LwIP learning socket (application)

Single connection TCP/IP signal communication

Client and server flowchart

Its flow chart is like making a customer service call , The server can be understood as the customer service phone of China Mobile , We are the client .
The server needs to use Socket（） Register a phone , Use bind（） Bind a phone number 10086,listen（） It's a customer service listening to the phone . Then enter accept（） Blocked . After all, at this time, no one calls and there is no need to deal with anything .
At this time, our client can also use socket（） Register a phone , And then use connect（） call 10086.
The customer service, who was originally idle, heard the jingling phone ring , It will start from accept（） The blocking state of jumps out , There will be a famous TCP Three handshake . after “ feed ~” “ feed ？” “ feed ~” after , You can complain about why you gave me a set meal fee barabarabara ……. then 10086 Give his explanation .
Client side usage close（） The function hung up angrily . adopt Four waves after ,10086 Also used close（） Hung up the phone .

The code analysis ：

If the basic used in the above flow chart socket API If you don't understand, you can read another article of mine 《Socket API piece 》
Here the code uses wildfire 《LwIP Application development practice guide 》 The routine in .

The server

 #include "tcpecho.h"

 #include "lwip/opt.h"

 #if LWIP_SOCKET
 #include <lwip/sockets.h>

 #include "lwip/sys.h"
 #include "lwip/api.h"
 /*--------------------------------------------------------------------*/

 #define PORT 5001
 #define RECV_DATA (1024)


 static void
 tcpecho_thread(void *arg)
 {
    
     int sock = -1,connected;
     char *recv_data;
     struct sockaddr_in server_addr,client_addr;
     socklen_t sin_size;
     int recv_data_len;

     recv_data = (char *)pvPortMalloc(RECV_DATA); // apply 1024 Byte memory , As a storage area for receiving data 
     if (recv_data == NULL)
     {
    
         printf("No memory\n");                  // If the application fails, jump to __exit
         goto __exit;
     }

     sock = socket(AF_INET, SOCK_STREAM, 0);    // Create a socket Socket sock
     if (sock < 0)
     {
    
         printf("Socket error\n");				// Failed to create, jump to __exit
         goto __exit;
     }

     server_addr.sin_family = AF_INET;        // choice IPV4 Protocol family 
     server_addr.sin_addr.s_addr = INADDR_ANY;// Allow any address links 
     server_addr.sin_port = htons(PORT);      // Set the port number 5001
     memset(&(server_addr.sin_zero), 0, sizeof(server_addr.sin_zero));

     if (bind(sock, (struct sockaddr *)&server_addr, sizeof(struct sockaddr)) == -1)// Use bind（） Information configured before binding 
     {
    
         printf("Unable to bind\n");
         goto __exit;
     }

     if (listen(sock, 5) == -1)//sock Monitor at most 5 A link 
     {
    
         printf("Listen error\n");
         goto __exit;
     }

     while (1)
     {
    
         sin_size = sizeof(struct sockaddr_in);

         connected = accept(sock, (struct sockaddr *)&client_addr, &sin_size);// Blocking waiting client Links , If there is no link, the task will enter a blocking state here .

         printf("new client connected from (%s, %d)\n",
             inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));// Print the address and port information of the client 
         {
    
             int flag = 1;

             setsockopt(connected,
                     IPPROTO_TCP,     /* set option at TCP level */
                     TCP_NODELAY,     /* name of option */
                     (void *) &flag, /* the cast is historical cruft */
                     sizeof(int));    /* length of option value */
         }

         while (1)
         {
    
             recv_data_len = recv(connected, recv_data, RECV_DATA, 0);
             // After the client connects, it will block here , Waiting to receive data 

             if (recv_data_len <= 0)
             // If the client disconnects , The client sends FIN package ,recv（） Returns the -1, Get out of this while Loop back to accept（） Blocking 
                 break;

             printf("recv %d len data\n",recv_data_len);

             write(connected,recv_data,recv_data_len);// Writing data 

         }
         if (connected >= 0)
             closesocket(connected);// If there was a customer connection before , The client connection will be closed 

         connected = -1;
     }
 __exit:
     if (sock >= 0) closesocket(sock);// The server socket Create success , Then shut down the server socket
     if (recv_data) free(recv_data);// If the memory request is received successfully , Then release the receiving memory 
 }

 void
 tcpecho_init(void)
 {
    
     sys_thread_new("tcpecho_thread", tcpecho_thread, NULL, 512, 4);
 }

client

 #include "client.h"

