PHP Content-Type negotiation

ContentType.php

<?php

/**
 * Represents a MIME content type
 * 
 * @author Chris Wright <github@daverandom.com>
 */
class ContentType
{
    /**
     * @var string
     */
    private $superType;

    /**
     * @var string
     */
    private $subType;

    /**
     * @var string[] Associative array of parameters
     */
    private $params;

    /**
     * @var float
     */
    private $qValue;

    /**
     * Constructor
     * 
     * @param string   $superType
     * @param string   $subType
     * @param string[] $params
     * @param float    $qValue
     */
    public function __construct($superType, $subType, array $params = [], $qValue = 1)
    {
        $this->superType = $superType;
        $this->subType = $subType;
        $this->params = $params;
        $this->qValue = $qValue;
    }

    /**
     * Get a match score against another content type
     *
     * Returns a value between 0 and 1, where 1 is an exact match and 0 is no match
     *
     * @param ContentType
     * @return float
     */
    public function match(ContentType $contentType)
    {
        $score = 0;
        $divisor = 2;

        if ($this->superType === '*' || $contentType->getSuperType() === $this->superType) {
            $score++;
        }

        if ($this->subType === '*' || $contentType->getSubType() === $this->subType) {
            $score++;
        }

        $params = $contentType->getParams();
        $divisor += count($params);

        foreach ($this->params as $key => $value) {
            if (isset($params[$key])) {
                if ($params[$key] === $value) {
                    $score++;
                }
            } else {
                $divisor++;
            }
        }

        return $score / $divisor;
    }

    /**
     * Get the string representation of this content type
     *
     * @return string
     */
    public function __toString()
    {
        if ($this->params) {
            $params = [];

            foreach ($this->params as $key => $val) {
                $params[] = $key . '=' . $val;
            }

            $params = ';' . implode(';', $params)
        } else {
            $params = '';
        }

        return $this->getType() . $params;
    }

    /**
     * Get the string representation without parameters
     *
     * @return string
     */
    public function getType()
    {
        return $this->superType . '/' . $this->subType;
    }

    /**
     * Get the super type
     *
     * @return string
     */
    public function getSuperType()
    {
        return $this->superType;
    }

    /**
     * Get the sub type
     *
     * @return string
     */
    public function getSubType()
    {
        return $this->subType;
    }

    /**
     * Get the super type of this content type
     *
     * @return string
     */
    public function getQValue()
    {
        return $this->qValue;
    }

    /**
     * Get the value of a parameter by name
     *
     * Returns NULL when the named parameter does not exist
     *
     * @return string|null
     */
    public function getParam($name)
    {
        return isset($this->params[$name]) ? $this->params[$name] : null;
    }

    /**
     * Get all parameters as an associative array
     *
     * @return string[]
     */
    public function getParams()
    {
        return $this->params;
    }
}

ContentTypeBuilder.php

<?php

/**
 * Builds ContentType objects from strings
 * 
 * @author Chris Wright <github@daverandom.com>
 */
class ContentTypeBuilder
{
    /**
     * @var ContentTypeFactory
     */
    private $contentTypeFactory;

    /**
     * Constructor
     *
     * @param ContentTypeFactory $contentTypeFactory
     */
    public function __construct(ContentTypeFactory $contentTypeFactory)
    {
        $this->contentTypeFactory = $contentTypeFactory;
    }

    /**
     * Parse a string into a ContentType object
     *
     * @param string $typeDef
     * @return ContentType
     */
    public function build($typeDef)
    {
        $parts = preg_split('#\s*;\s*#', trim($typeDef), -1, PREG_SPLIT_NO_EMPTY);

        $typeParts = preg_split('#\s*/\s*#', strtolower(array_shift($parts)), 2);
        if (!isset($typeParts[1])) {
            return null;
        }

        list($superType, $subType) = $typeParts;
        if ($superType === '*' && $subType !== '*') {
            return null;
        }

        $params = [];
        $qValue = 1;
        foreach ($parts as $param) {
            $paramParts = preg_split('#\s*=\s*#', $param, 2);

            if (isset($paramParts[1])) {
                if ($paramParts[0] === 'q') {
                    $qValue = (float) $paramParts[1];
                    break; // TODO: we don't account for accept-extensions
                           // It has been suggested by @rdlowrey that this should be a permanent state
                           // of affairs because extensions are a bad idea and I'm inclined to agree
                }

                $params[$paramParts[0]] = $paramParts[1];
            }
        }

        return $this->contentTypeFactory->create($superType, $subType, $params, $qValue);
    }
}

