在试验广播消息时（在Windows 7笔记本电脑上的VirtualBox 5.0.14上运行的Debian 8.3 VM上），我发现netcat（nc）只接收第一条广播消息。它不接收第二个广播消息。
这是客户端程序。
If IsLiability Then
Set BalanceCell = .Offset(0, 2).Resize(1, 1)
BalanceCell.FormulaR1C1 = "=""Bal. "" & TEXT(SUM(R[-" & x & "]C:R[-1]C)-SUM(R[-" & x & "]C[1]:R[-1]C[1]),""$#,###"")"
y = Mid(BalanceCell.Value, 6, Len(BalanceCell.Value))
Debug.Print "Common Stock Balance is "; y
这是服务器程序。
// client.c
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
int main()
{
int sockfd;
int ret;
char buffer[1024];
ssize_t bytes;
int yes = 1;
struct addrinfo hints, *ai, *aii;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
if ((ret = getaddrinfo("255.255.255.255", "9090", &hints, &ai)) == -1) {
fprintf(stderr, "client: getaddrinfo() error: %s\n", gai_strerror(ret));
return EXIT_FAILURE;
}
for (aii = ai; aii != NULL; aii = aii->ai_next) {
sockfd = socket(aii->ai_family, aii->ai_socktype, aii->ai_protocol);
if (sockfd == -1) {
perror("client: socket()");
continue;
}
break;
}
freeaddrinfo(ai);
if (aii == NULL) {
fprintf(stderr, "client: cannot create socket\n");
return EXIT_FAILURE;
}
if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &yes, sizeof yes) == -1) {
perror("client: setsockopt()");
return EXIT_FAILURE;
}
// 1st sendto().
strncpy(buffer, "hello from client\n", sizeof buffer);
bytes = sendto(sockfd, buffer, strlen(buffer), 0,
aii->ai_addr, aii->ai_addrlen);
printf("client: sent %jd bytes\n", (intmax_t) bytes);
// 2nd sendto().
strncpy(buffer, "bye from client\n", sizeof buffer);
bytes = sendto(sockfd, buffer, strlen(buffer), 0,
aii->ai_addr, aii->ai_addrlen);
printf("client: sent %jd bytes\n", (intmax_t) bytes);
close(sockfd);
return EXIT_SUCCESS;
}
编制了这些程序。
// server.c
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
int main()
{
int sockfd;
int ret;
struct addrinfo hints, *ai, *aii;
char ip[INET_ADDRSTRLEN];
struct sockaddr_in *sa;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
hints.ai_flags = AI_PASSIVE;
if ((ret = getaddrinfo(NULL, "9090", &hints, &ai)) == -1) {
fprintf(stderr, "server: getaddrinfo() error: %s\n", gai_strerror(ret));
return EXIT_FAILURE;
}
for (aii = ai; aii != NULL; aii = aii->ai_next) {
sockfd = socket(aii->ai_family, aii->ai_socktype, aii->ai_protocol);
if (sockfd == -1) {
perror("socket()");
continue;
}
if (bind(sockfd, aii->ai_addr, aii->ai_addrlen) == -1) {
perror("bind()");
close(sockfd);
continue;
}
break;
}
if (aii == NULL) {
fprintf(stderr, "server: error: could not bind to any address\n");
return EXIT_FAILURE;
}
sa = (struct sockaddr_in *) aii->ai_addr;
inet_ntop(AF_INET, &sa->sin_addr, ip, sizeof ip);
printf("Bound to %s:%d.\n", ip, ntohs(sa->sin_port));
freeaddrinfo(ai);
/* recvfrom() loop */
while (1) {
struct sockaddr_storage conn_addr;
socklen_t conn_addrlen = sizeof conn_addr;
char buffer[1024];
ssize_t bytes;
bytes = recvfrom(sockfd, buffer, sizeof buffer, 0,
(struct sockaddr *) &conn_addr, &conn_addrlen);
if (bytes <= 0)
break;
sa = (struct sockaddr_in *) &conn_addr;
inet_ntop(AF_INET, &sa->sin_addr, ip, sizeof ip);
printf("server: recvfrom() %jd bytes from %s:%d: %.*s",
(intmax_t) bytes, ip, ntohs(sa->sin_port), (int) bytes,
buffer);
}
close(sockfd);
return EXIT_FAILURE;
}
客户端程序显示以下输出。
gcc -std=c99 -pedantic -Wall -Wextra -D_POSIX_C_SOURCE=200112L client.c -o client
gcc -std=c99 -pedantic -Wall -Wextra -D_POSIX_C_SOURCE=200112L server.c -o server
服务器程序接收两个广播消息。
$ ./client
client: sent 18 bytes
client: sent 16 bytes
但是，如果netcat作为端口9090上的侦听器运行，那么它 只接收第一个广播消息。
以下是客户端程序的输出。
$ ./server
Bound to 0.0.0.0:9090.
