boost/iostreams/filter/gzip.hpp

   1 // (C) Copyright 2008 CodeRage, LLC (turkanis at coderage dot com)
   2 // (C) Copyright 2003-2007 Jonathan Turkanis
   3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.)
   5
   6 // See http://www.boost.org/libs/iostreams for documentation.
   7
   8 // Contains the definitions of the class templates gzip_compressor and
   9 // gzip_decompressor for reading and writing files in the gzip file format
  10 // (RFC 1952). Based in part on work of Jonathan de Halleux; see [...]
  11
  12 #ifndef BOOST_IOSTREAMS_GZIP_HPP_INCLUDED
  13 #define BOOST_IOSTREAMS_GZIP_HPP_INCLUDED
  14
  15 #if defined(_MSC_VER)
  16 # pragma once
  17 #endif
  18
  19 #include <boost/config.hpp> // STATIC_CONSTANT, STDC_NAMESPACE,
  20                             // DINKUMWARE_STDLIB, __STL_CONFIG_H.
  21 #include <algorithm>                      // min.
  22 #include <boost/assert.hpp>
  23 #include <cstdio>                         // EOF.
  24 #include <cstddef>                        // size_t.
  25 #include <ctime>                          // std::time_t.
  26 #include <memory>                         // allocator.
  27 #include <boost/config.hpp>               // Put size_t in std.
  28 #include <boost/detail/workaround.hpp>
  29 #include <boost/cstdint.hpp>              // uint8_t, uint32_t.
  30 #include <boost/iostreams/checked_operations.hpp>
  31 #include <boost/iostreams/constants.hpp>  // buffer size.
  32 #include <boost/iostreams/detail/adapter/non_blocking_adapter.hpp>
  33 #include <boost/iostreams/detail/adapter/range_adapter.hpp>
  34 #include <boost/iostreams/detail/char_traits.hpp>
  35 #include <boost/iostreams/detail/ios.hpp> // failure, streamsize.
  36 #include <boost/iostreams/detail/error.hpp>
  37 #include <boost/iostreams/operations.hpp>
  38 #include <boost/iostreams/device/back_inserter.hpp>
  39 #include <boost/iostreams/filter/zlib.hpp>
  40 #include <boost/iostreams/pipeline.hpp>
  41 #include <boost/iostreams/putback.hpp>
  42 #include <boost/throw_exception.hpp>
  43
  44 // Must come last.
  45 #if defined(BOOST_MSVC)
  46 # pragma warning(push)
  47 # pragma warning(disable:4244)    // Possible truncation
  48 # pragma warning(disable:4251)    // Missing DLL interface for std::string
  49 # pragma warning(disable:4309)    // Truncation of constant value.
  50 #endif
  51
  52 #ifdef BOOST_NO_STDC_NAMESPACE
  53 namespace std { using ::time_t; }
  54 #endif
  55
  56 namespace boost { namespace iostreams {
  57
  58 //------------------Definitions of constants----------------------------------//
  59
  60 namespace gzip {
  61
  62 using namespace boost::iostreams::zlib;
  63
  64     // Error codes used by gzip_error.
  65
  66 const int zlib_error        = 1;
  67 const int bad_crc           = 2; // Recorded crc doesn't match data.
  68 const int bad_length        = 3; // Recorded length doesn't match data.
  69 const int bad_header        = 4; // Malformed header.
  70 const int bad_footer        = 5; // Malformed footer.
  71 const int bad_method        = 6; // Unsupported compression method.
  72
  73 namespace magic {
  74
  75     // Magic numbers used by gzip header.
  76
  77 const int id1               = 0x1f;
  78 const int id2               = 0x8b;
  79
  80 } // End namespace magic.
  81
  82 namespace method {
  83
  84     // Codes used for the 'CM' byte of the gzip header.
  85
  86 const int deflate           = 8;
  87
  88 } // End namespace method.
  89
  90 namespace flags {
  91
  92     // Codes used for the 'FLG' byte of the gzip header.
