Creating your first ZOO Service¶
Introduction¶
In this part, you will create and publish a simple ZOO-Service named Hello
which
will simply return a hello message containing the input value provided. It will be usefull
to present in deeper details general concept on how ZOO-Kernel works and handles
Execute requests.
Service and publication process overview¶
Before starting developing a ZOO Service, you should remember that in ZOO-Project, a Service is a couple made of:
a metadata file: a ZOO Service Configuration File (ZCFG) containing metadata informations about a Service (providing informations about default / supported inputs and outputs for a Service)
a Services Provider: it depends on the programming language used, but for Python it is a module and for JavaScript a script file.
To publish your Service, which means make your ZOO Kernel aware of its presence,
you should copy a ZCFG file in the directory where zoo_loader.cgi
is located (in this workshop, /usr/lib/cgi-bin
) or in any subdirectory.
Warning
only the ZCFG file is required for the Service to be considerate as available. So if you don’t get the Service Provider, obviously your Execute request will fail as we will discuss later.
Before publication, you should store your ongoing work, so you’ll start by creating a directory to store the files of your Services Provider:
mkdir -p /home/user/zoo-ws/ws_sp/cgi-env
Once the ZCFG and the Python module are both ready, you can publish simply by copying the corresponding files in the same directory as the ZOO-Kernel.
Creating your first ZCFG file¶
You will start by creating the ZCFG file for the Hello
Service. Edit the
/home/user/zoo-ws/ws_sp/cgi-env/Hello.zcfg
file
and add the following content:
1[Hello]
2 Title = Return a hello message.
3 Abstract = Create a welcome string.
4 processVersion = 2
5 storeSupported = true
6 statusSupported = true
7 serviceProvider = test_service
8 serviceType = Python
9 <DataInputs>
10 [name]
11 Title = Input string
12 Abstract = The string to insert in the hello message.
13 minOccurs = 1
14 maxOccurs = 1
15 <LiteralData>
16 dataType = string
17 <Default />
18 </LiteralData>
19 </DataInputs>
20 <DataOutputs>
21 [Result]
22 Title = The resulting string
23 Abstract = The hello message containing the input string
24 <LiteralData>
25 dataType = string
26 <Default />
27 </LiteralData>
28 </DataOutputs>
Note
the name of the ZCFG file and the name between braket (here [Hello]
)
should be the same and correspond to the function name you will define in your
Services provider.
As you can see in the ZOO Service Configuration File presented above it is divided into three distinct sections:
Main Metadata information (from line 2 to 8)
List of Inputs metadata information (from 9 line to 19)
List of Outputs metadata information (from line 20 to 28)
You can get more informations about ZCFG from the reference documentation.
If you copy the Hello.zcfg
file in the same directory as your ZOO Kernel
then you will be able to request for DescribeProcess using the Hello
Identifier
. The Hello
service should also be listed from Capabilities
document.
Test requests¶
In this section you will tests each WPS requests : GetCapabilities, DescribeProcess and Execute. Note that only GetCapabilities and DescribeProcess should work at this step.
Test the GetCapabilities request¶
If you run the GetCapabilities
request:
http://localhost/cgi-bin/zoo_loader.cgi?request=GetCapabilities&service=WPS
Now, you should find your Hello Service in a Process
node in
ProcessOfferings
:
<wps:Process wps:processVersion="2">
<ows:Identifier>Hello</ows:Identifier>
<ows:Title>Return a hello message.</ows:Title>
<ows:Abstract>Create a welcome string.</ows:Abstract>
</wps:Process>
Using the 2.0.0 version of WPS, you should be able to use the following URL.
