--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Core/Compression/GzipCompressor.cpp	Mon Aug 10 16:01:37 2015 +0200
@@ -0,0 +1,277 @@
+/**
+ * Orthanc - A Lightweight, RESTful DICOM Store
+ * Copyright (C) 2012-2015 Sebastien Jodogne, Medical Physics
+ * Department, University Hospital of Liege, Belgium
+ *
+ * This program is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * In addition, as a special exception, the copyright holders of this
+ * program give permission to link the code of its release with the
+ * OpenSSL project's "OpenSSL" library (or with modified versions of it
+ * that use the same license as the "OpenSSL" library), and distribute
+ * the linked executables. You must obey the GNU General Public License
+ * in all respects for all of the code used other than "OpenSSL". If you
+ * modify file(s) with this exception, you may extend this exception to
+ * your version of the file(s), but you are not obligated to do so. If
+ * you do not wish to do so, delete this exception statement from your
+ * version. If you delete this exception statement from all source files
+ * in the program, then also delete it here.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+
+#include "../PrecompiledHeaders.h"
+#include "GzipCompressor.h"
+
+#include <stdio.h>
+#include <string.h>
+#include <zlib.h>
+
+#include "../OrthancException.h"
+#include "../Logging.h"
+
+namespace Orthanc
+{
+  uint64_t GzipCompressor::GuessUncompressedSize(const void* compressed,
+                                                 size_t compressedSize)
+  {
+    /**
+     * "Is there a way to find out the size of the original file which
+     * is inside a GZIP file? [...] There is no truly reliable way,
+     * other than gunzipping the stream. You do not need to save the
+     * result of the decompression, so you can determine the size by
+     * simply reading and decoding the entire file without taking up
+     * space with the decompressed result.
+     *
+     * There is an unreliable way to determine the uncompressed size,
+     * which is to look at the last four bytes of the gzip file, which
+     * is the uncompressed length of that entry modulo 232 in little
+     * endian order.
+     * 
+     * It is unreliable because a) the uncompressed data may be longer
+     * than 2^32 bytes, and b) the gzip file may consist of multiple
+     * gzip streams, in which case you would find the length of only
+     * the last of those streams.
+     * 
+     * If you are in control of the source of the gzip files, you know
+     * that they consist of single gzip streams, and you know that
+     * they are less than 2^32 bytes uncompressed, then and only then
+     * can you use those last four bytes with confidence."
+     *
+     * http://stackoverflow.com/a/9727599/881731
+     **/
+
+    if (compressedSize < 4)
+    {
+      throw OrthancException(ErrorCode_BadFileFormat);
+    }
+
+    const uint8_t* p = reinterpret_cast<const uint8_t*>(compressed) + compressedSize - 4;
+
+    return ((static_cast<uint32_t>(p[0]) << 0) +
+            (static_cast<uint32_t>(p[1]) << 8) +
+            (static_cast<uint32_t>(p[2]) << 16) +
+            (static_cast<uint32_t>(p[3]) << 24));            
+  }
+
+
+
+  void GzipCompressor::Compress(std::string& compressed,
+                                const void* uncompressed,
+                                size_t uncompressedSize)
+  {
+    uLongf compressedSize = compressBound(uncompressedSize) + 1024 /* security margin */;
+    if (compressedSize == 0)
+    {
+      compressedSize = 1;
+    }
+
+    uint8_t* target;
+    if (HasPrefixWithUncompressedSize())
+    {
+      compressed.resize(compressedSize + sizeof(uint64_t));
+      target = reinterpret_cast<uint8_t*>(&compressed[0]) + sizeof(uint64_t);
+    }
+    else
+    {
+      compressed.resize(compressedSize);
+      target = reinterpret_cast<uint8_t*>(&compressed[0]);
+    }
+
+    z_stream stream;
+    memset(&stream, 0, sizeof(stream));
+
+    stream.next_in = const_cast<Bytef*>(reinterpret_cast<const Bytef*>(uncompressed));
+    stream.next_out = reinterpret_cast<Bytef*>(target);
+
+    stream.avail_in = static_cast<uInt>(uncompressedSize);
+    stream.avail_out = static_cast<uInt>(compressedSize);
+
+    // Ensure no overflow (if the buffer is too large for the current archicture)
+    if (static_cast<size_t>(stream.avail_in) != uncompressedSize ||
