How to get CommonPrefixes from an Amazon S3 ListObjects Iterator

Question

I'm trying to get a list of objects in a bucket into an organised list, with folders and files.

In the documentation, S3 Listing Keys Hierarchically Using Prefix and Delimiter, Amazon states that when there are other directories in the currently selected directory:

Amazon S3 groups these keys and return a single CommonPrefixes element

I have the following code:

$iterator = $client->getIterator(
    'ListObjects',
    array(
        'Bucket' => $bucket,
        'Prefix' => $dir,
        'Delimiter' => '/'
    )
);

which does a good job. It gets all the objects in a bucket (unlike the low-level ListObjects method, which returns a max of 1000 objects) and displays them alphabetically.

If I tell this iterator to return an array like so:

$objects = $iterator->toArray();

I can then use this array in a foreach loop

foreach ($objects as $object) {
  echo $object['Key'] . "<br/>\n";
}

which gives me all the pointers to files:

• folder/subfolder/file.ext
• folder/subfolder/file2.ext
• folder/subfolder/file3.ext
• folder/subfolder/file4.ext
• folder/subfolder/file5.ext

It isn't showing the other directories in this directory though.

Calling $iterator->get('CommonPrefixes') returns null. Any other operations on the $iterator variable crash the code.

How can I get access to the full set of responses in the ListBucketResult?

Answer 1

The getIterator() method has a third parameter for options specific to the iterator object. The S3 ListObjects iterator is actually a concrete class and specifies some custom options in its docs: return_prefixes, sort_results, and names_only (see http://docs.aws.amazon.com/aws-sdk-php/latest/class-Aws.S3.Iterator.ListObjectsIterator.html). Use return_prefixes to get the CommonPrefixes intermingled with the objects. Try this:

$iterator = $client->getIterator(
    'ListObjects',
    array(
        'Bucket' => $bucket,
        'Prefix' => $dir,
        'Delimiter' => '/'
    ),
    array(
        'return_prefixes' => true,
    ),
);

foreach ($iterator as $object) {
    if (isset($object['Prefix'])) {
        // For Common Prefixes
        echo $object['Prefix'] . "<br/>\n";
    } else {
        // For Objects
        echo $object['Key'] . "<br/>\n";
    }
}

// Also Licensed under version 2.0 of the Apache License.