我在Linux上运行客户端和服务器代码。
服务器使用带有AF_INET和SOCK_STREAM协议的TCP / IP。
首先，在客户端，我（错误地？）使用bind从addr_info返回的链接列表中获取正确的getaddrinfo，并返回相应的sockaddr_in。我在客户端有一个看起来像这样的方法：
struct sockaddr_in *hostname_to_ip(char *hostname, struct addrinfo *servinfo)
{
int check_sfd;
struct addrinfo hints, *p;
//struct sockaddr_in* ret_value;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
int res = getaddrinfo(hostname, NULL, &hints, &servinfo)
if (res != 0) {
fprintf(stderr, "Error: error in getaddrinfo on hostname: %s\n", gai_strerror(res));
exit(EXIT_FAILURE);
}
// getaddrinfo returned a linked list of relevant addresses
// loop through the addresses and return the first one available
for (p = servinfo; p != NULL; p = p->ai_next) {
check_sfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if (checksfd < 0)
continue;
if (bind(check_sfd, p->ai_addr, p->ai_addrlen) == 0) { // bind successful
return (struct sockaddr_in*) p->ai_addr;
}
}
return NULL;
}
稍后连接到connect中的返回值。
代码的形式运行良好，客户端和服务器之间的连接成功建立（并且所有功能都有效）。但是，由于未正确使用freeaddrinfo，我发生了内存泄漏。
所以我决定将代码更改为以下内容：
void hostname_to_ip(char *hostname, int *connection)
{
int check_sfd;
struct addrinfo hints, *p, *servinfo;
//struct sockaddr_in* ret_value;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
int res = getaddrinfo(hostname, NULL, &hints, &servinfo)
if (res != 0) {
fprintf(stderr, "Error: error in getaddrinfo on hostname: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
// getaddrinfo returned a linked list of relevant addresses
// loop through the addresses and return the first one available
for (p = servinfo; p != NULL; p = p->ai_next) {
check_sfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if (check_sfd == -1)
continue;
if (connect(check_sfd, p->ai_addr, p->ai_addrlen) == 0) { // connection successful
*connection = check_sfd;
break;
}
close(check_sfd);
}
if (p == NULL) {
// print error
exit(EXIT_FAILURE);
}
freeaddrinfo(&servinfo);
}
但是，现在我似乎无法连接到服务器，因为connect始终返回-1（p以非NULL开头，因此连接到套接字失败了）。错误是connection refused。
当我将ai_socktype更改为SOCK_DGRAM时，连接成功但客户端在发送数据时失败（因为服务器正在使用SOCK_STREAM），这很有意思，这很奇怪
有什么想法吗？客户端和服务器的代码很长，所以我没有附加所有这些代码，但我尝试添加所有相关信息。如果遗漏了任何内容，请发表评论，我会添加它。
这是客户端上的strace信息：
execve("./pcc_client", ["./pcc_client", "localhost", "2001", "1000"], [/* 71 vars */]) = 0
brk(NULL) = 0x2446000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
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=88205, ...}) = 0
mmap(NULL, 88205, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f0a0f4fa000
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\t\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1868984, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f0a0f4f9000
mmap(NULL, 3971488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f0a0ef21000
mprotect(0x7f0a0f0e1000, 2097152, PROT_NONE) = 0
mmap(0x7f0a0f2e1000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c0000) = 0x7f0a0f2e1000
mmap(0x7f0a0f2e7000, 14752, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f0a0f2e7000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f0a0f4f8000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f0a0f4f7000
arch_prctl(ARCH_SET_FS, 0x7f0a0f4f8700) = 0
mprotect(0x7f0a0f2e1000, 16384, PROT_READ) = 0
mprotect(0x601000, 4096, PROT_READ) = 0
mprotect(0x7f0a0f510000, 4096, PROT_READ) = 0
munmap(0x7f0a0f4fa000, 88205) = 0
socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
getsockname(3, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, [16]) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
connect(4, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(4) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
connect(4, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(4) = 0
brk(NULL) = 0x2446000
brk(0x2467000) = 0x2467000
open("/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=529, ...}) = 0
read(4, "# /etc/nsswitch.conf\n#\n# Example"..., 4096) = 529
read(4, "", 4096) = 0
close(4) = 0
open("/etc/host.conf", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=92, ...}) = 0
read(4, "# The \"order\" line is only used "..., 4096) = 92
read(4, "", 4096) = 0
close(4) = 0
getpid() = 12014
open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=184, ...}) = 0
read(4, "# Dynamic resolv.conf(5) file fo"..., 4096) = 184
read(4, "", 4096) = 0
close(4) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=88205, ...}) = 0
mmap(NULL, 88205, PROT_READ, MAP_PRIVATE, 4, 0) = 0x7f0a0f4fa000
close(4) = 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) = 4
read(4, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260!\0\0\0\0\0\0"..., 832) = 832
fstat(4, {st_mode=S_IFREG|0644, st_size=47600, ...}) = 0
mmap(NULL, 2168600, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 4, 0) = 0x7f0a0ed0f000
mprotect(0x7f0a0ed1a000, 2093056, PROT_NONE) = 0
mmap(0x7f0a0ef19000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 4, 0xa000) = 0x7f0a0ef19000
mmap(0x7f0a0ef1b000, 22296, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f0a0ef1b000
close(4) = 0
mprotect(0x7f0a0ef19000, 4096, PROT_READ) = 0
munmap(0x7f0a0f4fa000, 88205) = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=233, ...}) = 0
read(4, "127.0.0.1\tlocalhost\n127.0.1.1\tmi"..., 4096) = 233
read(4, "", 4096) = 0
close(4) = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
write(1, "x\n", 2x
) = 2
socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 4
write(1, "4\n", 24
) = 2
write(1, "\n", 1
) = 1
connect(4, {sa_family=AF_INET, sin_port=htons(53511), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ECONNREFUSED (Connection refused)
close(4) = 0
write(1, "Error: couldn't connect to hostn"..., 56Error: couldn't connect to hostname. Connection refused
) = 56
exit_group(1) = ?
