compat: Add a stub container/stats handler for FreeBSD

The container/stats endpoint was unimplemented.  Copy over the structure
from the Linux endpoint handler, albeit with most of the stats
unpopulated.  This is similar to how "podman stats" returns very little
info on FreeBSD.  On the other hand, some orchestration tools will query
the stats endpoint to check liveness of a container, so it's useful to
implement it even though some fields are unimplemented for now.

Signed-off-by: Mark Johnston <mark.johnston@klarasystems.com>

pkg/api/handlers/compat/containers_stats_freebsd.go

@@ -3,15 +3,136 @@
 package compat
 
 import (
+	"encoding/json"
 	"fmt"
 	"net/http"
 	"time"
 
+	"github.com/containers/podman/v5/libpod"
+	"github.com/containers/podman/v5/libpod/define"
 	"github.com/containers/podman/v5/pkg/api/handlers/utils"
+	api "github.com/containers/podman/v5/pkg/api/types"
+	"github.com/docker/docker/api/types/container"
+	"github.com/sirupsen/logrus"
 )
 
 const DefaultStatsPeriod = 5 * time.Second
 
 func StatsContainer(w http.ResponseWriter, r *http.Request) {
-	utils.Error(w, http.StatusBadRequest, fmt.Errorf("compat.StatsContainer not supported on FreeBSD"))
+	runtime := r.Context().Value(api.RuntimeKey).(*libpod.Runtime)
+	decoder := utils.GetDecoder(r)
+
+	query := struct {
+		Stream  bool `schema:"stream"`
+		OneShot bool `schema:"one-shot"` // added schema for one shot
+	}{
+		Stream: true,
+	}
+	if err := decoder.Decode(&query, r.URL.Query()); err != nil {
+		utils.Error(w, http.StatusBadRequest, fmt.Errorf("failed to parse parameters for %s: %w", r.URL.String(), err))
+		return
+	}
+	if query.Stream && query.OneShot { // mismatch. one-shot can only be passed with stream=false
+		utils.Error(w, http.StatusBadRequest, define.ErrInvalidArg)
+		return
+	}
+
+	name := utils.GetName(r)
+	ctnr, err := runtime.LookupContainer(name)
+	if err != nil {
+		utils.ContainerNotFound(w, name, err)
+		return
+	}
+
+	stats, err := ctnr.GetContainerStats(nil)
+	if err != nil {
+		utils.InternalServerError(w, fmt.Errorf("failed to obtain Container %s stats: %w", name, err))
+		return
+	}
+
+	coder := json.NewEncoder(w)
+	// Write header and content type.
+	w.WriteHeader(http.StatusOK)
+	w.Header().Set("Content-Type", "application/json")
+	if flusher, ok := w.(http.Flusher); ok {
+		flusher.Flush()
+	}
+
+	// Set up JSON encoder for streaming.
+	coder.SetEscapeHTML(true)
+	var preRead time.Time
+	var preCPUStats CPUStats
+	if query.Stream {
+		preRead = time.Now()
+		preCPUStats = CPUStats{
+			CPUUsage: container.CPUUsage{
+				TotalUsage: stats.CPUNano,
+			},
+			CPU:            stats.CPU,
+			OnlineCPUs:     0,
+			ThrottlingData: container.ThrottlingData{},
+		}
+	}
+
+streamLabel: // A label to flatten the scope
+	select {
+	case <-r.Context().Done():
+		logrus.Debugf("Client connection (container stats) cancelled")
+
+	default:
+		stats, err = ctnr.GetContainerStats(stats)
+		if err != nil {
+			logrus.Errorf("Unable to get container stats: %v", err)
+			return
+		}
+		s := StatsJSON{
+			Stats: Stats{
+				Read:    time.Now(),
+				PreRead: preRead,
+				CPUStats: CPUStats{
+					CPUUsage: container.CPUUsage{
+						TotalUsage: stats.CPUNano,
+					},
+					CPU:            stats.CPU,
+					OnlineCPUs:     0,
+					ThrottlingData: container.ThrottlingData{},
+				},
+				PreCPUStats: preCPUStats,
+				MemoryStats: container.MemoryStats{},
+			},
+			Name: stats.Name,
+			ID:   stats.ContainerID,
+		}
+
+		var jsonOut interface{}
+		if utils.IsLibpodRequest(r) {
+			jsonOut = s
+		} else {
+			jsonOut = DockerStatsJSON(s)
+		}
+
+		if err := coder.Encode(jsonOut); err != nil {
+			logrus.Errorf("Unable to encode stats: %v", err)
+			return
+		}
+		if flusher, ok := w.(http.Flusher); ok {
+			flusher.Flush()
+		}
+
+		if !query.Stream || query.OneShot {
+			return
+		}
+
+		preRead = s.Read
+		bits, err := json.Marshal(s.CPUStats)
+		if err != nil {
+			logrus.Errorf("Unable to marshal cpu stats: %q", err)
+		}
+		if err := json.Unmarshal(bits, &preCPUStats); err != nil {
+			logrus.Errorf("Unable to unmarshal previous stats: %q", err)
+		}
+
+		time.Sleep(DefaultStatsPeriod)
+		goto streamLabel
+	}
 }