ContentTypeFactory.php

<?php

/**
 * Creates ContentType objects
 * 
 * @author Chris Wright <github@daverandom.com>
 */
class ContentTypeFactory
{
    /**
     * Factory method
     * 
     * @param string   $superType
     * @param string   $subType
     * @param string[] $params
     * @param float    $qValue
     * @return ContentType
     */
    public function create($superType, $subType, array $params = [], $qValue = 1)
    {
        return new ContentType($superType, $subType, $params, $qValue);
    }
}

ContentTypeResolver.php

<?php

/**
 * Reconciles acceptable type lists against available type lists
 * 
 * @author Chris Wright <github@daverandom.com>
 */
class ContentTypeResolver
{
    /**
     * @var ContentTypeBuilder
     */
    private $contentTypeBuilder;

    /**
     * Constructor
     *
     * @param ContentTypeBuilder $contentTypeBuilder
     */
    public function __construct(ContentTypeBuilder $contentTypeBuilder)
    {
        $this->contentTypeBuilder = $contentTypeBuilder;
    }

    /**
     * Parses an acceptable type list into an array of ContentType objects
     *
     * @param string $acceptedTypes
     * @return ContentType[]
     */
    private function parseAcceptedTypes($acceptedTypes)
    {
        $result = [];

        foreach (explode(',', $acceptedTypes) as $typeSpec) {
            if ($contentType = $this->contentTypeBuilder->build($typeSpec)) {
                $result[$contentType->getSuperType()][$contentType->getSubType()][] = $contentType;
            }
        }

        return $result;
    }

    /**
     * Normalise a type spec to a ContentType object
     *
     * @param string|ContentType $spec
     * @return ContentType
     */
    private function getParsedType($spec)
    {
        return $spec instanceof ContentType ? $spec : $this->contentTypeBuilder->build((string) $spec);
    }

    /**
     * Get the best matching accepted type from the list of available types
     *
     * @param string $acceptedTypes  Type specification as specified in an HTTP Accept: header
     * @param array  $availableTypes List of available types, as strings or ContentType objects
     * @return ContentType
     */
    public function getResponseType($acceptedTypes, array $availableTypes)
    {
        if (!$acceptedTypes = $this->parseAcceptedTypes($acceptedTypes)) {
            return $this->getParsedType(current($availableTypes));
        }

        $weightMap = [];

        foreach ($availableTypes as $typeSpec) {
            $availableType = $this->getParsedType($typeSpec);
            $superType = $availableType->getSuperType();
            $subType = $availableType->getSubType();

            if (isset($acceptedTypes[$superType][$subType])) {
                $candidates = $acceptedTypes[$superType][$subType];
            } else if (isset($acceptedTypes[$superType]['*'])) {
                $candidates = $acceptedTypes[$superType]['*'];
            } else if (isset($acceptedTypes['*']['*'])) {
                $candidates = $acceptedTypes['*']['*'];
            } else {
                continue;
            }

            $bestMatchFactor = 0;
            $bestMatch = null;
            foreach ($candidates as $acceptedType) {
                $factor = $acceptedType->match($availableType);
                if ($factor > $bestMatchFactor) {
                    $bestMatchFactor = $factor;
                    $bestMatch = $acceptedType;

                    if ($bestMatchFactor >= 1) {
                        break;
                    }
                }
            }

            $weightMap[(string) $bestMatch->getQValue()][] = $availableType;
        }

        if (!$weightMap) {
            return null;
        }

        ksort($weightMap, SORT_NUMERIC);

        return end($weightMap)[0];
    }
}

example.php

<?php

require 'ContentTypeResolver.php';
require 'ContentTypeBuilder.php';
require 'ContentTypeFactory.php';
require 'ContentType.php';

$resolver = new ContentTypeResolver(new ContentTypeBuilder(new ContentTypeFactory));

// Example from RFC 2616
$acceptHeader = 'text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5';
$availableTypes = [
    'text/html',
    'text/plain',
    'text/html;level=1',
    'image/jpeg',
    'text/html;level=2',
    'text/html;level=3',
];

echo $resolver->getResponseType($acceptHeader, $availableTypes);

wow such gist great timing nice headers

@PeeHaa added some docblocks and generally made this presentable.

It's a long time since I wrote this but I'm pretty sure it works fairly well, the main logic is in ContentTypeResolver::getResponseType(), all the rest is just fluff to turn content types into sexy objects :-)