Rebuild: the coordinator spools replies without inflating them

On homelab (1 Gbit, 20 connections, ~630k articles/s) the coordinator
used 1.3-1.7 cores, mostly GC of the text it inflated only to know a
compressed reply was complete, plus a copy of every reply. A raw reply
is now complete when it ends in ".\r\n" (no copy): 0.4-0.5 cores at
the same rate.

".\r\n" can also end a network read inside the compressed data (~1 in
16M reads, a few dozen times over the whole target). Such a chunk
doesn't inflate on the worker: it reports it (POST ranges/:id/corrupt),
the spooled chunk is removed and the range goes back to the queue; the
prefetcher fetches it again. The rest of that reply breaks the
connection's next command, so the connection is replaced.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/controllers/node_controller.ts

@@ -74,6 +74,12 @@ export default class NodeController {
     return this.lifecycle(ctx, (rangeId, nodeId) => Leases.finish(rangeId, nodeId))
   }
 
+  /** POST /ranges/:id/corrupt { from }: a chunk that doesn't inflate; the range goes back. */
+  async corrupt(ctx: HttpContext) {
+    const from = Number(ctx.request.input('from'))
+    return this.lifecycle(ctx, (rangeId, nodeId) => Leases.corrupt(rangeId, nodeId, from))
+  }
+
   async release(ctx: HttpContext) {
     return this.lifecycle(ctx, (rangeId, nodeId) => Leases.release(rangeId, nodeId))
   }

app/services/leases.ts

@@ -58,6 +58,18 @@ class Leases {
     await Spool.remove(rangeId)
   }
 
+  /**
+   * A worker got a chunk that doesn't inflate: the spooled chunk goes and
+   * the range back to the queue (the prefetcher fetches leased ranges'
+   * missing chunks again; the next worker resumes at the range's resume point).
+   */
+  async corrupt(rangeId: number, nodeId: number, from: number) {
+    const range = await this.leased(rangeId, nodeId)
+    const span = Spool.chunksOf({ start: Number(range.start_id), end: Number(range.end_id) }).find((s) => s.from === from)
+    if (span) await Spool.removeChunk(rangeId, span)
+    await db.from('ranges').where('id', rangeId).update({ status: 'planned', node_id: null })
+  }
+
   /** A stopping worker gives its range back; the next one resumes it. */
   async release(rangeId: number, nodeId: number) {
     await this.leased(rangeId, nodeId)

app/services/spool.ts

@@ -53,6 +53,11 @@ class Spool {
     return readFile(this.path(rangeId, span))
   }
 
+  /** One chunk, e.g. one that doesn't inflate (a false end of reply; see XoverClient.compressedRaw). */
+  async removeChunk(rangeId: number, span: ChunkSpan) {
+    await rm(this.path(rangeId, span), { force: true })
+  }
+
   async remove(rangeId: number) {
     await rm(join(this.dir, String(rangeId)), { recursive: true, force: true })
   }

commands/edge_node.ts

@@ -13,6 +13,8 @@ const gzipAsync = promisify(gzip)
 const RETRIES = 8
 
 class LeaseLost extends Error {}
+/** A spooled chunk that doesn't inflate (reported; the coordinator fetches it again). */
+class CorruptChunk extends Error {}
 
