目录:
维基百科
网络套接字（英语：Network socket；又译网络套接字、网络接口、网络插槽）在计算机科学中是电脑网络中进程间资料流的端点。使用以网际协议（Internet Protocol）为通信基础的网络套接字，称为网际套接字（Internet socket）。因为网际协议的流行，现代绝大多数的网络套接字，都是属于网际套接字。
socket是一种操作系统提供的进程间通信机制。
在操作系统中，通常会为应用程序提供一组应用程序接口（API），称为套接字接口（英语：socket API）。应用程序可以通过套接字接口，来使用网络套接字，以进行资料交换。最早的套接字接口来自于4.2 BSD，因此现代常见的套接字接口大多源自Berkeley套接字（Berkeley sockets）标准。在套接字接口中，以IP地址及端口组成套接字地址（socket address）。远程的套接字地址，以及本地的套接字地址完成连线后，再加上使用的协议（protocol），这个五元组（five-element tuple），作为套接字对（socket pairs），之后就可以彼此交换资料。例如，在同一台计算机上，TCP协议与UDP协议可以同时使用相同的port而互不干扰。 操作系统根据套接字地址，可以决定应该将资料送达特定的行程或线程。这就像是电话系统中，以电话号码加上分机号码，来决定通话对象一般。
- socket整体架构
include/linux/socket.h
/*
* 1003.1g requires sa_family_t and that sa_data is char.
*/
struct sockaddr {
sa_family_t sa_family; /* address family, AF_xxx */
char sa_data[14]; /* 14 bytes of protocol address */
};| Family | Description |
|---|---|
| AF_INET | IPv4 protocols |
| AF_INET6 | IPv6 protocols |
| AF_LOCAL | Unix domain protocols |
| AF_ROUTE | Routing Sockets |
| AF_KEY | Ket socket |
通信类型:
| Type | Description |
|---|---|
| SOCK_STREAM | Stream socket |
| SOCK_DGRAM | Datagram socket |
| SOCK_SEQPACKET | Sequenced packet socket |
| SOCK_RAW | Raw socket |
当两个对等点位于同一主机上时，Unix 域套接字的速度通常是 TCP 套接字的两倍.
/* Structure describing an Internet socket address. */
struct sockaddr_in
{
__SOCKADDR_COMMON (sin_);
in_port_t sin_port; /* Port number. */
struct in_addr sin_addr; /* Internet address. */
/* Pad to size of `struct sockaddr'. */
unsigned char sin_zero[sizeof (struct sockaddr)
- __SOCKADDR_COMMON_SIZE
- sizeof (in_port_t)
- sizeof (struct in_addr)];
}; /* INET An implementation of the TCP/IP protocol suite for the LINUX
* operating system. INET is implemented using the BSD Socket
* interface as the means of communication with the user level.
*
* PF_INET protocol family socket handler.
*/
const struct proto_ops inet_stream_ops = {
.family = PF_INET,
.owner = THIS_MODULE,
.release = inet_release,
.bind = inet_bind,
.connect = inet_stream_connect,
.socketpair = sock_no_socketpair,
.accept = inet_accept,
.getname = inet_getname,
.poll = tcp_poll,
.ioctl = inet_ioctl,
.gettstamp = sock_gettstamp,
.listen = inet_listen,
.shutdown = inet_shutdown,
.setsockopt = sock_common_setsockopt,
.getsockopt = sock_common_getsockopt,
.sendmsg = inet_sendmsg,
.recvmsg = inet_recvmsg,
#ifdef CONFIG_MMU
.mmap = tcp_mmap,
#endif
.sendpage = inet_sendpage,
.splice_read = tcp_splice_read,
.read_sock = tcp_read_sock,
.sendmsg_locked = tcp_sendmsg_locked,
.sendpage_locked = tcp_sendpage_locked,
.peek_len = tcp_peek_len,
#ifdef CONFIG_COMPAT
.compat_ioctl = inet_compat_ioctl,
#endif
.set_rcvlowat = tcp_set_rcvlowat,
};
EXPORT_SYMBOL(inet_stream_ops);
const struct proto_ops inet_dgram_ops = {
.family = PF_INET,
.owner = THIS_MODULE,
.release = inet_release,
.bind = inet_bind,
.connect = inet_dgram_connect,
.socketpair = sock_no_socketpair,
.accept = sock_no_accept,
.getname = inet_getname,
.poll = udp_poll,
.ioctl = inet_ioctl,
.gettstamp = sock_gettstamp,
.listen = sock_no_listen,
.shutdown = inet_shutdown,
.setsockopt = sock_common_setsockopt,
.getsockopt = sock_common_getsockopt,
.sendmsg = inet_sendmsg,
.read_sock = udp_read_sock,
.recvmsg = inet_recvmsg,
.mmap = sock_no_mmap,
.sendpage = inet_sendpage,
.set_peek_off = sk_set_peek_off,
#ifdef CONFIG_COMPAT
.compat_ioctl = inet_compat_ioctl,
#endif
};
EXPORT_SYMBOL(inet_dgram_ops);
/*
* For SOCK_RAW sockets; should be the same as inet_dgram_ops but without
* udp_poll
*/
static const struct proto_ops inet_sockraw_ops = {
.family = PF_INET,
.owner = THIS_MODULE,
.release = inet_release,
.bind = inet_bind,
.connect = inet_dgram_connect,
.socketpair = sock_no_socketpair,
.accept = sock_no_accept,
.getname = inet_getname,
.poll = datagram_poll,
.ioctl = inet_ioctl,
.gettstamp = sock_gettstamp,
.listen = sock_no_listen,
.shutdown = inet_shutdown,
.setsockopt = sock_common_setsockopt,
.getsockopt = sock_common_getsockopt,
.sendmsg = inet_sendmsg,
.recvmsg = inet_recvmsg,
.mmap = sock_no_mmap,
.sendpage = inet_sendpage,
#ifdef CONFIG_COMPAT
.compat_ioctl = inet_compat_ioctl,
#endif
};
.poll方式有三种tcp_poll、udp_poll、datagram_poll发送消息.sendmsg = inet_sendmsg,接收消息.recvmsg = inet_recvmsg,
