intro.3n

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)intro.3n	8.1	9/11/90
.TH intro 3n
.SH Name
intro \- introduction to network library functions
.SH Description
.NXR "intro(3n) keyword"
.NXR "IPC" "library functions"
.NXS "interprocess communication facility" "IPC"
This section describes functions that are available 
for interprocess communication (IPC).  IPC takes
place using sockets.  The
.MS socket 2
system call creates a communications channel based
on domain, type, and protocol. 
.PP
Sockets are created without names.  The
.MS bind 2
system call is used to connect a name to 
a socket.
.PP
A connection with another process must be made
before data can be transferred on a bound socket.  The
.MS connect 2
system call is used to rendezvous with another process.  This
process must be listening on a bound socket using the
.MS listen 2
system call.  This listening process can accept
a connection request using the
.MS accept 2
system call.
.PP
Once two processes have connected and accepted an IPC,
data can be transferred with the following system calls:
.MS read 2 ;
.MS write 2 ;
.MS send 2 ,
and
.MS recv 2 .
.PP
Connectionless sockets are also possible (a socket is
bound and data can be transferred).  They use the
following system calls to transfer data: 
.PN sendto
and
.PN recvfrom .
.PP
IPC operates in three domains:
.TP 17 
UNIX\^
Local node
.TP
INTERNET\^
Local area network (LAN)
.TP
DECNET\^
DECnet network
.PP
These types of sockets are available for IPC:
.TP 17
.I stream\^
Sequenced, reliable, unduplicated data
.br
CONNECTED socket
.br
record boundaries not preserved
.br
all domains
.TP
.I datagram\^
Not guaranteed to be sequenced, reliable, or
.br
unduplicated
.br
user protocol needed to give guarantees
.br
UNCONNECTED socket
.br
record boundaries preserved
.br
UNIX and INTERNET domains
.TP
.I sequenced packet\^
Like stream socket, except record boundaries preserved
.br
DECNET domain only
.TP
.I raw\^
Access to communications protocols
.SH Internet Addresses Routines  
The 
.I inet
routines manipulate Internet addresses.
.SH Network Data Base File Routines
Standard mapping routines are used to 
retrieve entries in network data base files.  
Several routines operating on each data base 
file are identified by a group name:
.TP 17
.PN gethostent\^
Retrieves entries from 
.PN /etc/hosts
.TP 
.PN getnetent\^
Retrieves entries from
.PN /etc/networks
.TP 
.PN getprotoent\^
Retrieves entries from
.PN /etc/protocols
.TP 
.PN getservent\^
Retrieves entries from
.PN /etc/services
.PP
Specific routines perform particular operations
on each data base file:
.TP 17 
.PN get...ent\^
Reads the next line of the file; opens
the file, if necessary.
.TP
.PN set...ent\^
Opens and rewinds the file.
.TP 
.PN end...ent\^
Closes the file.
.TP 
.PN get...byname\^
Searches the file sequentially from the beginning
until a matching 
.I name
is found, or EOF is
encountered.
.TP 
.PN get...byaddr\^
Searches the file sequentially from the beginning
until a matching 
.I address
is found, or EOF is
encountered.
.TP 
.PN get...byport\^
Searches the file sequentially from the beginning
until a matching 
.I port number
is found, or EOF is encountered.
.TP 
.PN get...bynumber\^
Searches the file sequentially from the beginning
until a matching 
.I protocol number
is found, or EOF is encountered.
.PP
Each network library routine returns a pointer
to a structure reflecting individual fields of a
line in one of the network data base files.  The
structure for each data base file contains some of
the fields in the following list, with the prefix
\fIx\fR replaced by a different letter in each 
file:
.TP 17
.PN x_addr\^
pointer to a network address,
returned in network-byte order
.TP 
.PN x_addrtype\^
address family of the address being returned
.TP 
.PN x_aliases\^
alternate names
.TP 
.PN x_length\^
length of an address, in bytes
.TP 
.PN x_name\^
official name
.TP 
.PN x_net\^
network number, returned in machine-byte order
.TP 
.PN x_port\^
resident port
.TP 
.PN x_proto\^
protocol number