Java程序辅导

Sockets
Distributed Systems
Philipp Kupferschmied
Universita¨t Karlsruhe, System Architecture Group
May 6th, 2009
Philipp Kupferschmied Sockets 1/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
1 The Socket Abstraction
Socket Basics
Characteristics
2 User’s Point of View
Connections
Single-Threaded Servers
Summary
3 Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Philipp Kupferschmied Sockets 2/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
What are Sockets?
Socket Socket
Kernel
Process
A
Process
B
Connection oriented IPC
“Phone connection” between processes
Protocol determines how the connection is used
Philipp Kupferschmied Sockets 3/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Socket Types
Socket
File descriptor (sock fd)
Protocol family
Unix-domain (AF UNIX)
Internet-domain (AF INET)
Socket type
Stream (SOCK STREAM)
Datagram (SOCK DGRAM)
Protocol
UNIX STREAM, UNIX DGRAM
TCP, UDP
Philipp Kupferschmied Sockets 4/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Socket Types
Socket
File descriptor (sock fd)
Protocol family
Unix-domain (AF UNIX)
Internet-domain (AF INET)
Socket type
Stream (SOCK STREAM)
Datagram (SOCK DGRAM)
Protocol
UNIX STREAM, UNIX DGRAM
TCP, UDP
Philipp Kupferschmied Sockets 4/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Socket Types
Socket
File descriptor (sock fd)
Protocol family
Unix-domain (AF UNIX)
Internet-domain (AF INET)
Socket type
Stream (SOCK STREAM)
Datagram (SOCK DGRAM)
Protocol
UNIX STREAM, UNIX DGRAM
TCP, UDP
Philipp Kupferschmied Sockets 4/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Socket Types
Socket
File descriptor (sock fd)
Protocol family
Unix-domain (AF UNIX)
Internet-domain (AF INET)
Socket type
Stream (SOCK STREAM)
Datagram (SOCK DGRAM)
Protocol
UNIX STREAM, UNIX DGRAM
TCP, UDP
Philipp Kupferschmied Sockets 4/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Unix-Domain Sockets
Implemented purely in memory
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Unix-domain addresses are file names
/tmp/server
sockaddr un
sun family = AF UNIX
sun path = /tmp/server Socket Socket
Client Server
 
Philipp Kupferschmied Sockets 5/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Unix-Domain Sockets
Implemented purely in memory
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Unix-domain addresses are file names
/tmp/server
sockaddr un
sun family = AF UNIX
sun path = /tmp/server Socket Socket
Client Server
/ tmp/server
Philipp Kupferschmied Sockets 5/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Unix-Domain Sockets
Implemented purely in memory
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Unix-domain addresses are file names
/tmp/server
sockaddr un
sun family = AF UNIX
sun path = /tmp/server Socket Socket
Client Server
/ tmp/server
request
Philipp Kupferschmied Sockets 5/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Unix-Domain Sockets
Implemented purely in memory
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Unix-domain addresses are file names
/tmp/server
sockaddr un
sun family = AF UNIX
sun path = /tmp/server Socket Socket
Client Server
/ tmp/server
request
reply
Philipp Kupferschmied Sockets 5/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Internet-Domain Sockets
Implemented via the network
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Internet-domain addresses consist of IP and port number
192.168.0.1:80
sockaddr in
sin family = AF INET
sin port = 80
sin addr = 0x0100A8C0
Socket Socket
Client Server
 
Philipp Kupferschmied Sockets 6/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Internet-Domain Sockets
Implemented via the network
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Internet-domain addresses consist of IP and port number
192.168.0.1:80
sockaddr in
sin family = AF INET
sin port = 80
sin addr = 0x0100A8C0
Socket Socket
Client Server
192.168.0.1:80192.168.0.1:3245
Philipp Kupferschmied Sockets 6/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Internet-Domain Sockets
Implemented via the network
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Internet-domain addresses consist of IP and port number
192.168.0.1:80
sockaddr in
sin family = AF INET
sin port = 80
sin addr = 0x0100A8C0
Socket Socket
Client Server
192.168.0.1:80
request
192.168.0.1:3245
Philipp Kupferschmied Sockets 6/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Internet-Domain Sockets
Implemented via the network
Users can bind a socket to an “address”
Socket becomes accessible at this “address”
Internet-domain addresses consist of IP and port number
192.168.0.1:80
sockaddr in
sin family = AF INET
sin port = 80
sin addr = 0x0100A8C0
Socket Socket
Client Server
192.168.0.1:80
request
reply
192.168.0.1:3245
Philipp Kupferschmied Sockets 6/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Socket Basics
Characteristics
Characteristics
Communication between two sockets
Connection-oriented or
Packet-based
Allow for error control (TCP, UNIX STREAM)
Network-capable IPC
Flexible
AX 25, APPLETALK, IPX, HTTP, RPC, . . .
