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< title > LuaSocket: Network support for the Lua language< / title >
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< tr > < td align = center valign = top > Network support for the Lua language
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< a href = "home.html" > home< / a > ·
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< a href = "introduction.html" > introduction< / a > ·
< a href = "reference.html" > reference< / a >
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<!-- introduction +++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
< h2 > Introduction< / h2 >
< p >
Communication in LuaSocket is performed via I/O objects. These can
represent different network domains. Currently, support is
provided for TCP and UDP, but there is work in progress to implement SSL,
Local Domain, Pipes, File Descriptors etc. I/O objects provide a standard
interface to I/O across different domains and operating systems.
LuaSocket 2.0 has been rewritten from scratch to simplify the future
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addition of new domains.
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< p >
The LuaSocket API was designed with two goals in mind. First, users
experienced with the C API to sockets should feel comfortable using LuaSocket.
Second, the simplicity and the feel of the Lua language should be
preserved. To achieve these goals, the LuaSocket API keeps the function names and semantics the C API whenever possible, but their usage in Lua has been greatly simplified.
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< p >
One of the simplifications is the timeout control
mechanism. As in C, all I/O operations are blocking by default. For
example, the < a href = tcp.html#send > < tt > send< / tt > < / a > ,
< a href = tcp.html#receive > < tt > receive< / tt > < / a > and
< a href = tcp.html#accept > < tt > accept< / tt > < / a > methods
of the TCP domain will block the caller application until
the operation is completed (if ever!). However, with a call to the
< a href = tcp.html#settimeout > < tt > settimeout< / tt > < / a >
method, an application can specify upper limits on
the time it can be blocked by LuaSocket (the "< tt > total< / tt > " timeout), on
the time LuaSocket can internally be blocked by any OS call (the
"< tt > block< / tt > " timeout) or a combination of the two. Each LuaSocket
call might perform several OS calls, so that the two timeout values are
< em > not< / em > equivalent.
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< p >
Another important difference is the receive pattern capability.
Applications can read data from stream domains (such as TCP)
line by line, block by block, or until the connection is closed.
All I/O reads are buffered and the performance differences between
different receive patterns are negligible.
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< p >
Finally, the host name resolution is transparent, meaning that most
functions and methods accept both IP addresses and host names. In case a
host name is given, the library queries the system's resolver and
tries the main returned IP address. Note that direct use of IP addresses
is more efficient, of course. The
< a href = dns.html#toip > < tt > toip< / tt > < / a >
and < a href = dns.html#tohostname > < tt > tohostname< / tt > < / a >
functions from the DNS module are provided to convert between host names and IP addresses.
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Previous versions of LuaSocket provided global functions for operating on
I/O objects. To give the library a Lua 5.0 feel, these have been eliminated
from LuaSocket 2.0. I/O operations are only available as methods of the
corresponding I/O objects. Naturally, different I/O objects accept
different operations. The core functionality for TCP and UDP objects is
introduced in the following sections, following a few words about
initialization.
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< h3 > Initializing the library< / h3 >
< p >
Beginning with version 2.0 and following the Lua 5.0 trend, all LuaSocket
functionality is defined inside a table (or rather a namespace) stored with
the global name < tt > socket< / tt > . To have this table created and its
contents made available to a Lua script, the interpreter running the script
must be linked to the LuaSocket library, and to whatever libraries the
host OS requires for network access (Windows requires ws2_32.lib, for
instance). LuaSocket is initialized in the
Lua state given as the argument to the function
< tt > luaopen_socket< / tt > , the only C function exported by the library.
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After initialization, scripts are free to use all of the LuaSocket API.
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<!-- tcp ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
< h3 id = tcp > TCP< / h3 >
< p >
TCP (Transfer Control Protocol) is reliable stream protocol. In other
words, applications communicating through TCP can send and receive data as
an error free stream of bytes. Data is split in one end and
reassembled transparently on the other end. There are no boundaries in
the data transfers. The library allows users to read data from the
sockets in several different granularity: patterns are available for
lines, arbitrary sized blocks or "read up to connection closed", all with
good performance.
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The library distinguishes three types of TCP sockets: master, client and server sockets.
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Master sockets are newly created TCP sockets returned by the function
< a href = tcp.html#tcp > < tt > socket.tcp< / tt > < / a > . A master socket is
transformed into a server socket
after it is associated with a < em > local< / em > address by a call to the
< a href = tcp.html#bind > < tt > bind< / tt > < / a > method. Conversely, it
can be changed into a client socket with the method
< a href = tcp.html#connect > < tt > connect< / tt > < / a > ,
that associates it with a < em > remote< / em > address.
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< p >
On server sockets, applications can use the
< a href = tcp.html#accept > < tt > accept< / tt > < / a > method
to wait for a client connection. Once a connection is established, a
client socket object is returned representing this connection. The
other methods available for server socket objects are
< a href = tcp.html#getsockname > < tt > getsockname< / tt > < / a > ,
< a href = tcp.html#setoption > < tt > setoption< / tt > < / a > ,
< a href = tcp.html#settimeout > < tt > settimeout< / tt > < / a > and
< a href = tcp.html#close > < tt > close< / tt > < / a > .
