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Forward mode blocks indefinitely upon certain content-disposition header value

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#546 2 commenti 0 reazioni 0 assegnatari Vedi su GitHub

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Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
35/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Ferma
Stack tecnologico
node.js, typescript
Ambito
backend, networking

Direzione di ricerca

Start in src/forward.ts, where the writeHead call throws and the error is silently swallowed around lines 97-113. Reproduce with the socat target and the curl -x localhost:8000 request from the issue, and confirm the request hangs. The issue offers three options (sanitize the content-disposition header, let the upstream error fail the request, or surface the error), and maintainers have not chosen one, so agree on an approach before coding. Done means the request either completes or fails with a visible error instead of blocking.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

backend bug low priority t-unblocking

Overview

proxy-chain is observed to block indefinitely when certain conditions are met:

  1. It works in the forward mode (plain HTTP).
  2. There is content-disposition header that contains certain non-ASCII content.
  3. There is content-length header.

The root cause of issue is believed to originate from Node.js. Before an upstream fix is made (which might take time) proxy-chain here could apply some mitigation.

Upstream Issue: ServerResponse.writeHead may throw an error

There are already several upstream issue reports, one of which is https://github.com/nodejs/node/issues/50213

Mostly relevant is this section of code https://github.com/nodejs/node/blob/v20.16.0/lib/_http_outgoing.js#L554-L567 where the improper type change later involves implicit type conversion and unexpected charset decoding at https://github.com/nodejs/node/blob/v20.16.0/lib/_http_common.js#L216-L225

A minimal example for the decoding error: /[^\t\x20-\x7e\x80-\xff]/v.test(Buffer.from('à', 'latin1')) This then result in an invalid character error to be thrown (code) during ServerResponse.writeHead.

Impact to proxy-chain

As of the current revision, said issue would cause an error thrown from this call: https://github.com/apify/proxy-chain/blob/a1ac3f287e895270f4e34306ac754a62a9848fa4/src/forward.ts#L97-L101

It is then silently ignore here therefore the observed blocking: https://github.com/apify/proxy-chain/blob/a1ac3f287e895270f4e34306ac754a62a9848fa4/src/forward.ts#L110-L113

In earlier versions of proxy-chain (that is used when I noticed this issue), said error is not caught thus exposed. This leads to the error as reported here: https://github.com/apify/proxy-chain/issues/20

Sample Steps to Reproduce the Issue

Target web server:

$ socat -v -v TCP-LISTEN:8080,fork,reuseaddr,crlf SYSTEM:'echo HTTP/1.1 200 OK; echo "content-length: 6"; echo -e "content-disposition: \\\\xe0"; echo; echo -n "foobar"'

proxy-chain instance (just the minimal example from README.md):

const ProxyChain = require('proxy-chain');

const server = new ProxyChain.Server({ port: 8000 });

server.listen(() => {
    console.log(`Proxy server is listening on port ${8000}`);
});

Sending the request:

$ curl -v -x localhost:8000 'http://localhost:8080'

Expected result: The request shall finish. (see also: curl -v 'http://localhost:8080')
Observed result: The request blocks indefinitely.
(checked with Node.js v20.16.0 which is the active LTS)

Proposed Actions

I'm afraid that it's unlikely that the upstream will make a fix soon, considering how long their tickets have been around (e.g. https://github.com/nodejs/node/issues/50213).

There are a few proposals on what could be done here:

  1. To manipulate the content-disposition header ahead, so that the call of ServerResponse.writeHead no longer fails.
  2. Or, alter the response handler upon forwarding, so that the upstream error no longer blocks the request. Perhaps letting it fail is (slightly?) better than blocking.
  3. Also, maybe expose the error message to users so that they may have an idea on what's going on.
Lingua principale
TypeScript
Stelle
1k
Fork
167
Merge medio
16h 22m
PR unite (30g)
16

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Come iniziare

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  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

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