fix(metrics): add cross-platform process metrics collector for non-Linux systems

The standard Prometheus ProcessCollector uses procfs (Linux-only /proc),
so process_resident_memory_bytes and process_virtual_memory_bytes were
silently absent on FreeBSD, Darwin, and other non-Linux platforms.

- Switch to a custom prometheus.Registry to isolate GOST metrics from
  the default registry auto-registrations
- Add gopsutil/v3-based process collector (process_other.go) for
  platforms without procfs (!linux && !windows)
- Keep standard ProcessCollector (process_standard.go) on Linux/Windows
- Update metrics service and handler/metrics to serve from
  promhttp.HandlerFor(customRegistry) instead of promhttp.Handler()
- Add Registry() accessor for the custom registry

Fixes go-gost/gost#509

go.mod

@@ -60,6 +60,7 @@ require (
 require (
 	github.com/andybalholm/brotli v1.0.6 // indirect
 	github.com/klauspost/compress v1.17.4 // indirect
+	github.com/shirou/gopsutil/v3 v3.24.5 // indirect
 	github.com/sirupsen/logrus v1.9.3 // indirect
 )
 

go.sum

@@ -206,6 +206,8 @@ github.com/sagikazarmark/slog-shim v0.1.0 h1:diDBnUNK9N/354PgrxMywXnAwEr1QZcOr6g
 github.com/sagikazarmark/slog-shim v0.1.0/go.mod h1:SrcSrq8aKtyuqEI1uvTDTK1arOWRIczQRv+GVI1AkeQ=
 github.com/shadowsocks/go-shadowsocks2 v0.1.5 h1:PDSQv9y2S85Fl7VBeOMF9StzeXZyK1HakRm86CUbr28=
 github.com/shadowsocks/go-shadowsocks2 v0.1.5/go.mod h1:AGGpIoek4HRno4xzyFiAtLHkOpcoznZEkAccaI/rplM=
+github.com/shirou/gopsutil/v3 v3.24.5 h1:i0t8kL+kQTvpAYToeuiVk3TgDeKOFioZO3Ztz/iZ9pI=
+github.com/shirou/gopsutil/v3 v3.24.5/go.mod h1:bsoOS1aStSs9ErQ1WWfxllSeS1K5D+U30r2NfcubMVk=
 github.com/sirupsen/logrus v1.7.0/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
 github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=

handler/metrics/handler.go

@@ -43,7 +43,7 @@ func (h *metricsHandler) Init(md md.Metadata) (err error) {
 
 	xmetrics.Enable(true)
 
-	h.handler = promhttp.Handler()
+	h.handler = promhttp.HandlerFor(xmetrics.Registry(), promhttp.HandlerOpts{})
 
 	mux := http.NewServeMux()
 	mux.Handle(h.md.path, http.HandlerFunc(h.handleFunc))

metrics/metrics.go

@@ -4,6 +4,8 @@ import (
 	"sync/atomic"
 
 	"github.com/go-gost/core/metrics"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
 )
 
 const (
@@ -30,10 +32,31 @@ const (
 )
 
 var (
-	defaultMetrics metrics.Metrics = NewMetrics()
+	defaultMetrics  metrics.Metrics
+	defaultRegistry *prometheus.Registry
 	enabled         atomic.Bool
 )
 
+func init() {
+	defaultRegistry = prometheus.NewRegistry()
+
+	// Register Go and process collectors on our custom registry so the metrics
+	// endpoint is self-contained. The process collector is platform-specific:
+	// Linux/Windows use the standard procfs/Win32-based collector; all other
+	// platforms (FreeBSD, Darwin, etc.) use a gopsutil-based collector.
+	defaultRegistry.MustRegister(collectors.NewGoCollector())
+	registerProcessCollector(defaultRegistry)
+
+	defaultMetrics = NewMetrics(defaultRegistry)
+}
+
+// Registry returns the custom Prometheus registry that holds all GOST metrics
+// plus the Go and process collectors. The metrics HTTP endpoint should serve
+// from this registry rather than prometheus.DefaultGatherer.
+func Registry() *prometheus.Registry {
+	return defaultRegistry
+}
+
 // Enable enables or disables metrics collection globally. When disabled, all
 // GetCounter, GetGauge, and GetObserver calls return noop implementations.
 func Enable(b bool) {

