OkHttp3 Call Factory for Google AppEngine (useful for using swagger with Retrofit2 template)

GoogleAppEngineOkHTTP3RetrofitCallFactory.java

package com.teevity.api.lowlevel.impl.googleappengine;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import com.google.common.base.Strings;
import com.teevity.api.lowlevel.impl.ApiException;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Headers;
import okhttp3.MediaType;
import okhttp3.Protocol;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;
import okio.BufferedSink;
import okio.BufferedSource;
import okio.Okio;

/**
 * 
 * @author Benoît Sauvère
 *
 */
public class GoogleAppEngineOkHTTP3RetrofitCallFactory implements Call {
	
	Request request;
	Headers commonHeaders;
	private Integer connectionTimeoutInMs;
	private Integer readTimeoutInMs;

	GoogleAppEngineOkHTTP3RetrofitCallFactory(Request request, Headers commonHeaders, Integer connectionTimeoutInMs, Integer readTimeoutInMs) {
		this.request = request;
		this.commonHeaders = commonHeaders;
		this.connectionTimeoutInMs = connectionTimeoutInMs;
		this.readTimeoutInMs = readTimeoutInMs;
	}

	@Override
	public Request request() {
		return request;
	}

	@Override
	public Response execute() throws IOException {
		URL url = request.url().url();
		final HttpURLConnection connection = (HttpURLConnection) url.openConnection();
		connection.setInstanceFollowRedirects(true);
		connection.setUseCaches(false);
		connection.setDoOutput(true);
		connection.setRequestMethod(request.method());
		if (connectionTimeoutInMs != null) {
			connection.setConnectTimeout(connectionTimeoutInMs);
		}
		
		if (readTimeoutInMs != null) {
			connection.setConnectTimeout(readTimeoutInMs);
		}
		
		Headers headers = request.headers();
		if (headers != null) {
			for (int i = 0; i < headers.size(); i++) {
				String name = headers.name(i);
				String value = headers.get(name);
				if (Strings.isNullOrEmpty(value) == false) {
					connection.setRequestProperty(name, value);
				}
			}
		}
		
		if (request.body() != null && request.body().contentType() != null) {
			String bodyContentType = request.body().contentType().toString();
			connection.setRequestProperty("Content-Type", bodyContentType);
		}

		if (commonHeaders != null && commonHeaders.size() > 0) {
			for (int i = 0; i < commonHeaders.size(); i++) {
				String name = commonHeaders.name(i);
				String value = commonHeaders.get(name);
				if (Strings.isNullOrEmpty(value) == false) {
					connection.setRequestProperty(name, value);
				}
			}
		}
		
		if (request.body() != null) {
			BufferedSink outbuf;
			outbuf = Okio.buffer(Okio.sink(connection.getOutputStream()));
			request.body().writeTo(outbuf);
			outbuf.close();
		}

		
		final BufferedSource source;
		InputStream connectionInputStream = connection.getInputStream();
		if (connectionInputStream != null) {
			source = Okio.buffer(Okio.source(connectionInputStream));
		} else {
			source = null;
		}
		
		Response response = new Response.Builder()
				.code(connection.getResponseCode())
				.message(connection.getResponseMessage())
				.request(request)
				.protocol(Protocol.HTTP_1_1)
				.body(new ResponseBody() {
					@Override
					public MediaType contentType() {
						return MediaType.parse(connection.getContentType());
					}
					
					@Override
					public long contentLength() {
						return connection.getContentLengthLong();
					}
					
					@Override
					public BufferedSource source() {
						return source;
					}
				}).build();
		
		
		// If the status is a redirection we need to perform the redirection manually (as HttpURLConnection seems to suffer from 
		// bug over redirections)
		int status = response.code();
		if (status == HttpURLConnection.HTTP_MOVED_TEMP || status == HttpURLConnection.HTTP_MOVED_PERM || status == HttpURLConnection.HTTP_SEE_OTHER) {
			String nextLocation = connection.getHeaderField("Location");
			if (Strings.isNullOrEmpty(nextLocation) == false) {
				Response redirectionResponse = new GoogleAppEngineOkHTTP3RetrofitCallFactory(new Request.Builder()
						.url(nextLocation)
						.method("GET", null)
						.build(),
						null,
						null,
						null).execute();
				response = redirectionResponse;
			}
		}
		
		if (response.isSuccessful() == false) {
			throw new ApiException(response);
		}
		
		return response;
	}

	@Override
	public void enqueue(Callback responseCallback) {
	}

	@Override
	public void cancel() {
	}

	@Override
	public boolean isExecuted() {
		return false;
	}

	@Override
	public boolean isCanceled() {
		return false;
	}
	
	public static class Factory implements Call.Factory {
	    
		private Headers commonHeaders;
		private Integer readTimeoutInMs;
		private Integer connectionTimeoutInMs;

		public Factory(Headers commonHeaders, Integer connectionTimeoutInMs, Integer readTimeoutInMs) {
			this.commonHeaders = commonHeaders;
			this.connectionTimeoutInMs = connectionTimeoutInMs;
			this.readTimeoutInMs = readTimeoutInMs;
		}
		
		@Override
	    public Call newCall(Request request) {
	        return new GoogleAppEngineOkHTTP3RetrofitCallFactory(request, commonHeaders, connectionTimeoutInMs, readTimeoutInMs);
	    }
	}
}