test(agentcompat): add process supervision harness

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

integration/agentcompat/internal/workspace/log.go

@@ -0,0 +1,117 @@
+//go:build linux
+
+package workspace
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"sync"
+
+	"github.com/nezhahq/nezha/integration/agentcompat/internal/evidence"
+)
+
+const workspaceTruncationMarker = "[TRUNCATED]\n"
+
+type LogFile struct {
+	file      *os.File
+	maxBytes  int
+	written   int
+	pending   []byte
+	dropLine  bool
+	closed    bool
+	closeOnce sync.Once
+	closeErr  error
+	mu        sync.Mutex
+}
+
+func newLogFile(path string, maxBytes int) (*LogFile, error) {
+	file, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
+	if err != nil {
+		return nil, fmt.Errorf("create workspace log: %w", err)
+	}
+	return &LogFile{file: file, maxBytes: maxBytes}, nil
+}
+
+func (logFile *LogFile) Name() string { return logFile.file.Name() }
+
+func (logFile *LogFile) WriteString(value string) (int, error) {
+	return logFile.Write([]byte(value))
+}
+
+func (logFile *LogFile) Write(data []byte) (int, error) {
+	logFile.mu.Lock()
+	defer logFile.mu.Unlock()
+	if logFile.closed {
+		return 0, errors.New("write closed workspace log")
+	}
+	inputLength := len(data)
+	for len(data) > 0 {
+		newline := bytes.IndexByte(data, '\n')
+		if newline < 0 {
+			logFile.appendFragment(data)
+			break
+		}
+		logFile.appendFragment(data[:newline+1])
+		if err := logFile.flushLine(); err != nil {
+			return 0, err
+		}
+		data = data[newline+1:]
+	}
+	return inputLength, nil
+}
+
+func (logFile *LogFile) appendFragment(fragment []byte) {
+	if logFile.dropLine {
+		return
+	}
+	if len(logFile.pending)+len(fragment) > logFile.maxBytes {
+		logFile.pending = nil
+		logFile.dropLine = true
+		return
+	}
+	logFile.pending = append(logFile.pending, fragment...)
+}
+
+func (logFile *LogFile) flushLine() error {
+	if logFile.dropLine {
+		logFile.dropLine = false
+		return logFile.writeBounded(workspaceTruncationMarker)
+	}
+	redacted := evidence.Redact(string(logFile.pending))
+	logFile.pending = nil
+	if len(redacted) > logFile.maxBytes-logFile.written {
+		return logFile.writeBounded(workspaceTruncationMarker)
+	}
+	return logFile.writeBounded(redacted)
+}
+
+func (logFile *LogFile) writeBounded(value string) error {
+	remaining := logFile.maxBytes - logFile.written
+	if remaining <= 0 || value == "" {
+		return nil
+	}
+	if len(value) > remaining {
+		value = value[:remaining]
+	}
+	written, err := logFile.file.WriteString(value)
+	logFile.written += written
+	if err != nil {
+		return fmt.Errorf("write workspace log: %w", err)
+	}
+	return nil
+}
+
+func (logFile *LogFile) Close() error {
+	logFile.closeOnce.Do(func() {
+		logFile.mu.Lock()
+		defer logFile.mu.Unlock()
+		if len(logFile.pending) > 0 || logFile.dropLine {
+			logFile.closeErr = logFile.flushLine()
+		}
+		logFile.closed = true
+		logFile.closeErr = errors.Join(logFile.closeErr, logFile.file.Close())
+	})
+	return logFile.closeErr
+}