 #include "lwip/opt.h"

 #include "lwip/sys.h"
 #include "lwip/api.h"

 #include <lwip/sockets.h>

 #define PORT 5001
 #define IP_ADDR "192.168.0.181"

 static void client(void *thread_param)
 {
    
     int sock = -1;
     struct sockaddr_in client_addr;

     uint8_t send_buf[]= "This is a TCP Client test...\n";

     while (1)
     {
    
         sock = socket(AF_INET, SOCK_STREAM, 0);// Create a client socket It's called sock
         if (sock < 0)
         {
    // If creation fails, delay 10ms Continue to create 
             printf("Socket error\n");
             vTaskDelay(10);
             continue;
         }

         client_addr.sin_family = AF_INET;// Address protocol family set by the server IPV4
         client_addr.sin_port = htons(PORT);// The port number set by the server 
         client_addr.sin_addr.s_addr = inet_addr(IP_ADDR);// The address of the server 
         memset(&(client_addr.sin_zero), 0, sizeof(client_addr.sin_zero));

         if (connect(sock,
                     (struct sockaddr *)&client_addr,
                     sizeof(struct sockaddr)) == -1)// Connect to server 
         {
    // If the connection fails, close socket（） Time delay 10ms Jump out of while（1）
             printf("Connect failed!\n");
             closesocket(sock);
             vTaskDelay(10);
             continue;
         }

         printf("Connect to iperf server successful!\n");

         while (1)
         {
    
             if (write(sock,send_buf,sizeof(send_buf)) < 0)// Writing data 
                 break;

             vTaskDelay(1000);
         }

         closesocket(sock);// Close socket 
     }

 }

 void
 client_init(void)
 {
    
     sys_thread_new("client", client, NULL, 512, 4);
 }

deficiencies ：
The above is provided by wildfire socket The usage of is Duplicate server , Only one connection can be processed at a time . When other clients use connect（） After the connection , If the client does not close（）, Then the server will be blocked in recv（） At function . The correct client connection will not be responded by the server .

Solutions ：
Use select（） function . stay recv（） Before using select（） First check whether the correct connection arrives .
select（） The return value of the function

1. When the corresponding set of file descriptors monitored meets the conditions , For example, when there is data in the read file descriptor set , kernel (I/O) Repair according to the state Change file descriptor set , And return a greater than 0 Number of numbers .
2. When there is no file descriptor that meets the conditions , And set timeval Monitoring time out ,select The function returns a value of 0 Value .
3. When select When a negative value is returned , An error occurred .

Now? FD Add clients to the queue that need to be monitored , Such as keys and com port .
Example reference ：

    FD_ZERO(&rds); 
    FD_SET(button_fd,&rds); // Add keys fd
    FD_SET(com,&rds)// add to com fd

    ret=select(fd+1,&rds,NULL,NULL,NULL); 

    if(ret<0) 
    {
     
        printf("select failure\n"); 
        exit(1); 
    } 

    if(ret==0) 
    {
     
        printf("select timeout\n"); 

    } 
     
    else if(FD_ISSET(button_fd,&rds)) // Key client connection 
    {
     
        read(button_fd,&but_status,sizeof(but_status));           
    } 
  
 
   else if(FD_ISSET(com_fd,&rds)) //com Client connection 
    {
     
        read(.......);           
    } 

reference ：
《LwIP Application development practice guide 》
qicheng777 The blog of