module.c

#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>


static char *ngx_http_hello(ngx_conf_t *cf, void *post, void*data);

static ngx_conf_post_handler_pt ngx_http_hello_p = ngx_http_hello;

/*
 * The structure will hold the value of the
 * module directive hello
 */
typedef struct {
    ngx_str_t   name;
} ngx_http_hello_loc_conf_t;

/* The function which initializes memory for the module configuration structure       
 */
static void *
ngx_http_hello_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_hello_loc_conf_t  *conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_hello_loc_conf_t));
    if (conf == NULL) {
        return NULL;
    }
    
    return conf;
}
/*
 * The command array or array, which holds one subarray for each module
 * directive along with a function which validates the value of the
 * directive and also initializes the main handler of this module
 */
static ngx_command_t ngx_http_hello_commands[] = {
    { ngx_string("hello_text"),
      NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      NGX_HTTP_LOC_CONF_OFFSET,
      offsetof(ngx_http_hello_loc_conf_t, name),
      &ngx_http_hello_p },

    ngx_null_command
};


static ngx_str_t hello_string;
 
/*
 * The module context has hooks , here we have a hook for creating
 * location configuration
 */
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 */

    ngx_http_hello_create_loc_conf, /* create location configuration */
    NULL                           /* merge location configuration */
};


/*
 * The module which binds the context and commands
 *
 */
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
};

/*
 * Main handler function of the module.
 */
static ngx_int_t
ngx_http_hello_handler(ngx_http_request_t *r)
{
    /* 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 */
    ngx_int_t rc = ngx_http_discard_request_body(r);
    if (rc != NGX_OK) {
        return rc;
    }

    /* set the 'Content-type' header */
    static const char mime_type[] = "text/html";
    r->headers_out.content_type_len = sizeof(mime_type) - 1;
    r->headers_out.content_type.data = (u_char *) mime_type;

    /* 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 = hello_string.len;
        return ngx_http_send_header(r);
    }

    /* allocate a buffer for your response body */
    ngx_buf_t *b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
    if (b == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    /* adjust the pointers of the buffer */
    b->pos = hello_string.data;
    b->last = hello_string.data + hello_string.len;
    b->memory = 1;    /* this buffer is in memory */
    b->last_buf = 1;  /* this is the last buffer in the buffer chain*/

    /* attach this buffer to the buffer chain */
    ngx_chain_t out = { b, NULL };

    /* set the status line */
    r->headers_out.status = NGX_HTTP_OK;
    r->headers_out.content_length_n = hello_string.len;

    /* 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);
}

/*
 * Function for the directive hello , it validates its value
 * and copies it to a static variable to be printed later
 */
static char *
ngx_http_hello(ngx_conf_t *cf, void *post, void *data)
{
    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;

    ngx_str_t  *name = data; // i.e., first field ofngx_http_hello_loc_conf_t

    if (ngx_strcmp(name->data, "") == 0) {
        return NGX_CONF_ERROR;
    }
    hello_string.data = name->data;
    hello_string.len = ngx_strlen(hello_string.data);

    return NGX_CONF_OK;
}