Imagine you run a PPC advertising campaign and you want to find out how many visitors coming from a search engine result in sales. We will create an Nginx module and use cookies for this purpose. Whenever a visitor clicks on your ad, a landing page is requested with a tracking argument in it. The tracking argument looks  like that: ‘?source=whatever’. We will put the content of tracking argument into a cookie that will be called a source cookie and write it into a log file. Whenever a visitor makes a transaction (e.g. buys an article or makes a booking), the name of the source will be recorded and we will be able to easily attribute every transaction to a source.

Let’s start with declaring a structure that will contain configuration of our module: Continue reading →

Let’s see what we need to do in order to return a simple page to a client using Nginx module. We need to generate a header and a body of the response. To send a response header we use function ngx_http_send_header:

#include <ngx_http.h>

ngx_int_t ngx_http_send_header(ngx_http_request_t *r);

The only argument r is the request for which you want to generate and send a header. This function serializes headers from the list of response headers r->headers_out into a buffer and sends this buffer to a client or queues this buffer into output queue r->out if the client socket is not writeable. The HTTP version in the status line will be determined for you automatically. The HTTP status code is taken from r->headers_out.status and the status text will be filled according to the status code.

Lets see how we can add some custom header line to our response header. Continue reading →

Nginx processes HTTP requests in multiple phases. In each of the phases there might be 0 or more handlers called. In the Nginx source code phases have specific constants associated with them. Here is a list of all phases:

1. NGX_HTTP_SERVER_REWRITE_PHASE — the phase of request URI transformation on the virtual server level;
2. NGX_HTTP_FIND_CONFIG_PHASE — the phase of the configuration location lookup;
3. NGX_HTTP_REWRITE_PHASE — the phase of request URI transformation on the location level;
4. NGX_HTTP_POST_REWRITE_PHASE — request URI transformation post-processing phase;
5. NGX_HTTP_PREACCESS_PHASE — access restrictions check preprocessing phase;
6. NGX_HTTP_ACCESS_PHASE — access restrictions check phase;
7. NGX_HTTP_POST_ACCESS_PHASE — access restrictions check post-processing phase;
8. NGX_HTTP_TRY_FILES_PHASE — try_files directive processing phase;
9. NGX_HTTP_CONTENT_PHASE — content generation phase;
10. NGX_HTTP_LOG_PHASE — logging phase.

On every phase you can register any number of your handlers. Continue reading →