PHP errors when users perform an empty search query

[chrislaick]

Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in handleTrackerWithSearch() (line 128 of modules/contrib/gdx_analytics_drupal_snowplow/gdx_analytics_drupal_snowplow.module).

When a user performs an empty search or visits a search path without query parameters (e.g., /search instead of /search?keys=drupal), parse_url($curr_uri, PHP_URL_QUERY) returns null because no query string exists.

Warning: Undefined array key 1 in handleTrackerWithSearch() (line 134 of modules/contrib/gdx_analytics_drupal_snowplow/gdx_analytics_drupal_snowplow.module).

[danhgov]

There are two different errors here. One is that the query-string could be null, which causes the warning about deprecated code, in the explode command on line 128:

    // Extract query string from the full URI
    $query_string = parse_url($curr_uri, PHP_URL_QUERY);

    // Split query string by '&' to get key-value pairs
    $params = explode('&', $query_string);

The fix is to have $query_string default to an empty string, not to NULL:

    $query_string = parse_url($curr_uri, PHP_URL_QUERY) ?? '';

The second is that there could be a key-value pair with no value. The code expects the query-string to be made up of key-value pairs of the form "normal_key=value". But occasionally, there might be a key added to the string with NO value, of the form "key_only". This causes a warning from line 134:

list($key, $value) = explode('=', $param);

... because the explode command returns an array with only one element instead of two, and then there is nothing to assign to $value. PHP defaults to assigning NULL to $value, and emits the warning.

The fix, is to change it to this:

    list($key, $value) = array_pad(explode('=', $param), 2, '');

If/when explode returns an array with only one element (because of a key with no value), array_pad will pad it with an extra element (containing an empty string), which will be used for the value.

I tested it with this snippet:

<?php

// Extract query string from the full URI

// $query_string = null;
// $query_string = '';
$query_string = 'keys=test1+test2&keys=test3&foo=bar&key_with_no_value';

$search_key = 'keys';

// Split query string by '&' to get key-value pairs
$params = explode('&', $query_string);

// Extract all values for the given key
// This also checks for multiple use of the same key (Example: /search/node?keys=test1+test2&keys=test3)
$all_keys = [];
foreach ($params as $param) {
    list($key, $value) = array_pad(explode('=', $param, 2), 2, '');   
    if ($key == $search_key) {
        $all_keys[] = urldecode($value);
    }
}

print_r($all_keys); // Output: Array ( [0] => test1+test2 [1] => test3 )

[danhgov]

Pull-request #31 contains fixes to both of these problems.