RGJ
1 Setembro , 2026 15:36
1
Um de nossos clientes encontrou um problema reproduzível ao fazer o upload de um backup local do Discourse pela interface administrativa.
O uploader de backups usa blocos fixos de 5 MB e, em uma conexão suficientemente rápida, pode gerar solicitações suficientes para exceder o próprio limite de taxa de solicitações em nível de aplicação do Discourse. Quando isso acontece, o servidor retorna HTTP 429, mas o uploader por blocos não repete as respostas 429 nem respeita o cabeçalho Retry-After. Como resultado, o upload do backup inteiro falha.
Respostas não-2xx são convertidas em um erro :
if (ev.target.status < 200 || ev.target.status >= 300) {
const error = new Error("Non 2xx");
error.source = ev.target;
reject(error);
return;
}
A lógica de repetição é:
_shouldRetry(err) {
if (err.source && typeof err.source.status === "number") {
const { status } = err.source;
return (
status === 0 ||
status === 409 ||
status === 423 ||
(status >= 500 && status < 600)
);
}
return false;
}
Portanto, o HTTP 429 não é explicitamente repetível.
Uma única resposta 429 é suficiente para a promessa de upload por blocos falhar, acionando eventualmente upload-error para o upload do backup inteiro.
Também não há tratamento do cabeçalho de resposta Retry-After.
Encontrei este tópico de 2021 que saiu dos trilhos rapidamente, mas parece ser exatamente a mesma coisa
obrigado pelo relato @RGJ
feature/rate-limit-client-helpers ← fix/retry-rate-limited-backup-chunks
approved 05:13PM - 10 Sep 26 UTC
Stacked on #43372. Fixes the report in https://meta.discourse.org/t/chunked-back… up-uploader-exceeds-discourse-request-rate-limit/411386.
Uploading a local backup through the admin UI fails outright on a fast connection. The uploader sends one POST per chunk, so throughput alone decides the request rate, and a large backup over a quick link trips the per-user request limiter. The server answers 429 and the upload dies, discarding however many gigabytes had already been sent. There is no resume, so a retry starts from chunk 1.
`_shouldRetry` allowed status 0, 409, 423 and 5xx. That list came from uppy's S3 multipart plugin, where it is correct — S3 does not answer 429 with a `Retry-After`. Discourse does, so the one status worth retrying was the one treated as fatal, and none of the four configured retry delays was ever consumed.
### Why three changes and not one
Adding 429 to the allowlist alone makes it worse. The limiters run in aggressive mode, so a rejected request re-arms the window; retrying on the existing sub-second ladder turns a fast failure into a permanent block. Measured against a persistent 429 on a 6-chunk file:
| | POSTs of the failing chunk |
|---|---|
| allowlist only | 15 in 10s, still fails |
| \+ honour `Retry-After` | 6 |
| \+ keep the chunk reserved | 2 — correct |
The third is needed because clearing `busy` before rejecting let every sibling completion re-pick the same chunk and start a second retry chain that POSTed immediately, defeating the backoff.
### Chunk size stays at 5 MB
An earlier revision of this PR raised it with the ladder S3 multipart has used since #22061. @Ethsim12 caught that this regresses stock installs, and reproduced it: these chunks go through the site's own nginx, whose shipped `client_max_body_size` is `10m`, and the multipart envelope puts a 10 MB chunk 962 bytes over that. nginx answers 413 before Rails sees the request, and 413 is not retryable — so every backup of 100 MB or more would have died on chunk 1. S3 parts have no proxy in front of them, which is why the ladder is correct there and stays there.
### Latent defects fixed alongside
- Registering the abort listener called `xhr.abort()` immediately and registered its return value, so aborting was a no-op and in-flight chunks kept running after a failure was reported.
- `chunkSize` was only assigned when no `getChunkSize` was supplied, so any caller providing one produced NaN bounds, a single empty chunk, and a silently truncated backup.
- The pause plumbing called a method the class never defined; nothing could reach it, so it is gone.
### Not a regression from the Uppy migration
Worth recording, since the linked topic asks. The 2021 report predates Uppy becoming the default backup uploader by two days — that reporter was on Resumable.js, which classified 429 as retryable but retried immediately, up to 100 times, against a limiter that was already aggressive. 429 has never been survivable here. What the port changed was the failure mode, from slow-and-noisy to instant-and-silent. The capability actually lost was resume, which this PR does not restore.
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