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< p >
Client sockets are used to exchange data between two applications over
the Internet. Applications can call the methods
< a href = tcp.html#send > < tt > send< / tt > < / a > and
< a href = tcp.html#receive > < tt > receive< / tt > < / a >
to send and receive data. The other methods
available for client socket objects are
< a href = tcp.html#getsockname > < tt > getsockname< / tt > < / a > ,
< a href = tcp.html#getpeername > < tt > getpeername< / tt > < / a > ,
< a href = tcp.html#setoption > < tt > setoption< / tt > < / a > ,
< a href = tcp.html#settimeout > < tt > settimeout< / tt > < / a > and
< a href = tcp.html#close > < tt > close< / tt > < / a > .
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< p >
Example:
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< blockquote >
< p >
A simple echo server, using LuaSocket. The program binds to an ephemeral
port (one that is chosen by the operating system) on the local host and
awaits client connections on that port. When a connection is established,
the program reads a line from the remote end and sends it back, closing
the connection immediately after. You can test it using the telnet
program.
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< pre class = example >
-- create a new TCP object
server, err = socket.tcp()
assert(server, err)
-- bind it to the local host, at any port
ret, err = server:bind("*", 0)
assert(ret, err)
-- find out which port the OS chose for us
ip, port = server:getsockname()
-- print a message informing what's up
print("Please telnet to localhost on port " .. port)
print("After connecting, you have 10s to enter a line to be echoed")
-- loop forever waiting for clients
while 1 do
-- wait for a conection from any client
client, err = server:accept()
-- make sure we don't block waiting for this client's line
client:settimeout(10)
-- receive the line
line, err = client:receive()
-- if there was no error, send it back to the client
if not err then
client:send(line .. "\n")
end
-- done with client, close the object
client:close()
end
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< h3 id = udp > UDP< / h3 >
< p >
UDP (User Datagram Protocol) is a non-reliable datagram protocol. In
other words, applications communicating through UDP send and receive
data as independent blocks, which are not guaranteed to reach the other
end. Even when they do reach the other end, they are not guaranteed to be
error free. Data transfers are atomic, one datagram at a time. Reading
only part of a datagram discards the rest, so that the following read
operation will act on the next datagram. The advantages are in
simplicity (no connection setup) and performance (no error checking or
error correction).
< / p >
< p >
An UDP socket object is created by the
< a href = udp.html#udp > < tt > socket.udp< / tt > < / a > function. UDP
sockets do not need to be connected before use. The method
< a href = udp.html#sendto > < tt > sendto< / tt > < / a >
can be used immediately after creation to
send a datagram to IP address and port. Host names are not allowed
because performing name resolution for each packet would be forbiddingly
slow. Methods
< a href = udp.html#receive > < tt > receive< / tt > < / a > and
< a href = udp.html#receivefrom > < tt > receivefrom< / tt > < / a >
can be used to retrieve datagrams, the latter returning the IP and port of
the sender as extra return values (thus being slightly less
efficient).
< / p >
< p >
When communication is performed repeatedly with a single peer, an
application should call the
< a href = udp.html#setpeername > < tt > setpeername< / tt > < / a > method to specify a
permanent partner. Methods
< a href = udp.html#sendto > < tt > sendto< / tt > < / a > and
< a href = udp.html#receivefrom > < tt > receivefrom< / tt > < / a >
can no longer be used, but the method
< a href = udp.html#send > < tt > send< / tt > < / a > can be used to send data
directly to the peer, and the method
< a href = udp.html#receive > < tt > receive< / tt > < / a >
will only return datagrams originating
from that peer. There is about 30% performance gain due to this practice.
< / p >
< p >
To associate an UDP socket with a local address, an application calls the
< a href = udp.html#setsockname > < tt > setsockname< / tt > < / a >
method < em > before< / em > sending any datagrams. Otherwise, the socket is
automatically bound to an ephemeral address before the first data
transmission and once bound the local address cannot be changed.
The other methods available for UDP sockets are
< a href = udp.html#getpeername > < tt > getpeername< / tt > < / a > ,
< a href = udp.html#getsockname > < tt > getsockname< / tt > < / a > ,
< a href = udp.html#settimeout > < tt > settimeout< / tt > < / a > ,
< a href = udp.html#setoption > < tt > setoption< / tt > < / a > and
< a href = udp.html#close > < tt > close< / tt > < / a > .
< / p >
< p >
Example:
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< blockquote >
< p >
A simple daytime client, using LuaSocket. The program connects to a remote
server and tries to retrieve the daytime, printing the answer it got or an
error message.
< / p >
< pre class = example >
host = "localhost" -- change here to the host you want to contact
port = port or 13
-- convert host name to ip address
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ip, err = socket.dns.toip(host)
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assert(ip, err)
-- create a new UDP object
udp = socket.udp()
-- contact daytime host
nsent, err = udp:sendto("anything", ip, port)
assert(not err, err)
-- retrieve the answer
dgram, err = udp:receive()
assert(dgram, err)
-- display to user
print(dgram)
< / pre >
< / blockquote >
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< a href = "home.html" > home< / a > ·
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Last modified by Diego Nehab on < br >
Sat Aug 9 01:00:41 PDT 2003
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