-rpi-sendspin/internal/pipewire/nodes.go

package pipewire

import (
	"encoding/json"
	"fmt"
	"os/exec"
	"strings"
)

type Node struct {
	ID          int
	Name        string
	Description string
	MediaClass  string
}

func (n Node) String() string {
	if n.Description != "" && n.Description != n.Name {
		return fmt.Sprintf("%s  [%s]", n.Description, n.Name)
	}
	return n.Name
}

type pwObject struct {
	ID   int    `json:"id"`
	Type string `json:"type"`
	Info struct {
		Props struct {
			MediaClass  string `json:"media.class"`
			NodeName    string `json:"node.name"`
			NodeDesc    string `json:"node.description"`
		} `json:"props"`
	} `json:"info"`
}

func listAllNodes() ([]Node, error) {
	out, err := exec.Command("pw-dump").Output()
	if err != nil {
		return nil, fmt.Errorf("pw-dump: %w", err)
	}

	var objects []pwObject
	if err := json.Unmarshal(out, &objects); err != nil {
		return nil, fmt.Errorf("parse pw-dump: %w", err)
	}

	var nodes []Node
	for _, o := range objects {
		if o.Type != "PipeWire:Interface:Node" {
			continue
		}
		if !strings.HasPrefix(o.Info.Props.MediaClass, "Audio/") || o.Info.Props.NodeName == "" {
			continue
		}
		nodes = append(nodes, Node{
			ID:          o.ID,
			Name:        o.Info.Props.NodeName,
			Description: o.Info.Props.NodeDesc,
			MediaClass:  o.Info.Props.MediaClass,
		})
	}
	return nodes, nil
}

func ListSinks() ([]Node, error) {
	all, err := listAllNodes()
	if err != nil {
		return nil, err
	}
	var out []Node
	for _, n := range all {
		if n.MediaClass == "Audio/Sink" {
			out = append(out, n)
		}
	}
	return out, nil
}

func ListSources() ([]Node, error) {
	all, err := listAllNodes()
	if err != nil {
		return nil, err
	}
	var out []Node
	for _, n := range all {
		switch n.MediaClass {
		case "Audio/Source", "Audio/Source.Virtual":
			out = append(out, n)
		}
	}
	return out, nil
}

// CaptureTarget is a node that can be fed to `pw-cat --capture --target`.
// Real microphones / line-ins / virtual sources have IsMonitor=false.
// Audio sinks are surfaced with IsMonitor=true: pw-cat reads the monitor
// port when given a sink as --target, so the live server can stream
// whatever audio the host is currently playing.
type CaptureTarget struct {
	Name        string
	Description string
	IsMonitor   bool
}

// ListCaptureTargets returns every PipeWire node usable as audio input
// for the live server. Sinks are surfaced as monitor capture targets
// (pw-cat captures the monitor port when given a sink as --target);
// `.monitor` pseudo-sources exposed by the PulseAudio compatibility
// layer are also included since `pw-cat --target <name>.monitor` is
// the canonical way to capture playback on many setups.
//
// Order: real microphones / line-ins first, then monitors (the things
// most users actually want for "stream what's playing").
func ListCaptureTargets() ([]CaptureTarget, error) {
	all, err := listAllNodes()
	if err != nil {
		return nil, err
	}

	var realSources, monitorSources, sinkMonitors []CaptureTarget
	monitorNames := map[string]bool{}

	for _, n := range all {
		switch n.MediaClass {
		case "Audio/Source", "Audio/Source.Virtual":
			if strings.HasSuffix(n.Name, ".monitor") {
				monitorSources = append(monitorSources, CaptureTarget{
					Name: n.Name, Description: n.Description, IsMonitor: true,
				})
				monitorNames[n.Name] = true
			} else {
				realSources = append(realSources, CaptureTarget{
					Name: n.Name, Description: n.Description,
				})
			}
		case "Audio/Sink":
			// Skip the sink itself when its corresponding ".monitor"
			// source already covers the same capture path — pick one
			// canonical name (the source) to avoid two indistinguishable
			// dropdown entries.
			if monitorNames[n.Name+".monitor"] {
				continue
			}
			sinkMonitors = append(sinkMonitors, CaptureTarget{
				Name: n.Name, Description: n.Description, IsMonitor: true,
			})
		}
	}

	out := make([]CaptureTarget, 0, len(realSources)+len(monitorSources)+len(sinkMonitors))
	out = append(out, realSources...)
	out = append(out, monitorSources...)
	out = append(out, sinkMonitors...)
	return out, nil
}