基本TCP客户端与服务器
Server
#include <cstdio>
#include <cstring>
#include <string>
#include <vector>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string>
using namespace std;
const int BUF_SIZE = 1024;
string addr_to_string(const sockaddr_in *addr) {
char addr_str[INET_ADDRSTRLEN];
const char *addr_str_ptr = inet_ntop(AF_INET, &addr->sin_addr, addr_str, sizeof(addr_str));
if (addr_str_ptr == NULL) {
fprintf(stderr, "inet_ntop failed\n");
return "";
}
return string(addr_str_ptr) + ":" + to_string(ntohs(addr->sin_port));
}
string get_sockname_string(int sockfd) {
sockaddr_in addr;
socklen_t len = sizeof(addr);
if (getsockname(sockfd, (sockaddr *) &addr, &len) == -1) {
fprintf(stderr, "getsockname failed\n");
return "";
}
return addr_to_string(&addr);
}
string get_peername_string(int sockfd) {
sockaddr_in addr;
socklen_t len = sizeof(addr);
if (getpeername(sockfd, (sockaddr *) &addr, &len) == -1) {
fprintf(stderr, "getpeername failed, errno: %d, str: %s\n", errno, strerror(errno));
return "";
}
return addr_to_string(&addr);
}
int init_server(int type, const sockaddr *addr, socklen_t alen, int qlen) {
int fd;
if ((fd = socket(addr->sa_family, type, 0)) == -1) {
fprintf(stderr, "create socket failed, errno: %d, str: %s\n", errno, strerror(errno));
return -1;
}
printf("create socket fd: %d, sock_name: %s, peer_name: %s\n", fd, get_sockname_string(fd).c_str(), get_peername_string(fd).c_str());
if (bind(fd, addr, alen) == -1) {
fprintf(stderr, "bind failed, errno: %d, str: %s\n", errno, strerror(errno));
close(fd);
return -1;
}
printf("bind socket fd: %d, sock_name: %s, peer_name: %s\n", fd, get_sockname_string(fd).c_str(), get_peername_string(fd).c_str());
if (type == SOCK_STREAM || type == SOCK_SEQPACKET) {
if (listen(fd, qlen) == -1) {
fprintf(stderr, "listen failed, errno: %d, str: %s\n", errno, strerror(errno));
close(fd);
return -1;
}
printf("listen fd: %d, sock_name: %s, peer_name: %s\n", fd, get_sockname_string(fd).c_str(), get_peername_string(fd).c_str());
}
return fd;
}
int main(int argc, char **argv) {
int sleep_before_recv = 0;
int sleep_after_listen = 0;
int qlen = 0;
int port = 27015;
for (int i = 1; i < argc;) {
if (argv[i] == string("--port")) {
port = atoi(argv[i + 1]);
i += 2;
continue;
}
if (argv[i] == string("--qlen")) {
qlen = atoi(argv[i + 1]);
i += 2;
continue;
}
if (argv[i] == string("--sleep-before-recv")) {
sleep_before_recv = atoi(argv[i + 1]);
i += 2;
continue;
}
if (argv[i] == string("--sleep-after-listen")) {
sleep_after_listen = atoi(argv[i + 1]);
i += 2;
continue;
}
i++;
}
printf("port: %d, qlen: %d, sleep-before-recv: %d, sleep-after-listen: %d\n", port, qlen, sleep_before_recv, sleep_after_listen);
sockaddr_in addr;
bzero(&addr, sizeof(addr)); // APUE 16.3.2 其中成员sin_zero为填充字段，应该全部被置为0
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = htons(port);
int sockfd = init_server(SOCK_STREAM, (sockaddr *) &addr, sizeof(addr), qlen);
if (sockfd == -1) return -1;
sleep(sleep_after_listen);
while (true) {
int clfd, n;
sockaddr_in accepted_addr;
socklen_t len = sizeof(accepted_addr);
if ((clfd = accept(sockfd, (sockaddr *) &accepted_addr, &len)) == -1) {
fprintf(stderr, "accept failed, errno: %d, str: %s\n", errno, strerror(errno));
continue;
}
printf("after accept sockfd: %d, sock_name: %s, peer_name: %s\n",
sockfd, get_sockname_string(sockfd).c_str(), get_peername_string(sockfd).c_str());
printf("accepted fd: %d, sock_name: %s, peer_name: %s, addr: %s\n",
clfd, get_sockname_string(clfd).c_str(), get_peername_string(clfd).c_str(), addr_to_string(&accepted_addr).c_str());
sleep(sleep_before_recv);
char buf[BUF_SIZE];
if ((n = recv(clfd, buf, BUF_SIZE - 1, 0)) == -1) {
fprintf(stderr, "recv failed, errno: %d, str: %s\n", errno, strerror(errno));
