Fixes #6086: Add transparent image detection and math tag validation by nikhilkumarpanigrahi · Pull Request #6144 · oppia/oppia-android

nikhilkumarpanigrahi · 2026-03-12T09:03:24Z

Explanation

This PR extends the existing asset download pipeline to detect:

Transparent images - Any pixels with alpha < 255 that may cause poor visibility in dark mode (ref [BUG]: Dark mode makes it difficult to see some images and LaTeX #5792)
Invalid math tags - oppia-noninteractive-math tags missing raw_latex content, which would force the app to use math SVGs directly.

Specifically, this PR:

Adds hasTransparentPixels() to ImageRepairer.ktto scan image pixel data for non-opaque alpha values, skipping SVGs.
Adds checkMathTagsForLatex() to StructureCompatibilityChecker.kt with MathTagMissingRawLatex failure type, integrated into checkHasValidHtml() flow.
Adds post-download transparency scan in DownloadLessons.kt with count-based summary and per-image reporting.
Adds comprehensive test coverage (ImageRepairerTest.kt with 7 tests, StructureCompatibilityCheckerTest.kt with 6 tests).
Fixes LocalizationTracker.kt to make extractMathContentsFromHtml() return non-nullable values and fail fast on parse errors.

Validation performed:

All new functionality tests passing.
ktlint compliance verified.
Static checks passing.

Essential Checklist

The PR title starts with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
The explanation section above starts with "Fixes #bugnum: " (If this PR fixes part of an issue, use instead: "Fixes part of #bugnum: ...".)
Any changes to scripts/assets files have their rationale included in the PR explanation.
The PR follows the style guide.
The PR does not contain any unnecessary code changes from Android Studio (reference).
The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

N/A

…sets

…rmat

nikhilkumarpanigrahi · 2026-03-12T09:08:40Z

@BenHenning
This is a clean re-submission replacing the closed #6120. All your previous review feedback has been addressed. I also found and fixed two bugs during testing:
RAW_LATEX_REGEX never matched real Oppia data (wrong trailing escape pattern)
checkHasValidMathTags was internal, which is inaccessible across Bazel module boundaries

PTAL when you get a chance. Thanks!

github-actions · 2026-03-12T09:39:03Z

@nikhilkumarpanigrahi this PR is being marked as draft because the PR description should not use 'Fix #' or 'Fix part of #' syntax. Instead use 'Fixes' and 'Fixes part of', per referenced issue(s): #6086.

github-actions · 2026-03-12T09:47:12Z

@nikhilkumarpanigrahi this PR is being marked as draft because the PR description should not use 'Fix #' or 'Fix part of #' syntax. Instead use 'Fixes' and 'Fixes part of', per referenced issue(s): #6086.

github-actions · 2026-03-12T12:34:35Z

Coverage Report

Results

Number of files assessed: 3
Overall Coverage: 9.58%
Coverage Analysis: FAIL ❌

Failure Cases

File	Failure Reason	Status
DownloadLessons.kt scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt.	❌

Failing coverage

File	Coverage	Lines Hit	Status	Min Required
ImageRepairer.kt scripts/src/java/org/oppia/android/scripts/assets/ImageRepairer.kt	16.44%	12 / 73	❌	70%
StructureCompatibilityChecker.kt scripts/src/java/org/oppia/android/scripts/gae/compat/StructureCompatibilityChecker.kt	8.08%	27 / 334	❌	70%

To learn more, visit the Oppia Android Code Coverage wiki page

nikhilkumarpanigrahi · 2026-03-12T16:05:21Z

Regarding coverage failures: The coverage bot flags DownloadLessons.kt, ImageRepairer.kt, and StructureCompatibilityChecker.kt due to low overall file coverage. However, the new functionality I added (hasTransparentPixels and checkMathTagsForLatex) is fully covered by the test files included in this PR (ImageRepairerTest.kt and StructureCompatibilityCheckerTest.kt). The low percentages (16% and 8%) come from pre-existing untested code in those files, not from my changes. I believe the coverage exemptions for these base-branch files would be addressed separately.

nikhilkumarpanigrahi · 2026-03-16T07:00:53Z

@BenHenning, @adhiamboperes PTAL

BenHenning · 2026-03-17T05:25:43Z

Apologies--hoping to look at this tomorrow.

