[dmihalcik-virtru]

What

• writeStream now calculates encryptedSegmentSizeDefault instead of measuring it. Before, it encrypted a throwaway full-size segment under the payload key and measured the output.
• New SymmetricCipher.encryptedPayloadSize(plaintextSize):
  • AesGcmCipher implements it exactly: 12-byte IV + plaintext + 16-byte tag.
  • The base class throws a named ConfigurationError, so a duck-typed cipher from an older release fails clearly instead of with a TypeError.
• Every written segment is checked against that number. A mismatch, such as an injected CryptoService returning a short tag, now fails the write instead of being absorbed by the per-segment encryptedSegmentSize.

Why

• The measurement spent one AES-GCM call, and one extra encryption under the caller's key, to learn a constant. That matters for the IV work later in this series, where every call under a key counts against an invocation limit.
• A cipher whose output length drifts from the manifest's default only showed up later, in readers that trust encryptedSegmentSizeDefault over the per-segment sizes.

How to test

cd lib && npm test. New tests:

• AesGcmCipher predicts the exact ciphertext length for several sizes, from 0 to 1 MiB.
• The base class names the cipher when a subclass has no size calculation.
• A writer whose CryptoService truncates the tag fails mid-stream with ConfigurationError.

Risk

Low to moderate. This touches the write path. The manifest values are unchanged for AesGcmCipher, which is the only cipher the SDK ships.

DSPX-4496 series

Part	PR	Base	Depends on
1 of 6	#1059 reject non-positive segment sizes	main	—
2 of 6	#1060 require 12-byte AES-GCM IVs	main	—
3 of 6	#1061 calculate encrypted segment size	main	—
4 of 6	#1062 default segment size 2 MiB	main	—
5 of 6	#1063 AesGcmEncryptor SPI	DSPX-4496-encrypted-segment-size	#1061
6 of 6	#1018 writer IVs from the CryptoService encryptor	DSPX-4496-aes-gcm-encryptor	#1063

#1059, #1060 and #1062 stand alone. #1061 ← #1063 ← #1018 is a stack.

Summary by CodeRabbit

• Bug Fixes
  • Encrypted streams now calculate segment sizes using the configured cipher and verify that each encrypted segment matches the expected size. A mismatch reports a configuration error instead of producing an invalid stream.
  • AES-GCM payload size estimates now account for the initialization vector and authentication tag.
• Tests
  • Added coverage for payload size calculations and for handling encrypted segments that differ from the expected size.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
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• Plan: Advanced
• Run ID: c7fa066a-4199-4b5c-8532-e55feb72c57a

📥 Commits

Reviewing files that changed from the base of the PR and between cae9a68 and e6951e2.

📒 Files selected for processing (5)

• lib/tdf3/src/ciphers/aes-gcm-cipher.ts
• lib/tdf3/src/ciphers/symmetric-cipher-base.ts
• lib/tdf3/src/tdf.ts
• lib/tests/mocha/encrypt-decrypt.spec.ts
• lib/tests/mocha/unit/aes-gcm-cipher.spec.ts

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📝 Walkthrough

Walkthrough

The cipher API now reports encrypted payload sizes. TDF stream writing uses this calculation to choose its default encrypted segment size and rejects encrypted segments whose actual size does not match the reported size.

Changes

Cipher Payload Sizing

Layer / File(s)	Summary
Cipher size contract lib/tdf3/src/ciphers/symmetric-cipher-base.ts, lib/tdf3/src/ciphers/aes-gcm-cipher.ts, lib/tests/mocha/unit/aes-gcm-cipher.spec.ts	SymmetricCipher provides a default encryptedPayloadSize method that throws ConfigurationError. AesGcmCipher reports plaintext size plus its 12-byte IV and 16-byte authentication tag. Unit tests check the size calculation and default error.
TDF stream size validation lib/tdf3/src/tdf.ts, lib/tests/mocha/encrypt-decrypt.spec.ts	writeStream uses the cipher’s size calculation instead of encrypting a zero-filled buffer to determine the default segment size. Segment encryption checks actual output length against the reported size. A stream test verifies that a mismatch rejects with ConfigurationError.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

Sequence Diagram(s)

sequenceDiagram
  participant TDF
  participant Cipher
  participant CryptoService
  TDF->>Cipher: Get encryptedPayloadSize for the default plaintext size
  TDF->>CryptoService: Encrypt each plaintext segment
  CryptoService-->>TDF: Return encrypted segment bytes
  TDF->>Cipher: Get expected size for the plaintext segment
  TDF->>TDF: Compare actual and expected encrypted sizes

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Suggested reviewers: elizabethhealy

Merge Risk: ⚪ Minimal · up to e6951

No actionable merge-blocking risk was identified; the change is ready for normal test checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states the main change: calculate encrypted segment size instead of measuring it. It is specific, concise, and includes the relevant SDK scope.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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_{A rabbit checks each cipher’s size,
And watches bytes as segments rise.
The IV and tag join every stream,
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[github-actions]

X-Test Results

✅ js@main-v0.9.0
✅ js@pull-1061-main
✅ js@v0.4.0-main
✅ js@main-main
✅ java@main-v0.9.0
✅ go@main-v0.9.0
✅ js@v0.4.0-v0.9.0
✅ js@pull-1061-v0.9.0
✅ go@main-main
✅ java@main-main
opentdf-sdk-lib
opentdf-ctl
coverage-lib
coverage-web-app
coverage-web-app-browser

[github-actions]

X-Test Results

✅ js@pull-1061-v0.9.0
✅ java@main-main
✅ js@pull-1061-main
✅ js@v0.4.0-main
✅ js@main-main
✅ js@v0.4.0-v0.9.0
opentdf-sdk-lib
✅ go@main-main
✅ js@main-v0.9.0
✅ java@main-v0.9.0
✅ go@main-v0.9.0
coverage-web-app-browser
coverage-web-app
coverage-roundtrip-browser
coverage-lib
opentdf-ctl

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

X-Test Results

coverage-web-app
✅ js@pull-1061-v0.9.0
✅ go@main-v0.9.0
coverage-lib
✅ js@main-main
✅ js@v0.4.0-main
✅ js@pull-1061-main
✅ java@main-v0.9.0
opentdf-sdk-lib
✅ js@v0.4.0-v0.9.0
✅ js@main-v0.9.0
opentdf-ctl
coverage-web-app-browser
coverage-roundtrip-browser
✅ java@main-main
✅ go@main-main