Adds JSON SPARQL results output

lib/src/sparql/json_results.rs

@@ -0,0 +1,123 @@
+//! Implementation of [SPARQL Query Results XML Format](https://www.w3.org/TR/sparql11-results-json/)
+
+use crate::model::*;
+use crate::sparql::model::*;
+use crate::Result;
+use failure::format_err;
+use std::io::Write;
+
+pub fn write_json_results<W: Write>(results: QueryResult<'_>, mut sink: W) -> Result<W> {
+    match results {
+        QueryResult::Boolean(value) => {
+            sink.write_all(b"{\"head\":{},\"boolean\":")?;
+            sink.write_all(if value { b"true" } else { b"false" })?;
+            sink.write_all(b"}")?;
+        }
+        QueryResult::Bindings(bindings) => {
+            let (variables, results) = bindings.destruct();
+            sink.write_all(b"{\"head\":{\"vars\":[")?;
+            let mut start_vars = true;
+            for variable in &variables {
+                if start_vars {
+                    start_vars = false;
+                } else {
+                    sink.write_all(b",")?;
+                }
+                write_escaped_json_string(variable.name()?, &mut sink)?;
+            }
+            sink.write_all(b"]},\"results\":{\"bindings\":[")?;
+            let mut start_bindings = true;
+            for result in results {
+                if start_bindings {
+                    start_bindings = false;
+                } else {
+                    sink.write_all(b",")?;
+                }
+                sink.write_all(b"{")?;
+
+                let result = result?;
+                let mut start_binding = true;
+                for (i, value) in result.into_iter().enumerate() {
+                    if let Some(term) = value {
+                        if start_binding {
+                            start_binding = false;
+                        } else {
+                            sink.write_all(b",")?;
+                        }
+                        write_escaped_json_string(variables[i].name()?, &mut sink)?;
+                        match term {
+                            Term::NamedNode(uri) => {
+                                sink.write_all(b":{\"type\":\"uri\",\"value\":")?;
+                                write_escaped_json_string(uri.as_str(), &mut sink)?;
+                                sink.write_all(b"}")?;
+                            }
+                            Term::BlankNode(bnode) => {
+                                sink.write_all(b":{\"type\":\"bnode\",\"value\":")?;
+                                sink.write_fmt(format_args!("{}", bnode.as_uuid().to_simple()))?;
+                                sink.write_all(b"}")?;
+                            }
+                            Term::Literal(literal) => {
+                                sink.write_all(b":{\"type\":\"literal\",\"value\":")?;
+                                write_escaped_json_string(&literal.value(), &mut sink)?;
+                                if let Some(language) = literal.language() {
+                                    sink.write_all(b",\"xml:lang\":")?;
+                                    write_escaped_json_string(language, &mut sink)?;
+                                } else if !literal.is_plain() {
+                                    sink.write_all(b",\"datatype\":")?;
+                                    write_escaped_json_string(
+                                        literal.datatype().as_str(),
+                                        &mut sink,
+                                    )?;
+                                }
+                                sink.write_all(b"}")?;
+                            }
+                        }
+                    }
+                }
+                sink.write_all(b"}")?;
+            }
+            sink.write_all(b"]}}")?;
+        }
+        QueryResult::Graph(_) => {
+            return Err(format_err!(
+                "Graphs could not be formatted to SPARQL query results XML format"
+            ));
+        }
+    }
+    Ok(sink)
+}
+
+fn write_escaped_json_string(s: &str, sink: &mut impl Write) -> Result<()> {
+    sink.write_all(b"\"")?;
+    for c in s.chars() {
+        match c {
+            '\\' => sink.write_all(b"\\\\"),
+            '"' => sink.write_all(b"\\\""),
+            c => {
+                if c < char::from(32) {
+                    match c {
+                        '\u{08}' => sink.write_all(b"\\b"),
+                        '\u{0C}' => sink.write_all(b"\\f"),
+                        '\n' => sink.write_all(b"\\n"),
+                        '\r' => sink.write_all(b"\\r"),
+                        '\t' => sink.write_all(b"\\t"),
+                        c => {
+                            let mut c = c as u8;
+                            let mut result = [b'\\', b'u', 0, 0, 0, 0];
+                            for i in (2..6).rev() {
+                                let ch = c % 16;
+                                result[i] = ch + if ch < 10 { b'0' } else { b'A' };
+                                c /= 16;
+                            }
+                            sink.write_all(&result)
+                        }
+                    }
+                } else {
+                    sink.write_fmt(format_args!("{}", c))
+                }
+            }
+        }?;
+    }
+    sink.write_all(b"\"")?;
+    Ok(())
+}

