Simplifies the definition of the ServiceHandler trait

lib/src/sparql/eval.rs

@@ -482,28 +482,24 @@ impl<'a, S: StoreConnection + 'a> SimpleEvaluator<S> {
     fn evaluate_service<'b>(
         &'b self,
         service_name: &PatternValue,
-        graph_pattern: &GraphPattern,
+        graph_pattern: &'b GraphPattern,
         variables: &'b [Variable],
         from: EncodedTuple,
     ) -> Result<EncodedTuplesIterator<'b>> {
-        let service_name =
-            self.dataset
-                .decode_named_node(get_pattern_value(service_name, &[]).ok_or_else(|| {
-                    format_err!("The SERVICE handler name variable is not bound")
-                })?)?;
-        let service = self.service_handler.handle(&service_name).ok_or_else(|| {
-            format_err!(
-                "The handler supplied was unable to produce any result set for service {}",
-                service_name
-            )
-        })?;
+        let service_name = self.dataset.decode_named_node(
+            get_pattern_value(service_name, &[])
+                .ok_or_else(|| format_err!("The SERVICE name is not bound"))?,
+        )?;
         Ok(Box::new(
-            self.encode_bindings(variables, service(graph_pattern.clone())?)
-                .flat_map(move |binding| {
-                    binding
-                        .map(|binding| combine_tuples(&binding, &from))
-                        .transpose()
-                }),
+            self.encode_bindings(
+                variables,
+                self.service_handler.handle(&service_name, &graph_pattern)?,
+            )
+            .flat_map(move |binding| {
+                binding
+                    .map(|binding| combine_tuples(&binding, &from))
+                    .transpose()
+            }),
         ))
     }
 

lib/src/sparql/mod.rs

@@ -18,6 +18,7 @@ use crate::sparql::plan::{DatasetView, PlanNode};
 use crate::sparql::plan_builder::PlanBuilder;
 use crate::store::StoreConnection;
 use crate::Result;
+use failure::format_err;
 use rio_api::iri::Iri;
 use std::fmt;
 
@@ -163,25 +164,31 @@ impl<S: StoreConnection> PreparedQuery for SimplePreparedQuery<S> {
 ///
 /// Might be used to implement [SPARQL 1.1 Federated Query](https://www.w3.org/TR/sparql11-federated-query/)
 pub trait ServiceHandler {
-    /// Get the handler for a given service identified by a RDF IRI.
-    ///
-    /// A service is a function that returns an iterator of bindings from a `GraphPattern`.
-    /// Returns `None` if there is no handler for the service.
+    /// Evaluates a `GraphPattern` against a given service identified by a `NamedNode`.
     fn handle<'a>(
         &'a self,
-        node: &NamedNode,
-    ) -> Option<(fn(GraphPattern) -> Result<BindingsIterator<'a>>)>;
+        service_name: &NamedNode,
+        graph_pattern: &'a GraphPattern,
+    ) -> Result<BindingsIterator<'a>>;
 }
 
-#[derive(Default)]
-struct EmptyServiceHandler {}
+impl<F: for<'a> Fn(&NamedNode, &'a GraphPattern) -> Result<BindingsIterator<'a>>> ServiceHandler
+    for F
+{
+    fn handle<'a>(
+        &'a self,
+        service_name: &NamedNode,
+        graph_pattern: &'a GraphPattern,
+    ) -> Result<BindingsIterator<'a>> {
+        self(service_name, graph_pattern)
+    }
+}
+
+struct EmptyServiceHandler;
 
 impl ServiceHandler for EmptyServiceHandler {
-    fn handle(
-        &self,
-        _node: &NamedNode,
-    ) -> Option<(fn(GraphPattern) -> Result<BindingsIterator<'static>>)> {
-        None
+    fn handle<'a>(&'a self, _: &NamedNode, _: &'a GraphPattern) -> Result<BindingsIterator<'a>> {
+        Err(format_err!("The SERVICE feature is not implemented"))
     }
 }
 
@@ -197,7 +204,7 @@ impl<'a> Default for QueryOptions<'a> {
         Self {
             base_iri: None,
             default_graph_as_union: false,
-            service_handler: Box::new(EmptyServiceHandler::default()),
+            service_handler: Box::new(EmptyServiceHandler),
         }
     }
 }
@@ -216,8 +223,8 @@ impl<'a> QueryOptions<'a> {
     }
 
     /// Consider the union of all graphs in the repository as the default graph
-    pub fn with_service_handler(mut self, service_handler: Box<dyn ServiceHandler>) -> Self {
-        self.service_handler = service_handler;
+    pub fn with_service_handler(mut self, service_handler: impl ServiceHandler + 'static) -> Self {
+        self.service_handler = Box::new(service_handler);
         self
     }
 }

lib/tests/service_test_cases.rs

@@ -12,15 +12,12 @@ fn simple_service_test() {
     impl ServiceHandler for TestServiceHandler {
         fn handle<'a>(
             &'a self,
-            _named_node: &NamedNode,
-        ) -> Option<(fn(GraphPattern) -> Result<BindingsIterator<'a>>)> {
-            fn pattern_handler<'a>(graph_pattern: GraphPattern) -> Result<BindingsIterator<'a>> {
-                let triples =
-                    b"<http://example.com/s> <http://example.com/p> <http://example.com/o> ."
-                        .as_ref();
-                do_pattern(triples, graph_pattern, QueryOptions::default())
-            };
-            Some(pattern_handler)
+            _: &NamedNode,
+            graph_pattern: &'a GraphPattern,
+        ) -> Result<BindingsIterator<'a>> {
+            let triples =
+                b"<http://example.com/s> <http://example.com/p> <http://example.com/o> .".as_ref();
+            do_pattern(triples, graph_pattern, QueryOptions::default())
         }
     }
 
