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| Network support for the Lua language |
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| Network support for the Lua language |
LuaSocket is a Lua extension library that is composed by two parts: a C core that provides support for the TCP and UDP transport layers, and a set of Lua modules that add support for the SMTP (sending e-mails), HTTP (WWW access) and FTP (uploading and downloading files) protocols and other functionality commonly needed by applications that deal with the Internet. This introduction is about the C core.
Communication in LuaSocket is performed via I/O objects. These can represent different network domains. Currently, support is provided for TCP and UDP, but nothing prevents other developers from implementing SSL, Local Domain, Pipes, File Descriptors etc. I/O objects provide a standard interface to I/O across different domains and operating systems.
The API design had 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.
One of the simplifications 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.
Another advantage is the flexible timeout control mechanism. As in C, all I/O operations are blocking by default. For example, the send, receive and accept methods of the TCP domain will block the caller application until the operation is completed (if ever!). However, with a call to the settimeout method, an application can specify upper limits on the time it can be blocked by LuaSocket (the "total" timeout), on the time LuaSocket can internally be blocked by any OS call (the "block" timeout) or a combination of the two. Each LuaSocket call might perform several OS calls, so that the two timeout values are not equivalent.
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 IP address returned. Note that direct use of IP addresses is more efficient, of course. The toip and tohostname functions from the DNS module are provided to convert between host names and IP addresses.