PHP zip_entry_compressedsize() - Get Compressed Size

In this tutorial, you will learn how to use the zip_entry_compressedsize() function in PHP to retrieve the compressed size of an entry inside a ZIP archive. This is particularly useful when you want to analyze or manage ZIP files programmatically and need to understand the compression details of individual files within the archive.

Prerequisites

Basic knowledge of PHP programming.
PHP installed on your system (version 5.2.0 and above, but zip_entry_compressedsize() is available with the ZIP extension).
The PHP ZIP extension enabled in your php.ini (zip module).
A sample ZIP file to work with (or the ability to create one).

Setup Steps

Verify ZIP extension enabled:
Open your terminal or command prompt and run:
```
php -m | grep zip
```
If you don't see zip listed, enable it in your php.ini or install the module:
- For Ubuntu/Debian: sudo apt-get install php-zip
- For Windows: Enable php_zip.dll in php.ini
Prepare a ZIP file for testing. For example, create sample.zip containing a few files.
Open your PHP editor and create a new script to implement zip_entry_compressedsize().

Understanding `zip_entry_compressedsize()`

This function returns the compressed size (in bytes) of the current entry in the ZIP archive, which means how large the file is in its compressed form.

Syntax:

int zip_entry_compressedsize(resource $zip_entry)

Here, $zip_entry is an open ZIP directory entry resource (obtained via zip_entry_open() after opening the ZIP file).

Example: Get Compressed Sizes of All Entries in a ZIP File

The example below opens a ZIP archive, iterates over each file entry, and outputs the original size and the compressed size for each file.

<?php
// Path to the ZIP archive
$zipFile = "sample.zip";

// Open the ZIP archive
$zip = zip_open($zipFile);
if (!$zip) {
    die("Failed to open archive: $zipFile");
}

while ($zipEntry = zip_read($zip)) {
    // Open the entry
    if (zip_entry_open($zip, $zipEntry)) {
        $name = zip_entry_name($zipEntry);
        $size = zip_entry_filesize($zipEntry);
        $compressedSize = zip_entry_compressedsize($zipEntry);

        echo "File: $name\n";
        echo "Original Size: $size bytes\n";
        echo "Compressed Size: $compressedSize bytes\n";
        echo "-------------------------\n";

        zip_entry_close($zipEntry);
    }
}

zip_close($zip);
?>

Output Sample

File: document.txt
Original Size: 2048 bytes
Compressed Size: 678 bytes
-------------------------
File: image.png
Original Size: 15000 bytes
Compressed Size: 14995 bytes
-------------------------

Best Practices

Always check the return values: Functions like zip_open() and zip_entry_open() can fail. Handle failures gracefully.
Close entries and ZIP handles: Always close ZIP entries with zip_entry_close() and the archive with zip_close() to free resources.
Use full path correctness: Ensure the ZIP file path is correct, especially when working on different environments.
Validate your ZIP files: When dealing with uploaded files, verify their integrity before processing.

Common Mistakes

Calling zip_entry_compressedsize() before opening the ZIP entry with zip_entry_open().
Confusing zip_entry_filesize() (original file size) with zip_entry_compressedsize() (compressed size).
Not checking if the ZIP archive was successfully opened.
Assuming the function works with remote ZIP files without downloading them first.

Interview Questions

Junior Level

What does zip_entry_compressedsize() return?
It returns the compressed size in bytes of a file entry inside a ZIP archive.
Which resource type should be passed to zip_entry_compressedsize()?
An open ZIP directory entry resource obtained from zip_entry_open().
What PHP extension provides zip_entry_compressedsize()?
The ZIP extension.
What function do you use to open a ZIP file before reading entries?
zip_open().
How do you get the original file size of an entry?
Use zip_entry_filesize().

Mid Level

Can you get the compressed size of the ZIP entry without opening it first?
No, you must open the ZIP entry using zip_entry_open() before calling zip_entry_compressedsize().
Why might the compressed size be larger than the original file size?
Some files do not compress well and may have compression overhead that makes them larger.
How would you handle errors while opening entries or the ZIP archive?
Check return values of zip_open() and zip_entry_open() and handle failures using error messages or fallback logic.
Is it possible to get compressed sizes of all entries without extracting the ZIP archive?
Yes, by reading each entry with zip_read() and using zip_entry_compressedsize().
Which PHP function closes a ZIP archive?
zip_close().

Senior Level

How does zip_entry_compressedsize() help in estimating decompression resource needs?
By knowing the compressed size, developers can manage memory and bandwidth efficiently before decompressing data.
Explain the relationship between zip_entry_filesize() and zip_entry_compressedsize() in ZIP compression.
zip_entry_filesize() returns the original file size, whereas zip_entry_compressedsize() returns the compressed (stored) size; their ratio indicates compression efficiency.
Discuss potential performance considerations when iterating over ZIP entries and calling zip_entry_compressedsize().
Each call requires opening the entry which can impact performance on large archives; caching sizes or batch processing may optimize throughput.
How does PHP internally retrieve the compressed size via zip_entry_compressedsize()?
It accesses the ZIP archive's central directory metadata that stores compressed sizes for each entry without decompressing files.
Can zip_entry_compressedsize() help in validating corrupt ZIP entries? How?
Yes; inconsistencies between reported compressed sizes and actual data length during extraction can hint at corrupted or incomplete entries.

FAQ

What type of value does zip_entry_compressedsize() return?: An integer representing the compressed size in bytes of the ZIP entry.
Can I use zip_entry_compressedsize() without opening the ZIP entry first?: No. The ZIP entry must be explicitly opened with zip_entry_open() before retrieving its compressed size.
Is zip_entry_compressedsize() available in PHP 8?: While the function exists in older PHP versions, it is deprecated as part of the older ZIP functions. It's recommended to use the ZipArchive class instead in PHP 7+.
How is zip_entry_compressedsize() different from zip_entry_filesize()?: zip_entry_filesize() gives the original uncompressed size, whereas zip_entry_compressedsize() returns the size after compression inside the archive.
What to do if zip_entry_compressedsize() returns zero?: This might mean the entry is empty or the file is stored without compression.

Conclusion

The zip_entry_compressedsize() function is a handy tool in PHP's ZIP extension that lets you retrieve the compressed size of files inside a ZIP archive, providing insight into compression efficiency and helping with resource management. While older ZIP functions are somewhat deprecated, understanding and using them can be valuable, especially in legacy codebases. For modern applications, consider using PHP's ZipArchive class, which offers improved control and easier ZIP file handling.

PHP zip_entry_compressedsize() Function