REST Lua Service
Introduction
The RestLuaService is a service for initiating Lua scripts running within the LogicApp.
The RestLuaService receives messages from one or more instances of the RestServerApp which is configured to receive REST/HTTP(S) Requests from an external client.
The RestLuaService communicates with the RestServerApp using the REST-S-… messages.
Configuring RestLuaService
The RestLuaService is configured within a LogicApp.
<?xml version="1.0" encoding="utf-8"?>
<n2svcd>
...
<applications>
...
<application name="Logic" module="LogicApp">
<include>
<lib>../apps/logic/lib</lib>
</include>
<parameters>
...
</parameters>
<config>
<services>
<service module="RestServerApp::RestLuaService" libs="../apps/rest_s/lib" script_dir="/var/lib/n2svcd/logic/rest"/>
</services>
<agents>
...
</agents>
</config>
</application>
...
</application>
...
</n2svcd>
In addition to the Common LogicApp Service Configuration, note the following specific attribute notes, and service-specific attributes.
Under normal installation, the following service
attributes apply:
Parameter Name
Type
XML Type
Description
module
String
Attribute
[Required] The module name containing the Lua Service code:
RestServerApp::RestLuaService
libs
String
Element
Location of the
module
for RestLuaService.
(Default: ../apps/rest_s/lib
)
script_dir
String
Attribute
[Required] The directory containing scripts used by this service.
Script Selection (REST Request)
Script selection is not configured. The script name is simply the part after the “/” of the path.
e.g. an inbound request with path /APP/rest/echo
will map to a script name of echo
,
which will be satisfied by a file named echo.lua
in any of the directories
configured as lua_script_dir
in the LogicApp.
Refer to the LogicApp configuration for more information on directories, library paths, and script caching parameters.
Script Global Variables
Scripts run with this service have access to the Common LUA Service Global Variables.
There are no service-specific global variables.
Script Entry Parameters (REST Request)
The Lua script must be a Lua chunk which returns an n2svcd.handler
, such as the following
example, which includes a single user-level HTTP header named Echo-Flag
:
local n2svcd = require "n2.n2svcd"
local handler = function (rest)
n2svcd.debug ("Echo Supplied REST Inputs:")
n2svcd.debug_var (rest)
return {
content_type = rest.content_type,
content = rest.content,
http_headers = { { name = 'Echo-Flag', value = 'true' } }
}
end
return n2svcd.handler (handler)
The handler will be executed with a single rest
entry parameter which is an object with the
following attributes:
Attribute
Type
Description
.remote_ip
String
The remote IP address from which the REST HTTP(S) request was sent.
.remote_port
Integer
The remote TCP/IP port from which the REST HTTP(S) request was sent.
.method
String
The HTTP Request method.
.uri
String
The URI for which the request was received.
Includes only path and query. No host/port/auth/user/fragment is present.
.path
String
The URI path.
.query
String
The URI query string (the part following “?” in the URI).
.query_args
String or Object
If the
.query
attribute contains &
or =
then this query_args
contains a table of the
name and values, decoded according to common web form conventions. If you wish to have
full control of the decoding, then you should directly reference the undecoded .query
.
.content_type
String
The HTTP Request Content-Type header value.
.content
String
The HTTP Request content.
.http_headers
Array of Object
The list of HTTP headers parsed from the HTTP Request (see below for object structure).
All HTTP headers are present, including Content-Length
and Content-Type
.
If a HTTP header was repeated in the HTTP Request, then it is repeated in this Array.
Each object in the .http_headers
Array for the rest
entry parameter has the following structure.
Field
Type
Description
.name
String
[Required] The name of the HTTP Request header.
.value
String
[Required] The full string value of the HTTP Request header.
Script Return Parameters (REST Response)
The Lua script is responsible for determing the REST Response which will be sent back in reply to the original REST Request.
The simplest way to do this is by the return value given back to the service at the end of script execution.
For full control over the REST response, the script return value may be a response
object with the following attributes:
Field
Type
Description
response
Object
Container for the REST response parameters we are to send.
.code
Integer
[Required] The HTTP Response Status Code to send (e.g. 200)
.content_type
String
The HTTP Response
Content-Type
header value to send.
(Default = Do not return Content-Type
header)
.content
String
The HTTP Request content to send.
(Default = None)
.http_headers
Array of Objects
Additional user-level header objects to apply to an outbound HTTP Response (see below for object structure).
These headers are added after any headers defined by static RestServerApp
application configuration.
You should not set the Content-Type
or Content-Length
headers.
(Default = No Additional Headers)
Each object in the .http_headers
Array for the response
object has the following structure.
Field
Type
Description
.name
String
[Required] The name of the HTTP Response header.
.value
String
[Required] The full string value of the HTTP Response header.
.replace
0
/ 1
If
1
then all previous headers of this name are removed, and this header replaces them.
(Default = Append to the existing headers, do not replace)
Alternatively, the script may return a simple string, or nil
.
Example (returning a Table REST Response):
local n2svcd = require "n2.n2svcd"
local handler = function (rest)
return ({ content_type = "application/json", content = '{ "numrows": 1 }'})
end
return n2svcd.handler (handler)
Alternatively, a script may return a simple string instead of a Table.
Example (returning a String REST Response):
local n2svcd = require "n2.n2svcd"
local handler = function (rest)
return "I AM OK YOU ARE OK"
end
return n2svcd.handler (handler)
This is a shorthand for code
= 200
, content_type
= text/plain
.
Alternatively, a script may return nil
.
Example (returning a 200 OK with no Content):
local n2svcd = require "n2.n2svcd"
local handler = function (rest)
return nil
end
return n2svcd.handler (handler)
This is a shorthand for code
= 200
, no Content, no Content-Type.
The RestLuaService API
The REST Service API can be loaded as follows.
local rest_service_api = require "n2.n2svcd.rest_service"
It is not necessary to load the REST Service API if you are only using the simple response mechanism described above. It is only required if you wish to use any of the extended features described below.
.response
When a Lua Script needs to perform extended processing, it may wish to send an early REST
response before the script completes. This can be done with the response
method on the
REST API.
The response
method takes a single response
parameter. The structure of this
response parameter is identical to the response
parameter which may be returned as
the script return parameter, as described above in
Script Return Parameters (REST Response)
The response
method returns true
.
[Fragment] Example (403 Early Response with text/plain content and cookie):
...
local headers = {}
http.response_headers_set_cookie (headers, "SESSION$", "<none>", { httponly = 1 })
rest_service_api.response ({
code = 403,
content = "ACCESS DENIED!",
content_type = "text/plain",
http_headers = headers
})
...
[post-processing after REST transaction is concluded]
...
[Fragment] Example (200 Early Response with text/plain content):
```lua … rest_service_api.response (“THANKS FOR CALLING”) … [post-processing after REST transaction is concluded]