nginx的源码确实比较难读，一大堆的函数回调指针，没有理清脉络，看源码就很费劲。
首先，要理顺nginx调用的主框架，nginx是以配置为中心的处理架构，想读懂，先了解配置。
nginx处理的一个阶段，
复制代码 代码示例:
typedef enum {
NGX_HTTP_POST_READ_PHASE = 0, //读取请求头
NGX_HTTP_SERVER_REWRITE_PHASE, //执行rewrite
NGX_HTTP_FIND_CONFIG_PHASE, //根据uri替换location
NGX_HTTP_REWRITE_PHASE, //根据替换结果继续执行rewrite
NGX_HTTP_POST_REWRITE_PHASE, //执行rewrite后处理
NGX_HTTP_PREACCESS_PHASE, //认证预处理 请求限制，连接限制
NGX_HTTP_ACCESS_PHASE, //认证处理
NGX_HTTP_POST_ACCESS_PHASE, //认证后处理， 认证不通过， 丢包
NGX_HTTP_TRY_FILES_PHASE, //尝试try标签
NGX_HTTP_CONTENT_PHASE, //内容处理
NGX_HTTP_LOG_PHASE //日志处理
} ngx_http_phases;
以上每个阶段的处理都是一个数组回调。
数据的初始化：
复制代码 代码示例:
static ngx_int_t
ngx_http_init_phases(ngx_conf_t *cf, ngx_http_core_main_conf_t *cmcf)
{
if (ngx_array_init(&cmcf->phases[NGX_HTTP_POST_READ_PHASE].handlers,
cf->pool, 1, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
if (ngx_array_init(&cmcf->phases[NGX_HTTP_SERVER_REWRITE_PHASE].handlers,
cf->pool, 1, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
if (ngx_array_init(&cmcf->phases[NGX_HTTP_REWRITE_PHASE].handlers,
cf->pool, 1, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
if (ngx_array_init(&cmcf->phases[NGX_HTTP_PREACCESS_PHASE].handlers,
cf->pool, 1, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
if (ngx_array_init(&cmcf->phases[NGX_HTTP_ACCESS_PHASE].handlers,
cf->pool, 2, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
if (ngx_array_init(&cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers,
cf->pool, 4, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
if (ngx_array_init(&cmcf->phases[NGX_HTTP_LOG_PHASE].handlers,
cf->pool, 1, sizeof(ngx_http_handler_pt))
!= NGX_OK)
{
return NGX_ERROR;
}
return NGX_OK;
}
可以看到：
NGX_HTTP_FIND_CONFIG_PHASE, //根据uri替换location
NGX_HTTP_POST_REWRITE_PHASE, //执行rewrite后处理
NGX_HTTP_POST_ACCESS_PHASE, //认证后处理， 认证不通过， 丢包
以上几个阶段都没有做数组的初始化化。
另外，真正执行时，并不是调用cmcf->phases处理的，而是调用cmcf->phase_engine.handlers。
复制代码 代码示例:
void ngx_http_core_run_phases(ngx_http_request_t *r)
{
ngx_int_t rc;
ngx_http_phase_handler_t *ph;
ngx_http_core_main_conf_t *cmcf;
cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
ph = cmcf->phase_engine.handlers;
while (ph[r->phase_handler].checker) {
rc = ph[r->phase_handler].checker(r, &ph[r->phase_handler]);
if (rc == NGX_OK) { //只要return不为NGX_OK就继续执行。
return;
}
}
}
phase_engine的初始化：
复制代码 代码示例:
static ngx_int_t
ngx_http_init_phase_handlers(ngx_conf_t *cf, ngx_http_core_main_conf_t *cmcf)
{
ngx_int_t j;
ngx_uint_t i, n;
ngx_uint_t find_config_index, use_rewrite, use_access;
ngx_http_handler_pt *h;
ngx_http_phase_handler_t *ph;
ngx_http_phase_handler_pt checker;
cmcf->phase_engine.server_rewrite_index = (ngx_uint_t) -1;
cmcf->phase_engine.location_rewrite_index = (ngx_uint_t) -1;
find_config_index = 0;
use_rewrite = cmcf->phases[NGX_HTTP_REWRITE_PHASE].handlers.nelts ? 1 : 0;
use_access = cmcf->phases[NGX_HTTP_ACCESS_PHASE].handlers.nelts ? 1 : 0;
n = use_rewrite + use_access + cmcf->try_files + 1 /* find config phase */;
for (i = 0; i < NGX_HTTP_LOG_PHASE; i++) {
n += cmcf->phases[i].handlers.nelts;
}
ph = ngx_pcalloc(cf->pool,
n * sizeof(ngx_http_phase_handler_t) + sizeof(void *));
if (ph == NULL) {
return NGX_ERROR;
}
cmcf->phase_engine.handlers = ph;
n = 0;
for (i = 0; i < NGX_HTTP_LOG_PHASE; i++) {
h = cmcf->phases[i].handlers.elts;
switch (i) {
case NGX_HTTP_SERVER_REWRITE_PHASE:
if (cmcf->phase_engine.server_rewrite_index == (ngx_uint_t) -1) {
cmcf->phase_engine.server_rewrite_index = n;
}
checker = ngx_http_core_rewrite_phase;
break;
case NGX_HTTP_FIND_CONFIG_PHASE:
find_config_index = n;
ph->checker = ngx_http_core_find_config_phase;
n++;
ph++;
continue;
case NGX_HTTP_REWRITE_PHASE:
if (cmcf->phase_engine.location_rewrite_index == (ngx_uint_t) -1) {
cmcf->phase_engine.location_rewrite_index = n;
}
checker = ngx_http_core_rewrite_phase;
break;
case NGX_HTTP_POST_REWRITE_PHASE:
if (use_rewrite) {
ph->checker = ngx_http_core_post_rewrite_phase;
ph->next = find_config_index;
n++;
ph++;
}
continue;
case NGX_HTTP_ACCESS_PHASE:
checker = ngx_http_core_access_phase;
n++;
break;
case NGX_HTTP_POST_ACCESS_PHASE:
if (use_access) {
ph->checker = ngx_http_core_post_access_phase;
ph->next = n;
ph++;
}
continue;
case NGX_HTTP_TRY_FILES_PHASE:
if (cmcf->try_files) {
ph->checker = ngx_http_core_try_files_phase;
n++;
ph++;
}
continue;
case NGX_HTTP_CONTENT_PHASE:
checker = ngx_http_core_content_phase;
break;
default:
checker = ngx_http_core_generic_phase;
}
n += cmcf->phases[i].handlers.nelts;
for (j = cmcf->phases[i].handlers.nelts - 1; j >=0; j--) {
ph->checker = checker;
ph->handler = h[j]; //数组是反向赋值的，刚好对应了数组操作的顺序
ph->next = n; //next永远执行下一个阶段的执行索引
ph++;
}
}
return NGX_OK;
}
从上面可以看到，nginx把所有阶段的回调函数组成了一个串行的执行函数数组。
cheker指针指向检测调用函数指针，hander指向该阶段的函数调用指针，next则指向下一阶段的ph索引。
当执行某一阶段到一半的时候，想跳到下一个阶段，只需要r->phase_handler = ph->next;
ph的返回值为NGX_OK时， 函数会跳出阶段的执行，但是在阶段执行的hander中却不是这样的。
NGX_DECLINED: 会直接执行下一个ph调用。
NGX_AGAIN: 会重复调用本ph
NGX_DOWN：终止阶段函数回调调用。
