I am having this problem with UDP client/server code. This code was copied from https://www.geeksforgeeks.org/udp-server-client-implementation-c/ and modified minimally to fix compilation errors and print errno in the server code.
// Client side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#define PORT 8080
#define MAXLINE 1024
// Driver code
int main() {
int sockfd;
char buffer[MAXLINE];
char *hello = "Hello from client";
struct sockaddr_in servaddr;
// Creating socket file descriptor
if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0, sizeof(servaddr));
// Filling server information
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(PORT);
servaddr.sin_addr.s_addr = INADDR_ANY;
int n; socklen_t len;
sendto(sockfd, (const char *)hello, strlen(hello),
MSG_CONFIRM, (const struct sockaddr *) &servaddr,
sizeof(servaddr));
printf("Hello message sent.\n");
n = recvfrom(sockfd, (char *)buffer, MAXLINE,
MSG_WAITALL, (struct sockaddr *) &servaddr,
&len);
buffer[n] = '\0';
printf("Server : %s\n", buffer);
close(sockfd);
return 0;
}
// Server side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <errno.h>
#define PORT 8080
#define MAXLINE 1024
// Driver code
int main() {
int sockfd;
char buffer[MAXLINE];
struct sockaddr_in servaddr, cliaddr;
// Creating socket file descriptor
if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
memset(&servaddr, 0, sizeof(servaddr));
memset(&cliaddr, 0, sizeof(cliaddr));
// Filling server information
servaddr.sin_family = AF_INET; // IPv4
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
// Bind the socket with the server address
if ( bind(sockfd, (const struct sockaddr *)&servaddr,
sizeof(servaddr)) < 0 )
{
perror("bind failed");
exit(EXIT_FAILURE);
}
int n; socklen_t len;
n = recvfrom(sockfd, (char *)buffer, MAXLINE,
MSG_WAITALL, ( struct sockaddr *) &cliaddr,
&len);
buffer[n] = '\0';
printf("Client : %s\n", buffer);
int str_len = 0;
sprintf(buffer, "%s", "hello from server");
str_len = strlen(buffer);
printf("Sendinger buffer: <%s>, size=%d\n", buffer, (int) (str_len+1));
n = sendto(sockfd,buffer, (int)(str_len+1),
MSG_CONFIRM, (const struct sockaddr *) &cliaddr,
len);
printf("n=%d, errno=%d\n", n, errno);
printf("Hello message sent.\n");
return 0;
}
I compiled the server and client with straight-forward commands:
g++ udpserv.cpp -o udpserv
g++ client.cpp -o client
What I am seeing is that client succesfully sends the message to the server, server prints the message from client, and when the server sends the reply back to client it gets -1 from sendto and errno is 22. Client remains hung waiting for the reply message.
Here is the output from server:
[user@localhost udpserver]$ ./udpserv
Client : Hello from client
Sendinger buffer: <hello from server>, size=18
n=-1, errno=22
Hello message sent.
[user@localhost udpserver]$
And here is the output from client:
[user@localhost client]$./client
Hello message sent.
