• Andrew Wiley (14/15) Jul 19 2011 I'm using std.zlib in an application, and I'm having trouble decompressi...
• Jesse Phillips (4/9) Jul 19 2011 The zlib format is different from the gzip format.
• Andrew Wiley (6/19) Jul 19 2011 I know, but if you look at the docs for the inflate functions, zlib is
• Jesse Phillips (3/7) Jul 19 2011 Not sure what documentation you are talking of. But it doesn't sound lik...
• Andrew Wiley (7/19) Jul 19 2011 Ah, I stand corrected:
• Andrew Wiley (5/28) Jul 19 2011 Looks like this is the solution:

Andrew Wiley <wiley.andrew.j gmail.com> writes:

I'm using std.zlib in an application, and I'm having trouble decompressing a
file. The file is gzipped, and I can easily see the contents with `cat file
| gzip -d` but this code doesn't work:
auto arr = read("file.gz");
ubyte[] realarr = cast(ubyte[])uncompress(arr);

output:
std.zlib.ZlibException std/zlib.d(59): data error

From the header file, it seems like zlib should be detecting a gzip header

and *just working*, but, well, it isn't. I have to store data in a
compressed format, and eventually the code I'm writing will be used
in-memory instead of on files, so I'm going to have to uncompress it
somehow.
Has anyone encountered this before?

Thanks,
Andrew

Jesse Phillips <jessekphillips+D gmail.com> writes:

Andrew Wiley Wrote:

 I'm using std.zlib in an application, and I'm having trouble decompressing a
 file. The file is gzipped, and I can easily see the contents with `cat file
 | gzip -d` but this code doesn't work:
 auto arr = read("file.gz");
 ubyte[] realarr = cast(ubyte[])uncompress(arr);

The zlib format is different from the gzip format.

http://www.zlib.net/zlib_faq.html#faq18

One is made for file storage and the other internal data transfer. D does not
provide a wrapper to the gzip functions at this time but they are available in
std.c.zlib (with the C interface).

Andrew Wiley <wiley.andrew.j gmail.com> writes:

On Tue, Jul 19, 2011 at 7:11 AM, Jesse Phillips
<jessekphillips+D gmail.com>wrote:

 Andrew Wiley Wrote:

 I'm using std.zlib in an application, and I'm having trouble

 decompressing a
 file. The file is gzipped, and I can easily see the contents with `cat

 file
 | gzip -d` but this code doesn't work:
 auto arr = read("file.gz");
 ubyte[] realarr = cast(ubyte[])uncompress(arr);

 The zlib format is different from the gzip format.

 http://www.zlib.net/zlib_faq.html#faq18

 One is made for file storage and the other internal data transfer. D does
 not provide a wrapper to the gzip functions at this time but they are
 available in std.c.zlib (with the C interface).

I know, but if you look at the docs for the inflate functions, zlib is
supposed to be autodetecting the gzip header and uncompressing the payload
correctly, if I understand the documentation (which I probably don't at this
point).

Jesse Phillips <jessekphillips+D gmail.com> writes:

Andrew Wiley Wrote:

 I know, but if you look at the docs for the inflate functions, zlib is
 supposed to be autodetecting the gzip header and uncompressing the payload
 correctly, if I understand the documentation (which I probably don't at this
 point).

Not sure what documentation you are talking of. But it doesn't sound like it
does auto detection, an answer to one of the question:

"You can request that deflate write the gzip format instead of the zlib format
using deflateInit2(). You can also request that inflate decode the gzip format
using inflateInit2(). Read zlib.h for more details."

Andrew Wiley <wiley.andrew.j gmail.com> writes:

On Tue, Jul 19, 2011 at 9:57 AM, Jesse Phillips
<jessekphillips+D gmail.com>wrote:

 Andrew Wiley Wrote:

 I know, but if you look at the docs for the inflate functions, zlib is
 supposed to be autodetecting the gzip header and uncompressing the

 payload
 correctly, if I understand the documentation (which I probably don't at

 this
 point).

 Not sure what documentation you are talking of. But it doesn't sound like
 it does auto detection, an answer to one of the question:

 "You can request that deflate write the gzip format instead of the zlib
 format using deflateInit2(). You can also request that inflate decode the
 gzip format using inflateInit2(). Read zlib.h for more details."

Ah, I stand corrected:
"inflate() can decompress and check either zlib-wrapped or gzip-wrapped
  deflate data.  The header type is detected automatically, if requested
when
  initializing with inflateInit2()."

Andrew Wiley <wiley.andrew.j gmail.com> writes:

On Tue, Jul 19, 2011 at 10:14 AM, Andrew Wiley <wiley.andrew.j gmail.com>wrote:

 On Tue, Jul 19, 2011 at 9:57 AM, Jesse Phillips <
 jessekphillips+D gmail.com> wrote:

 Andrew Wiley Wrote:

 I know, but if you look at the docs for the inflate functions, zlib is
 supposed to be autodetecting the gzip header and uncompressing the

 payload
 correctly, if I understand the documentation (which I probably don't at

 this
 point).

 Not sure what documentation you are talking of. But it doesn't sound like
 it does auto detection, an answer to one of the question:

 "You can request that deflate write the gzip format instead of the zlib
 format using deflateInit2(). You can also request that inflate decode the
 gzip format using inflateInit2(). Read zlib.h for more details."

 Ah, I stand corrected:
 "inflate() can decompress and check either zlib-wrapped or gzip-wrapped
   deflate data.  The header type is detected automatically, if requested
 when
   initializing with inflateInit2()."

Looks like this is the solution:
ubyte[] realarr = cast(ubyte[])uncompress(arr, 0, 47);
The 47 makes zlib autodetect the header (because the 32 bit is set; if you
wanted to force gzip, you'd set the 16 bit).