working on WPS output version selector

Author: fmigneault

twitcher/wps_restapi/utils.py

@@ -1,7 +1,25 @@
 from owslib.wps import ComplexData
 from twitcher.utils import parse_request_query
 from distutils.version import LooseVersion
-from pyramid.httpexceptions import HTTPError, HTTPInternalServerError
+from pyramid.httpexceptions import HTTPSuccessful, HTTPError, HTTPInternalServerError
+from lxml import etree
+import requests
+
+import logging
+LOGGER = logging.getLogger("TWITCHER")
+
+VERSION_100 = '1.0.0'
+VERSION_200 = '2.0.0'
+CONTENT_TYPE_XML = 'application/xml'
+CONTENT_TYPE_JSON = 'application/json'
+OUTPUT_FORMAT_JSON = 'json'
+OUTPUT_FORMAT_XML = 'xml'
+OUTPUT_FORMATS = {
+    VERSION_100: OUTPUT_FORMAT_XML,
+    VERSION_200: OUTPUT_FORMAT_JSON,
+    CONTENT_TYPE_XML: OUTPUT_FORMAT_XML,
+    CONTENT_TYPE_JSON: OUTPUT_FORMAT_JSON,
+}
 
 
 def wps_restapi_base_path(settings):
@@ -31,27 +49,59 @@ def jsonify(value):
         return value
 
 
-def get_wps_output_format(request):
+def get_wps_output_format(request, service_url=None):
     """
     Get the preferred output format from WPS after checking various hints:
         - 'version' in query string
-        - 'application/xml' or 'application/json' in accept headers
+        - Content-Type in accept headers
+        - GetCapabilities of the service
 
-    :param request:
-    :return: 'json' or 'xml' (default: 'json' if no direct hint matched)
+    :param request: request for which a response of WPS version-specific format must be generated.
+    :param service_url: endpoint URL of the service to request 'GetCapabilities' if version not found by previous hints.
+    :return: one of OUTPUT_FORMAT (default: 1.0.0 => 'xml' if no direct hint matched)
     """
-    # return specific type if requested by 'version'
+    # return specific type if requested by 'version' query
     queries = parse_request_query(request)
     if 'version' in queries and len(queries['version']) > 0:
-        max_version = max([LooseVersion(v) for v in queries['version']])
-        if max_version >= LooseVersion('2.0.0'):
-            return 'json'
-        return 'xml'
-    # version not specified as input, check accept headers
+        out_version = min([LooseVersion(v) for v in queries['version']])
+        out_format = OUTPUT_FORMATS.pop(out_version.version, None)
+        return out_format or OUTPUT_FORMATS[VERSION_100]
+
+    # version not specified as query, check accept headers for specific and unique case
     accepts = [accept[0] for accept in request.accept.parsed]
-    if 'application/xml' in accepts:
-        return 'xml'
-    return 'json'
+    matched_accepts = list(set(OUTPUT_FORMATS) & set(accepts))
+    if len(matched_accepts) == 1:
+        return OUTPUT_FORMATS[matched_accepts[0]]
+
+    # version still ambiguous, verify service's GetCapabilities
+    if service_url:
+        getcap_url_100 = '{}?service=WPS&request=GetCapabilities'
+        getcap_url_200 = '{}/processes'.format(service_url)
+        getcap_resp_100 = requests.get(getcap_url_100)
+        getcap_resp_200 = requests.get(getcap_url_200)
+
+        # analyse JSON response
+        if isinstance(getcap_resp_200, HTTPSuccessful):
+            try:
+                # TODO: update get version if it is ever added to 'GetCapabilities' from WPS REST response
+                # for now, suppose that a valid list in json body means that the service is WPS 2.0.0
+                if isinstance(getcap_resp_200.json()['processes'], list):
+                    return OUTPUT_FORMATS[VERSION_200]
+            except Exception as ex:
+                LOGGER.error('Got exception in `get_wps_output_format` JSON parsing: {}'.format(repr(ex)))
+
+        # analyse XML response
+        if isinstance(getcap_resp_100, HTTPSuccessful):
+            try:
+                # TODO XML implementation
+                etree.fromstring(getcap_resp_100.content)
+                return OUTPUT_FORMATS[VERSION_100]
+            except Exception as ex:
+                LOGGER.error('Got exception in `get_wps_output_format` XML parsing: {}'.format(repr(ex)))
+
+    # still not found, default to older version
+    # for most probable format supported by services
+    return OUTPUT_FORMATS[VERSION_100]
 
 
 def httpError(http_error_class, **body):