metrics/process_other.go

@@ -0,0 +1,154 @@
+//go:build !linux && !windows
+
+package metrics
+
+import (
+	"os"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	psutil "github.com/shirou/gopsutil/v3/process"
+)
+
+// gopsutilProcessCollector implements prometheus.Collector using gopsutil/v3
+// for cross-platform process metrics on non-Linux, non-Windows systems
+// (FreeBSD, Darwin, etc.) where procfs is unavailable.
+type gopsutilProcessCollector struct {
+	pidFn        func() (int, error)
+	cpuTotal     *prometheus.Desc
+	openFDs      *prometheus.Desc
+	maxFDs       *prometheus.Desc
+	vsize        *prometheus.Desc
+	maxVsize     *prometheus.Desc
+	rss          *prometheus.Desc
+	startTime    *prometheus.Desc
+	reportErrors bool
+}
+
+func getPID() (int, error) { return os.Getpid(), nil }
+
+func newGopsutilProcessCollector() prometheus.Collector {
+	return &gopsutilProcessCollector{
+		pidFn: getPID,
+		cpuTotal: prometheus.NewDesc(
+			"process_cpu_seconds_total",
+			"Total user and system CPU time spent in seconds.",
+			nil, nil,
+		),
+		openFDs: prometheus.NewDesc(
+			"process_open_fds",
+			"Number of open file descriptors.",
+			nil, nil,
+		),
+		maxFDs: prometheus.NewDesc(
+			"process_max_fds",
+			"Maximum number of open file descriptors.",
+			nil, nil,
+		),
+		vsize: prometheus.NewDesc(
+			"process_virtual_memory_bytes",
+			"Virtual memory size in bytes.",
+			nil, nil,
+		),
+		maxVsize: prometheus.NewDesc(
+			"process_virtual_memory_max_bytes",
+			"Maximum amount of virtual memory available in bytes.",
+			nil, nil,
+		),
+		rss: prometheus.NewDesc(
+			"process_resident_memory_bytes",
+			"Resident memory size in bytes.",
+			nil, nil,
+		),
+		startTime: prometheus.NewDesc(
+			"process_start_time_seconds",
+			"Start time of the process since unix epoch in seconds.",
+			nil, nil,
+		),
+		reportErrors: false,
+	}
+}
+
+func (c *gopsutilProcessCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- c.cpuTotal
+	ch <- c.openFDs
+	ch <- c.maxFDs
+	ch <- c.vsize
+	ch <- c.maxVsize
+	ch <- c.rss
+	ch <- c.startTime
+}
+
+func (c *gopsutilProcessCollector) Collect(ch chan<- prometheus.Metric) {
+	pid, err := c.pidFn()
+	if err != nil {
+		c.reportError(ch, nil, err)
+		return
+	}
+
+	p, err := psutil.NewProcess(int32(pid))
+	if err != nil {
+		c.reportError(ch, nil, err)
+		return
+	}
+
+	// Memory metrics: RSS (resident) and VMS (virtual).
+	if mem, err := p.MemoryInfo(); err == nil {
+		ch <- prometheus.MustNewConstMetric(c.rss, prometheus.GaugeValue, float64(mem.RSS))
+		ch <- prometheus.MustNewConstMetric(c.vsize, prometheus.GaugeValue, float64(mem.VMS))
+	} else {
+		c.reportError(ch, c.rss, err)
+	}
+
+	// CPU time.
+	if times, err := p.Times(); err == nil {
+		cpuSeconds := times.User + times.System
+		ch <- prometheus.MustNewConstMetric(c.cpuTotal, prometheus.CounterValue, cpuSeconds)
+	} else {
+		c.reportError(ch, c.cpuTotal, err)
+	}
+
+	// Open file descriptors.
+	if fds, err := p.NumFDs(); err == nil {
+		ch <- prometheus.MustNewConstMetric(c.openFDs, prometheus.GaugeValue, float64(fds))
+	} else {
+		c.reportError(ch, c.openFDs, err)
+	}
+
+	// Max file descriptors — not reliably available via gopsutil on all platforms.
+	// Try RLIMIT_NOFILE via gopsutil's RlimitUsage.
+	if rlimits, err := p.RlimitUsage(false); err == nil && len(rlimits) > 0 {
+		for _, rl := range rlimits {
+			switch rl.Resource {
+			case psutil.RLIMIT_NOFILE:
+				ch <- prometheus.MustNewConstMetric(c.maxFDs, prometheus.GaugeValue, float64(rl.Hard))
+			case psutil.RLIMIT_AS:
+				ch <- prometheus.MustNewConstMetric(c.maxVsize, prometheus.GaugeValue, float64(rl.Hard))
+			}
+		}
+	}
+
+	// Process start time.
+	if ct, err := p.CreateTime(); err == nil {
+		createTime := time.Unix(ct/1000, (ct%1000)*1e6)
+		ch <- prometheus.MustNewConstMetric(c.startTime, prometheus.GaugeValue, float64(createTime.Unix()))
+	} else {
+		c.reportError(ch, c.startTime, err)
+	}
+}
+
+func (c *gopsutilProcessCollector) reportError(ch chan<- prometheus.Metric, desc *prometheus.Desc, err error) {
+	if !c.reportErrors {
+		return
+	}
+	if desc == nil {
+		desc = prometheus.NewInvalidDesc(err)
+	}
+	ch <- prometheus.NewInvalidMetric(desc, err)
+}
+
+// registerProcessCollector registers a gopsutil-based process metrics collector
+// for platforms where procfs is unavailable.
+func registerProcessCollector(reg *prometheus.Registry) {
+	reg.MustRegister(newGopsutilProcessCollector())
+}

