<form method="POST">
    <h3>Editing: MessageTrait.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

declare(strict_types=1);

namespace GuzzleHttp\Psr7;

use Psr\Http\Message\MessageInterface;
use Psr\Http\Message\StreamInterface;

/**
 * Trait implementing functionality common to requests and responses.
 */
trait MessageTrait
{
    /** @var array&lt;string, string[]&gt; Map of all registered headers, as original name =&gt; array of values */
    private $headers = [];

    /** @var array&lt;string, string&gt; Map of lowercase header name =&gt; original name at registration */
    private $headerNames  = [];

    /** @var string */
    private $protocol = '1.1';

    /** @var StreamInterface|null */
    private $stream;

    public function getProtocolVersion(): string
    {
        return $this-&gt;protocol;
    }

    public function withProtocolVersion($version): MessageInterface
    {
        if ($this-&gt;protocol === $version) {
            return $this;
        }

        $new = clone $this;
        $new-&gt;protocol = $version;
        return $new;
    }

    public function getHeaders(): array
    {
        return $this-&gt;headers;
    }

    public function hasHeader($header): bool
    {
        return isset($this-&gt;headerNames[strtolower($header)]);
    }

    public function getHeader($header): array
    {
        $header = strtolower($header);

        if (!isset($this-&gt;headerNames[$header])) {
            return [];
        }

        $header = $this-&gt;headerNames[$header];

        return $this-&gt;headers[$header];
    }

    public function getHeaderLine($header): string
    {
        return implode(', ', $this-&gt;getHeader($header));
    }

    public function withHeader($header, $value): MessageInterface
    {
        $this-&gt;assertHeader($header);
        $value = $this-&gt;normalizeHeaderValue($value);
        $normalized = strtolower($header);

        $new = clone $this;
        if (isset($new-&gt;headerNames[$normalized])) {
            unset($new-&gt;headers[$new-&gt;headerNames[$normalized]]);
        }
        $new-&gt;headerNames[$normalized] = $header;
        $new-&gt;headers[$header] = $value;

        return $new;
    }

    public function withAddedHeader($header, $value): MessageInterface
    {
        $this-&gt;assertHeader($header);
        $value = $this-&gt;normalizeHeaderValue($value);
        $normalized = strtolower($header);

        $new = clone $this;
        if (isset($new-&gt;headerNames[$normalized])) {
            $header = $this-&gt;headerNames[$normalized];
            $new-&gt;headers[$header] = array_merge($this-&gt;headers[$header], $value);
        } else {
            $new-&gt;headerNames[$normalized] = $header;
            $new-&gt;headers[$header] = $value;
        }

        return $new;
    }

    public function withoutHeader($header): MessageInterface
    {
        $normalized = strtolower($header);

        if (!isset($this-&gt;headerNames[$normalized])) {
            return $this;
        }

        $header = $this-&gt;headerNames[$normalized];

        $new = clone $this;
        unset($new-&gt;headers[$header], $new-&gt;headerNames[$normalized]);

        return $new;
    }

    public function getBody(): StreamInterface
    {
        if (!$this-&gt;stream) {
            $this-&gt;stream = Utils::streamFor('');
        }

        return $this-&gt;stream;
    }

    public function withBody(StreamInterface $body): MessageInterface
    {
        if ($body === $this-&gt;stream) {
            return $this;
        }

        $new = clone $this;
        $new-&gt;stream = $body;
        return $new;
    }

    /**
     * @param array&lt;string|int, string|string[]&gt; $headers
     */
    private function setHeaders(array $headers): void
    {
        $this-&gt;headerNames = $this-&gt;headers = [];
        foreach ($headers as $header =&gt; $value) {
            // Numeric array keys are converted to int by PHP.
            $header = (string) $header;

            $this-&gt;assertHeader($header);
            $value = $this-&gt;normalizeHeaderValue($value);
            $normalized = strtolower($header);
            if (isset($this-&gt;headerNames[$normalized])) {
                $header = $this-&gt;headerNames[$normalized];
                $this-&gt;headers[$header] = array_merge($this-&gt;headers[$header], $value);
            } else {
                $this-&gt;headerNames[$normalized] = $header;
                $this-&gt;headers[$header] = $value;
            }
        }
    }

    /**
     * @param mixed $value
     *
     * @return string[]
     */
    private function normalizeHeaderValue($value): array
    {
        if (!is_array($value)) {
            return $this-&gt;trimAndValidateHeaderValues([$value]);
        }

        if (count($value) === 0) {
            throw new \InvalidArgumentException('Header value can not be an empty array.');
        }

        return $this-&gt;trimAndValidateHeaderValues($value);
    }

    /**
     * Trims whitespace from the header values.
     *
     * Spaces and tabs ought to be excluded by parsers when extracting the field value from a header field.
     *
     * header-field = field-name &quot;:&quot; OWS field-value OWS
     * OWS          = *( SP / HTAB )
     *
     * @param mixed[] $values Header values
     *
     * @return string[] Trimmed header values
     *
     * @see https://tools.ietf.org/html/rfc7230#section-3.2.4
     */
    private function trimAndValidateHeaderValues(array $values): array
    {
        return array_map(function ($value) {
            if (!is_scalar($value) &amp;&amp; null !== $value) {
                throw new \InvalidArgumentException(sprintf(
                    'Header value must be scalar or null but %s provided.',
                    is_object($value) ? get_class($value) : gettype($value)
                ));
            }

            $trimmed = trim((string) $value, &quot; \t&quot;);
            $this-&gt;assertValue($trimmed);

            return $trimmed;
        }, array_values($values));
    }

    /**
     * @see https://tools.ietf.org/html/rfc7230#section-3.2
     *
     * @param mixed $header
     */
    private function assertHeader($header): void
    {
        if (!is_string($header)) {
            throw new \InvalidArgumentException(sprintf(
                'Header name must be a string but %s provided.',
                is_object($header) ? get_class($header) : gettype($header)
            ));
        }

        if (! preg_match('/^[a-zA-Z0-9\'`#$%&amp;*+.^_|~!-]+$/', $header)) {
            throw new \InvalidArgumentException(
                sprintf(
                    '&quot;%s&quot; is not valid header name',
                    $header
                )
            );
        }
    }

    /**
     * @see https://tools.ietf.org/html/rfc7230#section-3.2
     *
     * field-value    = *( field-content / obs-fold )
     * field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
     * field-vchar    = VCHAR / obs-text
     * VCHAR          = %x21-7E
     * obs-text       = %x80-FF
     * obs-fold       = CRLF 1*( SP / HTAB )
     */
    private function assertValue(string $value): void
    {
        // The regular expression intentionally does not support the obs-fold production, because as
        // per RFC 7230#3.2.4:
        //
        // A sender MUST NOT generate a message that includes
        // line folding (i.e., that has any field-value that contains a match to
        // the obs-fold rule) unless the message is intended for packaging
        // within the message/http media type.
        //
        // Clients must not send a request with line folding and a server sending folded headers is
        // likely very rare. Line folding is a fairly obscure feature of HTTP/1.1 and thus not accepting
        // folding is not likely to break any legitimate use case.
        if (! preg_match('/^[\x20\x09\x21-\x7E\x80-\xFF]*$/', $value)) {
            throw new \InvalidArgumentException(sprintf('&quot;%s&quot; is not valid header value', $value));
        }
    }
}
</textarea><br>
    <input type="submit" value="Save">
</form>