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5aaf7b4937
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():
```php
$f = gzopen("out.txt.gz", "w");
gzwrite($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:
```php
$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"
```
Closes GH-17775.