Feature: sync all snapshot data in Pika process without rsync subprocess

[wangshao1]

fix issue #1228 ，这个版本的全量同步有如下 feature：

1 断点续传
2 速率限制
3 文件检验

[cr-gpt]

The provided code patch appears to be a header file related to a client thread for an rsync application. Here are some suggestions and areas to consider in your code review:

1. Licensing: Verify that the license information provided (BSD-style license) is accurate and consistent with your project's requirements.

2. Namespace Usage: It seems that the namespaces pstd and net are being used in this file. Ensure that these namespaces are correctly defined and included in the relevant source files.

3. Class Design: Review the design of the RsyncClientConn, RsyncClientConnFactory, and RsyncClientThread classes to ensure they align with your intended functionality. Consider whether any additional member variables or methods are needed or if any existing ones can be made more specific.

4. Error Handling: Check if proper error handling mechanisms, such as exception handling or error return codes, are implemented in the code. It is crucial to handle potential errors or exceptional scenarios gracefully.

5. Documentation: Consider adding appropriate comments/documentation to aid understanding and maintainability of the codebase. Include brief descriptions of the purpose of classes, methods, and important variables.

6. Thread Safety: If multiple threads will access the code in question, validate that proper synchronization mechanisms, like locks or atomic operations, are used where necessary to prevent race conditions.

7. Memory Management: Examine how memory allocation and deallocation are handled within your code. Ensure there are no memory leaks or undefined behavior and that destructors and smart pointers (if applicable) are used appropriately.

8. Code Style and Consistency: Verify that the coding style is consistent throughout the codebase, adhering to any existing conventions. Maintain readability by following best practices such as indentation, meaningful variable names, and appropriate use of white space.

Remember that a comprehensive code review requires access to the complete codebase including related implementation files, so these suggestions may not cover all aspects of your project.

[AlexStocks]

这个往下挪动下，很明显他不在 #include "include/pika_xx.h" 这块 include 代码块里面

[AlexStocks]

改成英文 comment

[AlexStocks]

改成英文 comment。而且现有的 comment 不清楚其含义：不知道要替换啥

[cr-gpt]

Based on the provided code patch, here is a brief code review:

1. The addition of a new constant kPortShiftRsync2 and the accompanying comment suggest that it is temporarily used for rsync server port shifting. Ensure that this temporary usage is properly communicated and documented to prevent confusion.

2. Overall, the code change seems to be straightforward and doesn't introduce any obvious bug risks.

Improvement suggestions:

1. Consider using more descriptive names for constants, such as kPortShiftRsyncTemporary, instead of kPortShiftRsync2. This will make the code more readable and maintainable.

2. Ensure that the use of this temporary variable kPortShiftRsync2 is properly removed or updated once its temporary usage is complete, to avoid leaving unused or misleading code in the system.

3. It's always good practice to include a comment explaining the reason behind certain code changes, especially when introducing temporary variables/constants or making non-obvious modifications that deviate from the existing codebase.

Remember to thoroughly test the code after making these changes to ensure proper functionality.

[AlexStocks]

// TODO: Temporarily used for rsync server port shift. will be deleted.

[cr-gpt]

Based on the code patch you provided, here are some observations:

1. The addition of kPortShiftRsync2 suggests a new port shift value for the rsync server. However, the comment mentions that it is temporary and will be deleted. Make sure to update or remove this code appropriately once it is no longer needed.

2. The variable name kPortShiftRsync2 could be improved for better clarity. Consider using a more descriptive name based on its purpose.

3. Ensure that there are no conflicts or issues arising from the new port shift values (kPortShiftRSync, kPortShiftReplServer, and kPortShiftRsync2) being used in the code elsewhere.

4. Review the usage of other constants (kPikaPidFile, kPikaSecretFile, and kDefaultRsyncAuth) to ensure they are accurate and consistent throughout the codebase.

5. It's important to review the surrounding code affected by the changes to confirm that the modifications align with the intended functionality.

Overall, without further context or the complete code, it is difficult to identify any potential bugs or suggest additional improvements beyond what has been mentioned. A comprehensive code review requires examining the broader codebase and understanding the overall architecture and requirements.