BenHenning

Thanks @nikhilkumarpanigrahi. I'm largely happy with these changes, but I do have one suggestion to make before I test them. PTAL.

scripts/src/java/org/oppia/android/scripts/gae/compat/StructureCompatibilityChecker.kt

scripts/src/java/org/oppia/android/scripts/assets/ImageRepairer.kt

oppiabot · 2026-03-27T13:38:44Z

Unassigning @nikhilkumarpanigrahi since a re-review was requested. @nikhilkumarpanigrahi, please make sure you have addressed all review comments. Thanks!

…t' into lesson-asset-validation-v4

- Fix ktlint import ordering and max-line-length violations - Remove deprecated worked_example fields from skills.textproto to match ConceptCard proto schema

nikhilkumarpanigrahi · 2026-03-28T03:49:42Z

Hi @BenHenning, I wanted to confirm the preferred base branch for this PR. It is currently based on introduce-asset-download-script, and I see Check base branch failing because of that. Should I keep it on this branch for now, or retarget/rebase it to develop? I’m happy to update it whichever way you prefer.

github-actions · 2026-03-28T05:22:31Z

Coverage Report

Results

Number of files assessed: 9
Overall Coverage: 36.04%
Coverage Analysis: FAIL ❌

Failure Cases

File	Failure Reason	Status
DownloadLessons.kt scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt.	❌
LocalizationTracker.kt scripts/src/java/org/oppia/android/scripts/gae/proto/LocalizationTracker.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/proto/LocalizationTracker.kt.	❌
AndroidActivityEndpointApi.kt scripts/src/java/org/oppia/android/scripts/gae/json/AndroidActivityEndpointApi.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/json/AndroidActivityEndpointApi.kt.	❌
GaeQuestion.kt scripts/src/java/org/oppia/android/scripts/gae/json/GaeQuestion.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/json/GaeQuestion.kt.	❌
GaeAndroidEndpointJsonImpl.kt scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt.	❌

Failing coverage

File	Coverage	Lines Hit	Status	Min Required
ImageRepairer.kt scripts/src/java/org/oppia/android/scripts/assets/ImageRepairer.kt	16.22%	12 / 74	❌	70%
StructureCompatibilityChecker.kt scripts/src/java/org/oppia/android/scripts/gae/compat/StructureCompatibilityChecker.kt	3.76%	12 / 319	❌	70%

Passing coverage

Files with passing code coverage

File	Coverage	Lines Hit	Status	Min Required
MavenDependenciesRetriever.kt scripts/src/java/org/oppia/android/scripts/license/MavenDependenciesRetriever.kt	95.45%	189 / 198	✅	70%

Exempted coverage

Files exempted from coverage

File	Exemption Reason
TopicController.kt domain/src/main/java/org/oppia/android/domain/topic/TopicController.kt	This file is incompatible with code coverage tooling; skipping coverage check.

Refer test_file_exemptions.textproto for the comprehensive list of file exemptions and their required coverage percentages.

