chore(facade): parse buffers eagerly and simplify IoLoopV2 drain

[romange]

Summary

• Parse incoming data eagerly via ParseFromBuffer() right after reading, instead of deferring to the main loop body
• Simplify IoLoopV2 drain loop assuming ParseFromBuffer fully depletes io_buf_ (enforced by CHECK)
• Move CheckIoBufCapacity into the drain loop so the buffer can grow between recv calls

Changes

• src/facade/dragonfly_connection.h — Add ParseFromBuffer() declaration
• src/facade/dragonfly_connection.cc — Add ParseFromBuffer() (calls ParseMCBatch/ParseRedisBatch). Call it after CommitWrite in the drain loop and after WriteAndCommit in the multishot recv path. Remove redundant ParseFromBuffer/NEED_MORE/CheckIoBufCapacity from main loop body. Add CHECK_EQ(io_buf_.InputLen(), 0u) after eager parse.

🤖 Generated with Claude Code

[augmentcode]

🤖 Augment PR Summary

Summary: This PR moves protocol parsing to happen immediately after socket reads (instead of deferring to the IoLoopV2 loop body).

Changes:

• Adds Connection::ParseFromBuffer() to dispatch to the appropriate batch parser.
• Invokes parsing right after reads in DoReadOnRecv and the IoLoopV2 drain loop.
• Refactors IoLoopV2 to always run execute+reply after awaiting, with an extra parse step when buffered data remains.

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[augmentcode]

Review completed. 1 suggestion posted.

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[augmentcode]

ParseMCBatch() uses a do { ... } while (parsed_cmd_q_len_ < 128 && ...), so calling ParseFromBuffer() repeatedly from the drain loop can still enqueue at least one command even when the parsed-queue is already at/over the intended cap. Can you double-check this can’t lead to unbounded growth of parsed_cmd_q_len_ under heavy pipelining before ExecuteBatch() gets a chance to run?

Severity: medium

Other Locations

• src/facade/dragonfly_connection.cc:2606
• src/facade/dragonfly_connection.cc:2738

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