+        static_cast<size_t>(stream.avail_out) != compressedSize)
+    {
+      throw OrthancException(ErrorCode_NotEnoughMemory);
+    }
+    
+    // Initialize the compression engine
+    int error = deflateInit2(&stream, 
+                             GetCompressionLevel(), 
+                             Z_DEFLATED,
+                             MAX_WBITS + 16,      // ask for gzip output
+                             8,                   // default memory level
+                             Z_DEFAULT_STRATEGY);
+
+    if (error != Z_OK)
+    {
+      // Cannot initialize zlib
+      compressed.clear();
+      throw OrthancException(ErrorCode_InternalError);
+    }
+
+    // Compress the input buffer
+    error = deflate(&stream, Z_FINISH);
+
+    if (error != Z_STREAM_END)
+    {
+      deflateEnd(&stream);
+      compressed.clear();
+
+      switch (error)
+      {
+      case Z_MEM_ERROR:
+        throw OrthancException(ErrorCode_NotEnoughMemory);
+
+      default:
+        throw OrthancException(ErrorCode_InternalError);
+      }  
+    }
+
+    size_t size = stream.total_out;
+
+    if (deflateEnd(&stream) != Z_OK)
+    {
+      throw OrthancException(ErrorCode_InternalError);
+    }
+
+    // The compression was successful
+    if (HasPrefixWithUncompressedSize())
+    {
+      uint64_t s = static_cast<uint64_t>(uncompressedSize);
+      memcpy(&compressed[0], &s, sizeof(uint64_t));
+      compressed.resize(size + sizeof(uint64_t));
+    }
+    else
+    {
+      compressed.resize(size);
+    }
+  }
+
+
+  void GzipCompressor::Uncompress(std::string& uncompressed,
+                                  const void* compressed,
+                                  size_t compressedSize)
+  {
+    uint64_t uncompressedSize;
+    const uint8_t* source = reinterpret_cast<const uint8_t*>(compressed);
+
+    if (HasPrefixWithUncompressedSize())
+    {
+      uncompressedSize = ReadUncompressedSizePrefix(compressed, compressedSize);
+      source += sizeof(uint64_t);
+      compressedSize -= sizeof(uint64_t);
+    }
+    else
+    {
+      uncompressedSize = GuessUncompressedSize(compressed, compressedSize);
+    }
+
+    try
+    {
+      uncompressed.resize(uncompressedSize);
+    }
+    catch (...)
+    {
+      throw OrthancException(ErrorCode_NotEnoughMemory);
+    }
+
+    z_stream stream;
+    memset(&stream, 0, sizeof(stream));
+
+    char dummy = '\0';  // zlib does not like NULL output buffers (even if the uncompressed data is empty)
+    stream.next_in = const_cast<Bytef*>(source);
+    stream.next_out = reinterpret_cast<Bytef*>(uncompressedSize == 0 ? &dummy : &uncompressed[0]);
+
+    stream.avail_in = static_cast<uInt>(compressedSize);
+    stream.avail_out = static_cast<uInt>(uncompressedSize);
+
+    // Ensure no overflow (if the buffer is too large for the current archicture)
+    if (static_cast<size_t>(stream.avail_in) != compressedSize ||
+        static_cast<size_t>(stream.avail_out) != uncompressedSize)
+    {
+      throw OrthancException(ErrorCode_NotEnoughMemory);
+    }
+
+    // Initialize the compression engine
+    int error = inflateInit2(&stream, 
+                             MAX_WBITS + 16);  // this is a gzip input
+
+    if (error != Z_OK)
+    {
+      // Cannot initialize zlib
+      uncompressed.clear();
+      throw OrthancException(ErrorCode_InternalError);
+    }
+
+    // Uncompress the input buffer
+    error = inflate(&stream, Z_FINISH);
+
+    if (error != Z_STREAM_END)
+    {
+      inflateEnd(&stream);
+      uncompressed.clear();
+
+      switch (error)
+      {
+        case Z_MEM_ERROR:
+          throw OrthancException(ErrorCode_NotEnoughMemory);
+          
+        case Z_BUF_ERROR:
+        case Z_NEED_DICT:
+          throw OrthancException(ErrorCode_BadFileFormat);
+          
+        default:
+          throw OrthancException(ErrorCode_InternalError);
+      }
+    }
+
+    size_t size = stream.total_out;
+
+    if (inflateEnd(&stream) != Z_OK)
+    {
+      uncompressed.clear();
+      throw OrthancException(ErrorCode_InternalError);
+    }
+
+    if (size != uncompressedSize)
+    {
+      uncompressed.clear();
+
+      // The uncompressed size was not that properly guess, presumably
+      // because of a file size over 4GB. Should fallback to
+      // stream-based decompression.
+      LOG(ERROR) << "The uncompressed size of a gzip-encoded buffer was not properly guessed";
+      throw OrthancException(ErrorCode_NotImplemented);
+    }
+  }
+}