GZIP 和 PKZIP 文件中的压缩字节是否兼容？
Are the compressed bytes inside GZIP and PKZIP files compatible?
这个问题是 follow-up 到 "How are zlib, gzip and zip related? What do they have in common and how are they different?" 的答案非常详细，但他们从来没有完全回答我的具体问题。
给定一个有效的 GZIP 文件，我是否应该始终能够提取其中的 deflate-bytes 并使用这些字节构建一个具有相同内容的有效 PKZIP 文件，无需解压和重新压缩字节流?
例如，假设我有 collection 个 GZIP 文件。我可以编写一个程序，通过从源文件中删除 GZIP headers 并围绕字节流构建 PKZIP 结构来快速（通过避免 deflate/inflate）构建这些文件的等效 PKZIP 文件吗？ （通过获取任何有效的 PKZIP 文件并快速将它们转换为许多 GZIP 文件，反过来也一样吗？）
两种文件格式似乎使用相同的“放气”算法，但完全相同放气算法吗？
是的。完全一样 deflate format.
（放气 算法 可以，而且实际上经常是不同的，产生不同的放气流。然而，这与您的应用程序无关。格式是兼容的，任何兼容的充气机都可以解压缩移植到zip文件中的gzip deflate数据。）
我忘了为什么要写这个，但下面的 C 代码会将 gzip 文件转换为单条目 zip 文件，对 gzip 文件有一些限制。
/*
gz2zip.c version 1.0, 31 July 2018
Copyright (C) 2018 Mark Adler
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
Mark Adler
madler@alumni.caltech.edu
*/
// Convert gzip (.gz) file to a single entry zip file. See the comments before
// gz2zip() for more details and caveats.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
# include <fcntl.h>
# include <io.h>
# define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
#else
# define SET_BINARY_MODE(file)
#endif
#define local static
// Exit on error.
local void bail(char *why) {
fprintf(stderr, "gz2zip abort: %s\n", why);
exit(1);
}
// Type to track number of bytes written.
typedef struct {
FILE *out;
off_t off;
} tally_t;
// Write len bytes at dat to t.
local void put(tally_t *t, void const *dat, size_t len) {
size_t ret = fwrite(dat, 1, len, t->out);
if (ret != len)
bail("write error");
t->off += len;
}
// Write 16-bit integer n in little-endian order to t.
local void put2(tally_t *t, unsigned n) {
unsigned char dat[2];
dat[0] = n;
dat[1] = n >> 8;
put(t, dat, 2);
}
// Write 32-bit integer n in little-endian order to t.
local void put4(tally_t *t, unsigned long n) {
put2(t, n);
put2(t, n >> 16);
}
// Write n zeros to t.
local void putz(tally_t *t, unsigned n) {
unsigned char const buf[1] = {0};
while (n--)
put(t, buf, 1);
}
// Convert the Unix time unix to DOS time in the four bytes at *dos. If there
// is a conversion error for any reason, store the current time in DOS format
// at *dos. The Unix time in seconds is rounded up to an even number of
// seconds, since the DOS time can only represent even seconds. If the Unix
// time is before 1980, the minimum DOS time of Jan 1, 1980 is used.
local void unix2dos(unsigned char *dos, time_t unix) {
unix += unix & 1;
struct tm *s = localtime(&unix);
if (s == NULL) {
unix = time(NULL); // on error, use current time
unix += unix & 1;
s = localtime(&unix);
if (s == NULL)
bail("internal error"); // shouldn't happen
}
if (s->tm_year < 80) { // no DOS time before 1980
dos[0] = 0; dos[1] = 0; // use midnight,
dos[2] = (1 << 5) + 1; dos[3] = 0; // Jan 1, 1980
}
else {
dos[0] = (s->tm_min << 5) + (s->tm_sec >> 1);
dos[1] = (s->tm_hour << 3) + (s->tm_min >> 3);
dos[2] = ((s->tm_mon + 1) << 5) + s->tm_mday;
dos[3] = ((s->tm_year - 80) << 1) + ((s->tm_mon + 1) >> 3);
}
}
// Chunk size for reading and writing raw deflate data.
#define CHUNK 16384
// Read the gzip file from in and write it as a single-entry zip file to out.
// This assumes that the gzip file has a single member, that it has no junk
// after the gzip trailer, and that it contains less than 4GB of uncompressed
// data. The gzip file is not decompressed or validated, other than checking
// for the proper header format. The modification time from the gzip header is
// used for the zip entry, unless it is not present, in which case the current
// local time is used for the zip entry. The file name from the gzip header is
// used for the zip entry, unless it is not present, in which case "-" is used.
