GZIP Format

+-------------------+
| Header (10+ bytes)|
+-------------------+
| Compressed Data   |
+-------------------+
| Footer (8 bytes)  |
+-------------------+

// Magic signature
static const Byte kSignature_0 = 0x1F;
static const Byte kSignature_1 = 0x8B;
static const Byte kSignature_2 = 8;  // Deflate method

// Header structure:
// Bytes 0-1:   Magic (0x1F 0x8B)
// Byte 2:      Compression method (8 = Deflate)
// Byte 3:      Flags
// Bytes 4-7:   Modification timestamp (Unix time)
// Byte 8:      Extra flags (compression level)
// Byte 9:      Operating system

namespace NFlags {
  const Byte kCrc     = 1 << 1;  // Header CRC present
  const Byte kExtra   = 1 << 2;  // Extra field present
  const Byte kName    = 1 << 3;  // Original filename present
  const Byte kComment = 1 << 4;  // Comment present
}

namespace NExtraFlags {
  const Byte kMaximum = 2;  // Maximum compression (-mx=9)
  const Byte kFastest = 4;  // Fastest compression (-mx=1)
}

Bytes 0-3:   CRC32 of uncompressed data
Bytes 4-7:   Size of uncompressed data (mod 2^32)

namespace NHostOS {
  kFAT = 0,      // MS-DOS, Windows
  kAMIGA,        // Amiga
  kVMS,          // VMS
  kUnix,         // Unix, Linux
  kVM_CMS,       // VM/CMS
  kAtari,        // Atari
  kHPFS,         // OS/2
  kMac,          // Macintosh
  kZ_System,     // Z-System
  kCPM,          // CP/M
  kTOPS20,       // TOPS-20
  kNTFS,         // Windows NT
  kQDOS,         // QDOS
  kAcorn,        // Acorn RISC OS
  kVFAT,         // Windows 95/NT
  kMVS,          // MVS
  kBeOS,         // BeOS
  kTandem,       // Tandem
  kUnknown = 255
}

7z a -tgzip file.txt.gz file.txt

7z a -tgzip -mx=9 file.txt.gz file.txt

7z a -tgzip -mx=1 file.txt.gz file.txt

7z x file.txt.gz

7z a -ttar archive.tar files/
7z a -tgzip archive.tar.gz archive.tar

tar -czf archive.tar.gz files/

7z a -tgzip -mx=9 compressed.gz original.txt

echo "Hello, World!" | 7z a -tgzip -si hello.gz

7z x -so file.gz

# Create TAR archive first
7z a -ttar data.tar folder/
# Compress TAR with GZIP
7z a -tgzip -mx=9 data.tar.gz data.tar
# Remove intermediate TAR
rm data.tar

7z t file.gz

7z l -slt file.gz

source/CPP/7zip/Archive/GzHandler.cpp

class CItem {
  Byte Flags;
  Byte ExtraFlags;
  Byte HostOS;
  UInt32 Time;
  UInt32 Crc;
  UInt32 Size32;
  AString Name;
  AString Comment;
};

source/CPP/7zip/Compress/DeflateDecoder.h
source/CPP/7zip/Compress/DeflateEncoder.h

# Compress JavaScript
7z a -tgzip -mx=9 script.min.js.gz script.min.js

# Compress CSS
7z a -tgzip -mx=9 styles.css.gz styles.css

# Compress yesterday's log
7z a -tgzip -mx=9 app-$(date -d yesterday +%Y%m%d).log.gz app.log.1

# Dump and compress database
mysqldump mydb | 7z a -tgzip -si backup-$(date +%Y%m%d).sql.gz

tar -cf - project/ | 7z a -tgzip -mx=9 -si project-$(date +%Y%m%d).tar.gz

Content-Encoding: gzip