sparql.go

//   Copyright 2019 Content Mine Ltd
//
//   Licensed 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 wikibase

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/url"
	"strings"
)

type SparqlHead struct {
	Vars []string `json:"vars"`
}

type SparqlValue struct {
	Type     string `json:"type"`
	Value    string `json:"value"`
	DataType string `json:"datatype"`
}

type SparqlResult map[string]SparqlValue

type SparqlResults struct {
	Bindings []SparqlResult `json:"bindings"`
}

type SparqlResponse struct {
	Head    SparqlHead    `json:"head"`
	Results SparqlResults `json:"results"`
}

func MakeSPARQLQuery(service_url string, sparql string) (*SparqlResponse, error) {

	params := url.Values{}
	params.Add("query", sparql)

	req, err := http.NewRequest("POST", service_url, strings.NewReader(params.Encode()))
	if err != nil {
		return nil, err
	}
	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Add("Accept", "application/sparql-results+json")

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, err := ioutil.ReadAll(resp.Body)
		if err != nil {
			return nil, fmt.Errorf("Status code %d", resp.StatusCode)
		} else {
			return nil, fmt.Errorf("Status code %d: %s", resp.StatusCode, body)
		}
	}

	data := SparqlResponse{}
	err = json.NewDecoder(resp.Body).Decode(&data)
	if err != nil {
		return nil, err
	}
	return &data, nil
}