To learn more, visit the Oppia Android Code Coverage wiki page

- Add explicit validation for missing/malformed math_content-with-value attribute in StructureCompatibilityChecker.checkMathTagsForLatex() - Add two new CompatibilityFailure types: - MathTagMissingContent: detects missing math_content-with-value attribute - MathTagHasInvalidContent: detects unparseable JSON in math content - Expand StructureCompatibilityCheckerTest with 3 new test cases covering missing content and malformed JSON edge cases - Create LocalizationTrackerTest with 3 test cases for extractMathContentsFromHtml() covering empty HTML, valid parsed content, and malformed JSON handling - Add ImageRepairerTest negative-path test for invalid image data exception handling - All 18 unit tests passing (StructureCompatibilityCheckerTest: 7, LocalizationTrackerTest: 3, ImageRepairerTest: 8) - Code formatted per ktlint and buildifier standards

- Fix repository fallback logic to preserve aar/jar extension when resolving Maven artifact URLs from maven_install.json - Add regression test for aar fallback coordinate resolution - Fix POM download retry bookkeeping to avoid mutable-set hash instability that could leave null POM content and crash with NPE - Switch zlib archive URL in WORKSPACE from HTTP to HTTPS to avoid checksum mismatch during remote fetch in CI

github-actions · 2026-03-28T10:40:09Z

Coverage Report

Results

Number of files assessed: 9
Overall Coverage: 25.86%
Coverage Analysis: FAIL ❌

Failure Cases

File	Failure Reason	Status
DownloadLessons.kt scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt.	❌
AndroidActivityEndpointApi.kt scripts/src/java/org/oppia/android/scripts/gae/json/AndroidActivityEndpointApi.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/json/AndroidActivityEndpointApi.kt.	❌
GaeQuestion.kt scripts/src/java/org/oppia/android/scripts/gae/json/GaeQuestion.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/json/GaeQuestion.kt.	❌
GaeAndroidEndpointJsonImpl.kt scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt.	❌

Failing coverage

File	Coverage	Lines Hit	Status	Min Required
ImageRepairer.kt scripts/src/java/org/oppia/android/scripts/assets/ImageRepairer.kt	17.57%	13 / 74	❌	70%
LocalizationTracker.kt scripts/src/java/org/oppia/android/scripts/gae/proto/LocalizationTracker.kt	5.33%	20 / 375	❌	70%
StructureCompatibilityChecker.kt scripts/src/java/org/oppia/android/scripts/gae/compat/StructureCompatibilityChecker.kt	8.63%	29 / 336	❌	70%

Passing coverage

Files with passing code coverage

File	Coverage	Lines Hit	Status	Min Required
MavenDependenciesRetriever.kt scripts/src/java/org/oppia/android/scripts/license/MavenDependenciesRetriever.kt	96.02%	193 / 201	✅	70%

Exempted coverage

Files exempted from coverage

File	Exemption Reason
TopicController.kt domain/src/main/java/org/oppia/android/domain/topic/TopicController.kt	This file is incompatible with code coverage tooling; skipping coverage check.

Refer test_file_exemptions.textproto for the comprehensive list of file exemptions and their required coverage percentages.

To learn more, visit the Oppia Android Code Coverage wiki page

BenHenning · 2026-03-30T22:10:25Z

Hi @BenHenning, I wanted to confirm the preferred base branch for this PR. It is currently based on introduce-asset-download-script, and I see Check base branch failing because of that. Should I keep it on this branch for now, or retarget/rebase it to develop? I’m happy to update it whichever way you prefer.

@nikhilkumarpanigrahi you can ignore basically all of the code coverage and CI failures here since the base branch isn't yet stable for merging (having other people work on the download script is a bit unusual in and of itself, and I think this is one of the first times we've had someone open an actual PR against it). Normally we don't ignore those, but in this case it's fine since I actually need to go and update a lot (most) of this code later on, anyway.

However, I can't quite take a review pass on this PR because it seems like there are a lot of unrelated changes per the 'Files changed' tab. I'm not sure if a merge went bad or something, but please make sure to self check your code and remove anything not directly related to the objective of the PR. Once that's done please assign this back to me to take another review pass.

This reverts commit 8759fad.

nikhilkumarpanigrahi · 2026-04-05T07:48:21Z

@BenHenning thank you for the guidance. I did a full self-check and removed unrelated changes so this PR is now scoped only to the objective of #6086 (transparent image detection + math tag validation). The branch has been updated with a regular push, and the Files changed tab should now reflect only relevant changes.