@@ -35,7 +32,7 @@ fn simple_service_test() {
   "#
     .to_string();
 
-    let options = QueryOptions::default().with_service_handler(Box::new(TestServiceHandler));
+    let options = QueryOptions::default().with_service_handler(TestServiceHandler);
     let results = do_query(b"".as_ref(), query, options).unwrap();
     let collected = results
         .into_values_iter()
@@ -57,36 +54,27 @@ fn two_service_test() {
         fn handle<'a>(
             &'a self,
             named_node: &NamedNode,
-        ) -> Option<(fn(GraphPattern) -> Result<BindingsIterator<'a>>)> {
+            graph_pattern: &'a GraphPattern,
+        ) -> Result<BindingsIterator<'a>> {
             let service1 = NamedNode::parse("http://service1.org").unwrap();
             let service2 = NamedNode::parse("http://service2.org").unwrap();
             if named_node == &service1 {
-                Some(TwoServiceTest::handle_service1)
-            } else if named_node == &service2 {
-                Some(TwoServiceTest::handle_service2)
-            } else {
-                None
-            }
-        }
-    }
-
-    impl TwoServiceTest {
-        fn handle_service1<'a>(graph_pattern: GraphPattern) -> Result<BindingsIterator<'a>> {
-            let triples = br#"
+                let triples = br#"
         <http://example.com/bob> <http://xmlns.com/foaf/0.1/name> "Bob" .
         <http://example.com/alice> <http://xmlns.com/foaf/0.1/name> "Alice" .
         "#
-            .as_ref();
-            do_pattern(triples, graph_pattern, QueryOptions::default())
-        }
-
-        fn handle_service2<'a>(graph_pattern: GraphPattern) -> Result<BindingsIterator<'a>> {
-            let triples = br#"
+                .as_ref();
+                do_pattern(triples, graph_pattern, QueryOptions::default())
+            } else if named_node == &service2 {
+                let triples = br#"
         <http://example.com/bob> <http://xmlns.com/foaf/0.1/mbox> <mailto:bob@example.com> .
         <http://example.com/alice> <http://xmlns.com/foaf/0.1/mbox> <mailto:alice@example.com> .
         "#
-            .as_ref();
-            do_pattern(triples, graph_pattern, QueryOptions::default())
+                .as_ref();
+                do_pattern(triples, graph_pattern, QueryOptions::default())
+            } else {
+                Err(format_err!("not found"))
+            }
         }
     }
 
@@ -107,7 +95,7 @@ fn two_service_test() {
   "#
     .to_string();
 
-    let options = QueryOptions::default().with_service_handler(Box::new(TwoServiceTest));
+    let options = QueryOptions::default().with_service_handler(TwoServiceTest);
     let results = do_query(b"".as_ref(), query, options).unwrap();
     let collected = results
         .into_values_iter()
@@ -133,14 +121,9 @@ fn silent_service_empty_set_test() {
     impl ServiceHandler for ServiceTest {
         fn handle<'a>(
             &'a self,
-            _named_node: &NamedNode,
-        ) -> Option<(fn(GraphPattern) -> Result<BindingsIterator<'a>>)> {
-            Some(ServiceTest::handle_service)
-        }
-    }
-
-    impl ServiceTest {
-        fn handle_service<'a>(_graph_pattern: GraphPattern) -> Result<BindingsIterator<'a>> {
+            _: &NamedNode,
+            _: &'a GraphPattern,
+        ) -> Result<BindingsIterator<'a>> {
             Err(format_err!("This is supposed to fail"))
         }
     }
@@ -160,7 +143,7 @@ fn silent_service_empty_set_test() {
     .to_string();
 
     let triples = b"".as_ref();
-    let options = QueryOptions::default().with_service_handler(Box::new(ServiceTest));
+    let options = QueryOptions::default().with_service_handler(ServiceTest);
     let results = do_query(triples, query, options).unwrap();
     let collected = results
         .into_values_iter()
@@ -177,14 +160,9 @@ fn non_silent_service_test() {
     impl ServiceHandler for ServiceTest {
         fn handle<'a>(
             &'a self,
-            _named_node: &NamedNode,
-        ) -> Option<(fn(GraphPattern) -> Result<BindingsIterator<'a>>)> {
-            Some(ServiceTest::handle_service)
-        }
-    }
-
-    impl ServiceTest {
-        fn handle_service<'a>(_graph_pattern: GraphPattern) -> Result<BindingsIterator<'a>> {
+            _: &NamedNode,
+            _: &'a GraphPattern,
+        ) -> Result<BindingsIterator<'a>> {
             Err(format_err!("This is supposed to fail"))
         }
     }
@@ -204,7 +182,7 @@ fn non_silent_service_test() {
     .to_string();
 
     let triples = b"".as_ref();
-    let options = QueryOptions::default().with_service_handler(Box::new(ServiceTest));
+    let options = QueryOptions::default().with_service_handler(ServiceTest);
     let results = do_query(triples, query, options).unwrap();
     let result = results.into_values_iter().next();
     match result {
@@ -263,7 +241,7 @@ fn query_repository<'a>(
 
 fn pattern_repository<'a>(
     repository: MemoryRepository,
-    pattern: GraphPattern,
+    pattern: &'a GraphPattern,
     options: QueryOptions<'a>,
 ) -> Result<BindingsIterator<'a>> {
     match repository
@@ -294,7 +272,7 @@ fn do_query<'a>(
 
 fn do_pattern<'a>(
     reader: impl BufRead,
-    pattern: GraphPattern,
+    pattern: &'a GraphPattern,
     options: QueryOptions<'a>,
 ) -> Result<BindingsIterator<'a>> {
     let repository = make_repository(reader)?;