  93
  94 const int text              = 1;
  95 const int header_crc        = 2;
  96 const int extra             = 4;
  97 const int name              = 8;
  98 const int comment           = 16;
  99
 100 } // End namespace flags.
 101
 102 namespace extra_flags {
 103
 104     // Codes used for the 'XFL' byte of the gzip header.
 105
 106 const int best_compression  = 2;
 107 const int best_speed        = 4;
 108
 109 } // End namespace extra_flags.
 110
 111     // Codes used for the 'OS' byte of the gzip header.
 112
 113 const int os_fat            = 0;
 114 const int os_amiga          = 1;
 115 const int os_vms            = 2;
 116 const int os_unix           = 3;
 117 const int os_vm_cms         = 4;
 118 const int os_atari          = 5;
 119 const int os_hpfs           = 6;
 120 const int os_macintosh      = 7;
 121 const int os_z_system       = 8;
 122 const int os_cp_m           = 9;
 123 const int os_tops_20        = 10;
 124 const int os_ntfs           = 11;
 125 const int os_qdos           = 12;
 126 const int os_acorn          = 13;
 127 const int os_unknown        = 255;
 128
 129 } // End namespace gzip.
 130
 131 //------------------Definition of gzip_params---------------------------------//
 132
 133 //
 134 // Class name: gzip_params.
 135 // Description: Subclass of zlib_params with an additional field
 136 //      representing a file name.
 137 //
 138 struct gzip_params : zlib_params {
 139
 140     // Non-explicit constructor.
 141     gzip_params( int level              = gzip::default_compression,
 142                  int method             = gzip::deflated,
 143                  int window_bits        = gzip::default_window_bits,
 144                  int mem_level          = gzip::default_mem_level,
 145                  int strategy           = gzip::default_strategy,
 146                  std::string file_name_  = "",
 147                  std::string comment_    = "",
 148                  std::time_t mtime_      = 0 )
 149         : zlib_params(level, method, window_bits, mem_level, strategy),
 150           file_name(file_name_), comment(comment_), mtime(mtime_)
 151         { }
 152     std::string  file_name;
 153     std::string  comment;
 154     std::time_t  mtime;
 155 };
 156
 157 //------------------Definition of gzip_error----------------------------------//
 158
 159 //
 160 // Class name: gzip_error.
 161 // Description: Subclass of std::ios_base::failure thrown to indicate
 162 //     zlib errors other than out-of-memory conditions.
 163 //
 164 class gzip_error : public BOOST_IOSTREAMS_FAILURE {
 165 public:
 166     explicit gzip_error(int error)
 167         : BOOST_IOSTREAMS_FAILURE("gzip error"),
 168           error_(error), zlib_error_code_(zlib::okay) { }
 169     explicit gzip_error(const zlib_error& e)
 170         : BOOST_IOSTREAMS_FAILURE("gzip error"),
 171           error_(gzip::zlib_error), zlib_error_code_(e.error())
 172         { }
 173     int error() const { return error_; }
 174     int zlib_error_code() const { return zlib_error_code_; }
 175 private:
 176     int error_;
 177     int zlib_error_code_;
 178 };
 179
 180 //------------------Definition of gzip_compressor-----------------------------//
 181
 182 //
 183 // Template name: gzip_compressor
 184 // Description: Model of OutputFilter implementing compression in the
 185 //      gzip format.
 186 //
 187 template<typename Alloc = std::allocator<char> >
 188 class basic_gzip_compressor : basic_zlib_compressor<Alloc> {
 189 private:
 190     typedef basic_zlib_compressor<Alloc>  base_type;
 191 public:
 192     typedef char char_type;
 193     struct category
 194         : dual_use,
 195           filter_tag,
 196           multichar_tag,
 197           closable_tag
 198         { };
 199     basic_gzip_compressor( const gzip_params& = gzip::default_compression,
 200                            std::streamsize buffer_size = default_device_buffer_size );
 201
 202     template<typename Source>
 203     std::streamsize read(Source& src, char_type* s, std::streamsize n)
 204     {
 205         std::streamsize result = 0;
 206
 207         // Read header.
