connectors/http/src/main/java/org/apache/edgent/connectors/http/HttpResponders.java

/*
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.edgent.connectors.http;

import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

import org.apache.edgent.function.BiFunction;
import org.apache.http.HttpStatus;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.util.EntityUtils;

import com.google.gson.JsonObject;
import com.google.gson.JsonStreamParser;

/**
 * Functions to process HTTP requests.
 *
 * @see HttpStreams
 */
public class HttpResponders {
    
    /**
     * Return the input tuple on OK.
     * Function that returns null (no output) if the HTTP response
     * is not OK (200), otherwise it returns the input tuple.
     * The HTTP entity in the response is consumed and discarded.
     * @param <T> Type of input tuple.
     * @return Function that returns the input tuple on OK.
     */
    public static <T> BiFunction<T,CloseableHttpResponse,T> inputOn200() {
        return inputOn(HttpStatus.SC_OK);
    }
    
    /**
     * Return the input tuple on specified codes.
     * Function that returns null (no output) if the HTTP response
     * is not one of {@code codes}, otherwise it returns the input tuple.
     * The HTTP entity in the response is consumed and discarded.
     * @param <T> Type of input tuple.
     * @param codes HTTP status codes to result in output
     * @return Function that returns the input tuple on matching codes.
     */
    public static <T> BiFunction<T, CloseableHttpResponse, T> inputOn(Integer... codes) {
        Set<Integer> uniqueCodes = new HashSet<>(Arrays.asList(codes));
        return (t, resp) -> {
            int sc = resp.getStatusLine().getStatusCode();
            try {
                EntityUtils.consume(resp.getEntity());
            } catch (Exception e) {
                ;
            }
            return uniqueCodes.contains(sc) ? t : null;
        };
    }
    
    /**
     * A HTTP response handler for {@code application/json}.
     * 
     * For each HTTP response a JSON object is produced that contains:
     * <UL>
     * <LI> {@code request} - the original input tuple that lead to the request  </LI>
     * <LI> {@code response} - JSON object containing information about the response
     * <UL>
     *    <LI> {@code status} - Status code for the response as an integer</LI>
     *    <LI> {@code entity} - JSON response entity if one exists </LI>
     * </UL>
     * </LI>
     * </UL>
     * 
     * @return Function that will process the {@code application/json} responses.
     */
    public static BiFunction<JsonObject, CloseableHttpResponse, JsonObject> json() {
        return (request,resp) -> {
            JsonObject out = new JsonObject();
            out.add("request", request);
            JsonObject response = new JsonObject();
            out.add("response", response);
            response.addProperty("status", resp.getStatusLine().getStatusCode());
            JsonStreamParser reader;
            try {
                reader = new JsonStreamParser(
                        new InputStreamReader(resp.getEntity().getContent(), StandardCharsets.UTF_8));
                if (reader.hasNext())
                    response.add("entity", reader.next());

            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            
            return out;
            
        };
    }
}