gzread()

(PHP 4, PHP 5, PHP 7)

Binary-safe gz-file read

说明

gzread() reads up to$lengthbytes from the given gz-file pointer. Reading stops when$length(uncompressed)bytes have been read or EOF is reached, whichever comes first.

参数

The gz-file pointer. It must be valid, and must point to a file successfully opened by gzopen().

The number of bytes to read.

返回值

The data that have been read.

范例

gzread() example

参见

• gzwrite()Binary-safe gz-file write
• gzopen()Open gz-file
• gzgets()Get line from file pointer
• gzgetss()Get line from gz-file pointer and strip HTML tags
• gzfile()Read entire gz-file into an array
• gzpassthru()Output all remaining data on a gz-file pointer

Be careful when reading data in a loop. gzread() behaves a little differently than bzread() or fread(), it does NOT return false when reading past the end of stream. It instead returns an empty string.
So a loop like:
$handle = gzopen($file);
while (false !== $chunk = gzread($handle, $bytes)) {
  //...
}
will loop indefinitely.

Here is a function for returning the uncompressed filesize of a gzip file. The filesize is stored as a 32-bit integer in the end of the compressed file, that's how this function works. Additionally, this function checks to see if it's a real gzip compressed file before doing the work; if it isn't, then just like other gz- functions, it'll treat it just like a regular file and perform a normal filesize operation. Enjoy! 

I don't think it would be wise to open a whole gzip file (it _is_ compressed for a reason, and likely to be a very big file) into a single string. You would most likely hit the php memory limits. Instead, if you need to process the file, put your gzread calls in a loop, and read incrementally by a setting $length to a constant value.

As was shown to me in another forum there is a way to get the uncompressed size of the gz file by viewing the last 4 bytes of the gz file.
Here is a piece of code that will do this

This will read the last 4 bytes of the gz file and use it as the file int for the gzread.
Thanks to stereofrog for helping me with this code.

Note that this functions' behavior differs from fread in case of EOF.
When you read the last chunk (mean the last bytes from file), it is EOF just after gzread, but in case of fread you need to read once more to get EOF.
Hope, I am clear :)

Regarding finding out the lenght of the gz file.
For some reason the seek() function didn't worked, so, I've tried finding out the last 4 bytes using string functions.
That worked pretty well. Here is the code. 

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