mongoose源码解读(二) -- mg_mgr_init 初始化-编程知识

mongoose源码解读(二) -- mg_mgr_init 初始化

在用 mongoose 源码开发的时候，这个初始化函数 mg_mgr_init（）则是必须的，我们看下它到底做了哪些初始化操作。

void mg_mgr_init(struct mg_mgr *m, void *user_data) {struct mg_mgr_init_opts opts;memset(&opts, 0, sizeof(opts));mg_mgr_init_opt(m, user_data, opts);
}

我们是这样调用的 mg_mgr_init(&mgr, nullptr); 所以 user_data 指针为 nullptr，所以mg_mgr_init_opt() 里后两个参数是都是空的。

用户数据指针赋给了入参 m->user_data，接下来就是 interface 相关的赋值了，因为 m->ifaces 是二级指针，所以给它申请了内存：

这里用到了一个全局变量 mg_ifaces，它的定义是这样的

const struct mg_iface_vtable *mg_ifaces[] = {&mg_default_iface_vtable,
};

而这个 mg_default_iface_vtable 就是函数指针的集合，

#define MG_SOCKET_IFACE_VTABLE                                          \{                                                                     \mg_socket_if_init,                                                  \mg_socket_if_free,                                                  \mg_socket_if_add_conn,                                              \mg_socket_if_remove_conn,                                           \mg_socket_if_poll,                                                  \mg_socket_if_listen_tcp,                                            \mg_socket_if_listen_udp,                                            \mg_socket_if_connect_tcp,                                           \mg_socket_if_connect_udp,                                           \mg_socket_if_tcp_send,                                              \mg_socket_if_udp_send,                                              \mg_socket_if_tcp_recv,                                              \mg_socket_if_udp_recv,                                              \mg_socket_if_create_conn,                                           \mg_socket_if_destroy_conn,                                          \mg_socket_if_sock_set,                                              \mg_socket_if_get_conn_addr,                                         \}#if MG_NET_IF == MG_NET_IF_SOCKET
const struct mg_iface_vtable mg_default_iface_vtable = MG_SOCKET_IFACE_VTABLE;
#endif

这些函数指针集合就是对应这个包含了函数指针定义的结构体：

struct mg_iface_vtable {void (*init)(struct mg_iface *iface);void (*free)(struct mg_iface *iface);void (*add_conn)(struct mg_connection *nc);void (*remove_conn)(struct mg_connection *nc);time_t (*poll)(struct mg_iface *iface, int timeout_ms);/* Set up a listening TCP socket on a given address. rv = 0 -> ok. */int (*listen_tcp)(struct mg_connection *nc, union socket_address *sa);/* Request that a "listening" UDP socket be created. */int (*listen_udp)(struct mg_connection *nc, union socket_address *sa);/* Request that a TCP connection is made to the specified address. */void (*connect_tcp)(struct mg_connection *nc, const union socket_address *sa);/* Open a UDP socket. Doesn't actually connect anything. */void (*connect_udp)(struct mg_connection *nc);/* Send functions for TCP and UDP. Sent data is copied before return. */int (*tcp_send)(struct mg_connection *nc, const void *buf, size_t len);int (*udp_send)(struct mg_connection *nc, const void *buf, size_t len);int (*tcp_recv)(struct mg_connection *nc, void *buf, size_t len);int (*udp_recv)(struct mg_connection *nc, void *buf, size_t len,union socket_address *sa, size_t *sa_len);/* Perform interface-related connection initialization. Return 1 on ok. */int (*create_conn)(struct mg_connection *nc);/* Perform interface-related cleanup on connection before destruction. */void (*destroy_conn)(struct mg_connection *nc);/* Associate a socket to a connection. */void (*sock_set)(struct mg_connection *nc, sock_t sock);/* Put connection's address into *sa, local (remote = 0) or remote. */void (*get_conn_addr)(struct mg_connection *nc, int remote,union socket_address *sa);
};

所以像源码里发送、接收数据的调用都是这样调用的：

nc->iface->vtable->tcp_send

nc->iface->vtable->tcp_recv

那调用的都是上面的函数指针，如果是启用了 ssl 的可能又是另外一套函数指针接口了。

其实我们还可以从 GDB 里看到：