+	if d.cfg.ResourceAttributes.HostMac.Enabled {
+		hostMACs, errMACs := d.provider.HostMACs()
+		if errMACs != nil {
+			return pcommon.NewResource(), "", fmt.Errorf("failed to get host MAC addresses: %w", errMACs)
+		}
+		for _, mac := range hostMACs {
+			hostMACAttribute = append(hostMACAttribute, toIEEERA(mac))
+		}
+	}
+
 	osDescription, err := d.provider.OSDescription(ctx)
 	if err != nil {
 		return pcommon.NewResource(), "", fmt.Errorf("failed getting OS description: %w", err)
@@ -119,6 +143,7 @@ func (d *Detector) Detect(ctx context.Context) (resource pcommon.Resource, schem
 			}
 			d.rb.SetHostArch(hostArch)
 			d.rb.SetHostIP(hostIPAttribute)
+			d.rb.SetHostMac(hostMACAttribute)
 			d.rb.SetOsDescription(osDescription)
 			if len(cpuInfo) > 0 {
 				err = setHostCPUInfo(d, cpuInfo[0])