http://localhost/cgi-bin/zoo_loader.cgi?request=GetCapabilities&service=WPS&AcceptVersion=2.0.0
Test the DescribeProcess request¶
You can access the ProcessDescription
of the Hello
service using the
following DescribeProcess
request:
http://localhost/cgi-bin/zoo_loader.cgi?request=DescribeProcess&service=WPS&version=1.0.0&Identifier=Hello
You should get the following response:
<wps:ProcessDescriptions xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsDescribeProcess_response.xsd" service="WPS" version="1.0.0" xml:lang="en-US">
<ProcessDescription wps:processVersion="2" storeSupported="true" statusSupported="true">
<ows:Identifier>Hello</ows:Identifier>
<ows:Title>Return a hello message.</ows:Title>
<ows:Abstract>Create a welcome string.</ows:Abstract>
<DataInputs>
<Input minOccurs="1" maxOccurs="1">
<ows:Identifier>name</ows:Identifier>
<ows:Title>Input string</ows:Title>
<ows:Abstract>The string to insert in the hello message.</ows:Abstract>
<LiteralData>
<ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#string">string</ows:DataType>
<ows:AnyValue/>
</LiteralData>
</Input>
</DataInputs>
<ProcessOutputs>
<Output>
<ows:Identifier>Result</ows:Identifier>
<ows:Title>The resulting string</ows:Title>
<ows:Abstract>The hello message containing the input string</ows:Abstract>
<LiteralOutput>
<ows:DataType ows:reference="http://www.w3.org/TR/xmlschema-2/#string">string</ows:DataType>
</LiteralOutput>
</Output>
</ProcessOutputs>
</ProcessDescription>
</wps:ProcessDescriptions>
Using the 2.0.0 version of WPS, you should be able to use the following URL.
http://localhost/cgi-bin/zoo_loader.cgi?request=DescribeProcess&service=WPS&version=2.0.0&Identifier=Hello
Test the Execute request¶
Obviously, you cannot run your Service because the Python file was not published
yet. If you try the following Execute
request:
http://localhost/cgi-bin/zoo_loader.cgi?request=Execute&service=WPS&version=1.0.0&Identifier=Hello&DataInputs=name=toto
You should get an ExceptionReport similar to the one provided in the following, which is normal behavior:
<ows:ExceptionReport xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsExceptionReport.xsd" xml:lang="en-US" version="1.1.0">
<ows:Exception exceptionCode="NoApplicableCode">
<ows:ExceptionText>Python module test_service cannot be loaded.</ows:ExceptionText>
</ows:Exception>
</ows:ExceptionReport>
Implementing the Python Service¶
General Principles¶
The most important thing you must know when implementing a new ZOO-Services
using the Python language is that the function corresponding to your Service
returns an integer value representing the status of execution
(SERVICE_FAILED
[1] or SERVICE_SUCCEEDED
[2]) and takes three
arguments (Python dictionaries):
conf
: the main environment configuration (corresponding to the main.cfg content)
inputs
: the requested / default inputs (used to access input values)
outputs
: the requested / default outputs (used to store computation result)
Note
when your service return SERVICE_FAILED
you can set
conf["lenv"]["message"]
to add a personalized message in the ExceptionReport
returned by the ZOO Kernel in such case.
You get in the following a sample conf
value based on the main.cfg
file you
saw before.
1{
2 "main": {
3 language: "en-US",
4 lang: "fr-FR,ja-JP",
5 version: "1.0.0",
6 encoding: "utf-8",
7 serverAddress: "http://localhost/cgi-bin/zoo_loader.cgi",
8 dataPath: "/var/data",
9 tmpPath: "/var/www/temp",
10 tmpUrl: "../temp",
11 cacheDir: "/var/www/temp/"
12 },
13 "identification": {
14 title: "ZOO-Project Workshop - FOSS4G 2017",
15 keywords: "WPS,GIS,buffer",
16 abstract: "Deploying Web Processing Services using ZOO-Project – Examples of Python based WPS using PgRouting",
17 accessConstraints: "none",
18 fees: "None"
19 },
20 "provider": {
21 positionName: "Developer",
22 providerName: "ZOO-Project",
23 addressAdministrativeArea: "Lattes",
24 addressCountry: "fr",
25 phoneVoice: "False",
26 addressPostalCode: "34970",
27 role: "Dev",
28 providerSite: "http://www.zoo-project.org",
29 phoneFacsimile: "False",
30 addressElectronicMailAddress: "gerald.fenoy@geolabs.fr",
31 addressCity: "Denver",
32 individualName: "Gérald FENOY"
33 }
In the following you get a sample outputs value passed to a Python or a JavaScript Service:
1{
2 'Result': {
3 'mimeType': 'application/json',
4 'inRequest': 'true',
5 'encoding': 'UTF-8'
6 }
7}
Note
the inRequest
value is set internally by the ZOO-Kernel and can be used to determine from the Service if the key was provided in the request.
