test(agentcompat): add process supervision harness

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

integration/agentcompat/internal/process/sampler.go

@@ -0,0 +1,109 @@
+//go:build linux
+
+package process
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/nezhahq/nezha/integration/agentcompat/internal/contract"
+)
+
+type Sample struct {
+	PID               int    `json:"pid"`
+	RSSBytes          uint64 `json:"rss_bytes"`
+	DescendantPIDs    []int  `json:"descendant_pids"`
+	DescendantCount   int    `json:"descendant_count"`
+	NonStdioFDCount   int    `json:"non_stdio_fd_count"`
+	TCPListenerCount  int    `json:"tcp_listener_count"`
+	TCP6ListenerCount int    `json:"tcp6_listener_count"`
+}
+
+type Window struct {
+	PID     int      `json:"pid"`
+	Samples []Sample `json:"samples"`
+}
+
+type WindowSpec struct {
+	PID             int
+	Interval        time.Duration
+	AllowTerminated bool
+	ObserveSample   func(context.Context, Sample) error
+}
+
+func SampleProcess(pid int) (Sample, error) {
+	rssBytes, err := readRSSBytes(pid)
+	if err != nil {
+		return Sample{}, err
+	}
+	descendants, err := descendantPIDs(pid)
+	if err != nil {
+		return Sample{}, err
+	}
+	fdCount, socketInodes, err := processFDs(pid)
+	if err != nil {
+		return Sample{}, err
+	}
+	tcpListeners, err := listeningSocketInodes(pid, "tcp")
+	if err != nil {
+		return Sample{}, err
+	}
+	tcp6Listeners, err := listeningSocketInodes(pid, "tcp6")
+	if err != nil {
+		return Sample{}, err
+	}
+	return Sample{
+		PID:               pid,
+		RSSBytes:          rssBytes,
+		DescendantPIDs:    descendants,
+		DescendantCount:   len(descendants),
+		NonStdioFDCount:   fdCount,
+		TCPListenerCount:  intersectionCount(socketInodes, tcpListeners),
+		TCP6ListenerCount: intersectionCount(socketInodes, tcp6Listeners),
+	}, nil
+}
+
+func SampleWindow(ctx context.Context, spec WindowSpec) (Window, error) {
+	if spec.PID < 1 || spec.Interval <= 0 {
+		return Window{}, errors.New("invalid sample window specification")
+	}
+	window := Window{PID: spec.PID, Samples: make([]Sample, 0, contract.ResourceSampleCount)}
+	for index := 0; index < contract.ResourceSampleCount; index++ {
+		if index > 0 {
+			timer := time.NewTimer(spec.Interval)
+			select {
+			case <-timer.C:
+			case <-ctx.Done():
+				timer.Stop()
+				return Window{}, ctx.Err()
+			}
+		}
+		sample, err := SampleProcess(spec.PID)
+		if err != nil {
+			if spec.AllowTerminated && os.IsNotExist(err) {
+				return window, nil
+			}
+			return Window{}, fmt.Errorf("sample %d of PID %d: %w", index+1, spec.PID, err)
+		}
+		window.Samples = append(window.Samples, sample)
+		if spec.ObserveSample != nil {
+			if err := spec.ObserveSample(ctx, sample); err != nil {
+				return window, err
+			}
+		}
+	}
+	return window, nil
+}
+
+func intersectionCount(left, right map[uint64]struct{}) int {
+	count := 0
+	for value := range left {
+		if _, exists := right[value]; exists {
+			count++
+		}
+	}
+	return count
+}