struct sockaddr_un {
__kernel_sa_family_t sun_family; /* AF_UNIX */
char sun_path[UNIX_PATH_MAX]; /* pathname */
};net/unix/af_unix.c
static const struct proto_ops unix_stream_ops = {
.family = PF_UNIX,
.owner = THIS_MODULE,
.release = unix_release,
.bind = unix_bind,
.connect = unix_stream_connect,
.socketpair = unix_socketpair,
.accept = unix_accept,
.getname = unix_getname,
.poll = unix_poll,
.ioctl = unix_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = unix_compat_ioctl,
#endif
.listen = unix_listen,
.shutdown = unix_shutdown,
.sendmsg = unix_stream_sendmsg,
.recvmsg = unix_stream_recvmsg,
.mmap = sock_no_mmap,
.sendpage = unix_stream_sendpage,
.splice_read = unix_stream_splice_read,
.set_peek_off = unix_set_peek_off,
.show_fdinfo = unix_show_fdinfo,
};
static const struct proto_ops unix_dgram_ops = {
.family = PF_UNIX,
.owner = THIS_MODULE,
.release = unix_release,
.bind = unix_bind,
.connect = unix_dgram_connect,
.socketpair = unix_socketpair,
.accept = sock_no_accept,
.getname = unix_getname,
.poll = unix_dgram_poll,
.ioctl = unix_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = unix_compat_ioctl,
#endif
.listen = sock_no_listen,
.shutdown = unix_shutdown,
.sendmsg = unix_dgram_sendmsg,
.recvmsg = unix_dgram_recvmsg,
.mmap = sock_no_mmap,
.sendpage = sock_no_sendpage,
.set_peek_off = unix_set_peek_off,
.show_fdinfo = unix_show_fdinfo,
};
static const struct proto_ops unix_seqpacket_ops = {
.family = PF_UNIX,
.owner = THIS_MODULE,
.release = unix_release,
.bind = unix_bind,
.connect = unix_stream_connect,
.socketpair = unix_socketpair,
.accept = unix_accept,
.getname = unix_getname,
.poll = unix_dgram_poll,
.ioctl = unix_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = unix_compat_ioctl,
#endif
.listen = unix_listen,
.shutdown = unix_shutdown,
.sendmsg = unix_seqpacket_sendmsg,
.recvmsg = unix_seqpacket_recvmsg,
.mmap = sock_no_mmap,
.sendpage = sock_no_sendpage,
.set_peek_off = unix_set_peek_off,
.show_fdinfo = unix_show_fdinfo,
};
static struct proto unix_proto = {
.name = "UNIX",
.owner = THIS_MODULE,
.obj_size = sizeof(struct unix_sock),
};
.poll的两种方式unix_poll、unix_dgram_poll; 发送消息.sendmsg = unix_stream_sendmsg,接收消息.recvmsg = unix_stream_recvmsg,
client.c
/**************************************************************************/
/* This sample program provides code for a client application that uses */
/* AF_UNIX address family */
/**************************************************************************/
/**************************************************************************/
/* Header files needed for this sample program */
/**************************************************************************/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
/**************************************************************************/
/* Constants used by this program */
/**************************************************************************/
#define SERVER_PATH "/tmp/server"
#define BUFFER_LENGTH 250
#define FALSE 0
/* Pass in 1 parameter which is either the */
/* path name of the server as a UNICODE */
/* string, or set the server path in the */
/* #define SERVER_PATH which is a CCSID */
/* 500 string. */
void main(int argc, char *argv[])
{
/***********************************************************************/
/* Variable and structure definitions. */
/***********************************************************************/
int sd=-1, rc, bytesReceived;
char buffer[BUFFER_LENGTH];
struct sockaddr_un serveraddr;
/***********************************************************************/
/* A do/while(FALSE) loop is used to make error cleanup easier. The */
/* close() of the socket descriptor is only done once at the very end */
/* of the program. */
/***********************************************************************/
do
{
/********************************************************************/
/* The socket() function returns a socket descriptor, which represents */
/* an endpoint. The statement also identifies that the UNIX */
/* address family with the stream transport (SOCK_STREAM) will be */
/* used for this socket. */
