trait MessageTrait in Auth0 Single Sign On 8.2

trait MessageTrait {

  /** @var array Map of all registered headers, as original name => array of values */
  private $headers = [];

  /** @var array Map of lowercase header name => original name at registration */
  private $headerNames = [];

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

  /** @var StreamInterface */
  private $stream;
  public function getProtocolVersion() {
    return $this->protocol;
  }
  public function withProtocolVersion($version) {
    if ($this->protocol === $version) {
      return $this;
    }
    $new = clone $this;
    $new->protocol = $version;
    return $new;
  }
  public function getHeaders() {
    return $this->headers;
  }
  public function hasHeader($header) {
    return isset($this->headerNames[strtolower($header)]);
  }
  public function getHeader($header) {
    $header = strtolower($header);
    if (!isset($this->headerNames[$header])) {
      return [];
    }
    $header = $this->headerNames[$header];
    return $this->headers[$header];
  }
  public function getHeaderLine($header) {
    return implode(', ', $this
      ->getHeader($header));
  }
  public function withHeader($header, $value) {
    $this
      ->assertHeader($header);
    $value = $this
      ->normalizeHeaderValue($value);
    $normalized = strtolower($header);
    $new = clone $this;
    if (isset($new->headerNames[$normalized])) {
      unset($new->headers[$new->headerNames[$normalized]]);
    }
    $new->headerNames[$normalized] = $header;
    $new->headers[$header] = $value;
    return $new;
  }
  public function withAddedHeader($header, $value) {
    $this
      ->assertHeader($header);
    $value = $this
      ->normalizeHeaderValue($value);
    $normalized = strtolower($header);
    $new = clone $this;
    if (isset($new->headerNames[$normalized])) {
      $header = $this->headerNames[$normalized];
      $new->headers[$header] = array_merge($this->headers[$header], $value);
    }
    else {
      $new->headerNames[$normalized] = $header;
      $new->headers[$header] = $value;
    }
    return $new;
  }
  public function withoutHeader($header) {
    $normalized = strtolower($header);
    if (!isset($this->headerNames[$normalized])) {
      return $this;
    }
    $header = $this->headerNames[$normalized];
    $new = clone $this;
    unset($new->headers[$header], $new->headerNames[$normalized]);
    return $new;
  }
  public function getBody() {
    if (!$this->stream) {
      $this->stream = stream_for('');
    }
    return $this->stream;
  }
  public function withBody(StreamInterface $body) {
    if ($body === $this->stream) {
      return $this;
    }
    $new = clone $this;
    $new->stream = $body;
    return $new;
  }
  private function setHeaders(array $headers) {
    $this->headerNames = $this->headers = [];
    foreach ($headers as $header => $value) {
      if (is_int($header)) {

        // Numeric array keys are converted to int by PHP but having a header name '123' is not forbidden by the spec
        // and also allowed in withHeader(). So we need to cast it to string again for the following assertion to pass.
        $header = (string) $header;
      }
      $this
        ->assertHeader($header);
      $value = $this
        ->normalizeHeaderValue($value);
      $normalized = strtolower($header);
      if (isset($this->headerNames[$normalized])) {
        $header = $this->headerNames[$normalized];
        $this->headers[$header] = array_merge($this->headers[$header], $value);
      }
      else {
        $this->headerNames[$normalized] = $header;
        $this->headers[$header] = $value;
      }
    }
  }
  private function normalizeHeaderValue($value) {
    if (!is_array($value)) {
      return $this
        ->trimHeaderValues([
        $value,
      ]);
    }
    if (count($value) === 0) {
      throw new \InvalidArgumentException('Header value can not be an empty array.');
    }
    return $this
      ->trimHeaderValues($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 ":" OWS field-value OWS
   * OWS          = *( SP / HTAB )
   *
   * @param string[] $values Header values
   *
   * @return string[] Trimmed header values
   *
   * @see https://tools.ietf.org/html/rfc7230#section-3.2.4
   */
  private function trimHeaderValues(array $values) {
    return array_map(function ($value) {
      if (!is_scalar($value) && null !== $value) {
        throw new \InvalidArgumentException(sprintf('Header value must be scalar or null but %s provided.', is_object($value) ? get_class($value) : gettype($value)));
      }
      return trim((string) $value, " \t");
    }, $values);
  }
  private function assertHeader($header) {
    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 ($header === '') {
      throw new \InvalidArgumentException('Header name can not be empty.');
    }
  }

}