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连接到来的处理步骤
通过上文知道，RTMP是通过ngx_rtmp_block()方式注册连接到来的回调ngx_rtmp_init_connection(). 当连接来到后，主要有如下几个步骤：
1、初始化RTMP SESSION，通过ngx_rtmp_init_session，这是一具重要结构，这个结构是每个连接保持必要信息，在后续的处理时作为入参使用。
typedef struct {
uint32_t signature; /* "RTMP" */ /* <-- FIXME wtf */
ngx_event_t close;
void **ctx;
void **main_conf;
void **srv_conf;
void **app_conf;
ngx_str_t *addr_text;
int connected;
#if (nginx_version >= 1007005)
ngx_queue_t posted_dry_events;
#else
ngx_event_t *posted_dry_events;
#endif
/* client buffer time in msec */
uint32_t buflen;
uint32_t ack_size;
/* connection parameters */
ngx_str_t app;
ngx_str_t args;
ngx_str_t flashver;
ngx_str_t swf_url;
ngx_str_t tc_url;
uint32_t acodecs;
uint32_t vcodecs;
ngx_str_t page_url;
/* handshake data */
ngx_buf_t *hs_buf;
u_char *hs_digest;
unsigned hs_old:1;
ngx_uint_t hs_stage;
/* connection timestamps */
ngx_msec_t epoch;
ngx_msec_t peer_epoch;
ngx_msec_t base_time;
uint32_t current_time;
/* ping */
ngx_event_t ping_evt;
unsigned ping_active:1;
unsigned ping_reset:1;
/* auto-pushed? */
unsigned auto_pushed:1;
unsigned relay:1;
unsigned static_relay:1;
/* input stream 0 (reserved by RTMP spec)
* is used as free chain link */
ngx_rtmp_stream_t *in_streams;
uint32_t in_csid;
ngx_uint_t in_chunk_size;
ngx_pool_t *in_pool;
uint32_t in_bytes;
uint32_t in_last_ack;
ngx_pool_t *in_old_pool;
ngx_int_t in_chunk_size_changing;
ngx_connection_t *connection;
/* circular buffer of RTMP message pointers */
ngx_msec_t timeout;
uint32_t out_bytes;
size_t out_pos, out_last;
ngx_chain_t *out_chain;
u_char *out_bpos;
unsigned out_buffer:1;
size_t out_queue;
size_t out_cork;
ngx_chain_t *out[0];
} ngx_rtmp_session_t;
2、初始化后如果配置有NGX_RTMP_CONNECT事件，则通过ngx_rtmp_fire_event触发HTTP事件，根据之前文章提到的，在ngx_rtmp_limit_module模块中注册，其回调是ngx_rtmp_limit_connect,此回调主要是判断是否超出了连接限制
3、通过ngx_rtmp_handshake进入握手阶段，通过ngx_rtmp_handshake_done结束
4、进入RTMP消息连循环ngx_rtmp_cycle，就是不停接收RTMP消息，处理RTMP消息。
5、流结束或出错等，都通过ngx_rtmp_finalize_session结束处理