ZOO-Project provide a ZOO-API which was originally only available for
JavaScript services, but thanks to the work of the ZOO-Project
community, now you have also access to a ZOO-API when using
the Python language. Thanks to the Python ZOO-API you don’t have to remember anymore
the value of SERVICE_SUCCEDED and SERVICE_FAILED, you
have the capability to translate any string from your Python service
by calling the _
function (ie: zoo._('My string to
translate')
) or to update the current status of a running service by
using the update_status
[3] function the same way you use it from
JavaScript or C services.
The Hello Service¶
You can copy and paste the following into the
/home/user/zoo-ws/ws_sp/cgi-env/test_service.py
file.
import zoo
def Hello(conf,inputs,outputs):
outputs["Result"]["value"]=\
"Hello "+inputs["name"]["value"]+" from the ZOO-Project Python world !"
return zoo.SERVICE_SUCCEEDED
Once you finish editing the file, you should copy it in the /usr/lib/cgi-bin
directory:
sudo cp /home/user/zoo-ws/ws_sp/cgi-env/* /usr/lib/cgi-bin
Interracting with your service using Execute requests
Now, you can request for Execute using the following basic url:
http://localhost/cgi-bin/zoo_loader.cgi?request=Execute&service=WPS&version=1.0.0&Identifier=Hello&DataInputs=name=toto
You can request the WPS Server to return a XML WPS Response containing the result of your computation, requesting for ResponseDocument or you can access the data directly requesting for RawDataOutput.
Sample request using the RawDataOutput parameter:
http://localhost/cgi-bin/zoo_loader.cgi?request=Execute&service=WPS&version=1.0.0&Identifier=Hello&DataInputs=name=toto&RawDataOutput=Result
Sample request using the default ResponseDocument parameter:
http://localhost/cgi-bin/zoo_loader.cgi?request=Execute&service=WPS&version=1.0.0&Identifier=Hello&DataInputs=name=toto&ResponseDocument=Result
When you are using ResponseDocument there is specific attribut you can use to ask
the ZOO Kernel to store the result: asReference
. You can use the following example:
http://localhost/cgi-bin/zoo_loader.cgi?request=Execute&service=WPS&version=1.0.0&Identifier=Hello&DataInputs=name=toto&ResponseDocument=Result@asReference=true
When computation take long time, the client should request the
execution of a Service by setting both storeExecuteResponse
and
status
parameter to true to force asynchronous execution. This
will make the ZOO-Kernel return, without waiting for the Service execution
completion but after starting another ZOO-Kernel process responsible
of the Service execution, a ResponseDocument containing a statusLocation
attribute which can be used to access the status of an ongoing service
or the result when the process ended [4].
http://localhost/cgi-bin/zoo_loader.cgi?request=Execute&service=WPS&version=1.0.0&Identifier=Hello&DataInputs=name=toto&ResponseDocument=Result&storeExecuteResponse=true&status=true
Conclusion¶
Even if this first service was really simple it was useful to illustrate how the
ZOO-Kernel fill conf
, inputs
and outputs
parameter prior to load
and run your function service, how to write a ZCFG file, how to publish a Services
Provider by placing the ZCFG and Python files in the same directory as the
ZOO-Kernel, then how to interract with your service using both
GetCapabilities
, DescribeProcess
and Execute
requests. We will see
in the next section how to write similar requests
using the XML syntax.
Footnotes