PTAL when you get a chance.

oppiabot · 2026-04-05T07:51:26Z

Unassigning @nikhilkumarpanigrahi since a re-review was requested. @nikhilkumarpanigrahi, please make sure you have addressed all review comments. Thanks!

github-actions · 2026-04-05T10:28:22Z

Coverage Report

Results

Number of files assessed: 8
Overall Coverage: 7.90%
Coverage Analysis: FAIL ❌

Failure Cases

File	Failure Reason	Status
DownloadLessonList.kt scripts/src/java/org/oppia/android/scripts/assets/DownloadLessonList.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/assets/DownloadLessonList.kt.	❌
DownloadLessons.kt scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/assets/DownloadLessons.kt.	❌
DtoProtoToLegacyProtoConverter.kt scripts/src/java/org/oppia/android/scripts/assets/DtoProtoToLegacyProtoConverter.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/assets/DtoProtoToLegacyProtoConverter.kt.	❌
TopicPackRepository.kt scripts/src/java/org/oppia/android/scripts/gae/compat/TopicPackRepository.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/compat/TopicPackRepository.kt.	❌
GaeAndroidEndpointJsonImpl.kt scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt	No appropriate test file found for scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt.	❌

Failing coverage

File	Coverage	Lines Hit	Status	Min Required
ImageRepairer.kt scripts/src/java/org/oppia/android/scripts/assets/ImageRepairer.kt	17.57%	13 / 74	❌	70%
LocalizationTracker.kt scripts/src/java/org/oppia/android/scripts/gae/proto/LocalizationTracker.kt	5.33%	20 / 375	❌	70%
StructureCompatibilityChecker.kt scripts/src/java/org/oppia/android/scripts/gae/compat/StructureCompatibilityChecker.kt	8.63%	29 / 336	❌	70%

To learn more, visit the Oppia Android Code Coverage wiki page

BenHenning

Thanks @nikhilkumarpanigrahi. I had some follow-up thoughts, PTAL.

BenHenning · 2026-04-11T01:55:31Z

scripts/src/javatests/org/oppia/android/scripts/gae/proto/LocalizationTrackerTest.kt

+      "<oppia-noninteractive-math math_content-with-value=\"" +
+        "{&amp;quot;raw_latex&amp;quot;:&amp;quot;x^2&amp;quot;\"></oppia-noninteractive-math>"
+
+    assertFailsWith<Exception> {


We should be using assertThrows from the main testing package for this as it's available for use in tests. See example:

oppia-android/scripts/src/javatests/org/oppia/android/scripts/lint/LintCommonTest.kt

Line 8 in bafece4

import org.oppia.android.testing.assertThrows

We also should always test the specific exception type (not Exception) that's thrown and its message, when populated, to ensure the correct exception is actually being thrown.

BenHenning · 2026-04-11T01:56:38Z

scripts/src/javatests/org/oppia/android/scripts/assets/ImageRepairerTest.kt

+  fun testHasTransparentPixels_invalidImageData_throwsError() {
+    val invalidImageData = "not-a-valid-image".toByteArray()
+
+    assertFailsWith<IllegalStateException> {


Ditto here--see my later comment for correctly asserting errors being thrown.

BenHenning · 2026-04-11T01:57:23Z

scripts/src/java/org/oppia/android/scripts/gae/GaeAndroidEndpointJsonImpl.kt

        )
      converterInitializer = ConverterInitializer(
-        activityService, coroutineDispatcher, topicDependencies, imageDownloader, downloadConfig
+        activityService, coroutineDispatcher, topicDependencies, imageDownloader, downloadConfig, filterInvalidTopics


Why is this showing up? Did you sync your branch to the latest changes from introduce-asset-download-script? This (& the other changes in this file) should already be in the base branch.

