/*
 * Copyright (C) Igor Sysoev
 */


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


typedef struct {
    ngx_int_t                          cached;

    ngx_http_upstream_init_pt          original_init_upstream;
    ngx_http_upstream_init_peer_pt     original_init_peer;

} ngx_http_upstream_keepalive_srv_conf_t;

typedef struct {
    void                              *data;

    ngx_event_get_peer_pt              original_get_peer;
    ngx_event_free_peer_pt             original_free_peer;

} ngx_http_upstream_keepalive_peer_data_t;


static ngx_int_t ngx_http_upstream_init_keepalive_peer(ngx_http_request_t *r,
    ngx_http_upstream_srv_conf_t *us);
static ngx_int_t ngx_http_upstream_get_keepalive_peer(ngx_peer_connection_t *pc,
    void *data);
static void ngx_http_upstream_free_keepalive_peer(ngx_peer_connection_t *pc,
    void *data, ngx_uint_t state);

static void *ngx_http_upstream_keepalive_create_conf(ngx_conf_t *cf);
static char *ngx_http_upstream_keepalive(ngx_conf_t *cf, ngx_command_t *cmd,
    void *conf);


static ngx_command_t  ngx_http_upstream_keepalive_commands[] = {

    { ngx_string("keepalive"),
      NGX_HTTP_UPS_CONF|NGX_CONF_NOARGS,
      ngx_http_upstream_keepalive,
      0,
      0,
      NULL },

      ngx_null_command
};


static ngx_http_module_t  ngx_http_upstream_keepalive_module_ctx = {
    NULL,                                  /* preconfiguration */
    NULL,                                  /* postconfiguration */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    ngx_http_upstream_keepalive_create_conf, /* create server configuration */
    NULL,                                  /* merge server configuration */

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


ngx_module_t  ngx_http_upstream_keepalive_module = {
    NGX_MODULE_V1,
    &ngx_http_upstream_keepalive_module_ctx, /* module context */
    ngx_http_upstream_keepalive_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
};


ngx_int_t
ngx_http_upstream_init_keepalive(ngx_conf_t *cf,
    ngx_http_upstream_srv_conf_t *us)
{
    ngx_http_upstream_keepalive_srv_conf_t  *kcf;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, cf->log, 0,
                   "init keepalive");

    kcf = ngx_http_conf_upstream_srv_conf(us,
                                          ngx_http_upstream_keepalive_module);

    if (kcf->original_init_upstream(cf, us) != NGX_OK) {
        return NGX_ERROR;
    }

    kcf->original_init_peer = us->peer.init;

    us->peer.init = ngx_http_upstream_init_keepalive_peer;

    return NGX_OK;
}


static ngx_int_t
ngx_http_upstream_init_keepalive_peer(ngx_http_request_t *r,
    ngx_http_upstream_srv_conf_t *us)
{
    ngx_http_upstream_keepalive_peer_data_t  *kp;
    ngx_http_upstream_keepalive_srv_conf_t   *kcf;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "init keepalive peer");

    kcf = ngx_http_conf_upstream_srv_conf(us,
                                          ngx_http_upstream_keepalive_module);

    kp = ngx_palloc(r->pool, sizeof(ngx_http_upstream_keepalive_peer_data_t));
    if (kp == NULL) {
        return NGX_ERROR;
    }

    if (kcf->original_init_peer(r, us) != NGX_OK) {
        return NGX_ERROR;
    }

    kp->data = r->upstream->peer.data;
    kp->original_get_peer = r->upstream->peer.get;
    kp->original_free_peer = r->upstream->peer.free;

    r->upstream->peer.data = kp;
    r->upstream->peer.get = ngx_http_upstream_get_keepalive_peer;
    r->upstream->peer.free = ngx_http_upstream_free_keepalive_peer;

    return NGX_OK;
}


static ngx_int_t
ngx_http_upstream_get_keepalive_peer(ngx_peer_connection_t *pc, void *data)
{
    ngx_http_upstream_keepalive_peer_data_t  *kp = data;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, pc->log, 0,
                   "get keepalive peer");

    return kp->original_get_peer(pc, kp->data);
}


static void
ngx_http_upstream_free_keepalive_peer(ngx_peer_connection_t *pc, void *data,
    ngx_uint_t state)
{
    ngx_http_upstream_keepalive_peer_data_t  *kp = data;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, pc->log, 0,
                   "free keepalive peer");

    return kp->original_free_peer(pc, kp->data, state);
}


static void *
ngx_http_upstream_keepalive_create_conf(ngx_conf_t *cf)
{
    ngx_http_upstream_keepalive_srv_conf_t  *conf;

    conf = ngx_pcalloc(cf->pool,
                       sizeof(ngx_http_upstream_keepalive_srv_conf_t));
    if (conf == NULL) {
        return NGX_CONF_ERROR;
    }

    /*
     * set by ngx_pcalloc():
     *
     *     conf->cached = 0;
     *     conf->original_init_upstream = NULL;
     *     conf->original_init_peer = NULL;
     */

    return conf;
}


static char *
ngx_http_upstream_keepalive(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_upstream_srv_conf_t            *uscf;
    ngx_http_upstream_keepalive_srv_conf_t  *kcf;

    uscf = ngx_http_conf_get_module_srv_conf(cf, ngx_http_upstream_module);

    kcf = ngx_http_conf_upstream_srv_conf(uscf,
                                          ngx_http_upstream_keepalive_module);

    kcf->original_init_upstream = uscf->peer.init_upstream
                                  ? uscf->peer.init_upstream
                                  : ngx_http_upstream_init_round_robin;

    uscf->peer.init_upstream = ngx_http_upstream_init_keepalive;

    return NGX_CONF_OK;
}