Boundary Issue Detection

Analyze PHP code for boundary and range violations.

Detection Patterns

1. Array Index Out of Bounds

// BUG: No bounds check
$items = [1, 2, 3];
$last = $items[count($items)]; // Off by one, should be count - 1

// BUG: Hardcoded index
$third = $data[2]; // May not have 3 elements

// BUG: Negative index
$item = $array[$index]; // $index could be negative

2. Empty Collection Access

// BUG: first() on empty
$users = $repository->findBy(['status' => 'vip']);
$topUser = $users[0]; // May be empty

// BUG: array_pop on empty
$items = [];
$last = array_pop($items); // Returns null

// BUG: reset() on empty
$first = reset($emptyArray); // Returns false

3. Off-by-One Errors

// BUG: Loop boundary
for ($i = 0; $i <= count($items); $i++) { // Should be <
    process($items[$i]); // Last iteration fails
}

// BUG: Substring
$sub = substr($string, 0, strlen($string) + 1); // Off by one

// BUG: Slice
$slice = array_slice($array, 0, count($array) + 1);

4. Integer Overflow/Underflow

// BUG: No overflow check
$total = $price * $quantity; // May overflow

// BUG: Negative result
$remaining = $stock - $ordered; // May go negative

// BUG: Division truncation
$average = $total / $count; // Integer division loses precision

5. String Length Issues

// BUG: Empty string access
$first = $string[0]; // Undefined if empty

// BUG: Multibyte issues
$length = strlen($utf8String); // Wrong for multibyte
$char = $string[5]; // May split multibyte char

// BUG: No length check
$sub = substr($name, 0, 10); // May be shorter than 10

6. Range Validation

// BUG: Unchecked range
$page = $request->get('page'); // Could be 0, negative, or huge
$items = $repository->findPage($page); // Invalid page

// BUG: Missing min/max
$age = (int) $input; // Could be negative or 1000

7. Date/Time Boundaries

// BUG: Invalid month/day
$date = new DateTime("2024-13-45"); // Invalid date

// BUG: Leap year
$date = new DateTime("2023-02-29"); // Not a leap year

Grep Patterns

# Direct array index access
Grep: "\$\w+\[\d+\]" --glob "**/*.php"

# count() in loop condition
Grep: "for\s*\([^;]+;\s*\$\w+\s*<=\s*count" --glob "**/*.php"

# Array access after find
Grep: "findBy[^;]+;\s*\n\s*\$\w+\[0\]" --glob "**/*.php"

# Hardcoded string index
Grep: '\$\w+\["\w+"\]\[\d+\]' --glob "**/*.php"

Severity Classification

Pattern	Severity
Unchecked array index	🟠 Major
Off-by-one in loop	🟠 Major
Empty collection access	🟠 Major
Integer overflow	🟡 Minor
Multibyte string issue	🟡 Minor

Output Format

### Boundary Issue: [Description]

**Severity:** 🔴/🟠/🟡
**Location:** `file.php:line`
**Type:** [Array Bounds|Off-by-One|Empty Access|Overflow|...]

**Issue:**
[Description of the boundary violation]

**Code:**
```php
// Problematic code

Fix:

// With bounds check