fix: make resource metrics platform aware

server/system_metrics.go

@@ -1,17 +1,8 @@
 package server
 
-// Container-level resource metrics. These deliberately read cgroups directly:
-// generic host libraries often report the host's capacity from inside Docker.
-
 import (
 	"encoding/json"
-	"os"
 	"net/http"
-	"path/filepath"
-	"runtime"
-	"strconv"
-	"strings"
-	"syscall"
 	"time"
 )
 
@@ -23,6 +14,7 @@ type metricValue struct {
 
 type systemMetricsResponse struct {
 	Scope     string      `json:"scope"`
+	Supported bool        `json:"supported"`
 	Timestamp time.Time   `json:"timestamp"`
 	CPU       metricValue `json:"cpu"`
 	Memory    metricValue `json:"memory"`
@@ -32,71 +24,8 @@ type systemMetricsResponse struct {
 }
 
 func (s *Server) systemMetrics(w http.ResponseWriter, r *http.Request) {
-	cpuUse, cpuLimit, ok := cgroupCPU()
-	cpuPct := 0.0
-	if ok {
-		now := time.Now()
-		s.metricsMu.Lock()
-		if !s.lastCPUAt.IsZero() && cpuUse >= s.lastCPUUse {
-			elapsed := now.Sub(s.lastCPUAt).Seconds()
-			if elapsed > 0 {
-				cpuPct = float64(cpuUse-s.lastCPUUse) / 1e6 / elapsed / cpuLimit * 100
-			}
-		}
-		s.lastCPUUse, s.lastCPUAt = cpuUse, now
-		s.metricsMu.Unlock()
-	}
-	memUsed, memTotal, memOK := cgroupMemory()
-	root := diskMetric("/")
-	data := diskMetric(s.dataDir)
-	if data.TotalBytes == 0 { data = root }
-	containerMetrics := ok || memOK
-	scope := "process"
-	if containerMetrics {
-		scope = "container"
-	}
-	out := systemMetricsResponse{Scope: scope, Timestamp: time.Now().UTC(), Container: containerMetrics,
-		CPU: metricValue{Percent: clampPercent(cpuPct)},
-		Memory: metricValue{UsedBytes: memUsed, TotalBytes: memTotal, Percent: percent(memUsed, memTotal)}, Disk: root, DataDisk: data}
+	out := systemMetricsSnapshot(s)
 	w.Header().Set("Cache-Control", "no-store")
 	w.Header().Set("Content-Type", "application/json")
 	_ = json.NewEncoder(w).Encode(out)
 }
-
-func cgroupCPU() (uint64, float64, bool) {
-	for _, dir := range []string{"/sys/fs/cgroup", "/sys/fs/cgroup/cpu"} {
-		b, err := os.ReadFile(filepath.Join(dir, "cpu.stat")); if err != nil { continue }
-		var use uint64
-		for _, line := range strings.Split(string(b), "\n") { f := strings.Fields(line); if len(f) == 2 && f[0] == "usage_usec" { use, _ = strconv.ParseUint(f[1], 10, 64) } }
-		limit := float64(runtime.NumCPU())
-		if q, err := os.ReadFile(filepath.Join(dir, "cpu.max")); err == nil { f := strings.Fields(string(q)); if len(f) == 2 && f[0] != "max" { quota, _ := strconv.ParseFloat(f[0], 64); period, _ := strconv.ParseFloat(f[1], 64); if period > 0 { limit = quota / period } } }
-		if use > 0 { return use, limit, true }
-	}
-	return 0, 0, false
-}
-
-func cgroupMemory() (uint64, uint64, bool) {
-	for _, dir := range []string{"/sys/fs/cgroup", "/sys/fs/cgroup/memory"} {
-		cur, e1 := readUint(filepath.Join(dir, "memory.current")); max, e2 := readUint(filepath.Join(dir, "memory.max"))
-		if e1 == nil && e2 == nil { return cur, max, max > 0 }
-		if e1 == nil {
-			if b, err := os.ReadFile(filepath.Join(dir, "memory.max")); err == nil && strings.TrimSpace(string(b)) == "max" {
-				return cur, hostMemoryTotal(), true
-			}
-		}
-		cur, e1 = readUint(filepath.Join(dir, "memory.usage_in_bytes")); max, e2 = readUint(filepath.Join(dir, "memory.limit_in_bytes")); if e1 == nil && e2 == nil && max < ^uint64(0)/2 { return cur, max, true }
-	}
-	return 0, 0, false
-}
-
-func hostMemoryTotal() uint64 {
-	b, err := os.ReadFile("/proc/meminfo"); if err != nil { return 0 }
-	for _, line := range strings.Split(string(b), "\n") { f := strings.Fields(line); if len(f) >= 2 && f[0] == "MemTotal:" { n, _ := strconv.ParseUint(f[1], 10, 64); return n * 1024 } }
-	return 0
-}
-
-func readUint(path string) (uint64, error) { b, err := os.ReadFile(path); if err != nil { return 0, err }; return strconv.ParseUint(strings.TrimSpace(string(b)), 10, 64) }
-
-func diskMetric(path string) metricValue { var st syscall.Statfs_t; if path == "" || syscall.Statfs(path, &st) != nil { return metricValue{} }; total := st.Blocks * uint64(st.Bsize); free := st.Bavail * uint64(st.Bsize); used := total - free; return metricValue{UsedBytes: used, TotalBytes: total, Percent: percent(used, total)} }
-func percent(used, total uint64) float64 { if total == 0 { return 0 }; return clampPercent(float64(used) / float64(total) * 100) }
-func clampPercent(v float64) float64 { if v < 0 { return 0 }; if v > 100 { return 100 }; return v }

