[Bug]: conn.Next not safe

[zhongweikang]

Actions I've taken before I'm here

• [X] I've thoroughly read the documentations on this issue but still have no clue.
• [X] I've searched the Github Issues but didn't find any duplicate issues that have been resolved.
• [X] I've searched the internet for this issue but didn't find anything helpful.

What happened?

https://github.com/panjf2000/gnet/blob/v2.5.9/connection_unix.go#L327-L330

代码329行，返回了c.inboundBuffer内部的字节数组 代码327行，defer c.inboundBuffer.Discard(n)，会回收c.inboundBuffer中的字节数组，回收到sync.Pool中

假设有两个goroutine 一个goroutine正在使用329行返回的字节数组 另一个goroutine读取到了327行回收的字节数组（因为被回收了，所以另一个goroutine能被复用） 导致两个goroutine同时操作了同一块字节数组，报文错乱！

Major version of gnet

v2

Specific version of gnet

V2

Operating system

Linux, macOS

OS version

Linux 3.10.0

Go version

go1.17.12

Relevant log output

无

Code snippets (optional)

defer c.inboundBuffer.Discard(n) //nolint:errcheck
    if len(head) >= n {
        return head[:n], err
    }

How to Reproduce

多个事件循环并发执行时概率复现

Does this issue reproduce with the latest release?

It can reproduce with the latest release

[panjf2000]

看文档，这个方法本来就是非线程安全的：https://pkg.go.dev/github.com/panjf2000/gnet/v2#Conn

[gh-translator]

🤖 Non-English text detected, translating ...

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Looking at the documentation, this method is inherently non-thread-safe: https://pkg.go.dev/github.com/panjf2000/gnet/v2#Conn