http框架核心之ngx_http.c源码分析

ngx_http.c内主要实现了一个模块:ngx_http_module。ngx_http_module是nginx的http框架的一部分，它是所有http模块能够被加载的唯一入口，承担了http块配置解析，合并，以及http框架及其相关数据结构的初始化。它本身是NGX_CORE_MODULE类型，只有一个指令，就是http，如下所示:
static ngx_command_t ngx_http_commands[] = {

{ ngx_string("http"),
NGX_MAIN_CONF|NGX_CONF_BLOCK|NGX_CONF_NOARGS,
ngx_http_block,
0,
0,
NULL },

ngx_null_command
};这个http指令就是我们在nginx配置文件中看到的http块指令。当nginx遇到这个http块指令的时候，会执行ngx_http_block回调，ngx_http_block的代码如下所示:
static char *
ngx_http_block(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
char *rv;
ngx_uint_t mi, m, s;
ngx_conf_t pcf;
ngx_http_module_t *module;
ngx_http_conf_ctx_t *ctx;
ngx_http_core_loc_conf_t *clcf;
ngx_http_core_srv_conf_t **cscfp;
ngx_http_core_main_conf_t *cmcf;

/* 判断http指令是否有重复，不允许存在多个http块指令 */
if (*(ngx_http_conf_ctx_t **) conf) {
return "is duplicate";
}

/* the main http context */

/* 创建配置上下文 */
ctx = ngx_pcalloc(cf->pool, sizeof(ngx_http_conf_ctx_t));
if (ctx == NULL) {
return NGX_CONF_ERROR;
}
/* 将创建好的上下文地址赋值给conf，这里的conf是cycle->conf_ctx[ngx_htp_module.index],index是
* ngx_http_module在所有模块中的位置 */
*(ngx_http_conf_ctx_t **) conf = ctx;

/* count the number of the http modules and set up their indices */
/* 计算http模块数量并且为每个http模块设置ctx_index，ctx_index是http模块在所有http模块中的位置 */
ngx_http_max_module = ngx_count_modules(cf->cycle, NGX_HTTP_MODULE);

/* the http main_conf context, it is the same in the all http contexts */
/* 创建main级别的http配置上下文 */
ctx->main_conf = ngx_pcalloc(cf->pool,
sizeof(void *) * ngx_http_max_module);
if (ctx->main_conf == NULL) {
return NGX_CONF_ERROR;
}

/*
* the http null srv_conf context, it is used to merge
* the server{}s' srv_conf's
*/
/* 创建main级别的http server配置上下文 */
ctx->srv_conf = ngx_pcalloc(cf->pool, sizeof(void *) * ngx_http_max_module);
if (ctx->srv_conf == NULL) {
return NGX_CONF_ERROR;
}

/*
* the http null loc_conf context, it is used to merge
* the server{}s' loc_conf's
*/
/* 创建main级别的http location配置文件上下文 */
ctx->loc_conf = ngx_pcalloc(cf->pool, sizeof(void *) * ngx_http_max_module);
if (ctx->loc_conf == NULL) {
return NGX_CONF_ERROR;
}

/*
* create the main_conf's, the null srv_conf's, and the null loc_conf's
* of the all http modules
*/
/* 遍历所有http模块，调用它们的create_main_conf,create_srv_conf,create_loc_conf
* 回调函数创建各http模块的配置上下文 */
for (m = 0; cf->cycle->modules[m]; m++) {
if (cf->cycle->modules[m]->type != NGX_HTTP_MODULE) {
continue;
}

module = cf->cycle->modules[m]->ctx;
mi = cf->cycle->modules[m]->ctx_index;

if (module->create_main_conf) {
ctx->main_conf[mi] = module->create_main_conf(cf);
if (ctx->main_conf[mi] == NULL) {
return NGX_CONF_ERROR;
}
}

if (module->create_srv_conf) {
ctx->srv_conf[mi] = module->create_srv_conf(cf);
if (ctx->srv_conf[mi] == NULL) {
return NGX_CONF_ERROR;
}
}

if (module->create_loc_conf) {
ctx->loc_conf[mi] = module->create_loc_conf(cf);
if (ctx->loc_conf[mi] == NULL) {
return NGX_CONF_ERROR;
}
}
}

/* 保存当前配置解析上下文环境 */
pcf = *cf;

