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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()