BenHenning · 2026-04-11T01:58:44Z

scripts/src/java/org/oppia/android/scripts/gae/compat/StructureCompatibilityChecker.kt

+          return@mapNotNull MathTagMissingContent(contentId, origin)
+        }
+
+        val parsedMathContent = runCatching {


Why is runCatching needed here? It's generally an antipattern to use exceptions for control flow so we really ought to avoid that.

nikhilkumarpanigrahi added 6 commits March 12, 2026 13:11

Add transparent image detection and math tag validation for lesson as…

17910d7

…sets

Fix regex line length to comply with ktlint 100-char limit

8db3e0e

Remove KDoc comment to match codebase style

2609c7f

Address review: remove SVG fallback check, fix summary, add tests

e27e6ce

Fix RAW_LATEX_REGEX to correctly match standard Oppia math content fo…

2ac8193

…rmat

Fix Bazel cross-module visibility for math tag validation tests

50b8ace

nikhilkumarpanigrahi requested review from a team as code owners March 12, 2026 09:03

nikhilkumarpanigrahi requested review from BenHenning and removed request for a team March 12, 2026 09:03

oppiabot bot assigned BenHenning Mar 12, 2026

nikhilkumarpanigrahi mentioned this pull request Mar 12, 2026

[Feature Request]: Add detection for transparency in lesson images & invalid math tags in download script #6086

Open

github-actions bot marked this pull request as draft March 12, 2026 09:39

nikhilkumarpanigrahi changed the title ~~Fix #6086: Add transparent image detection and math tag validation~~ Fixes #6086: Add transparent image detection and math tag validation Mar 12, 2026

nikhilkumarpanigrahi marked this pull request as ready for review March 12, 2026 09:40

github-actions bot marked this pull request as draft March 12, 2026 09:47

nikhilkumarpanigrahi marked this pull request as ready for review March 12, 2026 09:49

Fix ktlint formatting for MATH_TAG_REGEX multiline expression

7c5b892

oppiabot bot assigned adhiamboperes Mar 16, 2026

BenHenning reviewed Mar 19, 2026

View reviewed changes

BenHenning assigned nikhilkumarpanigrahi and unassigned BenHenning and adhiamboperes Mar 19, 2026

oppiabot bot assigned BenHenning and unassigned nikhilkumarpanigrahi Mar 27, 2026

nikhilkumarpanigrahi added 6 commits March 27, 2026 19:26

Merge remote-tracking branch 'upstream/introduce-asset-download-scrip…

561738b

…t' into lesson-asset-validation-v4

Fix scripts CI failures after base sync

7d97b71

- Fix ktlint import ordering and max-line-length violations - Remove deprecated worked_example fields from skills.textproto to match ConceptCard proto schema

Fix buildifier warning in scripts proto tests BUILD file

24f6060

Fix moshi runtime deps for Proguard builds

f008503

Fix static checks and shard test failures

b74ec9f

Fix ktlint line length issues

9ff0341

nikhilkumarpanigrahi added 2 commits March 28, 2026 09:29

Handle maven repo key fallback for aar artifacts

dfee115

Use textproto exemption paths in static checks

db7d94e

nikhilkumarpanigrahi added 2 commits March 28, 2026 13:49

BenHenning assigned nikhilkumarpanigrahi and unassigned BenHenning Mar 30, 2026

nikhilkumarpanigrahi added 3 commits March 31, 2026 08:26

Remove unrelated TestEnvironmentConfig exemption

8759fad

Revert "Remove unrelated TestEnvironmentConfig exemption"

825ee16

This reverts commit 8759fad.

Clean PR scope: revert unrelated changes from oppia#6144

9e6794d

oppiabot bot assigned BenHenning Apr 5, 2026

oppiabot bot unassigned nikhilkumarpanigrahi Apr 5, 2026

BenHenning requested changes Apr 11, 2026

View reviewed changes

BenHenning assigned nikhilkumarpanigrahi and unassigned BenHenning Apr 11, 2026

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nikhilkumarpanigrahi commented Mar 12, 2026 •

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