Add support to restrict @Core.AcceptableMediaTypes by samyuktaprabhu · Pull Request #732 · cap-java/cds-feature-attachments

samyuktaprabhu · 2026-02-11T14:39:28Z

Add Support to Restrict @Core.AcceptableMediaTypes

✨ New Features

Introduced support for restricting allowed MIME types for attachments using the @Core.AcceptableMediaTypes annotation. This feature enables validation of file types during upload at HandlerOrder.BEFORE, ensuring only specified media types are accepted before processing begins.

🔧 Changes

Core Implementation

CreateAttachmentsHandler.java: Added new @Before handler method processBeforeForMetadata that validates acceptable media types early in the request lifecycle. Updated constructor to accept CdsRuntime parameter for metadata validation support.
AttachmentValidationHelper.java (new): Comprehensive helper class for media type validation with support for wildcard patterns (image/*) and default fallback behavior (*/*). Validates file types against configured acceptable media types.
MediaTypeResolver.java (new): Extracts acceptable media types from CDS entity annotations, handling both direct media entities and composed attachments using the AssociationCascader.
MediaTypeService.java (new): Provides MIME type resolution from file extensions using Java's URLConnection.getFileNameMap() and validates against acceptable media types with support for exact matches and wildcard patterns.
AttachmentDataExtractor.java (new): Extracts and validates file names from attachment data using CdsDataProcessor, ensuring files have proper extensions before MIME type validation.
Registration.java: Updated handler registration to pass CdsRuntime instance to CreateAttachmentsHandler.
ApplicationHandlerHelper.java: Added deepSearchForAttachments() method functionality (refactored into AssociationCascader).
AssociationCascader.java: Enhanced with hasAttachmentPath() and findMediaEntityNames() methods to recursively check for attachment compositions in entity hierarchies and collect media entity names.

Documentation

README.md: Added comprehensive documentation section "Restrict allowed MIME types" with examples of:
- Exact matches (image/jpeg, image/png)
- Wildcard patterns (image/*)
- Default behavior (*/*)
- Usage scenarios for single and multiple media types

Test Suite

CreateAttachmentsHandlerTest.java: Added tests for new metadata validation handler with proper annotation verification
AttachmentValidationHelperTest.java (new): Comprehensive test suite with 16+ test cases covering MIME type detection, validation, wildcards, error scenarios, and edge cases including hidden files
MediaTypeResolverTest.java (new): Tests for media type extraction from entity annotations
MediaTypeServiceTest.java (new): Tests for MIME type resolution and validation logic including edge cases like hidden files (.gitignore)
MediaValidatedAttachmentsDraftTest.java (new): Integration tests for draft service media validation with parameterized tests for various file types
MediaValidatedAttachmentsNonDraftTest.java (new): Integration tests for non-draft service media validation, including deep create scenarios and multiple attachment validation
AssociationCascaderTest.java: Added tests for new hasAttachmentPath() and findMediaEntityNames() methods
Size validation tests: Updated to include fileName assignments for proper validation

Integration Test Configuration

data-model.cds: Added mediaValidatedAttachments and mimeValidatedAttachments compositions to Roots entity
test-service.cds: Configured annotations to accept only JPEG and PNG images for mediaValidatedAttachments, and PDFs for mimeValidatedAttachments
RootEntityBuilder.java: Enhanced builder to initialize sizeLimitedAttachments list in constructor for proper entity setup

Sample Application

samples/bookshop/srv/attachments.cds:
- Added mediaValidatedAttachments composition to Books entity
- Configured to accept only JPEG and PNG images
- Added UI annotations to hide the field from Browse Books App

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hyperspace-insights

The PR adds media type restriction support for attachments. I've identified a few issues: a typo in MIME type definitions (application/txt should be text/plain), potential security concerns with filename validation (missing path traversal checks), and a minor note about null handling. Overall the implementation is reasonable but needs these corrections before merging.

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Event Trigger: pull_request.opened
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Correlation ID: 78c854a0-0757-11f1-833c-299ee35f3dc8

...ap/cds/feature/attachments/handler/applicationservice/helper/AttachmentValidationHelper.java

...s/src/main/java/com/sap/cds/feature/attachments/handler/common/ApplicationHandlerHelper.java

...ap/cds/feature/attachments/handler/applicationservice/helper/AttachmentValidationHelper.java

hyperspace-insights

Summary

The pull request introduces MIME type validation for attachments with good test coverage. However, several null safety issues were identified in the validation logic that could lead to NullPointerException errors. Additionally, a minor CDS syntax inconsistency and a misleading test variable name should be addressed.