close(clfd);
continue;
}
buf[n] = '\0';
printf("read %d bytes from fd: %d, buf: %s\n", n, clfd, buf);
close(clfd);
}
return 0;
}
如果调用getsockname时没有地址绑定到传入的套接字，则其结果是未定义的。1
Client
#include <cstdio>
#include <cstring>
#include <vector>
#include <string>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
using namespace std;
const int BUF_SIZE = 1024;
string addr_to_string(const sockaddr_in *addr) {
char addr_str[INET_ADDRSTRLEN];
const char *addr_str_ptr = inet_ntop(AF_INET, &addr->sin_addr, addr_str, sizeof(addr_str));
if (addr_str_ptr == NULL) {
fprintf(stderr, "inet_ntop failed\n");
return "";
}
return string(addr_str_ptr) + ":" + to_string(ntohs(addr->sin_port));
}
string get_sockname_string(int sockfd) {
sockaddr_in addr;
socklen_t len = sizeof(addr);
if (getsockname(sockfd, (sockaddr *) &addr, &len) == -1) {
fprintf(stderr, "getsockname failed\n");
return "";
}
return addr_to_string(&addr);
}
string get_peername_string(int sockfd) {
sockaddr_in addr;
socklen_t len = sizeof(addr);
if (getpeername(sockfd, (sockaddr *) &addr, &len) == -1) {
fprintf(stderr, "getpeername failed, errno: %d, str: %s\n", errno, strerror(errno));
return "";
}
return addr_to_string(&addr);
}
int main(int argc, char **argv) {
sockaddr_in addr;
bzero(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(27015);
if (inet_pton(addr.sin_family, "127.0.0.1", &addr.sin_addr) <= 0) {
fprintf(stderr, "inet_pton failed\n");
return -1;
}
int sockfd = socket(addr.sin_family, SOCK_STREAM, 0);
if (sockfd == -1) {
fprintf(stderr, "create socket failed, errno: %d, str: %s\n", errno, strerror(errno));
return -1;
}
printf("fd: %d, sock_name: %s, peer_name: %s\n", sockfd, get_sockname_string(sockfd).c_str(), get_peername_string(sockfd).c_str());
if (connect(sockfd, (sockaddr *) &addr, sizeof(addr)) == -1) {
fprintf(stderr, "connect failed, errno: %d, str: %s\n", errno, strerror(errno));
close(sockfd);
return -1;
}
printf("fd: %d, sock_name: %s, peer_name: %s\n", sockfd, get_sockname_string(sockfd).c_str(), get_peername_string(sockfd).c_str());
vector<string> msgs = {"hello", "world", "cpp"};
for (const auto &msg : msgs) {
int n = send(sockfd, msg.c_str(), msg.size(), 0);
if (n == -1) {
fprintf(stderr, "send failed, errno: %d, str: %s\n", errno, strerror(errno));
break;
}
printf("fd: %d, send %d bytes\n", sockfd, n);
}
close(sockfd);
return 0;
}
Read
建连后客户端调用三次send，服务端在recv之前sleep 0秒
server:
$ ./server --sleep-before-recv 0 port: 27015, qlen: 0, sleep-before-recv: 0, sleep-after-listen: 0 getpeername failed, errno: 57, str: Socket is not connected create socket fd: 3, sock_name: 0.0.0.0:0, peer_name: getpeername failed, errno: 57, str: Socket is not connected bind socket fd: 3, sock_name: 0.0.0.0:27015, peer_name: getpeername failed, errno: 57, str: Socket is not connected listen fd: 3, sock_name: 0.0.0.0:27015, peer_name: getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:59932, addr: 127.0.0.1:59932 read 5 bytes from fd: 4, buf: hello ^C
client:
$ ./client getpeername failed, errno: 57, str: Socket is not connected fd: 3, sock_name: 0.0.0.0:0, peer_name: fd: 3, sock_name: 127.0.0.1:59932, peer_name: 127.0.0.1:27015 fd: 3, send 5 bytes fd: 3, send 5 bytes fd: 3, send 3 bytes
建连后客户端调用三次send，服务端在recv之前sleep 5秒
server:
$ ./server --sleep-before-recv 5 port: 27015, qlen: 0, sleep-before-recv: 5, sleep-after-listen: 0 getpeername failed, errno: 57, str: Socket is not connected create socket fd: 3, sock_name: 0.0.0.0:0, peer_name: getpeername failed, errno: 57, str: Socket is not connected bind socket fd: 3, sock_name: 0.0.0.0:27015, peer_name: getpeername failed, errno: 57, str: Socket is not connected listen fd: 3, sock_name: 0.0.0.0:27015, peer_name: getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:60018, addr: 127.0.0.1:60018 # 五秒后 read 13 bytes from fd: 4, buf: helloworldcpp ^C
