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 /*

  * ====================================================================

  *

  *  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.

  * ====================================================================

  *

  * This software consists of voluntary contributions made by many

  * individuals on behalf of the Apache Software Foundation.  For more

  * information on the Apache Software Foundation, please see

  * <http://www.apache.org/>.

  *

 */

 package ch.boye.httpclientandroidlib.client.entity;

 import java.io.IOException;

 import java.io.InputStream;

 import java.io.PushbackInputStream;

 import java.util.zip.DataFormatException;

 import java.util.zip.Inflater;

 import java.util.zip.InflaterInputStream;

 import ch.boye.httpclientandroidlib.Header;

 import ch.boye.httpclientandroidlib.HttpEntity;

 import ch.boye.httpclientandroidlib.entity.HttpEntityWrapper;

 /**

  * {@link HttpEntityWrapper} responsible for handling deflate Content Coded responses. In RFC2616

  * terms, <code>deflate</code> means a <code>zlib</code> stream as defined in RFC1950. Some server

  * implementations have misinterpreted RFC2616 to mean that a <code>deflate</code> stream as

  * defined in RFC1951 should be used (or maybe they did that since that's how IE behaves?). It's

  * confusing that <code>deflate</code> in HTTP 1.1 means <code>zlib</code> streams rather than

  * <code>deflate</code> streams. We handle both types in here, since that's what is seen on the

  * internet. Moral - prefer <code>gzip</code>!

  *

  * @see GzipDecompressingEntity

  *

  * @since 4.1

  */

 public class DeflateDecompressingEntity extends DecompressingEntity {

     /**

      * Creates a new {@link DeflateDecompressingEntity} which will wrap the specified

      * {@link HttpEntity}.

      *

      * @param entity

      *            a non-null {@link HttpEntity} to be wrapped

      */

     public DeflateDecompressingEntity(final HttpEntity entity) {

         super(entity);

     }

     /**

      * Returns the non-null InputStream that should be returned to by all requests to

      * {@link #getContent()}.

      *

      * @return a non-null InputStream

      * @throws IOException if there was a problem

      */

     @Override

     InputStream getDecompressingInputStream(final InputStream wrapped) throws IOException {

         /*

          * A zlib stream will have a header.

          *

          * CMF | FLG [| DICTID ] | ...compressed data | ADLER32 |

          *

          * * CMF is one byte.

          *

          * * FLG is one byte.

          *

          * * DICTID is four bytes, and only present if FLG.FDICT is set.

          *

          * Sniff the content. Does it look like a zlib stream, with a CMF, etc? c.f. RFC1950,

          * section 2.2. http://tools.ietf.org/html/rfc1950#page-4

          *

          * We need to see if it looks like a proper zlib stream, or whether it is just a deflate

          * stream. RFC2616 calls zlib streams deflate. Confusing, isn't it? That's why some servers

          * implement deflate Content-Encoding using deflate streams, rather than zlib streams.

          *

          * We could start looking at the bytes, but to be honest, someone else has already read

          * the RFCs and implemented that for us. So we'll just use the JDK libraries and exception

          * handling to do this. If that proves slow, then we could potentially change this to check

          * the first byte - does it look like a CMF? What about the second byte - does it look like

          * a FLG, etc.

          */

         /* We read a small buffer to sniff the content. */

         byte[] peeked = new byte[6];

         PushbackInputStream pushback = new PushbackInputStream(wrapped, peeked.length);

         int headerLength = pushback.read(peeked);

         if (headerLength == -1) {

             throw new IOException("Unable to read the response");

         }

         /* We try to read the first uncompressed byte. */

         byte[] dummy = new byte[1];

         Inflater inf = new Inflater();

         try {

             int n;

             while ((n = inf.inflate(dummy)) == 0) {

                 if (inf.finished()) {

                     /* Not expecting this, so fail loudly. */

                     throw new IOException("Unable to read the response");

                 }

                 if (inf.needsDictionary()) {

                     /* Need dictionary - then it must be zlib stream with DICTID part? */

                     break;

                 }

                 if (inf.needsInput()) {

                     inf.setInput(peeked);

                 }

             }

             if (n == -1) {

                 throw new IOException("Unable to read the response");

             }

             /*

              * We read something without a problem, so it's a valid zlib stream. Just need to reset

              * and return an unused InputStream now.

              */

             pushback.unread(peeked, 0, headerLength);

             return new InflaterInputStream(pushback);

         } catch (DataFormatException e) {

             /* Presume that it's an RFC1951 deflate stream rather than RFC1950 zlib stream and try

              * again. */

             pushback.unread(peeked, 0, headerLength);

             return new InflaterInputStream(pushback, new Inflater(true));

         }

     }

     /**

      * {@inheritDoc}

      */

     @Override

     public Header getContentEncoding() {

         /* This HttpEntityWrapper has dealt with the Content-Encoding. */

         return null;

     }

     /**

      * {@inheritDoc}

      */

     @Override

     public long getContentLength() {

         /* Length of inflated content is unknown. */

         return -1;

     }

 }