PR Bot Information

Version: 1.17.61 | 📖 Documentation | 🚨 Create Incident | 💬 Feedback

Event Trigger: issue_comment.created
Correlation ID: b7b79080-0bdb-11f1-9b97-78cdc3653ab1
LLM: anthropic--claude-4.5-sonnet

...ap/cds/feature/attachments/handler/applicationservice/helper/AttachmentValidationHelper.java

...s/src/main/java/com/sap/cds/feature/attachments/handler/common/ApplicationHandlerHelper.java

integration-tests/db/data-model.cds

...ture/attachments/integrationtests/nondraftservice/MediaValidatedAttachmentsNonDraftTest.java

Schmarvinius

Unit-Tests:

AttachmentCalidationHelperTest:
- Add a test for wildcard subtype rejection like image/* should reject application/pdf
- Add a test for files start with . like .gitignore or .ssh or .zshrc and so on

Integration-Tests:

MediaCalidatedAttachmentsDraftTest:
- Add a test for false inputs like an empty string. You have them for non draft but not for draft.
- Add tests for situations where it fails like upload a pdf when only jpeg or image/* is allowed
  - Also one for dotfiles
MediaValidatedAttachmentsNonDraftTest:
- Add a test for case sensitivity in the extension
- Add a test for no extension
- Add a test for hidden files again

...ap/cds/feature/attachments/handler/applicationservice/helper/AttachmentValidationHelper.java

...ds/feature/attachments/handler/applicationservice/helper/AttachmentValidationHelperTest.java

...ds/feature/attachments/integrationtests/draftservice/MediaValidatedAttachmentsDraftTest.java

hyperspace-insights

Summary

This PR introduces MIME type validation for attachments with generally solid implementation. I've identified 9 substantive issues requiring attention:

Critical: Missing file extension validation in MediaTypeService.resolveMimeType() could cause runtime errors
Important: Inconsistent filename validation between extractor and validator creates confusing error paths
Security consideration: FileNameValidator doesn't check for path traversal characters (e.g., ../, null bytes)
Several performance and code quality improvements around duplicate constants, inefficient stream operations, and wildcard matching logic

The test coverage is comprehensive, and the feature design is well-thought-out. Address the validation and error-handling gaps before merging.

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LLM: anthropic--claude-4.5-sonnet
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Correlation ID: a7941f80-1242-11f1-91ae-db28216a7610

...om/sap/cds/feature/attachments/handler/applicationservice/helper/media/MediaTypeService.java

...chments/handler/applicationservice/helper/mimeTypeValidation/AttachmentValidationHelper.java

...m/sap/cds/feature/attachments/handler/applicationservice/helper/AttachmentDataExtractor.java

.../cds/feature/attachments/handler/applicationservice/helper/validation/FileNameValidator.java

...ava/com/sap/cds/feature/attachments/handler/applicationservice/CreateAttachmentsHandler.java

...s/src/main/java/com/sap/cds/feature/attachments/handler/common/ApplicationHandlerHelper.java

Schmarvinius

I think your whole structe has gotten very complicated.
Why don't you merge FileNameValidator + MediaTypeService + MediaTypeResolver + AttachmentValidationHelper into one MediaTypeValidator
And keep the DataExtractor as-is. This reduces complexity and keeps separation of concern to a healthy degree.

...re-attachments/src/main/java/com/sap/cds/feature/attachments/configuration/Registration.java

...om/sap/cds/feature/attachments/handler/applicationservice/helper/media/MediaTypeService.java

...ure/attachments/handler/applicationservice/helper/validation/AttachmentValidationHelper.java

...m/sap/cds/feature/attachments/handler/applicationservice/helper/AttachmentDataExtractor.java

samyuktaprabhu · 2026-02-27T17:52:08Z

I think your whole structe has gotten very complicated.
Why don't you merge FileNameValidator + MediaTypeService + MediaTypeResolver + AttachmentValidationHelper into one MediaTypeValidator
And keep the DataExtractor as-is. This reduces complexity and keeps separation of concern to a healthy degree.

Thanks for your review &suggestion. I merged FileNameValidator & AttachmentDataExtractor. I tried doing the merge for the other 3 files, but, if we do that, we'd end up making it harder to test, and also make it harder to reuse later.

…chments/configuration/Registration.java Co-authored-by: Marvin <marvin.lindner@sap.com> Update cds-feature-attachments/src/main/java/com/sap/cds/feature/attachments/configuration/Registration.java Co-authored-by: Marvin <marvin.lindner@sap.com> Update cds-feature-attachments/src/main/java/com/sap/cds/feature/attachments/configuration/Registration.java Co-authored-by: Marvin <marvin.lindner@sap.com> Update cds-feature-attachments/src/main/java/com/sap/cds/feature/attachments/configuration/Registration.java Co-authored-by: Marvin <marvin.lindner@sap.com> apply mvnspotless:apply Rename AttachmentDataExtractor to validation package Refactor MediaTypeService to use URLConnection for MIME type resolution and update AttachmentValidationHelper method visibility Refactor AttachmentValidationHelper to streamline MIME type validation logic Add unit tests for AssociationCascader and refactor AttachmentValidationHelper and MediaTypeResolver to utilize AssociationCascader for media entity resolution Refactor MediaTypeResolver to remove dependency on ApplicationHandlerHelper and update related tests Refactor file name validation logic and migrate to mimeTypeValidation package Refactor AttachmentDataExtractor to integrate filename validation logic and remove FileNameValidator class Refactor AttachmentDataExtractor and update tests to improve structure and maintainability Refactor AttachmentValidationHelper and MediaTypeResolver to improve structure and add unit tests for media type resolution revert a change

Schmarvinius

Just noticed: do you cover PATCHING/Updating a Root entity when adding attachments?