/********************************************************************/
sd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sd < 0)
{
perror("socket() failed");
break;
}
/********************************************************************/
/* If an argument was passed in, use this as the server, otherwise */
/* use the #define that is located at the top of this program. */
/********************************************************************/
memset(&serveraddr, 0, sizeof(serveraddr));
serveraddr.sun_family = AF_UNIX;
if (argc > 1)
strcpy(serveraddr.sun_path, argv[1]);
else
strcpy(serveraddr.sun_path, SERVER_PATH);
/********************************************************************/
/* Use the connect() function to establish a connection to the */
/* server. */
/********************************************************************/
rc = connect(sd, (struct sockaddr *)&serveraddr, SUN_LEN(&serveraddr));
if (rc < 0)
{
perror("connect() failed");
break;
}
/********************************************************************/
/* Send 250 bytes of a's to the server */
/********************************************************************/
memset(buffer, 'a', sizeof(buffer));
rc = send(sd, buffer, sizeof(buffer), 0);
if (rc < 0)
{
perror("send() failed");
break;
}
/********************************************************************/
/* In this example we know that the server is going to respond with */
/* the same 250 bytes that we just sent. Since we know that 250 */
/* bytes are going to be sent back to us, we can use the */
/* SO_RCVLOWAT socket option and then issue a single recv() and */
/* retrieve all of the data. */
/* */
/* The use of SO_RCVLOWAT is already illustrated in the server */
/* side of this example, so we will do something different here. */
/* The 250 bytes of the data may arrive in separate packets, */
/* therefore we will issue recv() over and over again until all */
/* 250 bytes have arrived. */
/********************************************************************/
bytesReceived = 0;
while (bytesReceived < BUFFER_LENGTH)
{
rc = recv(sd, & buffer[bytesReceived],
BUFFER_LENGTH - bytesReceived, 0);
if (rc < 0)
{
perror("recv() failed");
break;
}
else if (rc == 0)
{
printf("The server closed the connection\n");
break;
}
/*****************************************************************/
/* Increment the number of bytes that have been received so far */
/*****************************************************************/
bytesReceived += rc;
}
} while (FALSE);
/***********************************************************************/
/* Close down any open socket descriptors */
/***********************************************************************/
if (sd != -1)
close(sd);
}server.c
/**************************************************************************/
/* This example program provides code for a server application that uses */
/* AF_UNIX address family */
/**************************************************************************/
/**************************************************************************/
/* Header files needed for this sample program */
/**************************************************************************/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
/**************************************************************************/
/* Constants used by this program */
/**************************************************************************/
#define SERVER_PATH "/tmp/server"
#define BUFFER_LENGTH 250
#define FALSE 0
void main()
{
/***********************************************************************/
/* Variable and structure definitions. */
/***********************************************************************/
int sd=-1, sd2=-1;
int rc, length;
char buffer[BUFFER_LENGTH];
struct sockaddr_un serveraddr;
/***********************************************************************/
/* A do/while(FALSE) loop is used to make error cleanup easier. The */
/* close() of each of the socket descriptors is only done once at the */
/* very end of the program. */
/***********************************************************************/
do
{
