Recv-Q +发送-Q>写入字节
[英]Recv-Q+Send-Q>write bytes
问题描述
I write a tcp server and a tcp client,the client only send data to server and print how many bytes it writed,the server only accept the connection,and then I use netstat to show the socket's Recv-Q and Send-Q,and I found that Recv-Q+send-Q > write bytes. 
我编写了一个TCP服务器和一个TCP客户端，客户端仅向服务器发送数据并打印写入的字节数，服务器仅接受连接，然后使用netstat显示套接字的Recv-Q和Send-Q，我发现Recv-Q + send-Q>写字节。 How does it happend? 它是怎么发生的？
client code:
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <stdarg.h>
#include <errno.h>
void error(int status, int err, const char *fmt, ...)
{
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
if (err != 0)
{
fprintf(stderr, "errno = %d, errmsg = %s\n", err, strerror(err));
}
if (status != 0)
{
exit(err);
}
}
int set_address(const char *host, const char *serv, const char *protocol, sockaddr_in *addr)
{
struct hostent *host_info;
struct servent *serv_info;
memset(addr, 0, sizeof(sockaddr_in));
addr->sin_family = AF_INET;
if (host != NULL)
{
if (inet_aton(host, &addr->sin_addr) != 0)
{
host_info = gethostbyname(host);
if (host_info == NULL)
{
error(1, h_errno, "set_address failed, gethostbyname(%s) failed, errno = %d, errmsg = %s\n", host, h_errno, hstrerror(h_errno));
}
else
{
inet_aton(host_info->h_addr_list[0], &addr->sin_addr);
}
}
}
else
{
addr->sin_addr.s_addr = INADDR_ANY;
}
if (serv != NULL)
{
char * end_pos;
addr->sin_port = htons(strtol(serv, &end_pos, 10));
if (*end_pos != '\0')
{
serv_info = getservbyname(serv, protocol);
if (serv_info == NULL)
{
error(1, h_errno, "set_address failed, getservbyname(%s, %s) faield\n", serv, protocol);
}
else
{
addr->sin_port = serv_info->s_port;
}
}
}
}
int tcp_client(const char *host, const char *serv)
{
struct sockaddr_in server;
int fd;
const int on = 1;
set_address(host, serv, "tcp", &server);
fd = socket(AF_INET, SOCK_STREAM, 0);
if (fd < 0)
{
error(1, errno, "create socket failed\n");
}
if (connect(fd, (struct sockaddr *)&server, sizeof(server)) != 0)
{
error(1, errno, "connect to server failed\n");
}
return fd;
}
int main (int argc, char **argv)
{
if (argc != 3)
{
printf("usage: %s <host> <port>\n", basename(argv[0]));
exit(1);
}
char buf[1024];
int fd;
int total_write_bytes = 0, cur_write_bytes = 0;
fd = tcp_client(argv[1], argv[2]);
while (true)
{
cur_write_bytes = write(fd, buf, sizeof(buf));
if (cur_write_bytes <= 0)
{
break;
}
total_write_bytes += cur_write_bytes;
printf("total_write_bytes = %d, curr_write_bytes = %d\n", total_write_bytes, cur_write_bytes);
}
return 0;
}
server code:
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <stdarg.h>
#include <errno.h>
void error(int status, int err, const char *fmt, ...)
{
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
if (err != 0)
{
fprintf(stderr, "errno = %d, errmsg = %s\n", err, strerror(err));
}
if (status != 0)
{
exit(err);
}
}
int set_address(const char *host, const char *serv, const char *protocol, sockaddr_in *addr)
{
struct hostent *host_info;
struct servent *serv_info;
memset(addr, 0, sizeof(sockaddr_in));
addr->sin_family = AF_INET;
if (host != NULL)
{
if (inet_aton(host, &addr->sin_addr) != 0)
{
host_info = gethostbyname(host);
if (host_info == NULL)
{
error(1, h_errno, "set_address failed, gethostbyname(%s) failed, errno = %d, errmsg = %s\n", host, h_errno, hstrerror(h_errno));
}
else
{
inet_aton(host_info->h_addr_list[0], &addr->sin_addr);
}
}
}
else
{
addr->sin_addr.s_addr = INADDR_ANY;
}
if (serv != NULL)
{
char * end_pos;
addr->sin_port = htons(strtol(serv, &end_pos, 10));
if (*end_pos != '\0')
{
serv_info = getservbyname(serv, protocol);
if (serv_info == NULL)
{
error(1, h_errno, "set_address failed, getservbyname(%s, %s) faield\n", serv, protocol);
}
else
{
addr->sin_port = serv_info->s_port;
}
}
}
}
int tcp_server(const char *host, const char *serv)
{
struct sockaddr_in local;
int fd;
const int on = 1;
set_address(host, serv, "tcp", &local);
fd = socket(AF_INET, SOCK_STREAM, 0);
if (fd < 0)
{
error(1, errno, "create socket failed");
}
if (bind(fd, (sockaddr *)&local, sizeof(local)) != 0)
{
error(1, errno, "bind to port %s:%s failed\n", host, serv);
}
if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) != 0)
{
error(1, errno, "set SO_REUSEADDR failed\n");
}
if (listen(fd, 100) != 0)
{
error(1, errno, "listen on %s:%s failed\n", host, serv);
}
return fd;
}
int main (int argc, char **argv)
{
if (argc != 3)
{
printf("usage: %s <host> <port>\n", basename(argv[0]));
exit(1);
}
int listen_fd, fd;
struct sockaddr_in addr;
socklen_t len;
listen_fd = tcp_server(argv[1], argv[2]);
fd = accept(listen_fd, (struct sockaddr *)&addr, &len);
if (fd < 0)
{
error(1, errno, "accept an connection failed\n");
}
while (true)
{
sleep(5);
}
return 0;
}
this is the resulte: 结果是：
standard output result: standard output 标准输出结果： 标准输出
netstat result: netstat result netstat结果： netstat结果
tcpdump result: tcpdump结果：
14:17:16.633105 IP localhost.54393 > localhost.personal-agent: S 4282375064:4282375064(0) win 32767 14:17:16.633106 IP localhost.personal-agent > localhost.54393: S 4268411460:4268411460(0) ack 4282375065 win 32767 14:17:16.633115 IP localhost.54393 > localhost.personal-agent: .
1 个解决方案
解决方案1
0 2016-03-28 05:31:17
Bytes that have been received but for which the acknowledge has not been received by the sender are in both the send queue and the receive queue. 发送队列和接收队列中都已收到但发送方尚未收到确认的字节。 They remain in the send queue because until they are acknowledged, the sender must be ready to re-send them. 它们保留在发送队列中，因为在被确认之前，发送者必须准备好重新发送它们。 They remain in the receive queue until the application calls a receive function and takes them out of the queue. 它们将保留在接收队列中，直到应用程序调用接收函数并将其从队列中取出为止。
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