ESP-IDF teaching WiFi of ESP32 -- TCP communication of LwIP

This article comes from the secondary column WiFi and Lwip protocol stack on ESP32 under the original column ESP32 teaching column (based on ESP-IDF), which explains how to use ESP-IDF to build ESP32 programs, publish articles and continue to add new content to published articles! Every article has been finely polished!

1, Establish connection - ESP32 as TCP Client

1. Basic idea of TCP client

2. TCP Client code example

The following code is a TCP function_ Task_ The client implements a FreeRTOS Task, in which the following contents are completed:

Wait for WiFi connection to succeed (Event Group based on FreeRTOS API)
Create a Socket object and initially set it to TCP (note line 7 of the code), and check whether the Socket is created successfully.
Configure the connection parameter structure (struct sockaddr_in type desk_addr)
Connect the server circularly until the connection is successful

See notes for details

void tcp_task_client(void *arg){ xEventGroupWaitBits(wifiEvent, wifiConnectedBit, pdFALSE, pdFALSE, portMAX_DELAY); int _socket; createSocket: // label _socket = socket(AF_INET, SOCK_STREAM, IPPROTO_IP); // AF_INET indicates IPv4, AF_INET6 stands for IPv6 // SOCK_STREAM means TCP; // SOCK_DGRAM stands for UDP; // SOCK_RAW means RAW // Protocol, which specifies which type of protocol data the socket sends and receives. // The most common is IPPROTO_TCP, IPPROTO_UDP, IPPROTO_UDPLITE,IPPROTO_ICMP. // If domain and type have determined a unique protocol, "0 (IPPROTO_IP)" can be used to select a default protocol. if(_socket < 0){ printf("Socket Creation failed, Error code:%d\n", errno); vTaskDelete(NULL); }else{ printf("Socket Created successfully"); } struct sockaddr_in desk_addr = { // The following IP 192.168.31.138 and port number 8080 are set by yourself. Please modify them as needed .sin_addr.s_addr = inet_addr("192.168.31.138"), .sin_family = AF_INET, .sin_port = htons(8080), // Small end mode to large end mode }; int err; while (1) { err = connect(_socket, (struct sockaddr*)&desk_addr, sizeof(desk_addr)); if (err == 0){ ESP_LOGI("CLIENT", "Connection succeeded"); break; }else{ ESP_LOGI("CLIENT", "Connection failed with error code:%d", errno); close(_socket); vTaskDelay(pdMS_TO_TICKS(200)); goto createSocket; // goto tag } } vTaskDelete(NULL); }

2, Establish connection - ESP32 as TCP Server

1. Code example

The following code is a TCP function_ Task_ Server implements a FreeRTOS Task, in which the following contents are completed:

Wait for WiFi connection to succeed (Event Group based on FreeRTOS API)
Create a Socket object and initially set it to TCP (note line 7 of the code), and check whether the Socket is created successfully.
Configure the connection parameter structure (struct sockaddr_in type desk_addr)
binding
Start listening
Execute the accept function to remove the Socket from the client Sockets that have established a TCP connection (this function will block, so please make it appear in the appropriate position as needed)

See notes for details

void tcp_task_server(void *arg){ xEventGroupWaitBits(wifiEvent, wifiConnectedBit, pdFALSE, pdFALSE, portMAX_DELAY); int _socket = socket(AF_INET, SOCK_STREAM, IPPROTO_IP); if(_socket < 0){ printf("Socket Creation failed, Error code:%d\n", errno); vTaskDelete(NULL); }else{ printf("Socket Created successfully"); } struct sockaddr_in desk_addr = { .sin_addr.s_addr = INADDR_ANY, .sin_family = AF_INET, .sin_port = htons(2501), // Small end mode to large end mode }; int err; while(1){ err = bind(_socket, (struct sockaddr*)&desk_addr, sizeof(desk_addr)); if(err == 0){ ESP_LOGI("SERVICE", "Binding succeeded"); break; }else{ ESP_LOGI("SERVICE", "Binding failed, error code : %d", errno); } vTaskDelay(pdMS_TO_TICKS(1000)); } err = listen(_socket, 5); if (err != 0){ ESP_LOGI("SERVICE", "Listening failed, error code: %d", errno); vTaskDelete(NULL); }else{ ESP_LOGI("SERVICE", "Listening succeeded"); } while (1){ struct sockaddr_in6 source_addr; uint addr_len; ESP_LOGI("SERVICE", "get ready accept"); int remote_sock = accept(_socket, (struct sockaddr *) &source_addr, &addr_len); //xTaskNotifyGive(tcp_client_handle); if(remote_sock < 0){ ESP_LOGI("SERVICE", "accept Failed, error code: %d", errno); }else{ ESP_LOGI("SERVICE", "Connection succeeded"); break; } vTaskDelay(pdMS_TO_TICKS(1000)); } vTaskDelete(NULL); }

3, Send and receive data

4, LwIP BSD API functions related to TCP/UDP

socket() bind() listen() connect() accept() send(), recv(), sendto(), recvfrom() close() gethostbyname() select() pool() getsockopt(), setsockopt()

Function namesocket()Function prototypeint socket(int domain, int type, int protocol)meaningThe function socket() creates an endpoint for communication and returns a file descriptor for the socket.Return valueint, returns - 1 if an error occursparameterdomain type: int; Represents the protocol family you want to create.
For example: AF_INET means IPv4,
AF_INET6 indicates IPv6,
AF_UNIX represents a local socket

type: int;
E.g. SOCK_STREAM means TCP,
SOCK_DGRAM stands for UDP,
SOCK_SEQPACKET means reliable sequential package service,
SOCK_RAW represents the original protocol on the network layer

The protocol type is: int; Indicates the actual transport protocol to use. The most common is IPPROTO_TCP, IPPROTO_SCTP, IPPROTO_UDP, IPPROTO_DCCP, etc. If 0 (IPPRORO_IP) is filled in, the protocol will be automatically selected according to the first two parameters