Philipp Kupferschmied Sockets 7/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
socket() socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
bind() socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
l isten() socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
accept() socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
accept()
socket()socket
socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
accept() connect()socketsocket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
socket’
socket
socket
read()
wri te()
close()
wri te()
read()
close()
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
accept() socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Establishing a Connection
socket() socket
bind()
l isten()
accept() connect()
socket()socket
socket
socket
socket’
socket
socket
read()
wri te()
close()
wri te()
read()
close()
socket
Philipp Kupferschmied Sockets 8/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Data Transfer
socket’ socketread()
wri te()
wri te()
read()
socket
socket’
socket’’ socket
socket
socket connect()
wri te()
wri te()read()
read()
accept()
 
Blocking syscalls ‘accept’ and ‘read’ require a thread per socket.
Philipp Kupferschmied Sockets 9/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Data Transfer
socket’ socketread()
wri te()
wri te()
read()
socket
socket’
socket’’ socket
socket
socket connect()
wri te()
wri te()
fd_set
select()
or poll()
Use ‘select’ or ‘poll’ to watch many sockets in one thread.
Philipp Kupferschmied Sockets 9/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Strengths and Weaknesses
+ Encapsulation of data transfer
+ Extensibility with new protocols
+ Flexibility (e.g., X server)
Unix-domain sockets for local clients
Internet-domain sockets for remote clients
Same code, except connect()
– Inconvenient programming interface
– Each process has to close its local socket
Philipp Kupferschmied Sockets 10/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Example (Unix-Domain)
Client:
int s = socket ( AF_UNIX, SOCK_STREAM, 0 );
struct sockaddr_un server_addr;
server_addr.sun_family = AF_UNIX;
strcpy( server_addr.sun_path, "/tmp/serversock" );
connect( s, (struct sockaddr *) &server_addr, sizeof(server_addr) );
Server:
s = socket( AF_UNIX, SOCK_STREAM, 0 );
struct sockaddr_un server_addr;
server_addr.sun_family = AF_UNIX;
strcpy( server_addr.sun_path, "/tmp/serversock" );
bind( s, (struct sockaddr *)&server_addr, sizeof(server_addr) );
listen( s, 5 );
Philipp Kupferschmied Sockets 11/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Connections
Single-Threaded Servers
Summary
Example (Internet-Domain)
Client:
int s = socket( AF_INET, SOCK_STREAM, 0 );
struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(15001);
inet_aton( "127.0.0.1", &server_addr.sin_addr );
connect( s, (struct sockaddr *)&server_addr, sizeof(server_addr) );
Server:
int s = socket( AF_INET, SOCK_STREAM, 0 );
struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(15001);
inet_aton( "127.0.0.1", &server_addr.sin_addr );
bind( s, (struct sockaddr *)&server_addr, sizeof(server_addr) );
listen( s, 5 );
Philipp Kupferschmied Sockets 12/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
struct socket
struct socket
state
flags
proto ops
fasync list
file
sk
wait
type
struct proto ops
inet write
inet read
. . .
struct sock
sock common
sk protocol
sk type
. . .
head
tail
struct sk buff
next
prev
sk
dev
data
. . .
Philipp Kupferschmied Sockets 13/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
struct socket
struct socket
state
flags
proto ops
fasync list
file
sk
wait
type
struct proto ops
inet write
inet read
. . .
struct sock
sock common
sk protocol
sk type
. . .
head
tail
struct sk buff
next
prev
sk
dev
data
. . .
