setup outcoming UDP port socket with constant port in esp32-CodePudding

How do I setup outcoming port socket constantly in ESP32? My full program is possible to destroy socket by close and recreate new socket. But I want new socket is keep using same port number.

I'm using sendto, whenever my program send data to a target UDP server, that server is seeing it as come from random port, commonly the port value is above 50000 and increment 1 everytime I recreate new socket. How do I make my UDP client constantly like 8888 so the UDP server will see it data come from port 8888?

this is how I define my UDP socket client:

int udpSock = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
struct timeval timeout;
timeout.tv_sec = sec;
timeout.tv_usec = usec;
setsockopt(uwcSock, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof timeout);

UDP Client: ESP32

UDP Server: <any platform, doesn't matter with question>

Update: I tried bind but the port still dynamic.


static u16_t CLNT_PORT = 8888;
static int uwcSock = 0;
struct sockaddr_in destAddr;
struct sockaddr_in clientAddr;
struct timeval timeout;

esp_err_t uwc_udp_init() {
  if (!uwcIsWifiInit) {
    return ESP_FAIL;
  }

  close(uwcSock);

  isUdpInit = false;

  destAddr.sin_addr.s_addr = inet_addr(SERV_IPV4);
  destAddr.sin_family = AF_INET;
  destAddr.sin_port = htons(SERV_PORT);

  clientAddr.sin_addr.s_addr = htonl(INADDR_ANY);
  clientAddr.sin_family = AF_INET;
  clientAddr.sin_port = htons(CLNT_PORT);

  uwcSock = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
  if (uwcSock < 0) {
    ESP_LOGE(uwc_tag_udp, "Unable to create socket: errno %d", errno);
    return ESP_FAIL;
  }

  int err = bind(uwcSock, (struct sockaddr*)&clientAddr, sizeof(clientAddr));
  if (err < 0) {
    ESP_LOGE(uwc_tag_udp, "Socket unable to bind: errno %d", errno);
  }
  ESP_LOGI(uwc_tag_udp, "Socket bound, port %d", 9999);

  uwc_udp_set_timeout(1, 0);
  int opt = 1;
  setsockopt(uwcSock, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
  uwc_udp_flush();
  uwc_udp_handshake();

  isUdpInit = true;

  ESP_LOGI(uwc_tag_udp, "ACK received!");
  ESP_LOGI(uwc_tag_udp, "UDP has been initialized!");
  return ESP_OK;
}

CodePudding user response：

You have to bind your client with bind function. With this function you are able to set an IP and port for your client. Here is bind function api:
int bind(int socket, const struct sockaddr *address, socklen_t address_len);
In sockaddr_in struct you can set your client IP and port for IPv4 and in sockaddr_in6 struct for IPv6. To use these structures in bind function, you need to cast them to sockaddr structure.