c - lwip netconn api - 无法接收来自 SNTP 服务器的应答

Question

我正在尝试使用 lwip netconn API(使用 esp-open-rtos)为 ESP8266 编写简单的 SNTP 客户端。问题是我无法从服务器收到答案。

代码(没有错误检查和调试消息):

#include <string.h>

#include <lwip/api.h>
#include <lwip/err.h>

struct sntp_message
{
    u8_t li : 2;
    u8_t vn : 3;
    u8_t mode : 3;
    u8_t stratum;
    u8_t poll;
    u8_t precision;
    u32_t root_delay;
    u32_t root_dispersion;
    u32_t reference_identifier;
    u32_t reference_timestamp[2];
    u32_t originate_timestamp[2];
    u32_t receive_timestamp[2];
    u32_t transmit_timestamp[2];
} __attribute__((packed));

#define SNTP_MSG_LEN (sizeof(struct sntp_message))

int16_t sntp_sync(char* server)
{
    err_t err;
    int16_t result = ERR_OK;
    ip_addr_t sntp_server_address;
    struct netconn* connection = NULL;
    struct netbuf* send_buffer = NULL;
    struct netbuf* receive_buffer = NULL;
    struct sntp_message* send_buffer_data = NULL;

    err = netconn_gethostbyname(server, &sntp_server_address);
    connection = netconn_new(NETCONN_UDP);
    err = netconn_connect(connection, &sntp_server_address, 123);
    send_buffer = netbuf_new();
    send_buffer_data = netbuf_alloc(send_buffer, SNTP_MSG_LEN);
    memset(send_buffer_data, 0, SNTP_MSG_LEN);
    send_buffer_data->vn = 4;
    send_buffer_data->mode = 3; // Mode client.
    err = netconn_send(connection, send_buffer);
    err = netconn_recv(connection, &receive_buffer); // Here netconn_recv block my thread, and no data received. If i set timeout, i have timeout error.
    return result;
}

我的代码有什么问题？我是否需要在接收数据之前绑定(bind)我的连接(通过 netconn_bind)？或者我忘了别的东西？

Answer 1

不要发明自行车。 Simon Goldschmidt 已经为 LwIP 编写了 SNTP。 Link .在那里你可以找到lwip-contrib描述和 git repo 。您还可以在 github 或任何地方寻找镜像(可能会升级)。