// This does not use the Zip64 format, so the offsets in the resulting zip file
// must be less than 4GB. If name is not NULL, then the zero-terminated string
// at name is used as the file name for the single entry. Whether the file name
// comes from the gzip header or from name, it is truncated to 64K-1 characters
// if necessary.
//
// It is recommended that unzip -t be used on the resulting file to verify its
// integrity. If the gzip files do not obey the constraints above, then the zip
// file will not be valid.
local void gz2zip(FILE *in, FILE *out, char *name) {
// zip file constant headers for local, central, and end record
unsigned char const loc[] = {'P', 'K', 3, 4, 20, 0, 8, 0, 8, 0};
unsigned char const cen[] = {'P', 'K', 1, 2, 20, 0, 20, 0, 8, 0, 8, 0};
unsigned char const end[] = {'P', 'K', 5, 6, 0, 0, 0, 0, 1, 0, 1, 0};
// gzip header
unsigned char head[10];
// zip file modification date, CRC, and sizes -- initialize to zero for the
// local header (the actual CRC and sizes follow the compressed data)
unsigned char desc[16] = {0};
// name from gzip header to use for the zip entry (the maximum size of the
// name is 64K-1 -- if the gzip name is longer, then it is truncated)
unsigned name_len;
char save[65535];
// read and interpret the gzip header, bailing if it is invalid or has an
// unknown compression method or flag bits set
size_t got = fread(head, 1, sizeof(head), in);
if (got < sizeof(head) ||
head[0] != 0x1f || head[1] != 0x8b || head[2] != 8 || (head[3] & 0xe0))
bail("input not gzip");
if (head[3] & 4) { // extra field (ignore)
unsigned extra = getc(in);
int high = getc(in);
if (high == EOF)
bail("premature end of gzip input");
extra += (unsigned)high << 8;
fread(name, 1, extra, in);
}
if (head[3] & 8) { // file name (save)
name_len = 0;
int ch;
while ((ch = getc(in)) != 0 && ch != EOF)
if (name_len < sizeof(name))
save[name_len++] = ch;
}
else { // no file name
name_len = 1;
save[0] = '-';
}
if (head[3] & 16) { // comment (ignore)
int ch;
while ((ch = getc(in)) != 0 && ch != EOF)
;
}
if (head[3] & 2) { // header crc (ignore)
getc(in);
getc(in);
}
// use name from argument if present, otherwise from gzip header
if (name == NULL)
name = save;
else {
name_len = strlen(name);
if (name_len > 65535)
name_len = 65535;
}
// set modification time and date in descriptor from gzip header
time_t mod = head[4] + (head[5] << 8) + ((time_t)(head[6]) << 16) +
((time_t)(head[7]) << 24);
unix2dos(desc, mod ? mod : time(NULL));
// initialize tally of output bytes
tally_t zip = {out, 0};
// write zip local header
off_t locoff = zip.off;
put(&zip, loc, sizeof(loc));
put(&zip, desc, sizeof(desc));
put2(&zip, name_len);
putz(&zip, 2);
put(&zip, name, name_len);
// copy raw deflate stream, saving eight-byte gzip trailer
unsigned char buf[CHUNK + 8];
if (fread(buf, 1, 8, in) != 8)
bail("premature end of gzip input");
off_t comp = 0;
while ((got = fread(buf + 8, 1, CHUNK, in)) != 0) {
put(&zip, buf, got);
comp += got;
memmove(buf, buf + got, 8);
}
// write descriptor based on gzip trailer and compressed count
memcpy(desc + 4, buf, 4);
desc[8] = comp;
desc[9] = comp >> 8;
desc[10] = comp >> 16;
desc[11] = comp >> 24;
memcpy(desc + 12, buf + 4, 4);
put(&zip, desc + 4, sizeof(desc) - 4);
// write zip central directory
off_t cenoff = zip.off;
put(&zip, cen, sizeof(cen));
put(&zip, desc, sizeof(desc));
put2(&zip, name_len);
putz(&zip, 12);
put4(&zip, locoff);
put(&zip, name, name_len);
// write zip end-of-central-directory record
off_t endoff = zip.off;
put(&zip, end, sizeof(end));
put4(&zip, endoff - cenoff);
put4(&zip, cenoff);
putz(&zip, 2);
}
// Convert the gzip file on stdin to a zip file on stdout. If present, the
// first argument is used as the file name in the zip entry.
int main(int argc, char **argv) {
// avoid end-of-line conversions on evil operating systems
SET_BINARY_MODE(stdin);
SET_BINARY_MODE(stdout);
// convert .gz on stdin to .zip on stdout -- error returns use exit()
gz2zip(stdin, stdout, argc > 1 ? argv[1] : NULL);
return 0;
}
这个问题是 follow-up 到 "How are zlib, gzip and zip related? What do they have in common and how are they different?" 的答案非常详细，但他们从来没有完全回答我的具体问题。
给定一个有效的 GZIP 文件，我是否应该始终能够提取其中的 deflate-bytes 并使用这些字节构建一个具有相同内容的有效 PKZIP 文件，无需解压和重新压缩字节流?
