stream: fix decoded fromList chunk boundary check

[watson]

Correct fromList() in decoded string mode to compare n against the current chunk length, not the buffer array length.

This prevents over-consuming chunks, which can corrupt readable state and crash with TypeError when mixing setEncoding() and read(n).

I reproduced this in all non-EoL release lines.

For reference, here's the script I used to make read() throw (usually it throws almost instantly, but a few times it can take a little while):

'use strict'

const https = require('node:https')

const url = process.argv[2] || 'https://www.google.com'
const maxRuns = Number(process.argv[3] || 2000)
let runs = 0

function runOnce () {
  runs++
  https.get(url, (res) => {
    res.setEncoding('utf8') // If this line is removed, the crash doesn't happen.

    res.on('readable', () => {
      // Race condition: The call to `res.read(100)` might throw
      while (res.read(100) !== null) {}
    })

    res.on('end', () => {
      if (runs >= maxRuns) {
        console.log(`completed ${runs} runs without crash`)
      } else {
        runOnce()
      }
    })
  })
}

console.log(`reproducing with ${url} for up to ${maxRuns} runs...`)
runOnce()

And here's the output:

reproducing with https://www.google.com for up to 2000 runs...
node:internal/streams/readable:1650
  } else if (n < buf[idx].length) {
                          ^

TypeError: Cannot read properties of undefined (reading 'length')
    at fromList (node:internal/streams/readable:1650:27)
    at Readable.read (node:internal/streams/readable:756:11)
    at IncomingMessage.<anonymous> (/Users/thomas.watson/go/src/github.com/DataDog/dd-trace-js/foo.js:16:18)
    at IncomingMessage.emit (node:events:508:20)
    at emitReadable_ (node:internal/streams/readable:837:12)
    at process.processTicksAndRejections (node:internal/process/task_queues:89:21)

Node.js v25.6.1

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71377/

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.73%. Comparing base (d5279e5) to head (2984f13).
⚠️ Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/streams/readable.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61884      +/-   ##
==========================================
- Coverage   91.81%   89.73%   -2.08%     
==========================================
  Files         338      675     +337     
  Lines      140073   204855   +64782     
  Branches    22081    39372   +17291     
==========================================
+ Hits       128605   183829   +55224     
- Misses      11242    13287    +2045     
- Partials      226     7739    +7513     

Files with missing lines	Coverage Δ
lib/internal/streams/readable.js	97.16% <0.00%> (+0.88%)	⬆️

... and 456 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mcollina]

lgtm

[nodejs-github-bot]

