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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
* deflate means a zlib stream as defined in RFC1950. Some server
* implementations have misinterpreted RFC2616 to mean that a deflate stream as
* defined in RFC1951 should be used (or maybe they did that since that's how IE behaves?). It's
* confusing that deflate in HTTP 1.1 means zlib streams rather than
* deflate streams. We handle both types in here, since that's what is seen on the
* internet. Moral - prefer gzip!
*
* @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);
}
/**
* {@inheritDoc}
*/
@Override
public InputStream getContent() throws IOException {
InputStream wrapped = this.wrappedEntity.getContent();
/*
* 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;
}
}