Enhance message parsing to preserve newlines from empty data fields

[fa3eng]

Fix: Preserve newlines from empty data fields in Server-Sent Events parsing

Issue：#50

Description

Problem

The current implementation of the Server-Sent Events (SSE) parser incorrectly handles empty data fields. When multiple consecutive empty data: fields are encountered, the parser was not preserving the newline characters that should be added for each empty field, causing data loss and incorrect message formatting.

According to the Server-Sent Events specification, each data: field should append its value to the data buffer followed by a single U+000A LINE FEED (LF) character. This means that empty data: fields should still contribute a newline character to the final message data.

Solution

Modified the getMessages function in src/parse.ts to properly handle empty data fields by ensuring that each data: field (including empty ones) contributes a newline character to the message data buffer.

Key changes:

• Updated the data field processing logic to always append a newline character (\n) after each data field value, regardless of whether the value is empty
• Added comprehensive test coverage for this edge case in src/parse.spec.ts

Example

Before (incorrect behavior):

event: message
data:
data:
data: foo

Would result in: data: "foo" (missing newlines from empty data fields)

After (correct behavior):

event: message
data:
data:
data: foo

Results in: data: "\n\nfoo" (preserving newlines from empty data fields)

Testing

• Added test case should preserve newlines from empty data fields to verify the fix
• All existing tests continue to pass
• Updated test configuration in jasmine.json to point to the correct spec directory

Impact

This fix ensures full compliance with the Server-Sent Events specification and prevents data loss when processing SSE streams that contain empty data fields, which is a common pattern for formatting multi-line messages or creating visual spacing in SSE data.

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Additional Information for the PR

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[fa3eng]

@microsoft-github-policy-service agree

[scravy]

We just stumbled across that very same issue; very glad to see the issue is known, tracked, and a solution is here. Will this be released anytime soon?

[arsen-a]

This issue should have been resolved by now. Any idea when this will be merged or what has to be done? @fa3eng