feat: implement network error handling and recovery for stmt2 operations

[qevolg]

Description

Issue(s)

• Close/close/Fix/fix/Resolve/resolve: Issue Link

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the resilience of stmt2 operations by introducing comprehensive network error handling and recovery. It refactors the statement execution flow to gracefully manage disconnections, allowing prepared statements to rebuild their context and retry operations without user intervention. This ensures greater stability and reliability for applications interacting with the database over potentially unstable network connections.

Highlights

• Network Error Handling for Stmt2 Operations: Implemented robust network error handling and recovery mechanisms for stmt2 operations, ensuring that prepared statements can recover from transient network disconnections and continue execution.
• Refactored Stmt2 Workflow: The WsStmt2 class was refactored to separate core statement execution logic (doInit, doPrepare, doSendBindBytes, doExec, doResult) from the error handling and retry logic, improving modularity and maintainability.
• Context Rebuilding on Disconnect: A new rebuildContext method was introduced in WsStmt2 to re-establish the statement's state (init, prepare, bind) after a network error, allowing operations to resume from the point of failure.
• Enhanced WsClient and WsConnector: The WsClient now exposes methods to check for network errors and wait for the connection to be ready, while WsConnector's isNetworkError method was made public to support broader error detection.
• Comprehensive Failover Testing: New test cases were added to validate the stmt2 failover capabilities across various phases (bind, prepare, result) and under conditions of multiple network disconnects, ensuring the reliability of the recovery mechanism.

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[gemini-code-assist]

Code Review

This pull request introduces network error handling and recovery for stmt2 operations, a valuable addition for client resilience. The implementation correctly saves statement context and replays operations upon network failure, centered around a rebuildContext method. The inclusion of a comprehensive test suite using a proxy to simulate failures is commendable. I have a couple of suggestions in wsStmt2.ts to enhance code clarity and robustness.

[gemini-code-assist]

Using non-null assertion operators (!) on _savedSql and _savedBindBytes can be brittle. While the current logic ensures these are non-null, future changes might break this assumption and lead to runtime errors. For improved robustness and clearer error handling, it would be better to add explicit checks for undefined and throw a descriptive error if the properties are not set when expected.

Suggested change

	await this.doPrepare(this._savedSql!);
	if (failedStep === StmtStep.PREPARE) return;
	await this.doSendBindBytes(this._savedBindBytes!);
	if (this._savedSql === undefined) {
	throw new TaosResultError(ErrorCode.ERR_INVALID_PARAMS, "Internal error: _savedSql is undefined during rebuild.");
	}
	await this.doPrepare(this._savedSql);
	if (failedStep === StmtStep.PREPARE) return;
	if (this._savedBindBytes === undefined) {
	throw new TaosResultError(ErrorCode.ERR_INVALID_PARAMS, "Internal error: _savedBindBytes is undefined during rebuild.");
	}
	await this.doSendBindBytes(this._savedBindBytes);

[gemini-code-assist]

The StmtStep.BIND enum member and this check appear to be unused. The rebuildContext method is never called with StmtStep.BIND. In exec(), failures in both doSendBindBytes and doExec trigger a rebuild with StmtStep.EXEC. To improve clarity and remove dead code, consider removing the BIND step from the StmtStep enum and this conditional block.