metrics/process_standard.go

@@ -0,0 +1,14 @@
+//go:build linux || windows
+
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+)
+
+// registerProcessCollector registers the standard prometheus ProcessCollector
+// which uses procfs on Linux and Win32 syscalls on Windows.
+func registerProcessCollector(reg *prometheus.Registry) {
+	reg.MustRegister(collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}))
+}

metrics/prom.go

@@ -16,8 +16,13 @@ type promMetrics struct {
 }
 
 // NewMetrics returns a Prometheus-based Metrics implementation. All metrics are
-// automatically registered with the default Prometheus registry.
-func NewMetrics() metrics.Metrics {
+// registered with the given registry. Use nil to register with the default
+// Prometheus registry.
+func NewMetrics(reg *prometheus.Registry) metrics.Metrics {
+	if reg == nil {
+		reg = prometheus.DefaultRegisterer.(*prometheus.Registry)
+	}
+
 	host, _ := os.Hostname()
 	m := &promMetrics{
 		host: host,
@@ -95,13 +100,13 @@ func NewMetrics() metrics.Metrics {
 		},
 	}
 	for k := range m.gauges {
-		prometheus.MustRegister(m.gauges[k])
+		reg.MustRegister(m.gauges[k])
 	}
 	for k := range m.counters {
-		prometheus.MustRegister(m.counters[k])
+		reg.MustRegister(m.counters[k])
 	}
 	for k := range m.histograms {
-		prometheus.MustRegister(m.histograms[k])
+		reg.MustRegister(m.histograms[k])
 	}
 
 	return m

metrics/service/service.go

@@ -7,7 +7,10 @@ import (
 
 	"github.com/go-gost/core/auth"
 	"github.com/go-gost/core/service"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+
+	xmetrics "github.com/go-gost/x/metrics"
 )
 
 const (
@@ -46,6 +49,8 @@ type metricService struct {
 }
 
 // NewService creates a metrics Service that exposes Prometheus metrics over HTTP.
+// It serves from the GOST custom registry rather than the default one so that
+// process metrics are available on all platforms.
 func NewService(network, addr string, opts ...Option) (service.Service, error) {
 	if network == "" {
 		network = "tcp"
@@ -82,7 +87,12 @@ func NewService(network, addr string, opts ...Option) (service.Service, error) {
 				return
 			}
 		}
-		promhttp.Handler().ServeHTTP(w, r)
+
+		reg := xmetrics.Registry()
+		if reg == nil {
+			reg = prometheus.DefaultRegisterer.(*prometheus.Registry)
+		}
+		promhttp.HandlerFor(reg, promhttp.HandlerOpts{}).ServeHTTP(w, r)
 	}))
 	return &metricService{
 		s: &http.Server{