| 196 | return { |
| 197 | root, |
| 198 | async writeFile( |
| 199 | absPath: string, |
| 200 | source: ReadableStream<Uint8Array>, |
| 201 | mode?: number, |
| 202 | ): Promise<void> { |
| 203 | checkPath(absPath); |
| 204 | if (maxEntries !== undefined && entriesWritten + 1 > maxEntries) { |
| 205 | throw new Error(`mount ${root}: maxEntries=${maxEntries} exceeded`); |
| 206 | } |
| 207 | entriesWritten += 1; |
| 208 | |
| 209 | // Ensure the parent directory chain exists. mkdir on an |
| 210 | // existing path is EEXIST, which is fine here because the |
| 211 | // recursive flag swallows that for the already-a-directory |
| 212 | // case. |
| 213 | const lastSlash = absPath.lastIndexOf("/"); |
| 214 | if (lastSlash > 0) { |
| 215 | await fs.mkdir(absPath.slice(0, lastSlash), { recursive: true }); |
| 216 | } |
| 217 | |
| 218 | // When a byte cap is set, tee the source stream so we can |
| 219 | // count bytes without buffering. The tee keeps the streaming |
| 220 | // contract: bytes still flow chunk-by-chunk into writeFile. |
| 221 | let toWrite: ReadableStream<Uint8Array> = source; |
| 222 | if (maxBytes !== undefined) { |
| 223 | const [counted, forwarded] = source.tee(); |
| 224 | toWrite = forwarded; |
| 225 | // Drain the counted side concurrently; if the cap is |
| 226 | // exceeded mid-stream, cancel the forwarded side to short |
| 227 | // circuit the write. |
| 228 | const cancelForwarded = (reason: unknown): void => { |
| 229 | forwarded.cancel(reason).catch(() => {}); |
| 230 | }; |
| 231 | const counter = (async () => { |
| 232 | const reader = counted.getReader(); |
| 233 | try { |
| 234 | while (true) { |
| 235 | const { value, done } = await reader.read(); |
| 236 | if (done) break; |
| 237 | if (value === undefined) continue; |
| 238 | bytesWritten += value.byteLength; |
| 239 | if (bytesWritten > maxBytes) { |
| 240 | const err = new Error( |
| 241 | `mount ${root}: maxBytes=${maxBytes} exceeded (saw ${bytesWritten})`, |
| 242 | ); |
| 243 | cancelForwarded(err); |
| 244 | throw err; |
| 245 | } |
| 246 | } |
| 247 | } finally { |
| 248 | reader.releaseLock(); |
| 249 | } |
| 250 | })(); |
| 251 | // Await both sides. If the counter rejects, surface that; |
| 252 | // otherwise let writeFile propagate. |
| 253 | const writePromise = fs.writeFile(absPath, toWrite, { mode }); |
| 254 | const [counterResult, writeResult] = await Promise.allSettled([counter, writePromise]); |
| 255 | if (counterResult.status === "rejected") throw counterResult.reason; |