Скачать или смотреть How to Cut Bytes into Separate Pieces from a Socket in Python

Learn how to efficiently “cut” bytes into separate pieces from a socket using Python with practical examples and best practices.
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This video is based on the question https://stackoverflow.com/q/63223138/ asked by the user 'MichaelT572' ( https://stackoverflow.com/u/13264269/ ) and on the answer https://stackoverflow.com/a/63223485/ provided by the user 'tdelaney' ( https://stackoverflow.com/u/642070/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Cut Bytes into Separate Pieces from a Socket in Python

In the world of socket programming, particularly in Python, managing data efficiently is crucial. If you're sending data quickly through a socket, you might face the challenge of ensuring each piece of information is sent and received as a complete unit. In this guide, we will explore the problem of receiving incomplete data and how to ensure that your data pieces remain intact when sent through sockets.

The Challenge: Sending and Receiving Data

Imagine you have a scenario where you are sending data continuously. For example, you might be sending different list elements to a socket. Here's a simplified version of what the code might look like:

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The concern here is how to ensure that the data you receive on the other side is always intact. If you're using conn.recv(), you might end up with truncated data, which leads to errors or inconsistencies in your application.

The Solution: Using pickle and Creating a File Object

The fundamental issue is how TCP byte streams work. They do not inherently demarcate messages, which means that data can come in chunks that need to be handled properly. Fortunately, we can utilize the pickle library effectively with blocking I/O to maintain our data integrity.

Sending Data Properly

On the sending side, the key is to use s.sendall() instead of s.send(). The sendall() function ensures that all the data you intend to send is actually sent over the connection. Here’s how you can structure your sending code:

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Using makefile with the socket makes it easier to deal with the byte stream like a file object.

Receiving Data Properly

On the receiving side, the ability to read the complete data is crucial. Here’s an example of how to do this correctly using pickle.Unpickler:

[[See Video to Reveal this Text or Code Snippet]]

In this method, pickle.Unpickler works seamlessly with the file object created from the socket, ensuring that the data is read completely before processing it.

Alternative Method: Implementing a Header

If you need a more flexible or complex solution, consider implementing a method to delimit each pickled buffer. This can be done by using a small header that indicates the size of the data being sent. Here’s a brief overview of how that works:

Create a header using struct that describes the size of the subsequent data.

Send the header first, followed by the actual data.

On the receiving side, read the header to determine how many bytes to read for the data.

This method may provide more control and allow your application to manage different types of messages effectively.

Conclusion

When dealing with sockets in Python, especially when using the pickle module for serialization and deserialization, maintaining the integrity of your data is paramount. By using sendall() for sending data and creating file objects for receiving, you can ensure that your messages are intact and correctly handled. For more complex applications, implementing a custom header might be the solution that provides greater flexibility.

With these strategies, you can effectively manage and "cut" bytes into separate pieces from a socket, ensuring that your application runs smoothly and efficiently.