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/*
 * Copyright 2010-2015 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Portions copyright 2006-2009 James Murty. Please see LICENSE.txt
 * for applicable license terms and NOTICE.txt for applicable notices.
 *
 * 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.services.s3.internal;

import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

import com.amazonaws.Request;
import com.amazonaws.services.s3.Headers;
import com.amazonaws.services.s3.model.ResponseHeaderOverrides;

/**
 * Utilities useful for REST/HTTP S3Service implementations.
 */
public class RestUtils {
    /**
     * The set of request parameters which must be included in the canonical
     * string to sign.
     */
    private static final List SIGNED_PARAMETERS = Arrays.asList(new String[] {
            "acl", "torrent", "logging", "location", "policy", "requestPayment", "versioning",
            "versions", "versionId", "notification", "uploadId", "uploads", "partNumber", "website",
            "delete", "lifecycle", "tagging", "cors", "restore",
            ResponseHeaderOverrides.RESPONSE_HEADER_CACHE_CONTROL,
            ResponseHeaderOverrides.RESPONSE_HEADER_CONTENT_DISPOSITION,
            ResponseHeaderOverrides.RESPONSE_HEADER_CONTENT_ENCODING,
            ResponseHeaderOverrides.RESPONSE_HEADER_CONTENT_LANGUAGE,
            ResponseHeaderOverrides.RESPONSE_HEADER_CONTENT_TYPE,
            ResponseHeaderOverrides.RESPONSE_HEADER_EXPIRES,
    });

    /**
     * Calculate the canonical string for a REST/HTTP request to S3.
     *
     * When expires is non-null, it will be used instead of the Date header.
     */
    public static  String makeS3CanonicalString(String method, String resource, Request request, String expires)
    {
        StringBuilder buf = new StringBuilder();
        buf.append(method + "\n");

        // Add all interesting headers to a list, then sort them.  "Interesting"
        // is defined as Content-MD5, Content-Type, Date, and x-amz-
        Map headersMap = request.getHeaders();
        SortedMap interestingHeaders = new TreeMap();
        if (headersMap != null && headersMap.size() > 0) {
            Iterator> headerIter = headersMap.entrySet().iterator();
            while (headerIter.hasNext()) {
                Map.Entry entry = (Map.Entry) headerIter.next();
                String key = entry.getKey();
                String value = entry.getValue();

                if (key == null) continue;
                String lk = key.toString().toLowerCase(Locale.getDefault());

                // Ignore any headers that are not particularly interesting.
                if (lk.equals("content-type") || lk.equals("content-md5") || lk.equals("date") ||
                    lk.startsWith(Headers.AMAZON_PREFIX))
                {
                    interestingHeaders.put(lk, value);
                }
            }
        }

        // Remove default date timestamp if "x-amz-date" is set.
        if (interestingHeaders.containsKey(Headers.S3_ALTERNATE_DATE)) {
            interestingHeaders.put("date", "");
        }

        // Use the expires value as the timestamp if it is available. This trumps both the default
        // "date" timestamp, and the "x-amz-date" header.
        if (expires != null) {
            interestingHeaders.put("date", expires);
        }

        // These headers require that we still put a new line in after them,
        // even if they don't exist.
        if (! interestingHeaders.containsKey("content-type")) {
            interestingHeaders.put("content-type", "");
        }
        if (! interestingHeaders.containsKey("content-md5")) {
            interestingHeaders.put("content-md5", "");
        }

        // Any parameters that are prefixed with "x-amz-" need to be included
        // in the headers section of the canonical string to sign
        for (Map.Entry parameter: request.getParameters().entrySet()) {
            if (parameter.getKey().startsWith("x-amz-")) {
                interestingHeaders.put(parameter.getKey(), parameter.getValue());
            }
        }

        // Add all the interesting headers (i.e.: all that startwith x-amz- ;-))
        for (Iterator> i = interestingHeaders.entrySet().iterator(); i.hasNext(); ) {
            Map.Entry entry = (Map.Entry) i.next();
            String key = (String) entry.getKey();
            String value = entry.getValue();

            if (key.startsWith(Headers.AMAZON_PREFIX)) {
                buf.append(key).append(':');
                if (value != null) {
                    buf.append(value);
                }
            } else if (value != null) {
                buf.append(value);
            }
            buf.append("\n");
        }

        // Add all the interesting parameters
        buf.append(resource);
        String[] parameterNames = request.getParameters().keySet().toArray(
                new String[request.getParameters().size()]);
        Arrays.sort(parameterNames);
        char separator = '?';
        for (String parameterName : parameterNames) {
            // Skip any parameters that aren't part of the canonical signed string
            if (SIGNED_PARAMETERS.contains(parameterName) == false) continue;

            buf.append(separator);
            buf.append(parameterName);
            String parameterValue = request.getParameters().get(parameterName);
            if (parameterValue != null) {
                buf.append("=").append(parameterValue);
            }

            separator = '&';
        }

        return buf.toString();
    }

}