Fix zlib support for large files

[nielsdos]

gzread() and gzwrite() have effectively a 4GiB limit at the moment because the APIs of the zlib library use unsigned ints. For example, this means that the count argument of gzread() and gzwrite() & co effectively are modulo 2**32.
Fix this by adding a loop to handle all bytes.

As for automated testing, I didn't find an easy way to write a phpt for this that wouldn't use a lot of memory or requires a large file. For instance, the gzread() test that I manually ran requires a 4MiB input file (and I can't shrink it because zlib has a max window size).

Here are the testing instructions, run on 64-bit:
To test for gzwrite():

$f = gzopen("out.txt.gz", "w");
gzwrite($f, str_repeat('a', 4*1024*1024*1024+64)); // 4GiB + 64 bytes

Then use zcat out.txt.gz|wc -c to check that all bytes were written (should be 4294967360).

To test for gzread():
Create a file containing all a's for example that is 4GiB + 64 bytes. Then compress it into out.txt.gz using the gzip command. Then run:

$f = gzopen("out.txt.gz", "r");
$str = gzread($f, 4*1024*1024*1024+64);
var_dump(strlen($str)); // 4294967360
var_dump(substr($str, -3)); // string (3) "aaa"

For automated testing we would first need #14895 and then generate a file dynamically using gzwrite() and then check it with gzread() I suppose.

[mvorisek]

With stream_wrapper_register it should be possible to test large file.

• generate/stream data with some deterministic pattern like 1234...
• gzip encode them
• gzip decode them
• test if the read data matches the expected data/pattern

[nielsdos]

That's true, but we would still need #14895 first to properly check for the memory limit