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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 | 14x 14x 14x | /**
* File Tailer
*
* Watches an output file and emits parsed events in real-time.
* Used for crash-resilient agent spawning where subprocesses write
* directly to files instead of using pipes.
*
* Uses fs.watch() for efficient change detection with a poll fallback
* since fs.watch isn't 100% reliable on all platforms.
*/
import { watch, type FSWatcher } from 'node:fs';
import { open, stat } from 'node:fs/promises';
import type { FileHandle } from 'node:fs/promises';
import type { StreamParser, StreamEvent } from './providers/stream-types.js';
import { createModuleLogger } from '../logger/index.js';
const log = createModuleLogger('file-tailer');
/** Poll interval for fallback polling (ms) */
const POLL_INTERVAL_MS = 500;
/** Read buffer size (bytes) */
const READ_BUFFER_SIZE = 64 * 1024;
export interface FileTailerOptions {
/** Path to the output file to watch */
filePath: string;
/** Agent ID for logging */
agentId: string;
/** Parser to convert lines to stream events */
parser: StreamParser;
/** Optional callback for each stream event */
onEvent?: (event: StreamEvent) => void;
/** If true, read from beginning of file; otherwise tail only new content (default: false) */
startFromBeginning?: boolean;
/** Callback for raw file content chunks (for DB persistence + event emission) */
onRawContent?: (content: string) => void;
}
/**
* FileTailer watches a file for changes and emits parsed stream events.
*
* Behavior:
* - Uses fs.watch() for efficient change detection
* - Falls back to polling every 500ms (fs.watch misses events sometimes)
* - Reads new content incrementally, splits into lines
* - Feeds each line to the parser, emits resulting events
* - Handles partial lines at buffer boundaries
*/
export class FileTailer {
private position = 0;
private watcher: FSWatcher | null = null;
private pollInterval: NodeJS.Timeout | null = null;
private fileHandle: FileHandle | null = null;
private stopped = false;
private partialLine = '';
private reading = false;
private readonly filePath: string;
private readonly agentId: string;
private readonly parser: StreamParser;
private readonly onEvent?: (event: StreamEvent) => void;
private readonly startFromBeginning: boolean;
private readonly onRawContent?: (content: string) => void;
constructor(options: FileTailerOptions) {
this.filePath = options.filePath;
this.agentId = options.agentId;
this.parser = options.parser;
this.onEvent = options.onEvent;
this.startFromBeginning = options.startFromBeginning ?? false;
this.onRawContent = options.onRawContent;
}
/**
* Start watching the file for changes.
* Initializes position, starts fs.watch, and begins poll fallback.
*/
async start(): Promise<void> {
if (this.stopped) return;
log.debug({ filePath: this.filePath, agentId: this.agentId }, 'starting file tailer');
try {
// Open file for reading
this.fileHandle = await open(this.filePath, 'r');
// Set initial position
if (this.startFromBeginning) {
this.position = 0;
} else {
// Seek to end
const stats = await stat(this.filePath);
this.position = stats.size;
}
// Start fs.watch for efficient change detection
this.watcher = watch(this.filePath, (eventType) => {
if (eventType === 'change' && !this.stopped) {
this.readNewContent().catch((err) => {
log.warn({ err: err instanceof Error ? err.message : String(err), agentId: this.agentId }, 'error reading new content');
});
}
});
this.watcher.on('error', (err) => {
log.warn({ err: err instanceof Error ? err.message : String(err), agentId: this.agentId }, 'watcher error');
});
// Start poll fallback (fs.watch misses events sometimes)
this.pollInterval = setInterval(() => {
if (!this.stopped) {
this.readNewContent().catch((err) => {
log.warn({ err: err instanceof Error ? err.message : String(err), agentId: this.agentId }, 'poll read error');
});
}
}, POLL_INTERVAL_MS);
// If starting from beginning, do initial read
if (this.startFromBeginning) {
await this.readNewContent();
}
} catch (err) {
log.error({ err: err instanceof Error ? err.message : String(err), filePath: this.filePath }, 'failed to start file tailer');
}
}
/**
* Read new content from the file since last position.
* Splits into lines, feeds to parser, emits events.
*/
private async readNewContent(): Promise<void> {
if (this.stopped || !this.fileHandle || this.reading) return;
this.reading = true;
try {
// Check current file size
const stats = await stat(this.filePath);
if (stats.size <= this.position) {
return; // No new content
}
// Read new bytes
const bytesToRead = stats.size - this.position;
const buffer = Buffer.alloc(Math.min(bytesToRead, READ_BUFFER_SIZE));
const { bytesRead } = await this.fileHandle.read(buffer, 0, buffer.length, this.position);
if (bytesRead === 0) return;
this.position += bytesRead;
// Fire raw content callback for DB persistence (before line splitting)
const rawChunk = buffer.toString('utf-8', 0, bytesRead);
if (this.onRawContent) {
this.onRawContent(rawChunk);
}
// Convert to string and process lines
const content = this.partialLine + rawChunk;
const lines = content.split('\n');
// Last element is either empty (if content ended with \n) or a partial line
this.partialLine = lines.pop() ?? '';
// Process complete lines
for (const line of lines) {
if (line.trim()) {
this.processLine(line);
}
}
// If there's more content to read, schedule another read
if (stats.size > this.position) {
setImmediate(() => {
this.readNewContent().catch(() => {});
});
}
} finally {
this.reading = false;
}
}
/**
* Process a single line through the parser and emit events.
*/
private processLine(line: string): void {
const events = this.parser.parseLine(line);
for (const event of events) {
if (this.onEvent) {
this.onEvent(event);
}
}
}
/**
* Stop watching the file.
* Cleans up watcher, poll timer, and file handle.
*/
async stop(): Promise<void> {
if (this.stopped) return;
this.stopped = true;
log.debug({ filePath: this.filePath, agentId: this.agentId }, 'stopping file tailer');
// Close watcher
if (this.watcher) {
this.watcher.close();
this.watcher = null;
}
// Clear poll timer
if (this.pollInterval) {
clearInterval(this.pollInterval);
this.pollInterval = null;
}
// Do one final read to catch any remaining content
try {
await this.readNewContent();
// Process any remaining partial line
if (this.partialLine.trim()) {
this.processLine(this.partialLine);
this.partialLine = '';
}
// Signal end of stream to parser
const endEvents = this.parser.end();
for (const event of endEvents) {
if (this.onEvent) {
this.onEvent(event);
}
}
} catch {
// Ignore errors during cleanup
}
// Close file handle
if (this.fileHandle) {
try {
await this.fileHandle.close();
} catch {
// Ignore close errors
}
this.fileHandle = null;
}
}
/**
* Check if the tailer has been stopped.
*/
get isStopped(): boolean {
return this.stopped;
}
}
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