 208         if (!(flags_ & f_header_done))
 209             result += read_string(s, n, header_);
 210
 211         // Read body.
 212         if (!(flags_ & f_body_done)) {
 213
 214             // Read from basic_zlib_filter.
 215             std::streamsize amt = base_type::read(src, s + result, n - result);
 216             if (amt != -1) {
 217                 result += amt;
 218                 if (amt < n - result) { // Double-check for EOF.
 219                     amt = base_type::read(src, s + result, n - result);
 220                     if (amt != -1)
 221                         result += amt;
 222                 }
 223             }
 224             if (amt == -1)
 225                 prepare_footer();
 226         }
 227
 228         // Read footer.
 229         if ((flags_ & f_body_done) != 0 && result < n)
 230             result += read_string(s + result, n - result, footer_);
 231
 232         return result != 0 ? result : -1;
 233     }
 234
 235     template<typename Sink>
 236     std::streamsize write(Sink& snk, const char_type* s, std::streamsize n)
 237     {
 238         if (!(flags_ & f_header_done)) {
 239             std::streamsize amt =
 240                 static_cast<std::streamsize>(header_.size() - offset_);
 241             offset_ += boost::iostreams::write_if(snk, header_.data() + offset_, amt);
 242             if (offset_ == header_.size())
 243                 flags_ |= f_header_done;
 244             else
 245                 return 0;
 246         }
 247         return base_type::write(snk, s, n);
 248     }
 249
 250     template<typename Sink>
 251     void close(Sink& snk, BOOST_IOS::openmode m)
 252     {
 253         try {
 254             if (m == BOOST_IOS::out && !(flags_ & f_header_done))
 255                 this->write(snk, 0, 0);
 256
 257             // Close zlib compressor.
 258             base_type::close(snk, m);
 259
 260             if (m == BOOST_IOS::out) {
 261                 if (flags_ & f_header_done) {
 262
 263                     // Write final fields of gzip file format.
 264                     write_long(this->crc(), snk);
 265                     write_long(this->total_in(), snk);
 266                 }
 267             }
 268         } catch(...) {
 269             close_impl();
 270             throw;
 271         }
 272         close_impl();
 273     }
 274 private:
 275     static gzip_params normalize_params(gzip_params p);
 276     void prepare_footer();
 277     std::streamsize read_string(char* s, std::streamsize n, std::string& str);
 278
 279     template<typename Sink>
 280     static void write_long(long n, Sink& next, boost::mpl::true_)
 281     {
 282         boost::iostreams::put(next, static_cast<char>(0xFF & n));
 283         boost::iostreams::put(next, static_cast<char>(0xFF & (n >> 8)));
 284         boost::iostreams::put(next, static_cast<char>(0xFF & (n >> 16)));
 285         boost::iostreams::put(next, static_cast<char>(0xFF & (n >> 24)));
 286     }
 287     template<typename Sink>
 288     static void write_long(long, Sink&, boost::mpl::false_)
 289     {
 290     }
 291     template<typename Sink>
 292     static void write_long(long n, Sink& next)
 293     {
 294         typedef typename category_of<Sink>::type category;
 295         typedef is_convertible<category, output> can_write;
 296         write_long(n, next, can_write());
 297     }
 298
 299     void close_impl()
 300     {
 301         footer_.clear();
 302         offset_ = 0;
 303         flags_ = 0;
 304     }
 305
 306     enum state_type {
 307         f_header_done = 1,
 308         f_body_done = f_header_done << 1,
 309         f_footer_done = f_body_done << 1
 310     };
 311     std::string  header_;
 312     std::string  footer_;
 313     std::size_t  offset_;
 314     int          flags_;
 315 };
 316 BOOST_IOSTREAMS_PIPABLE(basic_gzip_compressor, 1)
 317
 318 typedef basic_gzip_compressor<> gzip_compressor;
 319
 320 //------------------Definition of helper templates for decompression----------//
