Introduction
LuaSOAP is a Lua library to ease the use of SOAP. It enables a Lua program to:
- Encode and decode SOAP messages without having to deal directly with XML code
- Invoke remote Web Services without having to deal directly with SOAP messages
LuaSOAP provides a very simple API and an abstraction layer over XML avoiding manipulation of string representation of data structures.
LuaSOAP is based on LuaExpat and on Lua 5.1. The abstraction layer over HTTP depends on LuaSocket 2.0. An optional layer over HTTPS depends on LuaSec 0.4.
Installation
LuaSOAP is a Lua library composed by a main module (soap.lua
)
and some extensions: client.lua
and server.lua
.
The main module must be copied to your package.path
and the
other two files to a soap
directory in your
package.path
.
LuaSOAP can also be installed via LuaRocks
with the command luarocks install luasoap
.
You can check the available rocks at LuaRocks' main repository.
LuaSOAP elements
LuaSOAP elements are always represented by Lua tables except strings. A LuaSOAP element is a table of the form defined by the Lua Object Model from the LuaExpat library. The table has the following characteristics:
- a special field called
tag
with the element's name; - a special optional field called
attr
with the element's attributes (see next section); - the element's children are stored at the array-part of the table. A child could be an ordinary string or a LuaSOAP element (a Lua table following these same rules).
Attributes
The special field attr
is a Lua table that stores
the LuaSOAP element's attributes as pairs
<key>=<value>. To assure an order (if
necessary), the sequence of keys should be placed at the
array-part of that table.
This documentation provides a detailed example which shows some common use cases.
Escaping and special characters
Since LuaSOAP 3.0, the library took the responsibility to escape data
inside LuaSOAP elements (entries
field of soap envelope; see
function soap.encode below).
Therefore, XML special characters such as <
and
>
are automatically converted to the corresponding XML
entities (<
and >
, respectively).
This documentation provides examples which show some common use cases.
Basic support
The module soap
implements all basic support for
encoding and decoding SOAP messages. There are two functions:
encode(args) => envelope
Builds a SOAP document containing aSOAP-Envelope
element. It receives a table with the following fields:namespace
a string with an URI indicating the namespace (xmlns
) atribute of the request,method
a string with the method's name,entries
an array (a table with numeric keys) of LuaSOAP elements,header
(optional) a table of headers (soap:Header
element; a LuaSOAP element too),soapversion
(optional; default = 1.1) a number with the SOAP version (currently supported versions are 1.1 and 1.2),internal_namespace
(optional; default = "") a string with the `internal' namespace (xmlns:internal_namespace
)
The function can raise errors in case theargs
table is mal formed.decode (method_response) => namespace, method_name, elements
Disassembles a SOAP document into Lua objects. It receives a string containing the SOAP document. The results are: the namespace (string), the SOAP-element method's name (string) and a table with the contents of the SOAP Body. Each element of theelements
table can be a string or a LuaSOAP element.
Client side
The module soap.client
implements a stand-alone client
which works over HTTP and is based on LuaSocket 2.0.
The following function is provided:
call (args) => namespace, method_name, elements
It encapsulates the call ofencode
anddecode
over a connection to an HTTP server, thus the arguments are passed to theencode
function and the results received from thedecode
function. It receives a table with the following fields:url
a string with the URL of the service (the protocol should behttp
orhttps
, which requires the load of LuaSec'sssl.https
module),soapaction
a string with the value of theSOAPAction
header,encoding
(optional; default = "") a string with the text encoding (usually"utf-8"
or"iso-8859-1"
),- other arguments to the
encode
function
decode
function: the namespace (string), the SOAP-element method's name (string) and a table with the contents of the SOAP Body.
HTTPS and SOAP over other transport layers
LuaSOAP client module was designed to work over HTTP (via LuaSocket's
socket.http
module) and HTTPS (via LuaSec's
ssl.https
module).
In fact, it could be used over other protocols since they provide
LuaSocket's socket.http.request
function.
The soap.client.call
function inspects the URL to check
what protocol the SOAP message is supposed to be transfered upon.
Then, it looks for a function called request
at the
soap.client.protocol
(where protocol is a
table which has an entry called request
which is a
function with the same signature of
LuaSocket's socket.http.request
.
Thus, the support fot HTTPS can be enabled by a program with the following lines:
local soap_client = require"soap.client" soap_client.https = require"ssl.https"
By following this approach, one could extend LuaSOAP to use another protocol
by implementing a function equivalent to LuaSocket's socket.http.request
or LuaSec's ssl.https.request
.