Add support for streaming usage stats back to the calling process

server/resources.go

@@ -0,0 +1,51 @@
+package server
+
+import (
+	"github.com/docker/docker/api/types"
+	"math"
+)
+
+// Defines the current resource usage for a given server instance. If a server is offline you
+// should obviously expect memory and CPU usage to be 0. However, disk will always be returned
+// since that is not dependent on the server being running to collect that data.
+type ResourceUsage struct {
+	// The total amount of memory, in bytes, that this server instance is consuming.
+	Memory uint64 `json:"memory_bytes"`
+	// The total amount of memory this container or resource can use. Inside Docker this is
+	// going to be higher than you'd expect because we're automatically allocating overhead
+	// abilities for the container, so its not going to be a perfect match.
+	MemoryLimit uint64 `json:"memory_limit_bytes"`
+	// The absolute CPU usage is the amount of CPU used in relation to the entire system and
+	// does not take into account any limits on the server process itself.
+	CpuAbsolute float64 `json:"cpu_absolute"`
+	// The current disk space being used by the server. This is cached to prevent slow lookup
+	// issues on frequent refreshes.
+	Disk uint64 `json:"disk_bytes"`
+	// Current network transmit in & out for a container.
+	Network struct {
+		RxBytes uint64 `json:"rx_bytes"`
+		TxBytes uint64 `json:"tx_bytes"`
+	} `json:"network"`
+}
+
+// Calculates the absolute CPU usage used by the server process on the system, not constrained
+// by the defined CPU limits on the container.
+//
+// @see https://github.com/docker/cli/blob/aa097cf1aa19099da70930460250797c8920b709/cli/command/container/stats_helpers.go#L166
+func (ru *ResourceUsage) CalculateAbsoluteCpu(previousCpu, previousSystem float64, stats *types.CPUStats) float64 {
+	// Calculate the change in CPU usage between the current and previous reading.
+	cpuDelta := float64(stats.CPUUsage.TotalUsage) - float64(previousCpu)
+
+	// Calculate the change for the entire system's CPU usage between current and previous reading.
+	systemDelta := float64(stats.SystemUsage) - float64(previousSystem)
+
+	// Calculate the total number of CPU cores being used.
+	cpus := float64(len(stats.CPUUsage.PercpuUsage))
+
+	percent := 0.0
+	if systemDelta > 0.0 && cpuDelta > 0.0 {
+		percent = (cpuDelta / systemDelta) * cpus * 100.0
+	}
+
+	return math.Round(percent * 1000) / 1000
+}