Philipp Kupferschmied Sockets 13/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
struct socket
struct socket
state
flags
proto ops
fasync list
file
sk
wait
type
struct proto ops
inet write
inet read
. . .
struct sock
sock common
sk protocol
sk type
. . .
head
tail
struct sk buff
next
prev
sk
dev
data
. . .
Philipp Kupferschmied Sockets 13/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
struct socket
struct socket
state
flags
proto ops
fasync list
file
sk
wait
type
struct proto ops
inet write
inet read
. . .
struct sock
sock common
sk protocol
sk type
. . .
head
tail
struct sk buff
next
prev
sk
dev
data
. . .
Philipp Kupferschmied Sockets 13/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Linux Sockets in Action
write(fd)
sys_write(fd)
sock_write()
inet_sendmsg()
tcp_sendmsg()
tcp_send_skb()
tcp_transmit_skb()
ip_queue_xmit()
ei_start_xmit()
read()
sys_read()
sock_read()
inet_recvmsg()
tcp_recvmsg()
tcp_data()
tcp_rcv()
ip_recv()
ei_recv
ei_interrupt
proto_ops
data USER
VFS
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
socket
sock
data
data
Philipp Kupferschmied Sockets 14/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Linux Sockets in Action
write(fd)
sys_write(fd)
sock_write()
inet_sendmsg()
tcp_sendmsg()
tcp_send_skb()
tcp_transmit_skb()
ip_queue_xmit()
ei_start_xmit()
read(fd)
sys_read(fd)
sock_read()
inet_recvmsg()
tcp_recvmsg()
tcp_data()
tcp_rcv()
ip_recv()
ei_recv
ei_interrupt
proto_ops
data USER
VFS
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
socket
sock
data
Philipp Kupferschmied Sockets 14/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Linux Sockets in Action
write(fd)
sys_write(fd)
sock_write()
inet_sendmsg()
tcp_sendmsg()
tcp_send_skb()
tcp_transmit_skb()
ip_queue_xmit()
ei_start_xmit()
read(fd)
sys_read(fd)
sock_read()
inet_recvmsg()
tcp_recvmsg()
tcp_data()
tcp_rcv()
ip_recv()
ei_recv
ei_interrupt
proto_ops
data USER
VFS
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
socket
sock
data
data
Philipp Kupferschmied Sockets 14/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Linux Sockets in Action
write(fd)
sys_write(fd)
sock_write()
inet_sendmsg()
tcp_sendmsg()
tcp_send_skb()
tcp_transmit_skb()
ip_queue_xmit()
ei_start_xmit()
read(fd)
sys_read(fd)
sock_read()
inet_recvmsg()
tcp_recvmsg()
tcp_data()
tcp_rcv()
ip_recv()
ei_recv
ei_interrupt
proto_ops
data USER
VFS
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
socket
sock
data
Philipp Kupferschmied Sockets 14/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Conclusions
Sockets are an abstract communication interface
Hide different protocols (Unix-domain vs. Internet-domain)
Protocol dictates communication model
Transient vs. persistent
Unix’ish “everything is a file” paradigm
Linux implementations are similar for different protocols
Realized via function pointers and matching data structures
Homebrew inheritance, “object-oriented C”
(Questionable) solution to both performance and structured
software
Philipp Kupferschmied Sockets 15/ 16
The Socket Abstraction
User’s Point of View
Sockets in Linux
Data Structures
Traversing Layers
Conclusion
Literature
Sources of the Linux kernel 2.4/2.6
Helmut Herold: Linux/Unix Systemprogrammierung
Ju¨rgen Wolf: Linux-Unix-Programmierung
http://www.pronix.de/pronix-6.html
Beck: Linux Kernelprogrammierung
Online Tutorial:
http://www.cs.rpi.edu/academics/courses/netprog/
Programming Assignment
You can gain experience in socket programming by implementing
RPC via sockets in the programming assignment!
Philipp Kupferschmied Sockets 16/ 16