Schmarvinius · 2026-03-05T14:10:34Z

...ature/attachments/handler/applicationservice/helper/mimeTypeValidation/MediaTypeService.java

+            });
+  }
+
+  private static String fallbackToDefaultMimeType(String fileName) {


Why is an extra function needed?

Schmarvinius · 2026-03-05T14:25:46Z

...ature/attachments/handler/applicationservice/helper/mimeTypeValidation/MediaTypeService.java

+    if (acceptableMediaTypes == null
+        || acceptableMediaTypes.isEmpty()
+        || acceptableMediaTypes.contains("*/*")) return true;


Suggested change

if (acceptableMediaTypes == null

|| acceptableMediaTypes.isEmpty()

|| acceptableMediaTypes.contains("*/*")) return true;

if (acceptableMediaTypes == null || acceptableMediaTypes.isEmpty()) {

return true;

}

if (acceptableMediaTypes.stream().anyMatch(type -> type.trim().toLowerCase().equals("*/*"))) {

return true;

}

The contains("/") check runs on the raw annotation values before normalization (trim().toLowerCase()), so a value like " / " with surrounding whitespace would fail to short-circuit as a wildcard. Consider normalizing first, or moving this check after normalization.

Schmarvinius · 2026-03-05T14:36:32Z

...chments/handler/applicationservice/helper/mimeTypeValidation/AttachmentValidationHelper.java

+    boolean areAttachmentsAvailable =
+        ApplicationHandlerHelper.isMediaEntity(entity)
+            || cascader.hasAttachmentPath(cdsModel, entity);
+
+    if (!areAttachmentsAvailable) {
+      return;
+    }
+
+    // validate the media types of the attachments
+    Map<String, List<String>> allowedTypesByElementName =
+        MediaTypeResolver.getAcceptableMediaTypesFromEntity(entity, cdsModel);
+    Map<String, Set<String>> fileNamesByElementName =
+        AttachmentDataExtractor.extractAndValidateFileNamesByElement(entity, data);


hasAttachmentPath and findMediaEntityNames both internally call findEntityPath, so the entity tree is traversed twice per request. You could avoid this by calling findMediaEntityNames once and using its result to determine both conditions

Schmarvinius · 2026-03-05T14:41:38Z

...ttachments/handler/applicationservice/helper/mimeTypeValidation/AttachmentDataExtractor.java

+  private static String validateAndNormalize(String fileName) {
+    String trimmedFileName = fileName.trim();
+    if (trimmedFileName.isEmpty()) {
+      throw new ServiceException(ErrorStatuses.BAD_REQUEST, "Filename must not be blank");
+    }
+
+    int lastDotIndex = trimmedFileName.lastIndexOf('.');
+    if (lastDotIndex == -1 || lastDotIndex == trimmedFileName.length() - 1) {
+      throw new ServiceException(ErrorStatuses.BAD_REQUEST, "Invalid filename format: " + fileName);
+    }
+    return trimmedFileName;
+  }


validateAndNormalize throws BAD_REQUEST when a filename has no extension, while MediaTypeService.resolveMimeType handles the same case by falling back to a default MIME type (application/octet-stream). Since validateAndNormalize runs first in the flow, the fallback in resolveMimeType is unreachable for this code path.

hyperspace-insights bot reviewed Feb 11, 2026

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samyuktaprabhu changed the title ~~Add support to restrict media types~~ Add support to restrict @Core.AcceptableMediaTypes Feb 11, 2026

samyuktaprabhu force-pushed the sam-restrict-media-types-409 branch from 8b6c095 to a12bc05 Compare February 17, 2026 08:35

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samyuktaprabhu marked this pull request as ready for review February 17, 2026 08:36

samyuktaprabhu requested a review from Schmarvinius February 17, 2026 09:21

samyuktaprabhu force-pushed the sam-restrict-media-types-409 branch from e2b000e to 26b499c Compare February 17, 2026 09:36

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samyuktaprabhu requested a review from Schmarvinius February 18, 2026 15:27

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samyuktaprabhu requested a review from busehalis-sap February 26, 2026 08:44

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samyuktaprabhu marked this pull request as draft February 27, 2026 11:26

samyuktaprabhu force-pushed the sam-restrict-media-types-409 branch from 534423e to ab8ab07 Compare February 27, 2026 19:05

samyuktaprabhu force-pushed the sam-restrict-media-types-409 branch from 46592c3 to c458640 Compare February 27, 2026 19:07

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samyuktaprabhu commented Feb 11, 2026 • edited by hyperspace-insights bot Loading Uh oh! There was an error while loading. Please reload this page.

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Add Support to Restrict @Core.AcceptableMediaTypes

✨ New Features

🔧 Changes

Core Implementation

Documentation

Test Suite

Integration Test Configuration

Sample Application

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samyuktaprabhu commented Feb 27, 2026

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samyuktaprabhu commented Feb 11, 2026 •

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