 321
 322 namespace detail {
 323
 324 // Processes gzip headers
 325 class BOOST_IOSTREAMS_DECL gzip_header {
 326 public:
 327     gzip_header() { reset(); }
 328
 329     // Members for processing header data
 330     void process(char c);
 331     bool done() const { return state_ == s_done; }
 332     void reset();
 333
 334     // Members for accessing header data
 335     std::string file_name() const { return file_name_; }
 336     std::string comment() const { return comment_; }
 337     bool text() const { return (flags_ & gzip::flags::text) != 0; }
 338     int os() const { return os_; }
 339     std::time_t mtime() const { return mtime_; }
 340 private:
 341     enum state_type {
 342         s_id1       = 1,
 343         s_id2       = s_id1 + 1,
 344         s_cm        = s_id2 + 1,
 345         s_flg       = s_cm + 1,
 346         s_mtime     = s_flg + 1,
 347         s_xfl       = s_mtime + 1,
 348         s_os        = s_xfl + 1,
 349         s_xlen      = s_os + 1,
 350         s_extra     = s_xlen + 1,
 351         s_name      = s_extra + 1,
 352         s_comment   = s_name + 1,
 353         s_hcrc      = s_comment + 1,
 354         s_done      = s_hcrc + 1
 355     };
 356     std::string  file_name_;
 357     std::string  comment_;
 358     int          os_;
 359     std::time_t  mtime_;
 360     int          flags_;
 361     int          state_;
 362     int          offset_;  // Offset within fixed-length region.
 363     int          xlen_;    // Bytes remaining in extra field.
 364 };
 365
 366 // Processes gzip footers
 367 class BOOST_IOSTREAMS_DECL gzip_footer {
 368 public:
 369     gzip_footer() { reset(); }
 370
 371     // Members for processing footer data
 372     void process(char c);
 373     bool done() const { return state_ == s_done; }
 374     void reset();
 375
 376     // Members for accessing footer data
 377     zlib::ulong crc() const { return crc_; }
 378     zlib::ulong uncompressed_size() const { return isize_; }
 379 private:
 380     enum state_type {
 381         s_crc     = 1,
 382         s_isize   = s_crc + 1,
 383         s_done    = s_isize + 1
 384     };
 385     zlib::ulong  crc_;
 386     zlib::ulong  isize_;
 387     int          state_;
 388     int          offset_;
 389 };
 390
 391 } // End namespace boost::iostreams::detail.
 392
 393 //------------------Definition of basic_gzip_decompressor---------------------//
 394
 395 //
 396 // Template name: basic_gzip_decompressor
 397 // Description: Model of InputFilter implementing compression in the
 398 //      gzip format.
 399 //
 400 template<typename Alloc = std::allocator<char> >
 401 class basic_gzip_decompressor : basic_zlib_decompressor<Alloc> {
 402 private:
 403     typedef basic_zlib_decompressor<Alloc>   base_type;
 404     typedef typename base_type::string_type  string_type;
 405 public:
 406     typedef char char_type;
 407     struct category
 408         : dual_use,
 409           filter_tag,
 410           multichar_tag,
 411           closable_tag
 412         { };
 413     basic_gzip_decompressor( int window_bits = gzip::default_window_bits,
 414                              std::streamsize buffer_size = default_device_buffer_size );
 415
 416     template<typename Sink>
 417     std::streamsize write(Sink& snk, const char_type* s, std::streamsize n)
 418     {
 419         std::streamsize result = 0;
 420         while(result < n) {
 421             if(state_ == s_start) {
 422                 state_ = s_header;
 423                 header_.reset();
 424                 footer_.reset();
 425             }
 426             if (state_ == s_header) {
 427                 int c = s[result++];
 428                 header_.process(c);
 429                 if (header_.done())
 430                     state_ = s_body;
 431             } else if (state_ == s_body) {
 432                 try {
 433                     std::streamsize amt =
