Status code 200 when error in execution handler

[eran-pinhas]

Description

Hey,

I believe there's an issue with the status code. when the handler itself raises an error the Process.py catches it (lines below) sets the wps_request as failed (attached below) but then continues like no error occurred. As result the status code of the HTTP request is 200 and should be 500

pywps/pywps/app/Process.py

Line 232 in ec1d90f

wps_response._update_status(WPS_STATUS.FAILED, msg, 100)

I can think of 2 solutions:

• re-raise an NoApplicableCode at Process.py#L232
• before the return response (Service.py#L326) check whether the response is failed one and if so raise an NoApplicableCode that will be catched at Service.py#L335

What do you guys think? @cehbrecht @jachym

Environment

• operating system: ubuntu 18
• Python version: 3.6
• PyWPS version: latest from github
• source/distribution: git clone
• web server: Flask

[eran-pinhas]

@cehbrecht what do you think? I would be happy to help fixing the issue. just need your opinion on how to do it.

[cehbrecht]

We should use the Exceptions (HTTP status codes) according to the WPS protocol:
http://www.opengeospatial.org/standards/wps

For WPS 1.0.0 see Table 62 in the spec.

Here is a list of the WPS 2.0.0 protocol:
http://docs.opengeospatial.org/is/14-065/14-065.html

I'm not sure if we need to raise an exception when the process has failed. It will be reported with a status document ... and using status code=200.

The exceptions available look like to report that there is something wrong with my WPS service. But to report process failures you just use a status document.

@jachym You are more familiar with the WPS protocol.

[cehbrecht]

Execute Exceptions in WPS 2.0.0:
http://docs.opengeospatial.org/is/14-065/14-065.html#61

[cehbrecht]

WPS 1.0.0:

[..] If a process fails for some reason, the implementation raises an error and places it in the exception report included in this ProcessFailed structure.

It sounds confusing to me ... but the ProcessFailed structure is part of the status report ... not part of a WPS exception.

[jachym]

Hi,

this is confusing, as @cehbrecht says: ProcessFaild strucutre is part of status report - which returns 200 code.

But generally speaking, I would support more "aggressive" error handling and raise NoApplicableCode with 500 as response code.

Re-raising in Process.py sounds like less invasive solution?

[eran-pinhas]

I agree about the ProcessFailed structure. but this is right only in the case of status request (which makes sense - the service have not failed at the status requesting).

But I find both 1&2 protocols unclear in the case of synchronous request (status=false)

[eran-pinhas]

Re-raising in Process.py sounds like less invasive solution

Denote: the _run_process function is being called only in the sync mode (Process.py#L171) so I guess the status report is irrelevant in this discussion, isn't it?

Re-raising in Process.py sounds like less invasive solution?

I agree.

[cehbrecht]

@eran-pinhas ... _run_process is also called in async mode ... but it is a bit hidden:

pywps/pywps/processing/job.py

Line 20 in c351a11

self.method = '_run_process'

[cehbrecht]

Adding an example with returning status code 200 and status report containing an exception report:

<?xml version="1.0" encoding="UTF-8"?>
<wps:ExecuteResponse xmlns:wps="http://www.opengis.net/wps/1.0.0" xmlns:ows="http://www.opengis.net/ows/1.1" 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 ../wpsExecute_response.xsd"
  service="WPS" version="1.0.0" xml:lang="en-US" serviceInstance="http://localhost:5000/wps?request=GetCapabilities&amp;amp;service=WPS" statusLocation="">
  <wps:Process wps:processVersion="1.5">
    <ows:Identifier>hello</ows:Identifier>
    <ows:Title>Say Hello</ows:Title>
    <ows:Abstract>Just says a friendly Hello. Returns a literal string output with Hello plus the inputed name.</ows:Abstract>
  </wps:Process>
  <wps:Status creationTime="2019-01-08T18:23:27Z">
    <wps:ProcessFailed>
      <wps:ExceptionReport>
        <ows:Exception exceptionCode="NoApplicableCode" locator="None">
          <ows:ExceptionText>Process failed, please check server error log</ows:ExceptionText>
        </ows:Exception>
      </wps:ExceptionReport>
    </wps:ProcessFailed>
  </wps:Status>
</wps:ExecuteResponse>

[cehbrecht]

... and here is the response using PR #446:

<?xml version="1.0" encoding="UTF-8"?>
<!-- PyWPS 4.3.dev0 -->
<ows:ExceptionReport xmlns:ows="http://www.opengis.net/ows/1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.opengis.net/ows/1.1 http://schemas.opengis.net/ows/1.1.0/owsExceptionReport.xsd" version="1.0.0">
  <ows:Exception exceptionCode="NoApplicableCode" locator="">
    <ows:ExceptionText>Process failed, please check server error log</ows:ExceptionText>
  </ows:Exception>
</ows:ExceptionReport>

In both cases we get the info there is something wrong but the unpatched version provides more details (status, process identifier, ...).

[gschwind]

Hello,

For the WPS 1.0.0 state section 10.3.1 :

In the most primitive case, when a response form of RawDataOutput‖ is requested
[...]
In all other cases, the response to a valid Execute operation request is an
ExecuteResponse XML document.

As far I understand is that if the request is valid, the response status is 200 in WPS 1.0.0. In WPS 2.0.0 it's seems different.

Best regards