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ARQ is a SPARQL 1.1 query engine for Apache Jena
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.sparql.engine.http;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import org.apache.http.client.HttpClient;
import org.apache.jena.atlas.io.IO;
import org.apache.jena.query.Query ;
import org.apache.jena.query.QueryExecException ;
import org.apache.jena.query.ResultSet ;
import org.apache.jena.query.ResultSetFactory ;
import org.apache.jena.sparql.SystemARQ ;
import org.apache.jena.sparql.algebra.Op ;
import org.apache.jena.sparql.algebra.OpAsQuery ;
import org.apache.jena.sparql.algebra.OpVars ;
import org.apache.jena.sparql.algebra.op.OpService ;
import org.apache.jena.sparql.core.Var ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.engine.Rename ;
import org.apache.jena.sparql.engine.iterator.QueryIter ;
import org.apache.jena.sparql.engine.iterator.QueryIteratorResultSet ;
import org.apache.jena.sparql.mgt.Explain ;
import org.apache.jena.sparql.util.Context ;
import org.apache.jena.sparql.util.Symbol ;
/** Execution of OpService */
public class Service {
/* define the symbols that Service will use to set the HttpQuery parameters */
public static final String base = "http://jena.hpl.hp.com/Service#";
/**
* Use to set the HttpQuery.allowCompression flag.
*/
public static final Symbol queryCompression = SystemARQ.allocSymbol(base, "queryCompression");
/**
* Use to set the HTTP client for a service.
*/
public static final Symbol queryClient = SystemARQ.allocSymbol(base, "queryClient");
/**
* Use this Symbol to allow passing additional service context variables
* SERVICE call. Parameters need to be grouped by SERVICE , a
* Map is assumed. The key of the first map is the SERVICE
* IRI, the value is a Context who's values will override any defaults in
* the original context.
*
* @see org.apache.jena.sparql.engine.http.Service
*/
public static final Symbol serviceContext = SystemARQ.allocSymbol(base, "serviceContext");
/**
* Control whether SERVICE processing is allowed.
* If the context contains this, and it is set to "false",
* then SERVICE is not allowed.
*/
public static final Symbol serviceAllowed = SystemARQ.allocSymbol(base, "serviceAllowed");
/**
* Set timeout. The value of this symbol gives the value of the timeout in
* milliseconds
*
* - A Number; the long value is used
* - A string, e.g. "1000", parsed as a number
* - A string, as two numbers separated by a comma, e.g. "500,10000"
* parsed as two numbers
*
* The first value is passed to HttpQuery.setConnectTimeout() the second, if
* it exists, is passed to HttpQuery.setReadTimeout()
*/
public static final Symbol queryTimeout = SystemARQ.allocSymbol(base, "queryTimeout");
/**
* Executes a service operator
*
* @param op
* Service
* @param context
* Context
* @return Query iterator of service results
*/
public static QueryIterator exec(OpService op, Context context) {
if ( context != null && context.isFalse(serviceAllowed) )
throw new QueryExecException("SERVICE execution disabled") ;
if (!op.getService().isURI())
throw new QueryExecException("Service URI not bound: " + op.getService());
// This relies on the observation that the query was originally correct,
// so reversing the scope renaming is safe (it merely restores the
// algebra expression).
// Any variables that reappear should be internal ones that were hidden
// by renaming in the first place.
// Any substitution is also safe because it replaced variables by
// values.