/********************************************************************/
/* The socket() function returns a socket descriptor, which represents */
/* an endpoint. The statement also identifies that the UNIX */
/* address family with the stream transport (SOCK_STREAM) will be */
/* used for this socket. */
/********************************************************************/
sd = socket(AF_UNIX, SOCK_STREAM, 0);
if (sd < 0)
{
perror("socket() failed");
break;
}
/********************************************************************/
/* After the socket descriptor is created, a bind() function gets a */
/* unique name for the socket. */
/********************************************************************/
memset(&serveraddr, 0, sizeof(serveraddr));
serveraddr.sun_family = AF_UNIX;
strcpy(serveraddr.sun_path, SERVER_PATH);
rc = bind(sd, (struct sockaddr *)&serveraddr, SUN_LEN(&serveraddr));
if (rc < 0)
{
perror("bind() failed");
break;
}
/********************************************************************/
/* The listen() function allows the server to accept incoming */
/* client connections. In this example, the backlog is set to 10. */
/* This means that the system will queue 10 incoming connection */
/* requests before the system starts rejecting the incoming */
/* requests. */
/********************************************************************/
rc = listen(sd, 10);
if (rc< 0)
{
perror("listen() failed");
break;
}
printf("Ready for client connect().\n");
/********************************************************************/
/* The server uses the accept() function to accept an incoming */
/* connection request. The accept() call will block indefinitely */
/* waiting for the incoming connection to arrive. */
/********************************************************************/
sd2 = accept(sd, NULL, NULL);
if (sd2 < 0)
{
perror("accept() failed");
break;
}
/********************************************************************/
/* In this example we know that the client will send 250 bytes of */
/* data over. Knowing this, we can use the SO_RCVLOWAT socket */
/* option and specify that we don't want our recv() to wake up */
/* until all 250 bytes of data have arrived. */
/********************************************************************/
length = BUFFER_LENGTH;
rc = setsockopt(sd2, SOL_SOCKET, SO_RCVLOWAT,
(char *)&length, sizeof(length));
if (rc < 0)
{
perror("setsockopt(SO_RCVLOWAT) failed");
break;
}
/****************************************************/
/* Receive that 250 bytes data from the client */
/****************************************************/
rc = recv(sd2, buffer, sizeof(buffer), 0);
if (rc < 0)
{
perror("recv() failed");
break;
}
printf("%d bytes of data were received\n", rc);
if (rc == 0 ||
rc < sizeof(buffer))
{
printf("The client closed the connection before all of the\n");
printf("data was sent\n");
break;
}
/********************************************************************/
/* Echo the data back to the client */
/********************************************************************/
rc = send(sd2, buffer, sizeof(buffer), 0);
if (rc < 0)
{
perror("send() failed");
break;
}
/********************************************************************/
/* Program complete */
/********************************************************************/
} while (FALSE);
/***********************************************************************/
/* Close down any open socket descriptors */
/***********************************************************************/
if (sd != -1)
close(sd);
if (sd2 != -1)
close(sd2);
/***********************************************************************/
/* Remove the UNIX path name from the file system */
/***********************************************************************/
unlink(SERVER_PATH);
}- unix - sockets for local interprocess communication
#include <sys/socket.h>
#include <sys/un.h>
unix_socket = socket(AF_UNIX, type, 0);
error = socketpair(AF_UNIX, type, 0, int *sv);AF_UNIX（也称为 AF_LOCAL ）套接字用于同一台机器上的进程之间进行通信。 传统上，UNIX 域套接字可以是未命名的，或者绑定到文件系统路径名（标记为套接字类型）。UNIX 域中的有效套接字类型是：
- SOCK_STREAM 有保障的(即能保证数据正确传送到对方)面向连接的SOCKET，多用于资料(如文件)传送
- SOCK_DGRAM 是无保障的面向消息的socket，主要用于在网络上发广播信息