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Joshua Zhu’s Blog » 2009 » August » 13
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Archive for August 13, 2009

Creating a Hello World! Nginx Module


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Some of my friends think nginx modules are very difficult to write. Sure it’s not so easy but it’s not that hard either. The only problem is that the documentation is not enough. But don’t let this scare yourself away, the situation is improving.

So I write a hello world nginx module here. It’s pretty short and with enough comments. If you’re a new nginx module developer, feel free to take it as an example and replace hello with whatever your module name is, then start your happy nginx module hacking journey. And I’ll write more topics on nginx soon. Look for it!  :D

ngx_http_hello_module.c:

 
/*
 * Copyright (C) Joshua Zhu, http://www.zhuzhaoyuan.com
 */
 
 
#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>
 
 
static char *ngx_http_hello(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);
 
static ngx_command_t ngx_http_hello_commands[] = {
    { ngx_string("hello"),
      NGX_HTTP_LOC_CONF|NGX_CONF_NOARGS,
      ngx_http_hello,
      0,
      0,
      NULL },
 
    ngx_null_command
};
 
 
static u_char ngx_hello_string[] = "Hello, world!";
 
 
static ngx_http_module_t ngx_http_hello_module_ctx = {
    NULL,                          /* preconfiguration */
    NULL,                          /* postconfiguration */
 
    NULL,                          /* create main configuration */
    NULL,                          /* init main configuration */
 
    NULL,                          /* create server configuration */
    NULL,                          /* merge server configuration */
 
    NULL,                          /* create location configuration */
    NULL                           /* merge location configuration */
};
 
 
ngx_module_t ngx_http_hello_module = {
    NGX_MODULE_V1,
    &ngx_http_hello_module_ctx,    /* module context */
    ngx_http_hello_commands,       /* module directives */
    NGX_HTTP_MODULE,               /* module type */
    NULL,                          /* init master */
    NULL,                          /* init module */
    NULL,                          /* init process */
    NULL,                          /* init thread */
    NULL,                          /* exit thread */
    NULL,                          /* exit process */
    NULL,                          /* exit master */
    NGX_MODULE_V1_PADDING
};
 
 
static ngx_int_t
ngx_http_hello_handler(ngx_http_request_t *r)
{
    ngx_int_t    rc;
    ngx_buf_t   *b;
    ngx_chain_t  out;
 
    /* we response to 'GET' and 'HEAD' requests only */
    if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD))) {
        return NGX_HTTP_NOT_ALLOWED;
    }
 
    /* discard request body, since we don't need it here */
    rc = ngx_http_discard_request_body(r);
 
    if (rc != NGX_OK) {
        return rc;
    }
 
    /* set the 'Content-type' header */
    r->headers_out.content_type_len = sizeof("text/html") - 1;
    r->headers_out.content_type.len = sizeof("text/html") - 1;
    r->headers_out.content_type.data = (u_char *) "text/html";
 
    /* send the header only, if the request type is http 'HEAD' */
    if (r->method == NGX_HTTP_HEAD) {
        r->headers_out.status = NGX_HTTP_OK;
        r->headers_out.content_length_n = sizeof(ngx_hello_string) - 1;
 
        return ngx_http_send_header(r);
    }
 
    /* allocate a buffer for your response body */
    b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
    if (b == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }
 
    /* attach this buffer to the buffer chain */
    out.buf = b;
    out.next = NULL;
 
    /* adjust the pointers of the buffer */
    b->pos = ngx_hello_string;
    b->last = ngx_hello_string + sizeof(ngx_hello_string) - 1;
    b->memory = 1;    /* this buffer is in memory */
    b->last_buf = 1;  /* this is the last buffer in the buffer chain */
 
    /* set the status line */
    r->headers_out.status = NGX_HTTP_OK;
    r->headers_out.content_length_n = sizeof(ngx_hello_string) - 1;
 
    /* send the headers of your response */
    rc = ngx_http_send_header(r);
 
    if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
        return rc;
    }
 
    /* send the buffer chain of your response */
    return ngx_http_output_filter(r, &out);
}
 
 
static char *
ngx_http_hello(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_core_loc_conf_t *clcf;
 
    clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);
    clcf->handler = ngx_http_hello_handler; /* handler to process the 'hello' directive */
 
    return NGX_CONF_OK;
}

config:

ngx_addon_name=ngx_http_hello_module
HTTP_MODULES="$HTTP_MODULES ngx_http_hello_module"
NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_hello_module.c"

hello.conf:

# hello
 
worker_processes 1;
 
events {
       worker_connections 1024;
}
 
http {
     server {
     	    listen 8080;
	    server_name localhost;
 
	    location / {
	    	     hello;
	    }
     }     
}

If you want more detailed information, please consult Evan Miller’s Guide To Nginx Module Development.

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