lib/src/sparql/mod.rs

@@ -2,6 +2,7 @@
 
 mod algebra;
 mod eval;
+mod json_results;
 mod model;
 mod parser;
 mod plan;

lib/src/sparql/model.rs

@@ -1,6 +1,7 @@
 use crate::model::*;
+use crate::sparql::json_results::write_json_results;
 use crate::sparql::xml_results::{read_xml_results, write_xml_results};
-use crate::Result;
+use crate::{FileSyntax, Result};
 use failure::format_err;
 use std::fmt;
 use std::io::{BufRead, Write};
@@ -20,12 +21,14 @@ impl<'a> QueryResult<'a> {
     pub fn read(reader: impl BufRead + 'a, syntax: QueryResultSyntax) -> Result<Self> {
         match syntax {
             QueryResultSyntax::Xml => read_xml_results(reader),
+            QueryResultSyntax::Json => unimplemented!(),
         }
     }
 
     pub fn write<W: Write>(self, writer: W, syntax: QueryResultSyntax) -> Result<W> {
         match syntax {
             QueryResultSyntax::Xml => write_xml_results(self, writer),
+            QueryResultSyntax::Json => write_json_results(self, writer),
         }
     }
 }
@@ -35,6 +38,40 @@ impl<'a> QueryResult<'a> {
 pub enum QueryResultSyntax {
     /// [SPARQL Query Results XML Format](http://www.w3.org/TR/rdf-sparql-XMLres/)
     Xml,
+    /// [SPARQL Query Results JSON Format](https://www.w3.org/TR/sparql11-results-json/)
+    Json,
+}
+
+impl FileSyntax for QueryResultSyntax {
+    fn iri(self) -> &'static str {
+        unimplemented!()
+    }
+
+    fn media_type(self) -> &'static str {
+        match self {
+            QueryResultSyntax::Xml => "application/sparql-results+xml",
+            QueryResultSyntax::Json => "application/sparql-results+json",
+        }
+    }
+
+    fn file_extension(self) -> &'static str {
+        match self {
+            QueryResultSyntax::Xml => "srx",
+            QueryResultSyntax::Json => "srj",
+        }
+    }
+
+    fn from_mime_type(media_type: &str) -> Option<Self> {
+        if let Some(base_type) = media_type.split(';').next() {
+            match base_type {
+                "application/sparql-results+xml" => Some(QueryResultSyntax::Xml),
+                "application/sparql-results+json" => Some(QueryResultSyntax::Json),
+                _ => None,
+            }
+        } else {
+            None
+        }
+    }
 }
 