 434                         base_type::write(snk, s + result, n - result);
 435                     result += amt;
 436                     if (!this->eof()) {
 437                         break;
 438                     } else {
 439                         state_ = s_footer;
 440                     }
 441                 } catch (const zlib_error& e) {
 442                     boost::throw_exception(gzip_error(e));
 443                 }
 444             } else { // state_ == s_footer
 445                 if (footer_.done()) {
 446                     if (footer_.crc() != this->crc())
 447                         boost::throw_exception(gzip_error(gzip::bad_crc));
 448
 449                     base_type::close(snk, BOOST_IOS::out);
 450                     state_ = s_start;
 451                 } else {
 452                     int c = s[result++];
 453                     footer_.process(c);
 454                 }
 455             }
 456         }
 457         return result;
 458     }
 459
 460     template<typename Source>
 461     std::streamsize read(Source& src, char_type* s, std::streamsize n)
 462     {
 463         typedef char_traits<char>  traits_type;
 464         std::streamsize            result = 0;
 465         peekable_source<Source>    peek(src, putback_);
 466         while (result < n && state_ != s_done) {
 467             if (state_ == s_start) {
 468                 state_ = s_header;
 469                 header_.reset();
 470                 footer_.reset();
 471             }
 472             if (state_ == s_header) {
 473                 int c = boost::iostreams::get(peek);
 474                 if (traits_type::is_eof(c)) {
 475                     boost::throw_exception(gzip_error(gzip::bad_header));
 476                 } else if (traits_type::would_block(c)) {
 477                     break;
 478                 }
 479                 header_.process(c);
 480                 if (header_.done())
 481                     state_ = s_body;
 482             } else if (state_ == s_body) {
 483                 try {
 484                     std::streamsize amt =
 485                         base_type::read(peek, s + result, n - result);
 486                     if (amt != -1) {
 487                         result += amt;
 488                         if (amt < n - result)
 489                             break;
 490                     } else {
 491                         peek.putback(this->unconsumed_input());
 492                         state_ = s_footer;
 493                     }
 494                 } catch (const zlib_error& e) {
 495                     boost::throw_exception(gzip_error(e));
 496                 }
 497             } else { // state_ == s_footer
 498                 int c = boost::iostreams::get(peek);
 499                 if (traits_type::is_eof(c)) {
 500                     boost::throw_exception(gzip_error(gzip::bad_footer));
 501                 } else if (traits_type::would_block(c)) {
 502                     break;
 503                 }
 504                 footer_.process(c);
 505                 if (footer_.done()) {
 506                     if (footer_.crc() != this->crc())
 507                         boost::throw_exception(gzip_error(gzip::bad_crc));
 508                     c = boost::iostreams::get(peek);
 509                     if (traits_type::is_eof(c)) {
 510                         state_ = s_done;
 511                     } else {
 512                         peek.putback(c);
 513                         base_type::close(peek, BOOST_IOS::in);
 514                         state_ = s_start;
 515                         header_.reset();
 516                         footer_.reset();
 517                     }
 518                 }
 519             }
 520         }
 521         if (peek.has_unconsumed_input()) {
 522             putback_ = peek.unconsumed_input();
 523         } else {
 524             putback_.clear();
 525         }
 526         return result != 0 || state_ != s_done ?