server: recvfrom() 18 bytes from 10.0.2.15:45807: hello from client
server: recvfrom() 16 bytes from 10.0.2.15:45807: bye from client
服务器程序不接收第二个广播消息。
$ ./client
client: sent 18 bytes
client: sent 16 bytes
接下来修改客户端程序client.c以创建新程序 client2.c，它使它单播。
$ nc -vvnulp 9090
listening on [any] 9090 ...
connect to [10.0.2.15] from (UNKNOWN) [10.0.2.15] 39126
hello from client
以下是客户端程序的输出。
$ diff -u client.c client2.c
--- client.c 2016-10-22 16:13:46.637123187 +0530
+++ client2.c 2016-10-22 16:13:41.313123187 +0530
@@ -16,14 +16,13 @@
int ret;
char buffer[1024];
ssize_t bytes;
- int yes = 1;
struct addrinfo hints, *ai, *aii;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
- if ((ret = getaddrinfo("255.255.255.255", "9090", &hints, &ai)) == -1) {
+ if ((ret = getaddrinfo("10.0.2.15", "9090", &hints, &ai)) == -1) {
fprintf(stderr, "client: getaddrinfo() error: %s\n", gai_strerror(ret));
return EXIT_FAILURE;
}
@@ -44,11 +43,6 @@
return EXIT_FAILURE;
}
- if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &yes, sizeof yes) == -1) {
- perror("client: setsockopt()");
- return EXIT_FAILURE;
- }
-
// 1st sendto().
strncpy(buffer, "hello from client\n", sizeof buffer);
bytes = sendto(sockfd, buffer, strlen(buffer), 0,
这次netcat收到两条单播消息。
$ gcc -std=c99 -pedantic -Wall -Wextra -D_POSIX_C_SOURCE=200112L client2.c -o client2
$ ./client2
client: sent 18 bytes
client: sent 16 bytes
以下是实验2中netcat的系统调用跟踪。
$ nc -vvnulp 9090
listening on [any] 9090 ...
connect to [10.0.2.15] from (UNKNOWN) [10.0.2.15] 55522
hello from client
bye from client
以下是实验3中netcat的系统调用跟踪。
$ strace nc -vvnulp 9090
execve("/bin/nc", ["nc", "-vvnulp", "9090"], [/* 39 vars */]) = 0
brk(0) = 0xc19000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7ed000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=76016, ...}) = 0
mmap(NULL, 76016, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2fcd7da000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\34\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1738176, ...}) = 0
mmap(NULL, 3844640, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f2fcd224000
mprotect(0x7f2fcd3c6000, 2093056, PROT_NONE) = 0
mmap(0x7f2fcd5c5000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a1000) = 0x7f2fcd5c5000
mmap(0x7f2fcd5cb000, 14880, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd5cb000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7d9000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7d8000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7d7000
arch_prctl(ARCH_SET_FS, 0x7f2fcd7d8700) = 0
mprotect(0x7f2fcd5c5000, 16384, PROT_READ) = 0
mprotect(0x605000, 4096, PROT_READ) = 0
mprotect(0x7f2fcd7ef000, 4096, PROT_READ) = 0
munmap(0x7f2fcd7da000, 76016) = 0
getpid() = 4161
brk(0) = 0xc19000
brk(0xc3a000) = 0xc3a000
open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=248, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7ec000
read(3, "# Generated by NetworkManager\nna"..., 4096) = 248
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f2fcd7ec000, 4096) = 0
uname({sys="Linux", node="debian1", ...}) = 0
rt_sigaction(SIGINT, {0x4025d0, [INT], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGQUIT, {0x4025d0, [QUIT], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTERM, {0x4025d0, [TERM], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGURG, {SIG_IGN, [URG], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGPIPE, {SIG_IGN, [PIPE], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_DFL, [], 0}, 8) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3) = 0
open("/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=529, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7ec000
read(3, "# /etc/nsswitch.conf\n#\n# Example"..., 4096) = 529
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f2fcd7ec000, 4096) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=76016, ...}) = 0
mmap(NULL, 76016, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2fcd7da000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu/tls/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu/tls", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0
open("/usr/lib/x86_64-linux-gnu/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/tls/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/tls", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=49152, ...}) = 0
