test(agentcompat): add process supervision harness

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

integration/agentcompat/internal/process/proc.go

@@ -0,0 +1,159 @@
+//go:build linux
+
+package process
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strconv"
+	"strings"
+	"syscall"
+)
+
+func readRSSBytes(pid int) (uint64, error) {
+	path := filepath.Join("/proc", strconv.Itoa(pid), "status")
+	file, err := os.Open(path)
+	if err != nil {
+		return 0, err
+	}
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		fields := strings.Fields(scanner.Text())
+		if len(fields) == 3 && fields[0] == "VmRSS:" && fields[2] == "kB" {
+			kilobytes, err := strconv.ParseUint(fields[1], 10, 64)
+			if err != nil {
+				return 0, fmt.Errorf("parse VmRSS: %w", err)
+			}
+			return kilobytes * 1024, nil
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		return 0, fmt.Errorf("read %s: %w", path, err)
+	}
+	return 0, errors.New("VmRSS not found")
+}
+
+func descendantPIDs(rootPID int) ([]int, error) {
+	entries, err := os.ReadDir("/proc")
+	if err != nil {
+		return nil, fmt.Errorf("read /proc: %w", err)
+	}
+	children := make(map[int][]int)
+	for _, entry := range entries {
+		pid, err := strconv.Atoi(entry.Name())
+		if err != nil || !entry.IsDir() {
+			continue
+		}
+		parentPID, err := readParentPID(pid)
+		if err != nil {
+			// /proc is a live snapshot: an unrelated process can disappear
+			// between ReadDir and reading stat. Root PID reads stay strict.
+			if os.IsNotExist(err) || errors.Is(err, syscall.ESRCH) {
+				continue
+			}
+			return nil, err
+		}
+		children[parentPID] = append(children[parentPID], pid)
+	}
+	descendants := make([]int, 0)
+	queue := append([]int(nil), children[rootPID]...)
+	for len(queue) > 0 {
+		pid := queue[0]
+		queue = queue[1:]
+		descendants = append(descendants, pid)
+		queue = append(queue, children[pid]...)
+	}
+	sort.Ints(descendants)
+	return descendants, nil
+}
+
+func readParentPID(pid int) (int, error) {
+	path := filepath.Join("/proc", strconv.Itoa(pid), "stat")
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	closingParenthesis := strings.LastIndexByte(string(data), ')')
+	if closingParenthesis < 0 {
+		return 0, fmt.Errorf("parse %s: missing command terminator", path)
+	}
+	fields := strings.Fields(string(data[closingParenthesis+1:]))
+	if len(fields) < 2 {
+		return 0, fmt.Errorf("parse %s: missing parent PID", path)
+	}
+	parentPID, err := strconv.Atoi(fields[1])
+	if err != nil {
+		return 0, fmt.Errorf("parse %s parent PID: %w", path, err)
+	}
+	return parentPID, nil
+}
+
+func processFDs(pid int) (int, map[uint64]struct{}, error) {
+	directory := filepath.Join("/proc", strconv.Itoa(pid), "fd")
+	entries, err := os.ReadDir(directory)
+	if err != nil {
+		return 0, nil, err
+	}
+	count := 0
+	sockets := make(map[uint64]struct{})
+	for _, entry := range entries {
+		descriptor, err := strconv.Atoi(entry.Name())
+		if err != nil || descriptor < 3 {
+			continue
+		}
+		target, err := os.Readlink(filepath.Join(directory, entry.Name()))
+		if err != nil {
+			if os.IsNotExist(err) {
+				continue
+			}
+			return 0, nil, err
+		}
+		count++
+		if inode, exists := parseSocketInode(target); exists {
+			sockets[inode] = struct{}{}
+		}
+	}
+	return count, sockets, nil
+}
+
+func parseSocketInode(target string) (uint64, bool) {
+	if !strings.HasPrefix(target, "socket:[") || !strings.HasSuffix(target, "]") {
+		return 0, false
+	}
+	inode, err := strconv.ParseUint(strings.TrimSuffix(strings.TrimPrefix(target, "socket:["), "]"), 10, 64)
+	return inode, err == nil
+}
+
+func listeningSocketInodes(pid int, protocol string) (map[uint64]struct{}, error) {
+	path := filepath.Join("/proc", strconv.Itoa(pid), "net", protocol)
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	listeners := make(map[uint64]struct{})
+	scanner := bufio.NewScanner(file)
+	if scanner.Scan() {
+		// Skip the stable kernel table header.
+	}
+	for scanner.Scan() {
+		fields := strings.Fields(scanner.Text())
+		if len(fields) < 10 || fields[3] != "0A" {
+			continue
+		}
+		inode, err := strconv.ParseUint(fields[9], 10, 64)
+		if err != nil {
+			return nil, fmt.Errorf("parse %s listener inode: %w", path, err)
+		}
+		listeners[inode] = struct{}{}
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("read %s: %w", path, err)
+	}
+	return listeners, nil
+}