/* 将当前配置解析上下文环境设置成ctx */
cf->ctx = ctx;

for (m = 0; cf->cycle->modules[m]; m++) {
if (cf->cycle->modules[m]->type != NGX_HTTP_MODULE) {
continue;
}

module = cf->cycle->modules[m]->ctx;

if (module->preconfiguration) {
if (module->preconfiguration(cf) != NGX_OK) {
return NGX_CONF_ERROR;
}
}
}

/* parse inside the http{} block */
/* 将当前配置解析上下文环境切换为http块 */
cf->module_type = NGX_HTTP_MODULE;
cf->cmd_type = NGX_HTTP_MAIN_CONF;
/* 解析http块内指令 */
rv = ngx_conf_parse(cf, NULL);

if (rv != NGX_CONF_OK) {
goto failed;
}

/*
* init http{} main_conf's, merge the server{}s' srv_conf's
* and its location{}s' loc_conf's
*/
/* 调用所有http模块的init_main_conf，完成全局配置的最后设置，并合并配置 */
cmcf = ctx->main_conf[ngx_http_core_module.ctx_index];
cscfp = cmcf->servers.elts;

for (m = 0; cf->cycle->modules[m]; m++) {
if (cf->cycle->modules[m]->type != NGX_HTTP_MODULE) {
continue;
}

module = cf->cycle->modules[m]->ctx;
mi = cf->cycle->modules[m]->ctx_index;

/* init http{} main_conf's */

if (module->init_main_conf) {
rv = module->init_main_conf(cf, ctx->main_conf[mi]);
if (rv != NGX_CONF_OK) {
goto failed;
}
}

rv = ngx_http_merge_servers(cf, cmcf, module, mi);
if (rv != NGX_CONF_OK) {
goto failed;
}
}

/* create location trees */
/* 为所有server块创建location队列和静态location查找数 */
for (s = 0; s < cmcf->servers.nelts; s++) {

clcf = cscfp[s]->ctx->loc_conf[ngx_http_core_module.ctx_index];

if (ngx_http_init_locations(cf, cscfp[s], clcf) != NGX_OK) {
return NGX_CONF_ERROR;
}

if (ngx_http_init_static_location_trees(cf, clcf) != NGX_OK) {
return NGX_CONF_ERROR;
}
}

/* 初始化http框架的11个阶段 */
if (ngx_http_init_phases(cf, cmcf) != NGX_OK) {
return NGX_CONF_ERROR;
}

/* 创建http首部哈希表，方便处理请求时快速查找 */
if (ngx_http_init_headers_in_hash(cf, cmcf) != NGX_OK) {
return NGX_CONF_ERROR;
}

/* 调用所有http模块的postconfiguration回调函数。postconfiguration回调函数
* 多用于实现模块介入http处理的不同阶段 */
for (m = 0; cf->cycle->modules[m]; m++) {
if (cf->cycle->modules[m]->type != NGX_HTTP_MODULE) {
continue;
}

module = cf->cycle->modules[m]->ctx;

if (module->postconfiguration) {
if (module->postconfiguration(cf) != NGX_OK) {
return NGX_CONF_ERROR;
}
}
}

/* nginx的http变量初始化，包括设置索引，变量值获取方法，创建变量哈希表等 */
if (ngx_http_variables_init_vars(cf) != NGX_OK) {
return NGX_CONF_ERROR;
}

/*
* http{}'s cf->ctx was needed while the configuration merging
* and in postconfiguration process
*/
/* 将配置解析上下文环境还原成被调用前状态 */
*cf = pcf;

/* 为http各阶段设置处理函数及处理顺序 */
if (ngx_http_init_phase_handlers(cf, cmcf) != NGX_OK) {
return NGX_CONF_ERROR;
}

/* optimize the lists of ports, addresses and server names */
/* 构造server虚拟主机构成的支持通配符的哈希表，并且设置监听端口与server间的关联关系，
* 并且把所有http块内的监听端口的新建连接(accept)的回调函数设置为ngx_http_init_connection */
if (ngx_http_optimize_servers(cf, cmcf, cmcf->ports) != NGX_OK) {
return NGX_CONF_ERROR;
}

return NGX_CONF_OK;

failed:
/* 将配置解析上下文环境还原成被调用前状态 */
*cf = pcf;

return rv;
}