open("/lib/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/tls/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/lib/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/tls", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/lib/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/lib/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/usr/lib/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7ffe5c622430) = -1 ENOENT (No such file or directory)
open("/usr/lib/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0
munmap(0x7f2fcd7da000, 76016) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=76016, ...}) = 0
mmap(NULL, 76016, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2fcd7da000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\"\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=47712, ...}) = 0
mmap(NULL, 2144392, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f2fcd018000
mprotect(0x7f2fcd023000, 2093056, PROT_NONE) = 0
mmap(0x7f2fcd222000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xa000) = 0x7f2fcd222000
close(3) = 0
mprotect(0x7f2fcd222000, 4096, PROT_READ) = 0
munmap(0x7f2fcd7da000, 76016) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2fcd7ec000
read(3, "# Network services, Internet sty"..., 4096) = 4096
read(3, "\t\t# IPX\nipx\t\t213/udp\nimap3\t\t220/"..., 4096) = 4096
read(3, "nessus\t\t1241/tcp\t\t\t# Nessus vuln"..., 4096) = 4096
read(3, "347/tcp\t\t\t# gnutella\ngnutella-rt"..., 4096) = 4096
read(3, "ureg\t779/udp\t\tmoira_ureg\t# Moira"..., 4096) = 3221
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f2fcd7ec000, 4096) = 0
socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 3
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(3, SOL_SOCKET, SO_REUSEPORT, [1], 4) = 0
bind(3, {sa_family=AF_INET, sin_port=htons(9090), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
getsockname(3, {sa_family=AF_INET, sin_port=htons(9090), sin_addr=inet_addr("0.0.0.0")}, [16]) = 0
write(2, "listening on [any] 9090 ...", 27listening on [any] 9090 ...) = 27
write(2, "\n", 1
) = 1
rt_sigaction(SIGALRM, {SIG_IGN, [ALRM], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_DFL, [], 0}, 8) = 0
alarm(0) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
recvfrom(3, "hello from client\n", 8192, MSG_PEEK, {sa_family=AF_INET, sin_port=htons(44926), sin_addr=inet_addr("10.0.2.15")}, [16]) = 18
rt_sigaction(SIGALRM, {SIG_IGN, [ALRM], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, {SIG_IGN, [ALRM], SA_RESTORER|SA_RESTART, 0x7f2fcd2590e0}, 8) = 0
alarm(0) = 0
connect(3, {sa_family=AF_INET, sin_port=htons(44926), sin_addr=inet_addr("10.0.2.15")}, 16) = 0
getsockopt(3, SOL_IP, IP_OPTIONS, "", [0]) = 0
getsockname(3, {sa_family=AF_INET, sin_port=htons(9090), sin_addr=inet_addr("10.0.2.15")}, [16]) = 0
write(2, "connect to [10.0.2.15] from (UNK"..., 55connect to [10.0.2.15] from (UNKNOWN) [10.0.2.15] 44926) = 55
write(2, "\n", 1
) = 1
select(4, [0 3], NULL, NULL, NULL) = 1 (in [3])
read(3, "hello from client\n", 8192) = 18
write(1, "hello from client\n", 18hello from client
) = 18
select(4, [0 3], NULL, NULL, NULL
为什么netcat在实验2中没有收到两个广播消息？
答案 0 :(得分：4)
以下是客户端程序的修改副本。我添加了一些缺少的include语句，删除了一些强制转换，添加了更多错误检查，并且，重要的更改，将调用移动到freeaddrinfo（）。很多。 aii指针指向ai，用于调用sendto（），这不是一个好主意。
现在netcat看到两条消息都发送了，至少在我的机器上运行了Fedora 24.最初的客户端程序实际上在第二次调用sendto（）时报告了一个错误。
HTH
PS：赞成一个非常好的问题。#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(void)
{
int sockfd;
int ret;
ssize_t bytes;
int yes = 1;
struct addrinfo hints, *ai, *aii;
char *msg;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
if ((ret = getaddrinfo("255.255.255.255", "9090", &hints, &ai)) == -1) {
fprintf(stderr, "client: getaddrinfo() error: %s\n", gai_strerror(ret));
return EXIT_FAILURE;
}
for (aii = ai; aii != NULL; aii = aii->ai_next) {
sockfd = socket(aii->ai_family, aii->ai_socktype, aii->ai_protocol);
if (sockfd == -1) {
perror("client: socket()");
continue;
}
break;
}
if (aii == NULL) {
fprintf(stderr, "client: cannot create socket\n");
return EXIT_FAILURE;
}
if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &yes, sizeof yes) == -1) {
perror("client: setsockopt()");
return EXIT_FAILURE;
}
// 1st sendto().
msg = "hello from client\n";
bytes = sendto(sockfd, msg, strlen(msg), 0, aii->ai_addr, aii->ai_addrlen);
if (bytes == -1) {
perror("sendto 1");
return EXIT_FAILURE;
}
printf("client: sent %zd bytes\n", bytes);
// 2nd sendto().
msg = "bye from client\n";
bytes = sendto(sockfd, msg, strlen(msg), 0, aii->ai_addr, aii->ai_addrlen);
if (bytes == -1) {
perror("sendto 2");
return EXIT_FAILURE;
}
printf("client: sent %zd bytes\n", bytes);
close(sockfd);
freeaddrinfo(ai);
return EXIT_SUCCESS;
}