Op opRemote = Rename.reverseVarRename(op.getSubOp(), true);
// JENA-494 There is a bug here that the renaming means that if this is
// deeply nested and joined to other things at the same level of you end
// up with the variables being disjoint and the same results
// The naive fix for this is to map the variables visible in the inner
// operator to those visible in the rewritten operator
// There may be some cases where the re-mapping is incorrect due to
// deeply nested SERVICE clauses
Map varMapping = new HashMap<>();
Set originalVars = OpVars.visibleVars(op);
Set remoteVars = OpVars.visibleVars(opRemote);
boolean requiresRemapping = false;
for (Var v : originalVars) {
if (v.getName().contains("/")) {
// A variable which was scope renamed so has a different name
String origName = v.getName().substring(v.getName().lastIndexOf('/') + 1);
Var remoteVar = Var.alloc(origName);
if (remoteVars.contains(remoteVar)) {
varMapping.put(remoteVar, v);
requiresRemapping = true;
}
} else {
// A variable which does not have a different name
if (remoteVars.contains(v))
varMapping.put(v, v);
}
}
// Explain.explain("HTTP", opRemote, context) ;
Query query;
//@formatter:off
// Comment (for the future?)
// if ( false )
// {
// // ***** Interacts with substitution.
// Element el = op.getServiceElement().getElement() ;
// if ( el instanceof ElementSubQuery )
// query = ((ElementSubQuery)el).getQuery() ;
// else
// {
// query = QueryFactory.create() ;
// query.setQueryPattern(el) ;
// query.setResultVars() ;
// }
// }
// else
//@formatter:on
query = OpAsQuery.asQuery(opRemote);
Explain.explain("HTTP", query, context);
String uri = op.getService().getURI();
HttpQuery httpQuery = configureQuery(uri, context, query);
InputStream in = httpQuery.exec();
// Read the whole of the results now.
// Avoids the problems with calling back into the same system e.g.
// Fuseki+SERVICE
ResultSet rs = ResultSetFactory.fromXML(in);
QueryIterator qIter = QueryIter.materialize(new QueryIteratorResultSet(rs));
// And close connection now, not when qIter is closed.
IO.close(in);
// In some cases we may need to apply a re-mapping
// This solves JENA-494 the naive way and may be brittle for complex
// nested SERVICE clauses
if (requiresRemapping) {
qIter = QueryIter.map(qIter, varMapping);
}
return qIter;
}
/**
* Create and configure the HttpQuery object.
*
* The parentContext is not modified but is used to create a new context
* copy.
*
* @param uri
* The uri of the endpoint
* @param parentContext
* The initial context.
* @param Query
* the Query to execute.
* @return An HttpQuery configured as per the context.
*/
private static HttpQuery configureQuery(String uri, Context parentContext, Query query) {
HttpQuery httpQuery = new HttpQuery(uri);
Context context = new Context(parentContext);
// add the context settings from the service context
@SuppressWarnings("unchecked")
Map serviceContextMap = (Map) context.get(serviceContext);
if (serviceContextMap != null) {
Context serviceContext = serviceContextMap.get(uri);
if (serviceContext != null)
context.putAll(serviceContext);
}
// configure the query object.
httpQuery.merge(QueryEngineHTTP.getServiceParams(uri, context));
httpQuery.addParam(HttpParams.pQuery, query.toString());
httpQuery.setAllowCompression(context.isTrueOrUndef(queryCompression));
HttpClient client = context.get(queryClient);
if (client != null) httpQuery.setClient(client);
setAnyTimeouts(httpQuery, context);
return httpQuery;
}
/**
* Modified from QueryExecutionBase
*
* @see org.apache.jena.sparql.engine.QueryExecutionBase
*/
private static void setAnyTimeouts(HttpQuery query, Context context) {
if (context.isDefined(queryTimeout)) {
Object obj = context.get(queryTimeout);
if (obj instanceof Number) {
int x = ((Number) obj).intValue();
query.setConnectTimeout(x);
} else if (obj instanceof String) {
try {
String str = obj.toString();
if (str.contains(",")) {
String[] a = str.split(",");
int x1 = Integer.parseInt(a[0]);
int x2 = Integer.parseInt(a[1]);
query.setConnectTimeout(x1);
query.setReadTimeout(x2);
} else {
int x = Integer.parseInt(str);
query.setConnectTimeout(x);
}
} catch (NumberFormatException ex) {
throw new QueryExecException("Can't interpret string for timeout: " + obj);
}
} else {
throw new QueryExecException("Can't interpret timeout: " + obj);
}
}
}
}
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