feat(01-04): create per-process log writer
- ProcessLogWriter class for stdout/stderr capture - Timestamps each line with [YYYY-MM-DD HH:mm:ss.SSS] format - Backpressure handling via drain events - getStdoutStream/getStderrStream for direct piping - Module index exports types, classes, and createLogger helper - createLogger convenience function for default config
This commit is contained in:
Lukas May
38
src/logging/index.ts
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38
src/logging/index.ts
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/**
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* Logging Module
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*
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* File-based logging infrastructure for per-process stdout/stderr capture.
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*/
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// Types
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export type { LogLevel, LogEntry, LogConfig, LogStream } from './types.js';
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// Classes
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export { LogManager } from './manager.js';
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export { ProcessLogWriter } from './writer.js';
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// Convenience functions
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import { LogManager } from './manager.js';
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import { ProcessLogWriter } from './writer.js';
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/**
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* Creates a new ProcessLogWriter with default configuration.
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*
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* Convenience function for common use case of creating a log writer
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* for a specific process using default log directory (~/.cw/logs).
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*
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* @param processId - Unique identifier for the process
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* @returns A new ProcessLogWriter instance (call open() before writing)
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*
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* @example
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* ```typescript
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* const writer = createLogger('agent-001');
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* await writer.open();
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* await writer.writeStdout('Hello from agent\n');
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* await writer.close();
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* ```
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*/
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export function createLogger(processId: string): ProcessLogWriter {
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const manager = new LogManager();
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return new ProcessLogWriter(processId, manager);
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}
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182
src/logging/writer.ts
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182
src/logging/writer.ts
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/**
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* Process Log Writer
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*
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* Handles per-process stdout/stderr capture to individual log files.
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*/
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import { createWriteStream, type WriteStream } from 'node:fs';
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import type { LogManager } from './manager.js';
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/**
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* Formats a timestamp for log output.
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* Format: [YYYY-MM-DD HH:mm:ss.SSS]
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*/
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function formatTimestamp(date: Date): string {
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const pad = (n: number, w = 2) => n.toString().padStart(w, '0');
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const year = date.getFullYear();
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const month = pad(date.getMonth() + 1);
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const day = pad(date.getDate());
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const hours = pad(date.getHours());
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const minutes = pad(date.getMinutes());
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const seconds = pad(date.getSeconds());
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const ms = pad(date.getMilliseconds(), 3);
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return `[${year}-${month}-${day} ${hours}:${minutes}:${seconds}.${ms}]`;
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}
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/**
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* Writes stdout/stderr output to per-process log files.
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*
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* Each line of output is prefixed with a timestamp.
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* Handles backpressure by exposing drain events on the underlying streams.
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*/
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export class ProcessLogWriter {
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private readonly processId: string;
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private readonly logManager: LogManager;
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private stdoutStream: WriteStream | null = null;
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private stderrStream: WriteStream | null = null;
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constructor(processId: string, logManager: LogManager) {
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this.processId = processId;
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this.logManager = logManager;
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}
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/**
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* Opens file handles for stdout and stderr log files.
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* Creates the process log directory if it doesn't exist.
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*/
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async open(): Promise<void> {
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// Ensure the process directory exists
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await this.logManager.ensureProcessDir(this.processId);
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// Open write streams in append mode
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const stdoutPath = this.logManager.getLogPath(this.processId, 'stdout');
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const stderrPath = this.logManager.getLogPath(this.processId, 'stderr');
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this.stdoutStream = createWriteStream(stdoutPath, { flags: 'a' });
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this.stderrStream = createWriteStream(stderrPath, { flags: 'a' });
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// Wait for both streams to be ready
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await Promise.all([
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new Promise<void>((resolve, reject) => {
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this.stdoutStream!.once('open', () => resolve());
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this.stdoutStream!.once('error', reject);
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}),
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new Promise<void>((resolve, reject) => {
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this.stderrStream!.once('open', () => resolve());
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this.stderrStream!.once('error', reject);
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}),
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]);
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}
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/**
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* Writes data to the stdout log file with timestamps.
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* @param data - String or Buffer to write
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* @returns Promise that resolves when write is complete (including drain if needed)
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*/
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async writeStdout(data: string | Buffer): Promise<void> {
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if (!this.stdoutStream) {
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throw new Error('Log writer not open. Call open() first.');
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}
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return this.writeWithTimestamp(this.stdoutStream, data);
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}
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/**
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* Writes data to the stderr log file with timestamps.
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* @param data - String or Buffer to write
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* @returns Promise that resolves when write is complete (including drain if needed)
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*/
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async writeStderr(data: string | Buffer): Promise<void> {
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if (!this.stderrStream) {
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throw new Error('Log writer not open. Call open() first.');
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}
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return this.writeWithTimestamp(this.stderrStream, data);
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}
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/**
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* Writes data with timestamp prefix, handling backpressure.
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*/
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private async writeWithTimestamp(
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stream: WriteStream,
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data: string | Buffer
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): Promise<void> {
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const content = typeof data === 'string' ? data : data.toString('utf-8');
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const timestamp = formatTimestamp(new Date());
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// Prefix each line with timestamp
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const lines = content.split('\n');
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const timestampedLines = lines
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.map((line, index) => {
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// Don't add timestamp to empty trailing line from split
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if (index === lines.length - 1 && line === '') {
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return '';
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}
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return `${timestamp} ${line}`;
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})
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.join('\n');
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// Write with backpressure handling
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const canWrite = stream.write(timestampedLines);
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if (!canWrite) {
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// Wait for drain event before continuing
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await new Promise<void>((resolve) => {
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stream.once('drain', resolve);
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});
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}
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}
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/**
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* Flushes and closes both file handles.
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*/
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async close(): Promise<void> {
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const closePromises: Promise<void>[] = [];
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if (this.stdoutStream) {
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closePromises.push(
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new Promise<void>((resolve, reject) => {
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this.stdoutStream!.end(() => {
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this.stdoutStream = null;
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resolve();
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});
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this.stdoutStream!.once('error', reject);
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})
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);
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}
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if (this.stderrStream) {
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closePromises.push(
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new Promise<void>((resolve, reject) => {
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this.stderrStream!.end(() => {
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this.stderrStream = null;
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resolve();
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});
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this.stderrStream!.once('error', reject);
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})
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);
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}
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await Promise.all(closePromises);
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}
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/**
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* Gets the stdout write stream for direct piping.
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* @returns The stdout WriteStream or null if not open
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*/
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getStdoutStream(): WriteStream | null {
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return this.stdoutStream;
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}
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/**
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* Gets the stderr write stream for direct piping.
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* @returns The stderr WriteStream or null if not open
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*/
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getStderrStream(): WriteStream | null {
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return this.stderrStream;
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}
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/**
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* Gets the process ID for this writer.
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*/
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getProcessId(): string {
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return this.processId;
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}
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}
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