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Linux(程序设计):48---缓冲区大小(SO_RCVBUF、SO_SNDBUF套接字选项)


  • 套接字选项详细介绍​​​​

一、选项简单介绍


  • 当使用setsockopt来设置TCP的接收缓冲区和发送缓冲区的大小时,​系统都会将其值加倍​,并且​不得小于某个最小值​。TCP接收缓冲区的​最小值是256字节​(不同系统会有不同的值),而发送缓冲区的​最小值是2048字节​(不同系统会有不同的值)。系统这样做的目的主要是:确保一个TCP连接​拥有足够的空闲缓冲区来处理拥塞​(比如快速重传算法就期望TCP接收缓冲区能至少容纳4个大小为SMSS的TCP报文段)
  • 此外,我们还可以直接修改内核参数​/proc/sys/net/ipv4/tcp_rmem和/proc/sys/net/ipv4/tcp_wmem​来强制TCP接收缓冲区和发送缓冲区的大小没有最小值限制

二、演示案例

客户端

  • 客户端发送数据给服务端,并且设置了发送缓冲区的大小(大小由程序参数传入),设置完之后打印一下设置的缓冲区大小
//cli_send.c

#include <sys/socket.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <libgen.h>

#define BUFFER_SIZE 512

int main( int argc, char* argv[] )
{
if( argc <= 3 )
{
printf( "usage: %s ip_address port_number send_bufer_size\n", basename( argv[0] ) );
return 1;
}
const char* ip = argv[1];
int port = atoi( argv[2] );

struct sockaddr_in server_address;
bzero( &server_address, sizeof( server_address ) );
server_address.sin_family = AF_INET;
inet_pton( AF_INET, ip, &server_address.sin_addr );
server_address.sin_port = htons( port );

int sock = socket( PF_INET, SOCK_STREAM, 0 );
assert( sock >= 0 );

int sendbuf = atoi( argv[3] );
int len = sizeof( sendbuf );
setsockopt( sock, SOL_SOCKET, SO_SNDBUF, &sendbuf, sizeof( sendbuf ) );
getsockopt( sock, SOL_SOCKET, SO_SNDBUF, &sendbuf, ( socklen_t* )&len );
printf( "the tcp send buffer size after setting is %d\n", sendbuf );

if ( connect( sock, ( struct sockaddr* )&server_address, sizeof( server_address ) ) != -1 )
{
char buffer[ BUFFER_SIZE ];
memset( buffer, 'a', BUFFER_SIZE );
send( sock, buffer, BUFFER_SIZE, 0 );
}

close( sock );
return 0;
}

服务端

  • 服务端接收客户端的数据,并且设置了接收缓冲区的大小(大小由程序参数传入),设置完之后打印一下设置的缓冲区大小
//ser_recv.c

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <libgen.h>

#define BUFFER_SIZE 1024

int main( int argc, char* argv[] )
{
if( argc <= 3 )
{
printf( "usage: %s ip_address port_number receive_buffer_size\n", basename( argv[0] ) );
return 1;
}
const char* ip = argv[1];
int port = atoi( argv[2] );

struct sockaddr_in address;
bzero( &address, sizeof( address ) );
address.sin_family = AF_INET;
inet_pton( AF_INET, ip, &address.sin_addr );
address.sin_port = htons( port );

int sock = socket( PF_INET, SOCK_STREAM, 0 );
assert( sock >= 0 );
int recvbuf = atoi( argv[3] );
int len = sizeof( recvbuf );
setsockopt( sock, SOL_SOCKET, SO_RCVBUF, &recvbuf, sizeof( recvbuf ) );
getsockopt( sock, SOL_SOCKET, SO_RCVBUF, &recvbuf, ( socklen_t* )&len );
printf( "the receive buffer size after settting is %d\n", recvbuf );

int ret = bind( sock, ( struct sockaddr* )&address, sizeof( address ) );
assert( ret != -1 );

ret = listen( sock, 5 );
assert( ret != -1 );

struct sockaddr_in client;
socklen_t client_addrlength = sizeof( client );
int connfd = accept( sock, ( struct sockaddr* )&client, &client_addrlength );
if ( connfd < 0 )
{
printf( "errno is: %d\n", errno );
}
else
{
char buffer[ BUFFER_SIZE ];
memset( buffer, '\0', BUFFER_SIZE );
while( recv( connfd, buffer, BUFFER_SIZE-1, 0 ) > 0 ){}
close( connfd );
}

close( sock );
return 0;
}

运行程序

  • 运行服务端程序,将其接收缓冲区大小设置为50字节(但是输出的大小却是2304字节,说明此系统的TCP接收端缓冲区最小值为2304)

Linux(程序设计):48---缓冲区大小(SO_RCVBUF、SO_SNDBUF套接字选项)_缓冲区大小

  • 运行客户端程序,将其发送缓冲区大小设置为2304字节(但是输出的大小却是4608,这与缓冲区会被系统设置加倍的概念相符合)

Linux(程序设计):48---缓冲区大小(SO_RCVBUF、SO_SNDBUF套接字选项)_#include_02


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