Commit Queue failed

- Loading data for nodejs/node/pull/61884
✔  Done loading data for nodejs/node/pull/61884
----------------------------------- PR info ------------------------------------
Title      stream: fix decoded fromList chunk boundary check (#61884)
Author     Thomas Watson <w@tson.dk> (@watson)
Branch     watson:fix-readable-stream-bug -> nodejs:main
Labels     stream, author ready, needs-ci
Commits    2
 - stream: fix decoded fromList chunk boundary check
 - fix lint
Committers 1
 - Thomas Watson <w@tson.dk>
PR-URL: https://github.com/nodejs/node/pull/61884
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ilyas Shabi <ilyasshabi94@gmail.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/61884
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Ilyas Shabi <ilyasshabi94@gmail.com>
Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Thu, 19 Feb 2026 10:28:10 GMT
   ✔  Approvals: 9
   ✔  - Robert Nagy (@ronag) (TSC): https://github.com/nodejs/node/pull/61884#pullrequestreview-3824865677
   ✔  - Ruben Bridgewater (@BridgeAR) (TSC): https://github.com/nodejs/node/pull/61884#pullrequestreview-3824921277
   ✔  - Ilyas Shabi (@IlyasShabi): https://github.com/nodejs/node/pull/61884#pullrequestreview-3825273620
   ✔  - Gürgün Dayıoğlu (@gurgunday): https://github.com/nodejs/node/pull/61884#pullrequestreview-3825732569
   ✔  - Luigi Pinca (@lpinca): https://github.com/nodejs/node/pull/61884#pullrequestreview-3828304463
   ✔  - Matteo Collina (@mcollina) (TSC): https://github.com/nodejs/node/pull/61884#pullrequestreview-3828525776
   ✔  - Minwoo Jung (@JungMinu): https://github.com/nodejs/node/pull/61884#pullrequestreview-3830500467
   ✔  - Colin Ihrig (@cjihrig): https://github.com/nodejs/node/pull/61884#pullrequestreview-3832438069
   ✔  - Ethan Arrowood (@Ethan-Arrowood): https://github.com/nodejs/node/pull/61884#pullrequestreview-3832584001
   ✔  Last GitHub CI successful
   ℹ  Last Full PR CI on 2026-02-19T11:05:46Z: https://ci.nodejs.org/job/node-test-pull-request/71377/
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- Bringing origin/main up to date...
From https://github.com/nodejs/node
 * branch                  main       -> FETCH_HEAD
✔  origin/main is now up-to-date
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 * branch                  refs/pull/61884/merge -> FETCH_HEAD
✔  Fetched commits as 94df36a12199..2984f1316238
--------------------------------------------------------------------------------
[main 555cb3c22c] stream: fix decoded fromList chunk boundary check
 Author: Thomas Watson <w@tson.dk>
 Date: Thu Feb 19 11:25:19 2026 +0100
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 test/parallel/test-stream2-read-correct-num-bytes-in-utf8.js
[main 78184b3a60] fix lint
 Author: Thomas Watson <w@tson.dk>
 Date: Thu Feb 19 11:43:24 2026 +0100
 1 file changed, 1 insertion(+)
   ✔  Patches applied
There are 2 commits in the PR. Attempting autorebase.
(node:458) [DEP0190] DeprecationWarning: Passing args to a child process with shell option true can lead to security vulnerabilities, as the arguments are not escaped, only concatenated.
(Use `node --trace-deprecation ...` to show where the warning was created)
Rebasing (2/4)
Executing: git node land --amend --yes
--------------------------------- New Message ----------------------------------
stream: fix decoded fromList chunk boundary check
Correct fromList() in decoded string mode to compare n against the

current chunk length, not the buffer array length.
This prevents over-consuming chunks, which can corrupt readable state

and crash with TypeError when mixing setEncoding() and read(n).
PR-URL: #61884

Reviewed-By: Robert Nagy <ronagy@icloud.com>

Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Reviewed-By: Ilyas Shabi <ilyasshabi94@gmail.com>

Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>

Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
[detached HEAD ca615c81bd] stream: fix decoded fromList chunk boundary check

Author: Thomas Watson <w@tson.dk>

Date: Thu Feb 19 11:25:19 2026 +0100

2 files changed, 16 insertions(+), 1 deletion(-)

create mode 100644 test/parallel/test-stream2-read-correct-num-bytes-in-utf8.js

Rebasing (3/4)

Rebasing (4/4)

Executing: git node land --amend --yes

--------------------------------- New Message ----------------------------------

fix lint
PR-URL: #61884

Reviewed-By: Robert Nagy <ronagy@icloud.com>

Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

Reviewed-By: Ilyas Shabi <ilyasshabi94@gmail.com>

Reviewed-By: Gürgün Dayıoğlu <hey@gurgun.day>

Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>
[detached HEAD 403f5bd46a] fix lint

Author: Thomas Watson <w@tson.dk>

Date: Thu Feb 19 11:43:24 2026 +0100

1 file changed, 1 insertion(+)

Successfully rebased and updated refs/heads/main.
ℹ  Add commit-queue-squash label to land the PR as one commit, or commit-queue-rebase to land as separate commits.

https://github.com/nodejs/node/actions/runs/22255290326