 /**
  * An edge worker (REBUILD.md, part 2): leases a range from the coordinator,
@@ -134,9 +136,17 @@ export default class EdgeNode extends BaseCommand {
       posting.catch((error) => (postError ??= error))
     }
     let postError: Error | null = null
-    const handle = async (chunk: { to: number; text: Promise<Buffer> }) => {
+    const handle = async (chunk: { from: number; to: number; text: Promise<Buffer> }) => {
       if (postError) throw postError
-      indexer.addText((await chunk.text).toString('utf8'), chunk.to + 1)
+      let text: Buffer
+      try {
+        text = await chunk.text
+      } catch (error: any) {
+        await posting.catch(() => {})
+        await api.corrupt(range.id, chunk.from)
+        throw new CorruptChunk(`chunk ${chunk.from}–${chunk.to} doesn't inflate (${error.message}); reported, the range goes back`)
+      }
+      indexer.addText(text.toString('utf8'), chunk.to + 1)
       reachedEnd = chunk.to >= range.end
       if (reachedEnd) indexer.finish()
       if (reachedEnd || chunk.to + 1 - batchFrom >= this.batchArticles) {
@@ -146,11 +156,11 @@ export default class EdgeNode extends BaseCommand {
     }
     try {
       // Inflating runs on a thread-pool thread: the next chunk inflates while this one is indexed.
-      let pending: { to: number; text: Promise<Buffer> } | null = null
+      let pending: { from: number; to: number; text: Promise<Buffer> } | null = null
       for await (const frame of decodeFrames(await api.stream(range.id))) {
         if (this.stopping) break
         if (isKeepalive(frame)) continue
-        const next = { to: frame.to, text: unzipAsync(frame.data) }
+        const next = { from: frame.from, to: frame.to, text: unzipAsync(frame.data) }
         next.text.catch(() => {})
         if (pending) await handle(pending)
         pending = next
@@ -172,7 +182,7 @@ export default class EdgeNode extends BaseCommand {
       )
     } catch (error: any) {
       await posting.catch(() => {})
-      if (error instanceof LeaseLost) {
+      if (error instanceof LeaseLost || error instanceof CorruptChunk) {
         this.logger.warning(`Range ${range.id}: ${error.message}`)
         return
       }
@@ -227,6 +237,11 @@ class Api {
     return { ...((await response.json()) as { releases: number; candidates: number }), bytes: body.length }
   }
 
+  async corrupt(rangeId: number, from: number) {
+    const response = await this.request(`ranges/${rangeId}/corrupt`, { method: 'POST', body: JSON.stringify({ from }) })
+    if (!response.ok) throw new Error(`corrupt: HTTP ${response.status}`)
+  }
+
   async call(rangeId: number, action: 'finish' | 'release' | 'heartbeat') {
     const response = await this.request(`ranges/${rangeId}/${action}`, { method: 'POST', body: '{}' })
     if (!response.ok) throw new Error(`${action}: HTTP ${response.status}`)

lib/nntp/xover_client.ts

@@ -233,20 +233,31 @@ export class XoverClient {
   }
 
   /**
-   * A zlib/gzip stream followed by a "." line: complete once it ends in
+   * A zlib/gzip stream followed by a "." line. The pieces are joined only
-   * ".\r\n" and inflates. The pieces are joined only then: joining them on
+   * once the data ends in ".\r\n": joining them on every arrival was
-   * every arrival was quadratic, ~15% of a prefetcher's time (LOG.md 2026-10-09).
+   * quadratic, ~15% of a prefetcher's time (LOG.md 2026-10-09).
+   *
+   * Raw (the coordinator's spool) it is complete then: inflating every reply
+   * to be sure cost the coordinator ~1.5 cores at ~630 k articles/s (mostly
+   * GC of the inflated text). ".\r\n" can also end a network read inside
+   * the compressed data (~1 in 16 M reads): that chunk doesn't inflate on
+   * the worker, which reports it and the chunk is fetched again (REBUILD.md,
+   * prefetch), and the rest of the reply breaks this connection's next
+   * command. With the text wanted, it must inflate.
    */
   private async compressedRaw(wantText: boolean): Promise<{ raw: Buffer; text: string }> {
     while (true) {
       if (this.length > DOT_LINE.length && this.endsWith(DOT_LINE)) {
         const all = this.buffer()
         const raw = all.subarray(0, all.length - DOT_LINE.length)
+        if (!wantText) {
+          this.take(all.length)
+          return { raw, text: '' }
+        }
         try {
-          // On a thread-pool thread: a chunk's ~25 MB of text took the coordinator's event loop ~60 ms.
           const inflated = await unzipAsync(raw)
           this.take(all.length)
-          return { raw: Buffer.from(raw), text: wantText ? inflated.toString('utf8') : '' }
+          return { raw, text: inflated.toString('utf8') }
         } catch {
           // ".\r\n" inside the compressed data: wait for more.
         }

start/routes.ts

@@ -51,6 +51,7 @@ router
         router.post('ranges/:id/heartbeat', [controllers.Node, 'heartbeat'])
         router.post('ranges/:id/finish', [controllers.Node, 'finish'])
         router.post('ranges/:id/release', [controllers.Node, 'release'])
+        router.post('ranges/:id/corrupt', [controllers.Node, 'corrupt'])
       })
       .prefix('node')
       .as('node')