 527             result :
 528             -1;
 529     }
 530
 531     template<typename Source>
 532     void close(Source& src, BOOST_IOS::openmode m)
 533     {
 534         try {
 535             base_type::close(src, m);
 536         } catch (const zlib_error& e) {
 537             state_ = s_start;
 538             boost::throw_exception(gzip_error(e));
 539         }
 540         if (m == BOOST_IOS::out) {
 541             if (state_ == s_start || state_ == s_header)
 542                 boost::throw_exception(gzip_error(gzip::bad_header));
 543             else if (state_ == s_body)
 544                 boost::throw_exception(gzip_error(gzip::bad_footer));
 545             else if (state_ == s_footer) {
 546                 if (!footer_.done())
 547                     boost::throw_exception(gzip_error(gzip::bad_footer));
 548                 else if(footer_.crc() != this->crc())
 549                     boost::throw_exception(gzip_error(gzip::bad_crc));
 550             } else {
 551                 BOOST_ASSERT(!"Bad state");
 552             }
 553         }
 554         state_ = s_start;
 555     }
 556
 557     std::string file_name() const { return header_.file_name(); }
 558     std::string comment() const { return header_.comment(); }
 559     bool text() const { return header_.text(); }
 560     int os() const { return header_.os(); }
 561     std::time_t mtime() const { return header_.mtime(); }
 562 private:
 563     static gzip_params make_params(int window_bits);
 564
 565     // Source adapter allowing an arbitrary character sequence to be put back.
 566     template<typename Source>
 567     struct peekable_source {
 568         typedef char char_type;
 569         struct category : source_tag, peekable_tag { };
 570         explicit peekable_source(Source& src, const string_type& putback = "")
 571             : src_(src), putback_(putback), offset_(0)
 572             { }
 573         std::streamsize read(char* s, std::streamsize n)
 574         {
 575             std::streamsize result = 0;
 576
 577             // Copy characters from putback buffer
 578             std::streamsize pbsize =
 579                 static_cast<std::streamsize>(putback_.size());
 580             if (offset_ < pbsize) {
 581                 result = (std::min)(n, pbsize - offset_);
 582                 BOOST_IOSTREAMS_CHAR_TRAITS(char)::copy(
 583                     s, putback_.data() + offset_, result);
 584                 offset_ += result;
 585                 if (result == n)
 586                     return result;
 587             }
 588
 589             // Read characters from src_
 590             std::streamsize amt =
 591                 boost::iostreams::read(src_, s + result, n - result);
 592             return amt != -1 ?
 593                 result + amt :
 594                 result ? result : -1;
 595         }
 596         bool putback(char c)
 597         {
 598             if (offset_) {
 599                 putback_[--offset_] = c;
 600             } else {
 601                 boost::throw_exception(
 602                     boost::iostreams::detail::bad_putback());
 603             }
 604             return true;
 605         }
 606         void putback(const string_type& s)
 607         {
 608             putback_.replace(0, offset_, s);
 609             offset_ = 0;
 610         }
 611
 612         // Returns true if some characters have been putback but not re-read.
 613         bool has_unconsumed_input() const
 614         {
 615             return offset_ < static_cast<std::streamsize>(putback_.size());
 616         }
 617
 618         // Returns the sequence of characters that have been put back but not re-read.
 619         string_type unconsumed_input() const
 620         {
 621             return string_type(putback_, offset_, putback_.size() - offset_);
 622         }
 623         Source&          src_;
 624         string_type      putback_;
 625         std::streamsize  offset_;
 626     };
 627
 628     enum state_type {
 629         s_start   = 1,
 630         s_header  = s_start + 1,
 631         s_body    = s_header + 1,
 632         s_footer  = s_body + 1,
 633         s_done    = s_footer + 1
 634     };
 635     detail::gzip_header  header_;
 636     detail::gzip_footer  footer_;
 637     string_type          putback_;
 638     int                  state_;
 639 };
 640 BOOST_IOSTREAMS_PIPABLE(basic_gzip_decompressor, 1)
 641
 642 typedef basic_gzip_decompressor<> gzip_decompressor;
 643
 644 //------------------Implementation of gzip_compressor-------------------------//
 645
 646 template<typename Alloc>
 647 basic_gzip_compressor<Alloc>::basic_gzip_compressor
 648     (const gzip_params& p, std::streamsize buffer_size)
 649     : base_type(normalize_params(p), buffer_size),
 650       offset_(0), flags_(0)
 651 {
 652     // Calculate gzip header.