+++ exited with 1 +++
谢谢！
答案 0 :(得分：1)
只要编译器合作并且您不需要支持IPv6，您对该问题的修复就会起作用。但更好的解决方法是首先将端口号传递给getaddrinfo，作为＆＃34;服务＆＃34;论点。您必须将其转换为字符串才能执行此操作，但您可以返回使用AF_UNSPEC而无需在getaddrinfo的返回列表中强制转换或操纵sockaddrs：< / p>
void hostname_to_ip(char *hostname, int *connection_socket,
unsigned short port_number)
{
int check_sfd;
struct addrinfo hints, *p, *servinfo;
char port_number_s[sizeof("65535")];
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_NUMERICSERV;
hints.ai_protocol = 0;
snprintf(port_number_s, sizeof port_number_s, "%u", port_number);
int res = getaddrinfo(hostname, port_number_s, &hints, &servinfo);
if (res == EAI_SYSTEM) {
fprintf(stderr, "Error looking up %s: %s\n",
hostname, strerror(errno));
exit(1);
} else if (res != 0) {
fprintf(stderr, "Error looking up %s: %s\n",
hostname, gai_strerror(res));
exit(1);
} else if (servinfo == NULL) {
fprintf(stderr, "Error looking up %s: No addresses found\n",
hostname);
exit(1);
}
// getaddrinfo returned a linked list of relevant addresses
// loop through the addresses and return the first one we can connect to
for (p = servinfo; p != NULL; p = p->ai_next) {
check_sfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if (check_sfd == -1)
continue;
if (connect(check_sfd, p->ai_addr, p->ai_addrlen)) {
*connection_socket = check_sfd;
freeaddrinfo(servinfo);
return;
}
close(check_sfd);
}
// If we get here, we couldn't connect to any of the addresses.
fprintf(stderr, "Couldn't connect to %s: %s\n", hostname, strerror(errno));
exit(1);
}
我还修正了其他一些微妙的错误：
port_number应为unsigned short，因为它是TCP中的内容。getaddrinfo返回EAI_SYSTEM，则需要打印strerror(errno)而不是gai_strerror(res)。getaddrinfo可声称已成功但返回零地址。connect成功时使用循环内的早期返回，则不需要在循环后再次检查是否成功。当您即将打印错误消息并退出时，没有必要释放内存。按照难度的升序为您进行后续练习：
getnameinfo打印＆＃34;正在连接到128.52.0.2 ...＆＃34;像telnet这样的消息。select或poll（您的选择）获取第一个有效并关闭所有其他地址。答案 1 :(得分：0)
感谢@MarkPlotnick，我发现问题与链接列表中返回地址的未设置（或错误设置）端口号有关。以下代码更新修复了它（因为我知道调用函数时的端口号）：
void hostname_to_ip(char *hostname, int *connection_socket, int port_number)
{
int check_sfd;
struct addrinfo hints, *p, *servinfo;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC;//AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = 0;
hints.ai_protocol = 0;
int res = getaddrinfo(hostname, NULL, &hints, &servinfo);
if (res != 0) {
fprintf(stderr, "Error: error in getaddrinfo on hostname: %s\n", gai_strerror(res));
exit(EXIT_FAILURE);
}
// getaddrinfo returned a linked list of relevant addresses
// loop through the addresses and return the first one available
for (p = servinfo; p != NULL; p = p->ai_next) {
check_sfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
if (check_sfd == -1)
continue;
struct sockaddr_in *sockstruct = (struct sockaddr_in*) p->ai_addr;
sockstruct->sin_port = htons(port_number);
sockstruct->sin_family = AF_INET;
socklen_t addrsize = sizeof(struct sockaddr_in);
if (connect(check_sfd, (struct sockaddr*)sockstruct, addrsize) != -1) { // successfuly connected
*connection_socket = check_sfd;
break;
}
close(check_sfd);
}
if (p == NULL) { // couldn't connect to any item in the linked list
printf("Error: couldn't connect to hostname. %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
freeaddrinfo(servinfo);
}