ESP8266 上的 DNS

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RTOS v2.x 以及之前版本

#define EXAMPLE_DNS         "a3.tuyaus.com"
static void dns_task(void* pvParameters)
{
    printf("Waiting for WiFi access point ...");
    while(!got_ip_flag) {
        vTaskDelay(2000 / portTICK_RATE_MS);
    }

    int ret = 0, retry = 0;
    char *target_name = "www.baidu.com";
    struct hostent *hp = NULL;

    do {
        hp = gethostbyname(target_name);
    } while (hp == NULL && retry++ < 20);

    if(hp) {
        // DNS OK
        printf("DNS lookup succeeded. %s: %s\r\n", target_name, inet_ntoa(*(struct in_addr*)hp->h_addr));
    } else {
        // DNS failed
        printf("DNS failed!\r\n");
    }

    hp = NULL; retry = 0;
    do {
        hp = gethostbyname(EXAMPLE_DNS);
    } while (hp == NULL && retry++ < 20);

    if(hp) {
        // DNS OK
        printf("DNS lookup succeeded. %s: %s\r\n", EXAMPLE_DNS, inet_ntoa(*(struct in_addr*)hp->h_addr));
    } else {
        // DNS failed
        printf("DNS failed!\r\n");
    }

    vTaskDelete(NULL);
}

DNS 调试:

1. include/lwip/arch/cc.h 中打开宏 #define LWIP_DEBUG
2. include/lwip/lwip/opt.h 中使能宏 #define UDP_DEBUG LWIP_DBG_ON
3. 重新编译 lwip 库
4. 编译应用代码

RTOS v3.0 +

#define EXAMPLE_DNS       CONFIG_DNS_DOMAIN_NAME	// config by make menuconfig
static void dns_task(void* pvParameters)
{
    ESP_LOGI(TAG, "Waiting for WiFi access point ...");
    xEventGroupWaitBits(wifi_event_group, CONNECTED_BIT, false, true, portMAX_DELAY);

    int ret = 0, retry = 0;
    char *target_name = "www.baidu.com";
    struct hostent *hp = NULL;

    do {
        hp = gethostbyname(target_name);
        printf("retry1:%d\r\n", retry);
    } while (hp == NULL && retry++ < 20);

    if(hp) {
        // DNS OK
        ESP_LOGI(TAG, "DNS lookup succeeded. %s: %s", target_name, inet_ntoa(*(struct in_addr*)hp->h_addr));
    } else {
        // DNS failed
        ESP_LOGE(TAG, "DNS failed!");
    }

    hp = NULL; retry = 0;
    do {
        hp = gethostbyname(EXAMPLE_DNS);
        printf("retry2:%d\r\n", retry);
    } while (hp == NULL && retry++ < 20);

    if(hp) {
        // DNS OK
        ESP_LOGI(TAG, "DNS lookup succeeded. %s: %s", EXAMPLE_DNS, inet_ntoa(*(struct in_addr*)hp->h_addr));
    } else {
        // DNS failed
        ESP_LOGE(TAG, "DNS failed!");
    }

    vTaskDelete(NULL);
}

DNS 调试:
调试 DNS 建议打开 make menuconfig -> Component config -> LWIP -> Enable lwip Debug -> Enable debugging for DNS.