例如，假设我有 collection 个 GZIP 文件。我可以编写一个程序，通过从源文件中删除 GZIP headers 并围绕字节流构建 PKZIP 结构来快速（通过避免 deflate/inflate）构建这些文件的等效 PKZIP 文件吗？ （通过获取任何有效的 PKZIP 文件并快速将它们转换为许多 GZIP 文件，反过来也一样吗？）
两种文件格式似乎使用相同的“放气”算法，但完全相同放气算法吗？
是的。完全一样 deflate format.
（放气 算法 可以，而且实际上经常是不同的，产生不同的放气流。然而，这与您的应用程序无关。格式是兼容的，任何兼容的充气机都可以解压缩移植到zip文件中的gzip deflate数据。）
我忘了为什么要写这个，但下面的 C 代码会将 gzip 文件转换为单条目 zip 文件，对 gzip 文件有一些限制。
/*
gz2zip.c version 1.0, 31 July 2018
Copyright (C) 2018 Mark Adler
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
Mark Adler
madler@alumni.caltech.edu
*/
// Convert gzip (.gz) file to a single entry zip file. See the comments before
// gz2zip() for more details and caveats.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#if defined(MSDOS) || defined(OS2) || defined(WIN32) || defined(__CYGWIN__)
# include <fcntl.h>
# include <io.h>
# define SET_BINARY_MODE(file) setmode(fileno(file), O_BINARY)
#else
# define SET_BINARY_MODE(file)
#endif
#define local static
// Exit on error.
local void bail(char *why) {
fprintf(stderr, "gz2zip abort: %s\n", why);
exit(1);
}
// Type to track number of bytes written.
typedef struct {
FILE *out;
off_t off;
} tally_t;
// Write len bytes at dat to t.
local void put(tally_t *t, void const *dat, size_t len) {
size_t ret = fwrite(dat, 1, len, t->out);
if (ret != len)
bail("write error");
t->off += len;
}
// Write 16-bit integer n in little-endian order to t.
local void put2(tally_t *t, unsigned n) {
unsigned char dat[2];
dat[0] = n;
dat[1] = n >> 8;
put(t, dat, 2);
}
// Write 32-bit integer n in little-endian order to t.
local void put4(tally_t *t, unsigned long n) {
put2(t, n);
put2(t, n >> 16);
}
// Write n zeros to t.
local void putz(tally_t *t, unsigned n) {
unsigned char const buf[1] = {0};
while (n--)
put(t, buf, 1);
}
// Convert the Unix time unix to DOS time in the four bytes at *dos. If there
// is a conversion error for any reason, store the current time in DOS format
// at *dos. The Unix time in seconds is rounded up to an even number of
// seconds, since the DOS time can only represent even seconds. If the Unix
// time is before 1980, the minimum DOS time of Jan 1, 1980 is used.
local void unix2dos(unsigned char *dos, time_t unix) {
unix += unix & 1;
struct tm *s = localtime(&unix);
if (s == NULL) {
unix = time(NULL); // on error, use current time
unix += unix & 1;
s = localtime(&unix);
if (s == NULL)
bail("internal error"); // shouldn't happen
}
if (s->tm_year < 80) { // no DOS time before 1980
dos[0] = 0; dos[1] = 0; // use midnight,
dos[2] = (1 << 5) + 1; dos[3] = 0; // Jan 1, 1980
}
else {
dos[0] = (s->tm_min << 5) + (s->tm_sec >> 1);
dos[1] = (s->tm_hour << 3) + (s->tm_min >> 3);
dos[2] = ((s->tm_mon + 1) << 5) + s->tm_mday;
dos[3] = ((s->tm_year - 80) << 1) + ((s->tm_mon + 1) >> 3);
}
}
// Chunk size for reading and writing raw deflate data.
#define CHUNK 16384
// Read the gzip file from in and write it as a single-entry zip file to out.
// This assumes that the gzip file has a single member, that it has no junk
// after the gzip trailer, and that it contains less than 4GB of uncompressed
// data. The gzip file is not decompressed or validated, other than checking
// for the proper header format. The modification time from the gzip header is
// used for the zip entry, unless it is not present, in which case the current
// local time is used for the zip entry. The file name from the gzip header is
// used for the zip entry, unless it is not present, in which case "-" is used.
