fix: do not crash on SSE comment line

[ishymko]

Description

The cause is florimondmanca/httpx-sse#35: using comments among events with id field causes httpx-sse to emit an event with empty data.

Although according to the standard (item 2) empty buffer shouldn't produce an event, with the way how httpx-sse API is defined it may still be reasonable to emit an object with just retry field for instance so that consumer could handle it. The standard defines retry field handling outside of events dispatching, so in the context of this library it's up to the client (see here). That being said, even if comment handling bug is fixed, it still makes sense to add this check against data field unconditionally without any TODOs.

Tested by mocking one level lower to put httpx-sse under test as well as it's an integration issue.

Fixes #540

[gemini-code-assist]

Summary of Changes

Hello @ishymko, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where the client would unexpectedly terminate upon receiving comment lines within Server-Sent Events (SSE) streams. The solution involves a targeted modification to the streaming message processing logic, ensuring that empty data events, characteristic of SSE comments, are gracefully ignored. This enhancement improves the stability and resilience of the client's streaming capabilities, backed by new tests confirming the fix.

Highlights

• Bug Fix: Implemented a fix to prevent client crashes when encountering Server-Sent Events (SSE) comment lines in streaming responses.
• Robustness: Added a conditional check to skip processing SSE events that do not contain actual data, specifically targeting comment lines, in both JSON-RPC and REST transport mechanisms.
• Testing: Introduced new unit tests for both JsonRpcTransport and RestTransport to explicitly verify the correct handling of SSE comment lines during streaming operations.

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[gemini-code-assist]

Code Review

This pull request effectively addresses a crash that occurs when processing Server-Sent Events (SSE) containing comment lines. The fix, applied to both jsonrpc and rest transports, correctly skips events with no data, preventing parsing errors. The addition of new tests for both transports using respx to mock SSE streams with comments is a great way to ensure the fix is working as expected. The changes are solid and improve the client's robustness. I have one minor suggestion to clean up some leftover debug code in a test file.