server/system_metrics_linux.go

@@ -0,0 +1,62 @@
+//go:build linux
+
+package server
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+)
+
+func systemMetricsSnapshot(s *Server) systemMetricsResponse {
+	use, limit, cpuOK := cgroupCPU()
+	cpuPct := 0.0
+	if cpuOK {
+		now := time.Now()
+		s.metricsMu.Lock()
+		if !s.lastCPUAt.IsZero() && use >= s.lastCPUUse && limit > 0 {
+			elapsed := now.Sub(s.lastCPUAt).Seconds()
+			if elapsed > 0 { cpuPct = float64(use-s.lastCPUUse) / 1e6 / elapsed / limit * 100 }
+		}
+		s.lastCPUUse, s.lastCPUAt = use, now
+		s.metricsMu.Unlock()
+	}
+	memUsed, memTotal, memOK := cgroupMemory()
+	root, data := diskMetric("/"), diskMetric(s.dataDir)
+	if data.TotalBytes == 0 { data = root }
+	return systemMetricsResponse{Scope: "container", Supported: true, Timestamp: time.Now().UTC(), Container: cpuOK || memOK,
+		CPU: metricValue{Percent: clampPercent(cpuPct)}, Memory: metricValue{UsedBytes: memUsed, TotalBytes: memTotal, Percent: percent(memUsed, memTotal)}, Disk: root, DataDisk: data}
+}
+
+func cgroupCPU() (uint64, float64, bool) {
+	for _, dir := range []string{"/sys/fs/cgroup", "/sys/fs/cgroup/cpu"} {
+		b, err := os.ReadFile(filepath.Join(dir, "cpu.stat")); if err != nil { continue }
+		var use uint64
+		for _, line := range strings.Split(string(b), "\n") { f := strings.Fields(line); if len(f) == 2 && f[0] == "usage_usec" { use, _ = strconv.ParseUint(f[1], 10, 64) } }
+		limit := float64(runtime.NumCPU())
+		if q, err := os.ReadFile(filepath.Join(dir, "cpu.max")); err == nil { f := strings.Fields(string(q)); if len(f) == 2 && f[0] != "max" { quota, _ := strconv.ParseFloat(f[0], 64); period, _ := strconv.ParseFloat(f[1], 64); if period > 0 { limit = quota / period } } }
+		if use > 0 { return use, limit, true }
+	}
+	return 0, 0, false
+}
+
+func cgroupMemory() (uint64, uint64, bool) {
+	for _, dir := range []string{"/sys/fs/cgroup", "/sys/fs/cgroup/memory"} {
+		cur, ce := readUint(filepath.Join(dir, "memory.current")); max, me := readUint(filepath.Join(dir, "memory.max"))
+		if ce == nil && me == nil { return cur, max, max > 0 }
+		if ce == nil { if b, err := os.ReadFile(filepath.Join(dir, "memory.max")); err == nil && strings.TrimSpace(string(b)) == "max" { return cur, hostMemoryTotal(), true } }
+		cur, ce = readUint(filepath.Join(dir, "memory.usage_in_bytes")); max, me = readUint(filepath.Join(dir, "memory.limit_in_bytes"))
+		if ce == nil && me == nil && max < ^uint64(0)/2 { return cur, max, true }
+	}
+	return 0, 0, false
+}
+
+func hostMemoryTotal() uint64 { b, err := os.ReadFile("/proc/meminfo"); if err != nil { return 0 }; for _, line := range strings.Split(string(b), "\n") { f := strings.Fields(line); if len(f) >= 2 && f[0] == "MemTotal:" { n, _ := strconv.ParseUint(f[1], 10, 64); return n * 1024 } }; return 0 }
+func readUint(path string) (uint64, error) { b, err := os.ReadFile(path); if err != nil { return 0, err }; return strconv.ParseUint(strings.TrimSpace(string(b)), 10, 64) }
+func diskMetric(path string) metricValue { var st syscall.Statfs_t; if path == "" || syscall.Statfs(path, &st) != nil { return metricValue{} }; total, free := st.Blocks*uint64(st.Bsize), st.Bavail*uint64(st.Bsize); used := total-free; return metricValue{UsedBytes: used, TotalBytes: total, Percent: percent(used, total)} }
+func percent(used, total uint64) float64 { if total == 0 { return 0 }; return clampPercent(float64(used)/float64(total)*100) }
+func clampPercent(v float64) float64 { if v < 0 { return 0 }; if v > 100 { return 100 }; return v }

server/system_metrics_test.go

@@ -3,6 +3,7 @@ package server
 import (
 	"encoding/json"
 	"net/http/httptest"
+	"runtime"
 	"testing"
 )
 
@@ -21,6 +22,12 @@ func TestSystemMetricsReturnsContainerAndDiskValues(t *testing.T) {
 	if got.Scope == "" || got.Timestamp.IsZero() {
 		t.Fatalf("unexpected response metadata: %+v", got)
 	}
+	if runtime.GOOS != "linux" {
+		if got.Supported || got.Scope != "unsupported" {
+			t.Fatalf("unsupported platform returned metrics: %+v", got)
+		}
+		return
+	}
 	if got.Disk.TotalBytes == 0 || got.DataDisk.TotalBytes == 0 {
 		t.Fatalf("disk metrics missing: %+v", got)
 	}

server/system_metrics_unsupported.go

@@ -0,0 +1,9 @@
+//go:build !linux
+
+package server
+
+import "time"
+
+func systemMetricsSnapshot(_ *Server) systemMetricsResponse {
+	return systemMetricsResponse{Scope: "unsupported", Supported: false, Timestamp: time.Now().UTC()}
+}