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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2011-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.http;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.List;
import java.util.Map.Entry;

import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.AmazonServiceException.ErrorType;
import com.amazonaws.transform.JsonErrorUnmarshaller;
import com.amazonaws.util.json.JSONObject;

public class JsonErrorResponseHandler implements HttpResponseHandler {

    /**
     * Services using AWS JSON 1.1 protocol with HTTP binding send the error
     * type information in the response headers, instead of the content.
     */
    private static final String X_AMZN_ERROR_TYPE = "x-amzn-ErrorType";

    /**
     * The list of error response unmarshallers to try to apply to error
     * responses.
     */
    private List unmarshallerList;

    public JsonErrorResponseHandler(List exceptionUnmarshallers) {
        this.unmarshallerList = exceptionUnmarshallers;
    }

    public AmazonServiceException handle(HttpResponse response) throws Exception {
        String streamContents = readStreamContents(response.getContent());
        JSONObject jsonErrorMessage;
        try {
            String s = streamContents;
            if (s.length() == 0 || s.trim().length() == 0) s = "{}";
            jsonErrorMessage = new JSONObject(s);
        } catch (Exception e) {
            throw new AmazonClientException("Unable to parse error response: '" + streamContents + "'", e);
        }

        String errorTypeFromHeader = parseErrorTypeFromHeader(response);

        AmazonServiceException ase = runErrorUnmarshallers(response, jsonErrorMessage, errorTypeFromHeader);
        if (ase == null) return null;

        ase.setServiceName(response.getRequest().getServiceName());
        ase.setStatusCode(response.getStatusCode());
        if (response.getStatusCode() < 500) {
            ase.setErrorType(ErrorType.Client);
        } else {
            ase.setErrorType(ErrorType.Service);
        }

        for (Entry headerEntry : response.getHeaders().entrySet()) {
            if (headerEntry.getKey().equalsIgnoreCase("X-Amzn-RequestId")) {
                ase.setRequestId(headerEntry.getValue());
            }
        }

        return ase;
    }

    private AmazonServiceException runErrorUnmarshallers(HttpResponse errorResponse, JSONObject json, String errorTypeFromHeader) throws Exception {
        /*
         * We need to select which exception unmarshaller is the correct one to
         * use from all the possible exceptions this operation can throw.
         * Currently we rely on JsonErrorUnmarshaller.match(...) method which
         * checks for the error type parsed either from response headers or the
         * content.
         */
        for (JsonErrorUnmarshaller unmarshaller : unmarshallerList) {
            if (unmarshaller.match(errorTypeFromHeader, json)) {
                AmazonServiceException ase = unmarshaller.unmarshall(json);
                ase.setStatusCode(errorResponse.getStatusCode());
                return ase;
            }
        }

        return null;
    }

    public boolean needsConnectionLeftOpen() {
        return false;
    }

    private String readStreamContents(final InputStream stream) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
            StringBuilder sb = new StringBuilder();
            while (true) {
                String line = reader.readLine();
                if (line == null) break;
                sb.append(line);
            }

            return sb.toString();
        } catch (Exception e) {
            try {stream.close();} catch (Exception ex) {}
            throw new AmazonClientException("Unable to read error response: " + e.getMessage(), e);
        }
    }

    /**
     * Attempt to parse the error type from the response headers.
     * Returns null if such information is not available in the header.
     */
    private String parseErrorTypeFromHeader(HttpResponse response) {
        String headerValue = response.getHeaders().get(X_AMZN_ERROR_TYPE);
        if (headerValue != null) {
            int separator = headerValue.indexOf(':');
            if (separator != -1) {
                headerValue  = headerValue.substring(0, separator);
            }
        }
        return headerValue;
    }
}