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/*
 * Copyright 2010-2015 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.services.s3.internal;

import java.util.Date;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.amazonaws.AmazonClientException;
import com.amazonaws.Request;
import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.auth.AWSSessionCredentials;
import com.amazonaws.auth.AbstractAWSSigner;
import com.amazonaws.auth.Signer;
import com.amazonaws.auth.SigningAlgorithm;
import com.amazonaws.services.s3.Headers;
import com.amazonaws.util.HttpUtils;

/**
 * Implementation of the {@linkplain Signer} interface specific to S3's signing
 * algorithm.
 */
public class S3Signer extends AbstractAWSSigner {

    /** Shared log for signing debug output */
    private static final Log log = LogFactory.getLog(S3Signer.class);

    /**
     * The HTTP verb (GET, PUT, HEAD, DELETE) the request to sign
     * is using.
     *
     * TODO: We need to know the HTTP verb in order to
     *       create the authentication signature, but we don't
     *       have easy access to it through the request object.
     *
     *       Maybe it'd be better for the S3 signer (or all signers?)
     *       to work directly off of the HttpRequest instead of
     *       the Request object?
     */
    private final String httpVerb;

    /**
     * The canonical resource path portion of the S3 string to sign.
     * Examples: "/", "//", or "//"
     *
     * TODO: We don't want to hold the resource path as member data in the S3
     *       signer, but we need access to it and can't get it through the
     *       request yet.
     */
    private final String resourcePath;

    /**
     * Create a dummy instance of the S3Signer.
     */
    public S3Signer() {
        this.httpVerb = null;
        this.resourcePath = null;
    }

    /**
     * Constructs a new S3Signer to sign requests based on the
     * AWS credentials, HTTP method and canonical S3 resource path.
     *
     * @param httpVerb
     *            The HTTP verb (GET, PUT, POST, HEAD, DELETE) the request is
     *            using.
     * @param resourcePath
     *            The canonical S3 resource path (ex: "/", "//", or
     *            "//".
     */
    public S3Signer(String httpVerb, String resourcePath) {
        this.httpVerb = httpVerb;
        this.resourcePath = resourcePath;

        if (resourcePath == null)
            throw new IllegalArgumentException("Parameter resourcePath is empty");
    }

    @Override
    public void sign(Request request, AWSCredentials credentials) {

        if (resourcePath == null) {
            throw new UnsupportedOperationException(
                "Cannot sign a request using a dummy S3Signer instance with "
                + "no resource path"
            );
        }

        if (credentials == null || credentials.getAWSSecretKey() == null) {
            log.debug("Canonical string will not be signed, as no AWS Secret Key was provided");
            return;
        }

        AWSCredentials sanitizedCredentials = sanitizeCredentials(credentials);
        if ( sanitizedCredentials instanceof AWSSessionCredentials ) {
            addSessionCredentials(request, (AWSSessionCredentials) sanitizedCredentials);
        }

        /*
         * In s3 sigv2, the way slash characters are encoded should be
         * consistent in both the request url and the encoded resource path.
         * Since we have to encode "//" to "/%2F" in the request url to make
         * httpclient works, we need to do the same encoding here for the
         * resource path.
         */
        String encodedResourcePath = HttpUtils.appendUri(request.getEndpoint().getPath(), resourcePath, true);

        int timeOffset = getTimeOffset(request);
        Date date = getSignatureDate(timeOffset);
        request.addHeader(Headers.DATE, ServiceUtils.formatRfc822Date(date));
        String canonicalString = RestUtils.makeS3CanonicalString(
                httpVerb, encodedResourcePath, request, null);
        log.debug("Calculated string to sign:\n\"" + canonicalString + "\"");

        String signature = super.signAndBase64Encode(canonicalString, sanitizedCredentials.getAWSSecretKey(), SigningAlgorithm.HmacSHA1);
        request.addHeader("Authorization", "AWS " + sanitizedCredentials.getAWSAccessKeyId() + ":" + signature);
    }

    @Override
    protected void addSessionCredentials(Request request, AWSSessionCredentials credentials) {
        request.addHeader("x-amz-security-token", credentials.getSessionToken());
    }
}