client:
先执行服务端，再执行客户端，客服端执行完三次send后未等服务端read就已返回
$ ./client getpeername failed, errno: 57, str: Socket is not connected fd: 3, sock_name: 0.0.0.0:0, peer_name: fd: 3, sock_name: 127.0.0.1:60018, peer_name: 127.0.0.1:27015 fd: 3, send 5 bytes fd: 3, send 5 bytes fd: 3, send 3 bytes
Listen Backlog
backlog传2
server:
$ ./server --sleep-after-listen 10 --qlen 2 port: 27015, qlen: 2, sleep-before-recv: 0, sleep-after-listen: 10 getpeername failed, errno: 57, str: Socket is not connected create socket fd: 3, sock_name: 0.0.0.0:0, peer_name: getpeername failed, errno: 57, str: Socket is not connected bind socket fd: 3, sock_name: 0.0.0.0:27015, peer_name: getpeername failed, errno: 57, str: Socket is not connected listen fd: 3, sock_name: 0.0.0.0:27015, peer_name: # sleep here getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:63689, addr: 127.0.0.1:63689 read 13 bytes from fd: 4, buf: helloworldcpp getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:63690, addr: 127.0.0.1:63690 read 13 bytes from fd: 4, buf: helloworldcpp getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:63691, addr: 127.0.0.1:63691 read 13 bytes from fd: 4, buf: helloworldcpp ^C
client:
$ ./client getpeername failed, errno: 57, str: Socket is not connected fd: 3, sock_name: 0.0.0.0:0, peer_name: fd: 3, sock_name: 127.0.0.1:63689, peer_name: 127.0.0.1:27015 fd: 3, send 5 bytes fd: 3, send 5 bytes fd: 3, send 3 bytes $ ./client getpeername failed, errno: 57, str: Socket is not connected fd: 3, sock_name: 0.0.0.0:0, peer_name: fd: 3, sock_name: 127.0.0.1:63690, peer_name: 127.0.0.1:27015 fd: 3, send 5 bytes fd: 3, send 5 bytes fd: 3, send 3 bytes $ ./client getpeername failed, errno: 57, str: Socket is not connected fd: 3, sock_name: 0.0.0.0:0, peer_name: # block here fd: 3, sock_name: 127.0.0.1:63691, peer_name: 127.0.0.1:27015 fd: 3, send 5 bytes fd: 3, send 5 bytes fd: 3, send 3 bytes
backlog传0
参数backlog提供了一个提示，提示系统该进程所要入队的未完成连接请求数量。其实际值由系统决定。具体的最大值取决于每个协议的实现。对于TCP，其默认值为128。2 通过下面的脚本，在macOs上测试，验证了TCP的默认值为128。
run-server.sh
#!/bin/bash
for i in {1..256}; do
echo "do $i"
./client 1>/dev/null 2>&1
echo "$i finished"
done
server:
$ ./server --sleep-after-listen 10 port: 27015, qlen: 0, sleep-before-recv: 0, sleep-after-listen: 10 getpeername failed, errno: 57, str: Socket is not connected create socket fd: 3, sock_name: 0.0.0.0:0, peer_name: getpeername failed, errno: 57, str: Socket is not connected bind socket fd: 3, sock_name: 0.0.0.0:27015, peer_name: getpeername failed, errno: 57, str: Socket is not connected listen fd: 3, sock_name: 0.0.0.0:27015, peer_name: # sleep here getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:63789, addr: 127.0.0.1:63789 read 13 bytes from fd: 4, buf: helloworldcpp getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:63790, addr: 127.0.0.1:63790 read 13 bytes from fd: 4, buf: helloworldcpp ................ getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:64050, addr: 127.0.0.1:64050 read 5 bytes from fd: 4, buf: hello getpeername failed, errno: 57, str: Socket is not connected after accept sockfd: 3, sock_name: 0.0.0.0:27015, peer_name: accepted fd: 4, sock_name: 127.0.0.1:27015, peer_name: 127.0.0.1:64051, addr: 127.0.0.1:64051 read 13 bytes from fd: 4, buf: helloworldcpp ^C
client:
$ ./run-server.sh do 1 1 finished do 2 2 finished do 3 3 finished do 4 4 finished .................. do 126 126 finished do 127 127 finished do 128 128 finished do 129 # block here 129 finished do 130 130 finished do 131 131 finished do 132 132 finished .................. do 255 255 finished do 256 256 finished