Thin assertion library for use in libraries and business-model
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A simple php library which contains assertions and guard methods for input validation (not filtering!) in business-model, libraries and application low-level code. The library can be used to implement pre-/post-conditions on input data.

Idea is to reduce the amount of code for implementing assertions in your model and also simplify the code paths to implement assertions. When assertions fail, an exception is thrown, removing the necessity for if-clauses in your code.

The library is not using Symfony or Zend Validators for a reason: The checks have to be low-level, fast, non-object-oriented code to be used everywhere necessary. Using any of the two libraries requires instantiation of several objects, using a locale component, translations, you name it. Its too much bloat.


Using Composer:

    "require": {
        "beberlei/assert": "*"

Example usages

use Assert\Assertion;

function duplicateFile($file, $times)

    for ($i = 0; $i < $times; $i++) {
        copy($file, $file . $i);

Real time usage with Azure Blob Storage:

public function putBlob($containerName = '', $blobName = '', $localFileName = '', $metadata = array(), $leaseId = null, $additionalHeaders = array())
    Assertion::notEmpty($containerName, 'Container name is not specified');
    Assertion::notEmpty($blobName, 'Blob name is not specified.');
    Assertion::notEmpty($localFileName, 'Local file name is not specified.');
    Assertion::file($localFileName, 'Local file name is not specified.');
    self::assertValidRootContainerBlobName($containerName, $blobName);

    // Check file size
    if (filesize($localFileName) >= self::MAX_BLOB_SIZE) {
        return $this->putLargeBlob($containerName, $blobName, $localFileName, $metadata, $leaseId, $additionalHeaders);

    // Put the data to Windows Azure Storage
    return $this->putBlobData($containerName, $blobName, file_get_contents($localFileName), $metadata, $leaseId, $additionalHeaders);

NullOr helper

A helper method (Assertion::nullOr*) is provided to check if a value is null OR holds for the assertion:

Assertion::nullOrMax(null, 42); // success
Assertion::nullOrMax(1, 42);    // success
Assertion::nullOrMax(1337, 42); // exception

All helper

The Assertion::all* method checks if all provided values hold for the assertion. It will throw an exception of the assertion does not hold for one of the values:

Assertion::allIsInstanceOf(array(new \stdClass, new \stdClass), 'stdClass'); // success
Assertion::allIsInstanceOf(array(new \stdClass, new \stdClass), 'PDO');      // exception

\Assert\that() Chaining

Using the static API on values is very verbose when checking values against multiple assertions. Starting with 2.0 of Assert there is a much nicer fluent API for assertions, starting with \Assert\that($value) and then receiving the assertions you want to call on the fluent interface. You only have to specify the $value once.


There are also two shortcut function \Assert\thatNullOr() and \Assert\thatAll() enabling the "nullOr" or "all" helper respectively.

Lazy Assertions

There are many cases in web development, especially when involving forms, you want to collect several errors instead of aborting directly on the first error. This is what lazy assertions are for. Their API works exactly like the fluent \Assert\that() API, but instead of throwing an Exception directly, they collect all errors and only trigger the exception when the method verifyNow() is called on the Assert\SoftAssertion object.

    ->that(10, 'foo')->string()
    ->that(null, 'bar')->notEmpty()
    ->that('string', 'baz')->isArray()

The method that($value, $propertyPath) requires a property path (name), so that you know how to differentiate the errors afterwards.

On failure verifyNow()` will throw an exceptionAssert\LazyAssertionException(this does not extendAssertionFailedException``) with a combined message:

The following 3 assertions failed:
1) foo: Value "10" expected to be string, type integer given.
2) bar: Value "<NULL>" is empty, but non empty value was expected.
3) baz: Value "string" is not an array.

You can also retrieve all the AssertionFailedExceptions by calling getErrorExceptions(). This can be useful for example to build a failure response for the user.

List of assertions

use Assert\Assertion;

Assertion::range($value, $minValue, $maxValue);
Assertion::regex($value, $regex);
Assertion::length($value, $length);
Assertion::minLength($value, $length);
Assertion::maxLength($value, $length);
Assertion::betweenLength($value, $minLength, $maxLength);
Assertion::startsWith($value, $needle);
Assertion::endsWith($value, $needle);
Assertion::contains($value, $needle);
Assertion::choice($value, $choices);
Assertion::inArray($value, $choices);
Assertion::keyExists($value, $key);
Assertion::notEmptyKey($value, $key);
Assertion::isInstanceOf($value, $className);
Assertion::notIsInstanceOf($value, $className);
Assertion::subclassOf($value, $className);
Assertion::min($value, $min);
Assertion::max($value, $max);
Assertion::eq($actual, $expected);
Assertion::same($actual, $expected);
Assertion::implementsInterface($value, $interfaceName);

Remember: When a configuration parameter is necessary, it is always passed AFTER the value. The value is always the first parameter.

Exception & Error Handling

If any of the assertions fails a Assert\AssertionFailedException is thrown. You can pass an argument called $message to any assertion to control the exception message. Every exception contains a default message and unique message code by default.

use Assert\Assertion;
use Assert\InvalidArgumentException;

try {
    Assertion::integer($value, "The pressure of gas is measured in integers.");
} catch(AssertionFailedException $e) {
    // error handling
    $e->getValue(); // the value that caused the failure
    $e->getConstraints(); // the additional constraints of the assertion.

Assert\AssertionFailedException is just an interface and the default implementation is Assert\InvalidArgumentException which extends the SPL InvalidArgumentException. You can change the exception being used on a package based level.

Your own Assertion class

To shield your library from possible bugs, misinterpretations or BC breaks inside Assert you should introduce a library/project based assertion subclass, where you can override the exception thrown as well:

namespace MyProject;

use Assert\Assertion as BaseAssertion;

class Assertion extends BaseAssertion
    protected static $exceptionClass = 'MyProject\AssertionFailedException';