How nginx handles http requests

nginx processing http requests is the most important function of nginx and the most complex part. You can roughly talk about the execution process:

Read the request header;

Parse the request line;

Parse the request header;

Read the request body;

Start the most important part, That is, multi-stage processing; nginx divides request processing into 11 stages, which means that after nginx reads the request line and request header, it encapsulates the request in the structure ngx_http_request_t, and then the handler of each stage will based on this ngx_http_request_t, Process the request, such as rewriting uri, permission control, path search, generating content and logging, etc.;

Return the result to the client;

The main function of the ngx_http_process_request_line function is to parse the request line. Also due to the network IO operation involved, even a short request line may not be read at once, so in the previous ngx_http_init_request function, the ngx_http_process_request_line function is set to The processing function of the read event only has a unique ngx_event_t * type parameter, and at the beginning of the function, it is also necessary to determine whether it is a timeout event. If so, close the request and connection; otherwise, start the normal parsing process. First call the ngx_http_read_request_header function to read the data.

Multi-stage processing is the most important part of the nginx module, because third-party modules are also registered here;

For example, someone wrote a third-party that uses nginx and memcache for page caching Module, you can also replace memcache with redis cluster, etc.;

And nginx multi-stage processing is somewhat similar to the middleware of python and golang web framework. The latter mainly uses the decorator mode to layer the handler. Encapsulation, while nginx uses an array (linked list) to combine multi-stage handlers, and then executes them according to the handler linked list;

The uniform resource locator (url) sent by the client corresponds to a certain path on the server For resources, all the web server needs to do is map the URL to the path of the local file system, then read the corresponding file and return it to the client. But this was only the demand of the initial Internet. Nowadays, the Internet has a variety of complex demands, requiring web servers to handle issues such as security and permission control, multimedia content and dynamic web pages. These complex requirements have caused the web server to no longer be a short program, but into a system that must be carefully designed and modularized.

The good modularity of nginx is reflected in its multi-stage division of the request processing process. The multi-stage processing process is like an assembly line. One nginx process can concurrently process multiple requests at different stages. nginx allows developers to register modules at any stage of the processing process. During the startup phase, nginx will organize all module processing functions registered at each stage into an execution chain in order.

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