// This does not use the Zip64 format, so the offsets in the resulting zip file
// must be less than 4GB. If name is not NULL, then the zero-terminated string
// at name is used as the file name for the single entry. Whether the file name
// comes from the gzip header or from name, it is truncated to 64K-1 characters
// if necessary.
//
// It is recommended that unzip -t be used on the resulting file to verify its
// integrity. If the gzip files do not obey the constraints above, then the zip
// file will not be valid.
local void gz2zip(FILE *in, FILE *out, char *name) {
// zip file constant headers for local, central, and end record
unsigned char const loc[] = {'P', 'K', 3, 4, 20, 0, 8, 0, 8, 0};
unsigned char const cen[] = {'P', 'K', 1, 2, 20, 0, 20, 0, 8, 0, 8, 0};
unsigned char const end[] = {'P', 'K', 5, 6, 0, 0, 0, 0, 1, 0, 1, 0};
// gzip header
unsigned char head[10];
// zip file modification date, CRC, and sizes -- initialize to zero for the
// local header (the actual CRC and sizes follow the compressed data)
unsigned char desc[16] = {0};
// name from gzip header to use for the zip entry (the maximum size of the
// name is 64K-1 -- if the gzip name is longer, then it is truncated)
unsigned name_len;
char save[65535];
// read and interpret the gzip header, bailing if it is invalid or has an
// unknown compression method or flag bits set
size_t got = fread(head, 1, sizeof(head), in);
if (got < sizeof(head) ||
head[0] != 0x1f || head[1] != 0x8b || head[2] != 8 || (head[3] & 0xe0))
bail("input not gzip");
if (head[3] & 4) { // extra field (ignore)
unsigned extra = getc(in);
int high = getc(in);
if (high == EOF)
bail("premature end of gzip input");
extra += (unsigned)high << 8;
fread(name, 1, extra, in);
}
if (head[3] & 8) { // file name (save)
name_len = 0;
int ch;
while ((ch = getc(in)) != 0 && ch != EOF)
if (name_len < sizeof(name))
save[name_len++] = ch;
}
else { // no file name
name_len = 1;
save[0] = '-';
}
if (head[3] & 16) { // comment (ignore)
int ch;
while ((ch = getc(in)) != 0 && ch != EOF)
;
}
if (head[3] & 2) { // header crc (ignore)
getc(in);
getc(in);
}
// use name from argument if present, otherwise from gzip header
if (name == NULL)
name = save;
else {
name_len = strlen(name);
if (name_len > 65535)
name_len = 65535;
}
// set modification time and date in descriptor from gzip header
time_t mod = head[4] + (head[5] << 8) + ((time_t)(head[6]) << 16) +
((time_t)(head[7]) << 24);
unix2dos(desc, mod ? mod : time(NULL));
// initialize tally of output bytes
tally_t zip = {out, 0};
// write zip local header
off_t locoff = zip.off;
put(&zip, loc, sizeof(loc));
put(&zip, desc, sizeof(desc));
put2(&zip, name_len);
putz(&zip, 2);
put(&zip, name, name_len);
// copy raw deflate stream, saving eight-byte gzip trailer
unsigned char buf[CHUNK + 8];
if (fread(buf, 1, 8, in) != 8)
bail("premature end of gzip input");
off_t comp = 0;
while ((got = fread(buf + 8, 1, CHUNK, in)) != 0) {
put(&zip, buf, got);
comp += got;
memmove(buf, buf + got, 8);
}
// write descriptor based on gzip trailer and compressed count
memcpy(desc + 4, buf, 4);
desc[8] = comp;
desc[9] = comp >> 8;
desc[10] = comp >> 16;
desc[11] = comp >> 24;
memcpy(desc + 12, buf + 4, 4);
put(&zip, desc + 4, sizeof(desc) - 4);
// write zip central directory
off_t cenoff = zip.off;
put(&zip, cen, sizeof(cen));
put(&zip, desc, sizeof(desc));
put2(&zip, name_len);
putz(&zip, 12);
put4(&zip, locoff);
put(&zip, name, name_len);
// write zip end-of-central-directory record
off_t endoff = zip.off;
put(&zip, end, sizeof(end));
put4(&zip, endoff - cenoff);
put4(&zip, cenoff);
putz(&zip, 2);
}
// Convert the gzip file on stdin to a zip file on stdout. If present, the
// first argument is used as the file name in the zip entry.
int main(int argc, char **argv) {
// avoid end-of-line conversions on evil operating systems
SET_BINARY_MODE(stdin);
SET_BINARY_MODE(stdout);
// convert .gz on stdin to .zip on stdout -- error returns use exit()
gz2zip(stdin, stdout, argc > 1 ? argv[1] : NULL);
return 0;
}