LwIP learning socket (API)

Socket API

1.Socket（）

Interface prototype

int
lwip_socket(int domain, int type, int protocol)

Function function ：

Used according to the specified address family 、 Data type and protocol to allocate the description word of a socket interface and the resources it uses

Function into the reference ：

domain Address family AF_INET（IP_V4）、AF_INET6(IP_V6)
type Three protocol types are supported Socket protocol types (TCP/UDP/RAW)

#define SOCK_STREAM 1 // Streaming sockets provide reliable 、 Connection oriented traffic ; It USES TCP  agreement , So as to ensure the correctness and order of data transmission .
#define SOCK_DGRAM 2//  Datagram sockets define a connectionless service  , Data is transmitted through independent messages , Is chaotic , And it's not guaranteed to be reliable 、 Error free . It uses datagram protocol UDP.
#define SOCK_RAW 3//  Raw sockets allow for underlying protocols such as IP or ICMP Make a direct visit , Powerful but inconvenient to use , Mainly used for the development of some protocols .

protocol
The protocol used by the system , Its definition is as follows

#define IPPROTO_IP 0
#define IPPROTO_ICMP 1
#define IPPROTO_TCP 6
#define IPPROTO_UDP 17

Can be protocol The value of the set 0, The system will automatically deduce what protocol should be used . So it is generally written 0.

Return value

Create error return -1
Index number returned after creation

2.blind（）

Interface prototype blind

int
lwip_bind(int s, const struct sockaddr *name, socklen_t namelen)

Function function ：

take sockaddr Some properties described in the structure （IP Address 、 Port number 、 Address cluster ） And socket Socket binding , Also called naming sockets .

Function into the reference ：

int s ：socket() Returns the socket represented by the file descriptor
const struct sockaddr *name： It stores the address and port used by the server for communication .
sockaddr The structure is as follows ：

struct sockaddr {
    
  u8_t sa_len;
  u8_t sa_family;
  char sa_data[14];
};

The actual structure of this parameter depends on the network protocol family , Then add the forced conversion to sockaddr Type in API function . such as AF_INET Will use sockaddr_in Structure as actual structure .
AF_INET6 Will use sockaddr_in6 Structure as actual structure . And then force it to const struct sockaddr *name Solve the warning and error on compilation .

socklen_t namelen
The length of the previous parameter structure .

Return value

Successfully returns 0;
Error return -1; The cause of the error is saved in errno in .（ Generally, the address binding is wrong 、 Port occupied ）

3.listen（）

Interface prototype

int
lwip_listen(int s, int backlog)

Function function ：

listen Function uses the active socket interface to be connected socket interface , Make one process accept requests from other processes , And become a server process .

Function into the reference ：

int s ：socket() Returns the socket represented by the file descriptor
backlog： The length of the listening queue , When the number of connections > This value , The requested connection of the client will be rejected

Return value

Successfully returns 0;
Error return -1;

4.accept（）

Interface prototype

int
lwip_accept(int s, struct sockaddr *addr, socklen_t *addrlen)

Function function ：

Extract the first connection request in the waiting connection queue of the listening socket , Create a new socket , And returns the file descriptor pointing to the socket . It is generally used to block processes in the server , Wait for the client to connect .

Function into the reference ：

With the above blind（） The input parameters of are consistent and will not be repeated here .

Return value

Returns the file descriptor pointing to the socket .
Failure to return ：-1; The cause of the error is saved in errno in .

5.connect（）

Interface prototype

int
lwip_connect(int s, const struct sockaddr *name, socklen_t namelen)

Function function ：

Used to establish and specify socket The connection of . Generally used for client ,

Function into the reference ：

With the above blind（） The input parameters of are consistent and will not be repeated here .

Return value

Successfully returns ：0
Failure to return ：-1; The cause of the error is saved in errno in .

6. read / Write read（）/write（）、recv（）/send（）

Here is lwip in read（） and write（） Function source code , Just for recvfrom（） and send（） Subpackaging
read() Function definition ：

int
lwip_read(int s, void *mem, size_t len)
{
    
  return lwip_recvfrom(s, mem, len, 0, NULL, NULL);
}

write（） Function definition ：

int
lwip_write(int s, const void *data, size_t size)
{
    
  return lwip_send(s, data, size, 0);
}

recv（） Function definition ：

int
lwip_recv(int s, void *mem, size_t len, int flags)
{
    
  return lwip_recvfrom(s, mem, len, flags, NULL, NULL);
}

send（） Function definition ：

int
lwip_send(int s, const void *data, size_t size, int flags)

Function into the reference ：

int s： The socket represented by the target connection file descriptor
const void *data： Pointer to send data
void *mem： Memory address to receive data
int flags： Sign a

7.close（）

Interface prototype

int
lwip_close(int s)

Function function ：

close socket Connect

Function into the reference ：

int s: The socket represented by the file descriptor

Return value

Successfully returns ：0
Failure to return ：-1

First, let's briefly introduce the common socket Of api function , also select（）、lwip_shutdown（） Then fill in . After that, we will analyze each api Source code . Deepen the understanding . If there is something wrong in the article, please point it out