compute cpu and memory stats for docker on windows (#653)

The Docker daemon's API returns different values on Windows and non-Windows systems. This impacts
the calculation of `cpuPct` and `usedMemory` for each container. The systems are disciminate on the
`Server` header send by the server. Uses the unix stats calculation in case the header is not set.

`docker stats` implementation for reference:
https://github.com/docker/cli/blob/master/cli/command/container/stats_helpers.go#L100

Co-authored-by: Benoit VIRY <benoit.viry@cgx-group.com>

beszel/internal/agent/docker.go

@@ -14,9 +14,13 @@ import (
 	"sync"
 	"time"
 
+	"regexp"
+
 	"github.com/blang/semver"
 )
 
+var headerRegexp = regexp.MustCompile(`\ADocker/.+\s\((.+)\)\z`)
+
 type dockerManager struct {
 	client              *http.Client                // Client to query Docker API
 	wg                  sync.WaitGroup              // WaitGroup to wait for all goroutines to finish
@@ -167,22 +171,31 @@ func (dm *dockerManager) updateContainerStats(ctr *container.ApiInfo) error {
 		return err
 	}
 
+	var usedMemory uint64
+	var cpuPct float64
+
+	if getDockerOS(resp.Header.Get("Server")) == "windows" {
+
+		usedMemory = res.MemoryStats.PrivateWorkingSet
+		cpuPct = calculateCPUPercentWindows(res, stats.PrevCpu[0], stats.PrevRead)
+		stats.PrevRead = res.Read
+
+	} else {
 		// check if container has valid data, otherwise may be in restart loop (#103)
 		if res.MemoryStats.Usage == 0 {
 			return fmt.Errorf("%s - no memory stats - see https://github.com/henrygd/beszel/issues/144", name)
 		}
-
-	// memory (https://docs.docker.com/reference/cli/docker/container/stats/)
 		memCache := res.MemoryStats.Stats.InactiveFile
 		if memCache == 0 {
 			memCache = res.MemoryStats.Stats.Cache
 		}
-	usedMemory := res.MemoryStats.Usage - memCache
+		usedMemory = res.MemoryStats.Usage - memCache
 
-	// cpu
 		cpuDelta := res.CPUStats.CPUUsage.TotalUsage - stats.PrevCpu[0]
 		systemDelta := res.CPUStats.SystemUsage - stats.PrevCpu[1]
-	cpuPct := float64(cpuDelta) / float64(systemDelta) * 100
+		cpuPct = float64(cpuDelta) / float64(systemDelta) * 100
+	}
+
 	if cpuPct > 100 {
 		return fmt.Errorf("%s cpu pct greater than 100: %+v", name, cpuPct)
 	}
@@ -324,3 +337,31 @@ func getDockerHost() string {
 	}
 	return scheme + socks[0]
 }
+
+// getDockerOS returns the operating system based on the server header from the daemon.
+// from: https://github.com/docker/cli/blob/master/vendor/github.com/docker/docker/client/utils.go#L34
+func getDockerOS(serverHeader string) string {
+	var osType string
+	matches := headerRegexp.FindStringSubmatch(serverHeader)
+	if len(matches) > 0 {
+		osType = matches[1]
+	}
+	return osType
+}
+
+// from: https://github.com/docker/cli/blob/master/cli/command/container/stats_helpers.go#L185
+func calculateCPUPercentWindows(v container.ApiStats, prevCPUSsage uint64, prevRead time.Time) float64 {
+	// Max number of 100ns intervals between the previous time read and now
+	possIntervals := uint64(v.Read.Sub(prevRead).Nanoseconds())
+	possIntervals /= 100                // Convert to number of 100ns intervals
+	possIntervals *= uint64(v.NumProcs) // Multiple by the number of processors
+
+	// Intervals used
+	intervalsUsed := v.CPUStats.CPUUsage.TotalUsage - prevCPUSsage
+
+	// Percentage avoiding divide-by-zero
+	if possIntervals > 0 {
+		return float64(intervalsUsed) / float64(possIntervals) * 100.0
+	}
+	return 0.00
+}

beszel/internal/entities/container/container.go

@@ -28,7 +28,7 @@ type ApiInfo struct {
 // Docker container resources from /containers/{id}/stats
 type ApiStats struct {
 	// Common stats
-	// Read    time.Time `json:"read"`
+	Read time.Time `json:"read"`
 	// PreRead time.Time `json:"preread"`
 
 	// Linux specific stats, not populated on Windows.
@@ -36,7 +36,7 @@ type ApiStats struct {
 	// BlkioStats BlkioStats `json:"blkio_stats,omitempty"`
 
 	// Windows specific stats, not populated on Linux.
-	// NumProcs uint32 `json:"num_procs"`
+	NumProcs uint32 `json:"num_procs"`
 	// StorageStats StorageStats `json:"storage_stats,omitempty"`
 	// Networks request version >=1.21
 	Networks map[string]NetworkStats
@@ -101,7 +101,7 @@ type MemoryStats struct {
 	// // peak committed bytes
 	// CommitPeak uint64 `json:"commitpeakbytes,omitempty"`
 	// // private working set
-	// PrivateWorkingSet uint64 `json:"privateworkingset,omitempty"`
+	PrivateWorkingSet uint64 `json:"privateworkingset,omitempty"`
 }
 
 type MemoryStatsStats struct {
@@ -131,4 +131,5 @@ type Stats struct {
 	NetworkRecv float64      `json:"nr"`
 	PrevCpu     [2]uint64    `json:"-"`
 	PrevNet     prevNetStats `json:"-"`
+	PrevRead    time.Time    `json:"-"`
 }