 /// An iterator over results bindings

server/src/main.rs

@@ -1,6 +1,7 @@
 use clap::App;
 use clap::Arg;
 use clap::ArgMatches;
+use rouille::input::priority_header_preferred;
 use rouille::url::form_urlencoded;
 use rouille::{start_server, Request, Response};
 use rudf::sparql::QueryResult;
@@ -89,20 +90,22 @@ fn handle_request<R: RepositoryConnection>(
                 Response::text("No content given").with_status_code(400)
             }
         }
-        ("/query", "GET") => {
-            evaluate_urlencoded_sparql_query(connection, request.raw_query_string().as_bytes())
-        }
+        ("/query", "GET") => evaluate_urlencoded_sparql_query(
+            connection,
+            request.raw_query_string().as_bytes(),
+            request,
+        ),
         ("/query", "POST") => {
             if let Some(mut body) = request.data() {
                 if let Some(content_type) = request.header("Content-Type") {
                     if content_type.starts_with("application/sparql-query") {
                         let mut buffer = String::default();
                         body.read_to_string(&mut buffer).unwrap();
-                        evaluate_sparql_query(connection, &buffer)
+                        evaluate_sparql_query(connection, &buffer, request)
                     } else if content_type.starts_with("application/x-www-form-urlencoded") {
                         let mut buffer = Vec::default();
                         body.read_to_end(&mut buffer).unwrap();
-                        evaluate_urlencoded_sparql_query(connection, &buffer)
+                        evaluate_urlencoded_sparql_query(connection, &buffer, request)
                     } else {
                         Response::text(format!(
                             "No supported content Content-Type given: {}",
@@ -124,31 +127,77 @@ fn handle_request<R: RepositoryConnection>(
 fn evaluate_urlencoded_sparql_query<R: RepositoryConnection>(
     connection: R,
     encoded: &[u8],
+    request: &Request,
 ) -> Response {
     if let Some((_, query)) = form_urlencoded::parse(encoded).find(|(k, _)| k == "query") {
-        evaluate_sparql_query(connection, &query)
+        evaluate_sparql_query(connection, &query, request)
     } else {
         Response::text("You should set the 'query' parameter").with_status_code(400)
     }
 }
 
-fn evaluate_sparql_query<R: RepositoryConnection>(connection: R, query: &str) -> Response {
+fn evaluate_sparql_query<R: RepositoryConnection>(
+    connection: R,
+    query: &str,
+    request: &Request,
+) -> Response {
     //TODO: stream
     match connection.prepare_query(query, None) {
         Ok(query) => match query.exec().unwrap() {
             QueryResult::Graph(triples) => {
+                let supported_formats = [
+                    GraphSyntax::NTriples.media_type(),
+                    GraphSyntax::Turtle.media_type(),
+                ];
+                let format = if let Some(accept) = request.header("Accept") {
+                    if let Some(media_type) =
+                        priority_header_preferred(accept, supported_formats.iter().cloned())
+                            .and_then(|p| GraphSyntax::from_mime_type(supported_formats[p]))
+                    {
+                        media_type
+                    } else {
+                        return Response::text(format!(
+                            "No supported Accept given: {}. Supported format: {:?}",
+                            accept, supported_formats
+                        ))
+                        .with_status_code(415);
+                    }
+                } else {
+                    GraphSyntax::NTriples
+                };
                 let mut result = String::default();
                 for triple in triples {
                     writeln!(&mut result, "{}", triple.unwrap()).unwrap()
                 }
-                Response::from_data(GraphSyntax::NTriples.media_type(), result.into_bytes())
+                Response::from_data(format.media_type(), result.into_bytes())
+            }
+            result => {
+                let supported_formats = [
+                    QueryResultSyntax::Xml.media_type(),
+                    QueryResultSyntax::Json.media_type(),
+                ];
+                let format = if let Some(accept) = request.header("Accept") {
+                    if let Some(media_type) =
+                        priority_header_preferred(accept, supported_formats.iter().cloned())
+                            .and_then(|p| QueryResultSyntax::from_mime_type(supported_formats[p]))
+                    {
+                        media_type
+                    } else {
+                        return Response::text(format!(
+                            "No supported Accept given: {}. Supported format: {:?}",
+                            accept, supported_formats
+                        ))
+                        .with_status_code(415);
+                    }
+                } else {
+                    QueryResultSyntax::Xml
+                };
+
+                Response::from_data(
+                    format.media_type(),
+                    result.write(Vec::default(), format).unwrap(),
+                )
             }
-            result => Response::from_data(
-                "application/sparql-results",
-                result
-                    .write(Vec::default(), QueryResultSyntax::Xml)
-                    .unwrap(),
-            ),
         },
         Err(error) => Response::text(error.to_string()).with_status_code(400),
     }