regression: prevent S3 region empty string from blocking env var fallback

[ricardogarim]

This PR fixes a regression introduced in #36659 (AWS SDK v3 upgrade) where users configuring S3 file storage without explicitly setting a region in Rocket.Chat settings would see an uncaught exception:

UnCaughtException
Error: Region is missing
    at Object.resolveRegionConfig (@smithy/config-resolver/dist-cjs/index.js:103:15)
    at new S3Client (@aws-sdk/client-s3/dist-cjs/index.js:128:42)
    at new AmazonS3Store (app/file-upload/ufs/AmazonS3/server.ts:59:14)

Root cause

The FileUpload_S3_Region setting defaults to an empty string (''). Previously, AWS SDK v2 handled this gracefully by defaulting to us-east-1:

if (!this.config.region) this.config.region = 'us-east-1';

However, AWS SDK v3 throws an error when region is falsy:

if (!region) {
    throw new Error("Region is missing");
}

The key difference is that SDK v3 still accepts undefined (falling back to AWS_REGION env var), but rejects empty string ''.

Proposed changes (including videos or screenshots)

Align region handling with the existing pattern used for credentials and endpoint - only pass to SDK when value is truthy. This allows users to either:

• Set region via Rocket.Chat admin settings
• Use AWS_REGION environment variable (SDK fallback)

Issue(s)

• CORE-1287
• Regression from chore(deps): upgrade aws sdk to v3 #36659

Steps to test or reproduce

Before fix:

1. Configure S3 storage in Admin > File Upload > Storage Type > Amazon S3
2. Set Bucket name but leave Region empty
3. Set AWS_REGION=us-east-1 environment variable
4. Upload a file
5. See "Region is missing" error in console

After fix:

1. Same setup as above
2. Upload a file
3. File uploads successfully using AWS_REGION from environment

Further comments

Didn’t add a changeset since the fix is within the same release window as the bug that introduced it.

Summary by CodeRabbit

• Bug Fixes
  • Enhanced AWS S3 region configuration handling to conditionally apply region settings, providing better flexibility in file upload setup.

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Latest commit: 7073215

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between eb1cd8f and 7073215.

📒 Files selected for processing (1)

• apps/meteor/app/file-upload/server/config/AmazonS3.ts

📜 Recent review details

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Files:

• apps/meteor/app/file-upload/server/config/AmazonS3.ts

🧠 Learnings (3)

📓 Common learnings

Learnt from: smirk-dev
Repo: RocketChat/Rocket.Chat PR: 39625
File: apps/meteor/app/api/server/v1/push.ts:85-97
Timestamp: 2026-03-14T14:58:58.834Z
Learning: In RocketChat/Rocket.Chat, the `push.token` POST/DELETE endpoints in `apps/meteor/app/api/server/v1/push.ts` were already migrated to the chained router API pattern on `develop` prior to PR `#39625`. `cleanTokenResult` (which strips `authToken` and returns `PushTokenResult`) and `isPushTokenPOSTProps`/`isPushTokenDELETEProps` validators already exist on `develop`. PR `#39625` only migrates `push.get` and `push.info` to the chained pattern. Do not flag `cleanTokenResult` or `PushTokenResult` as newly introduced behavior-breaking changes when reviewing this PR.

📚 Learning: 2026-02-26T19:25:44.063Z

Learnt from: gabriellsh
Repo: RocketChat/Rocket.Chat PR: 38778
File: packages/ui-voip/src/providers/useMediaSession.ts:192-192
Timestamp: 2026-02-26T19:25:44.063Z
Learning: In the Rocket.Chat repository, do not reference Biome lint rules in code review feedback. Biome is not used even if biome.json exists; only reference Biome rules if there is explicit, project-wide usage documented. For TypeScript files, review lint implications without Biome guidance unless the project enables Biome rules.

Applied to files:

• apps/meteor/app/file-upload/server/config/AmazonS3.ts

📚 Learning: 2026-02-26T19:25:44.063Z

Learnt from: gabriellsh
Repo: RocketChat/Rocket.Chat PR: 38778
File: packages/ui-voip/src/providers/useMediaSession.ts:192-192
Timestamp: 2026-02-26T19:25:44.063Z
Learning: In this repository (RocketChat/Rocket.Chat), Biome lint rules are not used even if a biome.json exists. When reviewing TypeScript files (e.g., packages/ui-voip/src/providers/useMediaSession.ts), ensure lint suggestions do not reference Biome-specific rules. Rely on general ESLint/TypeScript lint rules and project conventions instead.

Applied to files:

• apps/meteor/app/file-upload/server/config/AmazonS3.ts

🔇 Additional comments (1)

apps/meteor/app/file-upload/server/config/AmazonS3.ts (1)

93-95: Conditionally setting region here is the correct fix.

Good change. Not passing config.connection.region when the setting is '' prevents the AWS SDK v3 “Region is missing” failure and preserves AWS_REGION fallback behavior.

---

Walkthrough

The Amazon S3 configuration file was refactored to conditionally assign the region property only when a Region value is provided, rather than unconditionally including it in the connection configuration.

Changes

Cohort / File(s)	Summary
AWS S3 Configuration apps/meteor/app/file-upload/server/config/AmazonS3.ts	Region setting changed from unconditional static config to conditional assignment that only appends region to connection when Region has a truthy value.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested labels

type: bug

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: preventing an empty S3 region string from blocking environment variable fallback, which directly addresses the regression in the changeset.
Linked Issues check	✅ Passed	The PR addresses the AWS SDK v3 upgrade objective by fixing a regression in region handling that arose from the v2-to-v3 migration, ensuring compatibility and correcting SDK upgrade-related issues.
Out of Scope Changes check	✅ Passed	The change is narrowly focused on fixing S3 region configuration handling in AmazonS3.ts, which is directly scoped to resolving the AWS SDK v3 upgrade regression without introducing unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.86%. Comparing base (4f88165) to head (7073215).
⚠️ Report is 5 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #39711      +/-   ##
===========================================
- Coverage    70.91%   70.86%   -0.06%     
===========================================
  Files         3209     3209              
  Lines       113893   113893              
  Branches     20689    20636      -53     
===========================================
- Hits         80765    80708      -57     
- Misses       31071    31129      +58     
+ Partials      2057     2056       -1     

Flag	Coverage Δ
e2e	60.36% <ø> (-0.05%)	⬇️
e2e-api	48.17% <ø> (-0.06%)	⬇️
unit	71.53% <ø> (-0.06%)	⬇️

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[cubic-dev-ai]

No issues found across 1 file

[KevLehman]

is there any way to test this?