 653     bool has_name = !p.file_name.empty();
 654     bool has_comment = !p.comment.empty();
 655
 656     std::string::size_type length =
 657         10 +
 658         (has_name ? p.file_name.size() + 1 : 0) +
 659         (has_comment ? p.comment.size() + 1 : 0);
 660         // + 2; // Header crc confuses gunzip.
 661     int flags =
 662         //gzip::flags::header_crc +
 663         (has_name ? gzip::flags::name : 0) +
 664         (has_comment ? gzip::flags::comment : 0);
 665     int extra_flags =
 666         ( p.level == zlib::best_compression ?
 667               gzip::extra_flags::best_compression :
 668               0 ) +
 669         ( p.level == zlib::best_speed ?
 670               gzip::extra_flags::best_speed :
 671               0 );
 672     header_.reserve(length);
 673     header_ += gzip::magic::id1;                         // ID1.
 674     header_ += gzip::magic::id2;                         // ID2.
 675     header_ += gzip::method::deflate;                    // CM.
 676     header_ += static_cast<char>(flags);                 // FLG.
 677     header_ += static_cast<char>(0xFF & p.mtime);        // MTIME.
 678     header_ += static_cast<char>(0xFF & (p.mtime >> 8));
 679     header_ += static_cast<char>(0xFF & (p.mtime >> 16));
 680     header_ += static_cast<char>(0xFF & (p.mtime >> 24));
 681     header_ += static_cast<char>(extra_flags);           // XFL.
 682     header_ += static_cast<char>(gzip::os_unknown);      // OS.
 683     if (has_name) {
 684         header_ += p.file_name;
 685         header_ += '\0';
 686     }
 687     if (has_comment) {
 688         header_ += p.comment;
 689         header_ += '\0';
 690     }
 691 }
 692
 693 template<typename Alloc>
 694 gzip_params basic_gzip_compressor<Alloc>::normalize_params(gzip_params p)
 695 {
 696     p.noheader = true;
 697     p.calculate_crc = true;
 698     return p;
 699 }
 700
 701 template<typename Alloc>
 702 void basic_gzip_compressor<Alloc>::prepare_footer()
 703 {
 704     boost::iostreams::back_insert_device<std::string> out(footer_);
 705     write_long(this->crc(), out);
 706     write_long(this->total_in(), out);
 707     flags_ |= f_body_done;
 708     offset_ = 0;
 709 }
 710
 711 template<typename Alloc>
 712 std::streamsize basic_gzip_compressor<Alloc>::read_string
 713     (char* s, std::streamsize n, std::string& str)
 714 {
 715     std::streamsize avail =
 716         static_cast<std::streamsize>(str.size() - offset_);
 717     std::streamsize amt = (std::min)(avail, n);
 718     std::copy( str.data() + offset_,
 719                str.data() + offset_ + amt,
 720                s );
 721     offset_ += amt;
 722     if ( !(flags_ & f_header_done) &&
 723          offset_ == static_cast<std::size_t>(str.size()) )
 724     {
 725         flags_ |= f_header_done;
 726     }
 727     return amt;
 728 }
 729
 730 //------------------Implementation of gzip_decompressor-----------------------//
 731
 732 template<typename Alloc>
 733 basic_gzip_decompressor<Alloc>::basic_gzip_decompressor
 734     (int window_bits, std::streamsize buffer_size)
 735     : base_type(make_params(window_bits), buffer_size),
 736       state_(s_start)
 737     { }
 738
 739 template<typename Alloc>
 740 gzip_params basic_gzip_decompressor<Alloc>::make_params(int window_bits)
 741 {
 742     gzip_params p;
 743     p.window_bits = window_bits;
 744     p.noheader = true;
 745     p.calculate_crc = true;
 746     return p;
 747 }
 748
 749 //----------------------------------------------------------------------------//
 750
 751 } } // End namespaces iostreams, boost.
 752
 753 #if defined(BOOST_MSVC)
 754 # pragma warning(pop)
 755 #endif
 756
 757 #endif // #ifndef BOOST_IOSTREAMS_GZIP_HPP_INCLUDED