added %header magic to prepend sparql query with some aritrary command

gpotdevin · gpotdevin · commit d50d8711aa9e · 2018-08-13T15:47:09.000+02:00
diff --git a/README.rst b/README.rst
@@ -153,6 +153,14 @@ value::
   %qparam <name>
 
 
+``%header``
+............
+Adds a certain header to each sparql queries. This can be used to set some 
+(potentially non SPARQL) command in the query. For instance virtuoso endpoints 
+accept the _define_ keyword which can be used to trigger the server reasoner.
+
+
+
 ``%auth``
 ...........
 
diff --git a/sparqlkernel/connection.py b/sparqlkernel/connection.py
@@ -55,6 +55,7 @@
     '%endpoint' : [ '<url>', 'set SPARQL endpoint. **REQUIRED**'],
     '%auth':      ['(basic|digest) <username> <passwd>', 'send HTTP authentication'],
     '%qparam' :   [ '<name> [<value>]', 'add (or delete) a persistent custom parameter to the endpoint query'],
+    '%header' :   [ '<value>', 'set (or delete) a persistent header to all queries (precedes all other lines of the SPARQL query)'],
     '%prefix' :   [ '<name> [<uri>]', 'set (or delete) a persistent URI prefix for all queries'],
     '%graph' :    [ '<uri>', 'set default graph for the queries' ],
     '%format' :   [ 'JSON | N3 | XML | any | default', 'set requested result format' ],
@@ -374,7 +375,7 @@ def __init__( self, logger=None ):
         self.log = logger or logging.getLogger(__name__)
         self.srv = None
         self.log.info( "START" )
-        self.cfg = CfgStruct( pfx={}, lmt=20, fmt=None, out=None, aut=None,
+        self.cfg = CfgStruct( header={}, pfx={}, lmt=20, fmt=None, out=None, aut=None,
                               grh=None, dis='table', typ=False, lan=[], par={} )
 
     def magic( self, line ):
@@ -521,8 +522,19 @@ def magic( self, line ):
             except ValueError:
                 raise KrnlException( 'unknown log level: {}', param )
 
+        elif cmd == 'header':
+            v = param.split(None, 1)
+            if len(v) == 0:
+                raise KrnlException("missing %header value")
+            elif len(v) == 1:
+                self.cfg.header.pop(v[0], None)
+                return ['header deleted: {}', v[0]], 'magic'
+            else:
+                self.cfg.header[v[0]] = v[1]
+                return ['header set: {} = {}'] + v, 'magic'
+
         else:
-            raise KrnlException( "magic not found: {}", cmd )
+                raise KrnlException( "magic not found: {}", cmd )
 
 
     def query( self, query, num=0, silent=False ):
@@ -532,12 +544,19 @@ def query( self, query, num=0, silent=False ):
         if self.srv is None:
             raise KrnlException('no endpoint defined')             
 
-        # Prepend to the query all predefined SPARQL prefixes
+        # Add to the query all predefined SPARQL prefixes
         if self.cfg.pfx:
-            prefix = '\n'.join( ( 'PREFIX {} {}'.format(*v) 
+            prefix = '\n'.join( ( 'PREFIX {} {}'.format(*v)
                                   for v in self.cfg.pfx.items() ) )
             query = prefix  + '\n' + query
 
+        # Prepend to the query all predefined Header entries
+        # The header should be before the prefix and other sparql commands
+        if self.cfg.header:
+            header = '\n'.join( ( '{}'.format(v[1])
+                                  for v in self.cfg.header.items() ) )
+            query = header  + '\n' + query
+
         if self.log.isEnabledFor(logging.DEBUG):
             self.log.debug( "\n%50s%s", query, '...' if len(query)>50 else '' )
 
