nginx 如何处理 TCP/UDP 会话
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How nginx processes a TCP/UDP session - nginx 如何处理 TCP/UDP 会话
https://nginx.org/en/docs/stream/stream_processing.html
A TCP/UDP session from a client is processed in successive steps called phases:
客户端的 TCP/UDP 会话在称为阶段的连续步骤中进行处理：
Post-accept
The first phase after accepting a client connection. The ngx_stream_realip_module module is invoked at this phase.
在接受客户端连接后的第一个阶段。此阶段调用 ngx_stream_realip_module 模块。
Pre-access
Preliminary check for access. The ngx_stream_limit_conn_module and ngx_stream_set_module modules are invoked at this phase.
用于预先检查访问权限。在此阶段，调用 ngx_stream_limit_conn_module 和 ngx_stream_set_module 模块。
Access
Client access limitation before actual data processing. At this phase, the ngx_stream_access_module module is invoked, for njs, the js_access directive is invoked.
在实际数据处理之前对客户端访问进行限制。在此阶段，调用 ngx_stream_access_module 模块；对于 njs，调用 js_access 指令。
SSL
TLS/SSL termination. The ngx_stream_ssl_module module is invoked at this phase.
TLS/SSL 终止。在此阶段，调用 ngx_stream_ssl_module 模块。
Preread
Reading initial bytes of data into the preread buffer to allow modules such as ngx_stream_ssl_preread_module analyze the data before its processing. For njs, the js_preread directive is invoked at this phase.
将初始数据的前几个字节读入 预读缓冲区，以便让模块（例如 ngx_stream_ssl_preread_module）在处理数据之前分析数据。对于 njs，在此阶段调用 js_preread 指令。
Content
Mandatory phase where data is actually processed, usually proxied to upstream servers, or a specified value is returned to a client. For njs, the js_filter directive is invoked at this phase.
数据实际处理的必要阶段，通常将数据 代理 到 上游 服务器，或者将指定的值 返回 给客户端。对于 njs，在此阶段调用 js_filter 指令。
Log
The final phase where the result of a client session processing is recorded. The ngx_stream_log_module module is invoked at this phase.
客户端会话处理结果记录的最终阶段。在此阶段调用 ngx_stream_log_module 模块。